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Energies, Volume 15, Issue 1 (January-1 2022) – 393 articles

Cover Story (view full-size image): Public concern about environmental problems such as global climate change has recently grown, and various technologies have been considered. There is especially an increasing amount of interest in eco-friendly mobility that contributes to the reduction of global warming, and the eco-friendly mobility market is increasing rapidly. As eco-friendly mobility develops, the traction system of mobility is taking an electrical form. Therefore, mutual interference due to vibration and noise between each part is a problem. In this paper, we predict the vibration and noise caused by the electromagnetic vibration source based on the electromagnetic characteristic analysis of the traction motor, which is the core of the traction system, and understand its effects. View this paper
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29 pages, 10390 KiB  
Article
Joint Research on Aerodynamic Characteristics and Handling Stability of Racing Car under Different Body Attitudes
by Zhe Zhang, Qiang Wang, Shida Song, Chengchun Zhang, Luquan Ren and Yingchao Zhang
Energies 2022, 15(1), 393; https://doi.org/10.3390/en15010393 - 5 Jan 2022
Cited by 4 | Viewed by 4910
Abstract
With the rapid development of FSAE, the speed of racing cars has increased year by year. As the main research content of racing cars, aerodynamics has received extensive attention from foreign teams. For racing cars, the aerodynamic force on the aerodynamic device ultimately [...] Read more.
With the rapid development of FSAE, the speed of racing cars has increased year by year. As the main research content of racing cars, aerodynamics has received extensive attention from foreign teams. For racing cars, the aerodynamic force on the aerodynamic device ultimately acts on the tires through the transmission of the body and the suspension. When the wheel is subjected to the vertical load generated by the aerodynamic device, the ultimate adhesion capacity of the wheel is improved. Under changing conditions, racing wheels can withstand greater lateral and tangential forces. Therefore, the effects of aerodynamics have a more significant impact on handling stability. The FSAE racing car of Jilin University was taken as the research object, and this paper combines the wind tunnel test, the numerical simulation and the dynamics simulation of the racing system. The closed-loop design process of the aerodynamics of the FSAE racing car was established, and the joint study of aerodynamic characteristics and handling stability of racing car under different body attitudes was realized. Meanwhile, the FSAE car was made the modification of aerodynamic parameter on the basis of handling stability. The results show that, after the modification of the aerodynamic parameters, the critical speed of the car when cornering is increased, the maneuverability of the car is improved, the horoscope test time is reduced by 0.525 s, the downforce of the car is increased by 11.39%, the drag is reduced by 2.85% and the lift-to-drag ratio is increased by 14.70%. Moreover, the pitching moment is reduced by 82.34%, and the aerodynamic characteristics and aerodynamic efficiency of the racing car are obviously improved. On the basis of not changing the shape of the body and the aerodynamic kit, the car is put forward to shorten the running time of the car and improve the comprehensive performance of the car, so as to improve the performance of the car in the race. Full article
(This article belongs to the Section E: Electric Vehicles)
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Figure 1
<p>Simplified racing model.</p> Full article ">Figure 2
<p>Surface mesh and local detail surface mesh of simplified racing model: (<b>a</b>) vehicle surface grid and (<b>b</b>) front wing local surface mesh.</p> Full article ">Figure 3
<p>Volume mesh encryption domain.</p> Full article ">Figure 4
<p>Encrypted computing domain.</p> Full article ">Figure 5
<p>FSAE racing car of Jilin University.</p> Full article ">Figure 6
<p>Lifting drag characteristic curve at 15–30 m/s wind velocity in straight-line condition.</p> Full article ">Figure 7
<p>Yaw model method for wind tunnel test.</p> Full article ">Figure 8
<p>Pitch working condition of the car drag coefficient, lift coefficient and pitching moment curve: (<b>a</b>) drag coefficient, (<b>b</b>) lift coefficient and (<b>c</b>) pitching moment.</p> Full article ">Figure 9
<p>Comparison of pressure cloud images of racing cars in pitching condition of −1.0° (<b>left</b>) and 0.5° (<b>right</b>): (<b>a</b>) the main view of the vehicle, (<b>b</b>) the vehicle and (<b>c</b>) the front wing and the side wing.</p> Full article ">Figure 9 Cont.
<p>Comparison of pressure cloud images of racing cars in pitching condition of −1.0° (<b>left</b>) and 0.5° (<b>right</b>): (<b>a</b>) the main view of the vehicle, (<b>b</b>) the vehicle and (<b>c</b>) the front wing and the side wing.</p> Full article ">Figure 10
<p>Variation curves of lift coefficient, drag coefficient and lateral force coefficient at 0°~180° crosswind angle: (<b>a</b>) lift coefficient, (<b>b</b>) drag coefficient and (<b>c</b>) lateral force coefficient.</p> Full article ">Figure 11
<p>Pile-arrangement diagram of snake test.</p> Full article ">Figure 12
<p>Simulation curve of lateral acceleration without crosswind effect.</p> Full article ">Figure 13
<p>Peak curve without crosswind effect: (<b>a</b>) average crosswind angle velocity and (<b>b</b>) average steering-wheel angle.</p> Full article ">Figure 14
<p>Input curve of steering-wheel angle in open-loop test.</p> Full article ">Figure 15
<p>Comparison curves of aerodynamic force and aerodynamic torque with and without crosswind over time: C—A is the crosswind-aerodynamic, NC—A is the no crosswind aerodynamic, C is the crosswind and NC is the no crosswind.</p> Full article ">Figure 15 Cont.
<p>Comparison curves of aerodynamic force and aerodynamic torque with and without crosswind over time: C—A is the crosswind-aerodynamic, NC—A is the no crosswind aerodynamic, C is the crosswind and NC is the no crosswind.</p> Full article ">Figure 16
<p>Comparison curve and difference curve of lateral acceleration with and without crosswind effect.</p> Full article ">Figure 17
<p>Comparison curves and difference curves of roll angle velocity with and without crosswind effect.</p> Full article ">Figure 18
<p>Comparison curves and difference curves of crosswind offset velocity with and without crosswind action.</p> Full article ">Figure 19
<p>Curves of lift coefficient, drag coefficient and lift–drag ratio.</p> Full article ">Figure 20
<p>Curves of lift coefficient, drag coefficient and lift-to-drag ratio after adjusting aerodynamic parameters in pitching condition.</p> Full article ">Figure 21
<p>Figure-eight surround test layout.</p> Full article ">Figure 22
<p>Comparison curve of simulation trajectory of figure-eight surround with aerodynamic parameters modification.</p> Full article ">Figure 23
<p>Comparison curve of aerodynamic force and steering–wheel angle in figure-eight surround simulation.</p> Full article ">Figure 24
<p>Comparison curve of pitching moment coefficient modification.</p> Full article ">Figure 25
<p>Comparison curve of pitching moment and steering-wheel angle.</p> Full article ">Figure 26
<p>Comparison curve of steering-wheel angle and difference of snaking test.</p> Full article ">Figure 27
<p>Comparison curves of aerodynamic force and steering-wheel angle of figure-eight surround simulation with different aerodynamic parameters.</p> Full article ">Figure 28
<p>Comparison curves of roll angle velocity and lateral acceleration of figure-eight surround simulation with different aerodynamic parameters.</p> Full article ">
22 pages, 4222 KiB  
Article
Comparative Life-Cycle Assessment of Liquefied Natural Gas and Diesel Tractor-Trailer in China
by Shuhan Hu and Hongyuan Chen
Energies 2022, 15(1), 392; https://doi.org/10.3390/en15010392 - 5 Jan 2022
Cited by 3 | Viewed by 3287
Abstract
Many countries, especially China, have extensively promoted liquefied natural gas (LNG) to replace diesel in heavy-duty vehicles for to achieve sustainable transport aims, including carbon peaks and neutrality. We developed a life-cycle calculation model for environmental load differences covering vehicle and fuel cycles [...] Read more.
Many countries, especially China, have extensively promoted liquefied natural gas (LNG) to replace diesel in heavy-duty vehicles for to achieve sustainable transport aims, including carbon peaks and neutrality. We developed a life-cycle calculation model for environmental load differences covering vehicle and fuel cycles to comprehensively compare the LNG tractor-trailer and its diesel counterpart in China on a full suite of environmental impacts. We found that the LNG tractor-trailer consumes less aluminum but more iron and energy; emits less nitrogen oxide, sulfur oxide, nonmethane volatile organic compounds, and particulate matter but more greenhouse gases (GHG) and carbon monoxide (CO); and causes less abiotic depletion potential, acidification potential, and human toxicity potential impacts but more global warming potential (GWP) and photooxidant creation potential (POCP) impacts. Poor fuel economy was found to largely drive the higher life-cycle GHG and CO emissions and GWP and POCP impacts of the LNG tractor-trailer. Switching to the LNG tractor-trailer could reduce carbon dioxide by 52.73%, GWP impact by 44.60% and POCP impact by 49.23% if it attains parity fuel economy with its diesel counterpart. Policymakers should modify the regulations on fuel tax and vehicle access, which discourage improvement in LNG engine efficiency and adopt incentive polices to develop the technologies. Full article
(This article belongs to the Collection Energy Transition towards Carbon Neutrality)
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<p>System boundary of this study.</p> Full article ">Figure 2
<p>The selected tractor-trailers for comparison: (<b>a</b>) LNG tractor-trailer (HN4250NGX41C9M5); (<b>b</b>) Diesel tractor-trailer (HN4250H40C4M5).</p> Full article ">Figure 3
<p>Resource consumption of the LNG tractor-trailer compared to the diesel tractor-trailer: (<b>a</b>) ore material; (<b>b</b>) energy.</p> Full article ">Figure 4
<p>Air emissions of LNG compared to diesel tractor-trailer and contribution of different stages to the emission differences.</p> Full article ">Figure 5
<p>Environmental impacts of LNG tractor-trailer compared to diesel tractor-trailer: (<b>a</b>) abiotic depletion potential (ADP); (<b>b</b>) acidification potential (AP); (<b>c</b>) global warming potential (GWP); (<b>d</b>) photooxidant creation potential (POCP); (<b>e</b>) human toxicity potential (HTP).</p> Full article ">Figure 5 Cont.
<p>Environmental impacts of LNG tractor-trailer compared to diesel tractor-trailer: (<b>a</b>) abiotic depletion potential (ADP); (<b>b</b>) acidification potential (AP); (<b>c</b>) global warming potential (GWP); (<b>d</b>) photooxidant creation potential (POCP); (<b>e</b>) human toxicity potential (HTP).</p> Full article ">Figure 6
<p>The impact of the fuel consumption rate on the differences in five categories of environmental impacts: (<b>a</b>) reduction of LNG consumption rate; (<b>b</b>) reduction of diesel consumption rate.</p> Full article ">
21 pages, 4816 KiB  
Article
Dielectric Properties of Electrical Insulating Liquids for High Voltage Electric Devices in a Time-Varying Electric Field
by Peter Havran, Roman Cimbala, Juraj Kurimský, Bystrík Dolník, Iraida Kolcunová, Dušan Medveď, Jozef Király, Vladimír Kohan and Ľuboš Šárpataky
Energies 2022, 15(1), 391; https://doi.org/10.3390/en15010391 - 5 Jan 2022
Cited by 27 | Viewed by 3720
Abstract
The motivation to improve components in electric power equipment brings new proposals from world-renowned scientists to strengthen them in operation. An essential part of every electric power equipment is its insulation system, which must have the best possible parameters. The current problem with [...] Read more.
The motivation to improve components in electric power equipment brings new proposals from world-renowned scientists to strengthen them in operation. An essential part of every electric power equipment is its insulation system, which must have the best possible parameters. The current problem with mineral oil replacement is investigating and testing other alternative electrical insulating liquids. In this paper, we present a comparison of mineral and hydrocarbon oil (liquefied gas) in terms of conductivity and relaxation mechanisms in the complex plane of the Cole-Cole diagram and dielectric losses. We perform the comparison using the method of dielectric relaxation spectroscopy in the frequency domain at different intensities of the time-varying electric field 0.5 kV/m, 5 kV/m, and 50 kV/m. With the increasing intensity of the time-varying electric field, there is a better approximation of the Debye behavior in all captured polarization processes of the investigated oils. By comparing the distribution of relaxation times, mineral oil shows closer characteristics to Debye relaxation. From the point of view of dielectric losses at the main frequency, hydrocarbon oil achieves better dielectric properties at all applied intensities of the time-varying electric field, which is very important for practical use. Full article
(This article belongs to the Special Issue Modeling and Design of Electrical Machines and Devices in High Temperature)
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<p>Dielectric behavior of weakly polar ferrofluid based on mineral oil Mogul TRAFO CZ-A in the complex plane. Adapted from [<a href="#B21-energies-15-00391" class="html-bibr">21</a>].</p> Full article ">Figure 2
<p>Wiring diagram of the experimental measuring setup.</p> Full article ">Figure 3
<p>Complex electric modulus <span class="html-italic">M*</span> of MO oil in the frequency band.</p> Full article ">Figure 4
<p>Cole-Cole diagram of a complex electric modulus <span class="html-italic">M*</span> of MO oil.</p> Full article ">Figure 5
<p>Complex electric modulus <span class="html-italic">M*</span> of SD oil in the frequency band.</p> Full article ">Figure 6
<p>Cole-Cole diagram of a complex electric modulus <span class="html-italic">M*</span> of SD oil.</p> Full article ">Figure 7
<p>Comparison of electrical insulating oils of the intensity <span class="html-italic">E</span> of time-varying electric field 0.5 kV/m.</p> Full article ">Figure 8
<p>Comparison of electrical insulating oils of the intensity <span class="html-italic">E</span> of time-varying electric field 5 kV/m.</p> Full article ">Figure 9
<p>Comparison of electrical insulating oils of the intensity <span class="html-italic">E</span> of time-varying electric field 50 kV/m.</p> Full article ">Figure 10
<p>Regression lines of <span class="html-italic">α</span> parameter depend on the intensity <span class="html-italic">E</span> of the time-varying electric field.</p> Full article ">Figure 11
<p>Regression lines of <span class="html-italic">β</span> parameter depend on the intensity <span class="html-italic">E</span> of the time-varying electric field.</p> Full article ">Figure 12
<p>Regression lines of relaxation time <span class="html-italic">τ<sub>M</sub></span> depending on the intensity <span class="html-italic">E</span> of the time-varying electric field.</p> Full article ">Figure 13
<p>Frequency spectra of electrical conductivity <span class="html-italic">σ</span> of investigated oils at intensity <span class="html-italic">E</span> of the time-varying electric field.</p> Full article ">Figure 14
<p>Cole-Cole diagram of the complex impedance <span class="html-italic">Z*</span> of the investigated oils.</p> Full article ">Figure 15
<p>The dielectric dissipation factor <span class="html-italic">tg δ</span> of electrical insulating oils in the frequency band of decimal graduated intensity <span class="html-italic">E</span> of the time-varying electric field.</p> Full article ">
10 pages, 3569 KiB  
Article
First-Principles Study of Amorphous Al2O3 ALD Coating in Li-S Battery Electrode Design
by Jake A. Klorman, Qing Guo and Kah Chun Lau
Energies 2022, 15(1), 390; https://doi.org/10.3390/en15010390 - 5 Jan 2022
Cited by 5 | Viewed by 3113
Abstract
The Li-S battery is exceptionally appealing as an alternative candidate beyond Li-ion battery technology due to its promising high specific energy capacity. However, several obstacles (e.g., polysulfides’ dissolution, shuttle effect, high volume expansion of cathode, etc.) remain and thus hinder the commercialization of [...] Read more.
The Li-S battery is exceptionally appealing as an alternative candidate beyond Li-ion battery technology due to its promising high specific energy capacity. However, several obstacles (e.g., polysulfides’ dissolution, shuttle effect, high volume expansion of cathode, etc.) remain and thus hinder the commercialization of the Li-S battery. To overcome these challenges, a fundamental study based on atomistic simulation could be very useful. In this work, a comprehensive investigation of the adsorption of electrolyte (solvent and salt) molecules, lithium sulfide, and polysulfide (Li2Sx with 2 ≤x≤ 8) molecules on the amorphous Al2O3 atomic layer deposition (ALD) surface was performed using first-principles density functional theory (DFT) calculations. The DFT results indicate that the amorphous Al2O3 ALD surface is selective in chemical adsorption towards lithium sulfide and polysulfide molecules compared to electrolytes. Based on this work, it suggests that the Al2O3 ALD is a promising coating material for Li-S battery electrodes to mitigate the shuttling problem of soluble polysulfides. Full article
(This article belongs to the Special Issue Advance in Lithium-Sulfur Battery)
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<p>The adsorption energy, <span class="html-italic">E<sub>a</sub></span> (in eV) on amorphous Al<sub>2</sub>O<sub>3</sub> ALD surface of various systems that consists of electrolyte (i.e., DME, MeCN, LiFSI in the white region), reactant (Li, S<sub>8</sub> in light green region), and Li<sub>2</sub>S<span class="html-italic"><sub>x</sub></span> with 1 <math display="inline"><semantics> <mrow> <mo>≤</mo> <mi>x</mi> <mo>≤</mo> </mrow> </semantics></math> 8 (in pink region) molecules based on DFT calculations. In general, <span class="html-italic">E<sub>a</sub></span> &gt; 0 implies that the system is thermodynamically feasible. Each data point represents an individual configuration of geometry optimization in DFT calculations.</p> Full article ">Figure 2
<p>The lowest energy configuration for each system during adsorption on Al<sub>2</sub>O<sub>3</sub> ALD surface: (<b>a</b>) DME, (<b>b</b>) Li<sub>2</sub>S, (<b>c</b>) Li<sub>2</sub>S<sub>2,</sub> and (<b>d</b>) Li<sub>2</sub>S<sub>8</sub> molecule. Color of atoms: oxygen (red), carbon (brown), hydrogen (white), aluminum (blue), sulfur (yellow), and lithium (green).</p> Full article ">Figure 3
<p>Two low energy configurations for Li<sub>2</sub>S<sub>3</sub> during chemisorption on Al<sub>2</sub>O<sub>3</sub> ALD surface. (<b>a</b>) The non-fragmented configuration is found with <span class="html-italic">E<sub>a</sub></span> ~ 3.55 eV, whereas (<b>b</b>) is the optimized geometry which yields fragmented Li<sub>2</sub>S<sub>3</sub> (i.e., Li + LiS<sub>3</sub>) with <span class="html-italic">E<sub>a</sub></span> ~ 3.75 eV.</p> Full article ">Figure 4
<p>The partial electronic density of states (DOS) of the lowest energy configuration for each system during adsorption on Al<sub>2</sub>O<sub>3</sub> ALD surface are plotted within the vicinity of Fermi level (i.e., −3.0 eV, 3.0 eV): (<b>a</b>) DME, (<b>b</b>) Li<sub>2</sub>S, (<b>c</b>) Li<sub>2</sub>S<sub>2</sub> and (<b>d</b>) Li<sub>2</sub>S<sub>8</sub> molecule. The dotted black line is the Fermi level. The total DOS, O-DOS, Al-DOS are in the black, red, and brown lines. The inset is the representative reference molecular system: the DME molecule DOS which O-DOS, C-DOS, H-DOS is in purple, green, and blue line (<b>a</b>: bottom right); the Li<sub>2</sub>S molecule DOS which Li-DOS, S-DOS is in orange and pink line (<b>b</b>: bottom right); the Li<sub>2</sub>S<sub>2</sub> molecule DOS (<b>c</b>: bottom right) and the Li<sub>2</sub>S<sub>8</sub> molecule DOS (<b>d</b>: bottom right).</p> Full article ">Figure 5
<p>The electronic charge density difference distribution at the interface between adsorbate (<b>a</b>) DME, (<b>b</b>) Li<sub>2</sub>S, (<b>c</b>) Li<sub>2</sub>S<sub>2</sub>, (<b>d</b>) Li<sub>2</sub>S<sub>8</sub> and Al<sub>2</sub>O<sub>3</sub> ALD surface. The yellow is electronic charge accumulation (negative charge) region, while the blue is electronic charge depletion (positive charge) region. The isosurface values are ~0.001 e/<math display="inline"><semantics> <mrow> <msup> <mo>Å</mo> <mn>3</mn> </msup> </mrow> </semantics></math> with the figures generated using VESTA software [<a href="#B45-energies-15-00390" class="html-bibr">45</a>].</p> Full article ">
38 pages, 5910 KiB  
Article
OC6 Phase Ia: CFD Simulations of the Free-Decay Motion of the DeepCwind Semisubmersible
by Lu Wang, Amy Robertson, Jason Jonkman, Jang Kim, Zhi-Rong Shen, Arjen Koop, Adrià Borràs Nadal, Wei Shi, Xinmeng Zeng, Edward Ransley, Scott Brown, Martyn Hann, Pranav Chandramouli, Axelle Viré, Likhitha Ramesh Reddy, Xiang Li, Qing Xiao, Beatriz Méndez López, Guillén Campaña Alonso, Sho Oh, Hamid Sarlak, Stefan Netzband, Hyunchul Jang and Kai Yuadd Show full author list remove Hide full author list
Energies 2022, 15(1), 389; https://doi.org/10.3390/en15010389 - 5 Jan 2022
Cited by 25 | Viewed by 5115
Abstract
Currently, the design of floating offshore wind systems is primarily based on mid-fidelity models with empirical drag forces. The tuning of the model coefficients requires data from either experiments or high-fidelity simulations. As part of the OC6 (Offshore Code Comparison Collaboration, Continued, with [...] Read more.
Currently, the design of floating offshore wind systems is primarily based on mid-fidelity models with empirical drag forces. The tuning of the model coefficients requires data from either experiments or high-fidelity simulations. As part of the OC6 (Offshore Code Comparison Collaboration, Continued, with Correlation, and unCertainty (OC6) is a project under the International Energy Agency Wind Task 30 framework) project, the present investigation explores the latter option. A verification and validation study of computational fluid dynamics (CFD) models of the DeepCwind semisubmersible undergoing free-decay motion is performed. Several institutions provided CFD results for validation against the OC6 experimental campaign. The objective is to evaluate whether the CFD setups of the participants can provide valid estimates of the hydrodynamic damping coefficients needed by mid-fidelity models. The linear and quadratic damping coefficients and the equivalent damping ratio are chosen as metrics for validation. Large numerical uncertainties are estimated for the linear and quadratic damping coefficients; however, the equivalent damping ratios are more consistently predicted with lower uncertainty. Some difference is observed between the experimental and CFD surge-decay motion, which is caused by mechanical damping not considered in the simulations that likely originated from the mooring setup, including a Coulomb-friction-type force. Overall, the simulations and the experiment show reasonable agreement, thus demonstrating the feasibility of using CFD simulations to tune mid-fidelity models. Full article
(This article belongs to the Special Issue Numerical Analysis, Field Testing and Experimental Assessment of Offshore Wind Turbines)
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<p>The OC6-DeepCwind floating offshore wind turbine (FOWT) semisubmersible. (<b>a</b>) The geometry of the floater and the adopted coordinate system. The surge, sway, and heave motions are along the <span class="html-italic">x</span>-, <span class="html-italic">y</span>-, and <span class="html-italic">z</span>-directions, respectively. The roll, pitch, and yaw motions are also about the <span class="html-italic">x</span>-, <span class="html-italic">y</span>-, and <span class="html-italic">z</span>-axes, respectively. (<b>b</b>) Setup of the free-decay experiment in the MARIN Concept Basin (photo by Amy Robertson, NREL).</p> Full article ">Figure 2
<p>Numerical domain for CFD simulations. The three taut-spring mooring lines attached to the heave plates are also shown.</p> Full article ">Figure 3
<p>Vertical section of the baseline mesh.</p> Full article ">Figure 4
<p>Free-decay motion of the floater in (<b>a</b>) surge (Load Case [LC] 4.2), (<b>b</b>) heave (LC 4.4), and (<b>c</b>) pitch (LC 4.6). Legend: CENER = National Renewable Energy Centre; CLNK = ClassNK; DTU = Technical University of Denmark; DUT = Dalian University of Technology; IFPEN = IFP Energies nouvelles; TUD = Delft University of Technology; UOP = University of Plymouth; UOS = University of Strathclyde; TUHH = Hamburg University of Technology; ABS = American Bureau of Shipping; MARIN = Maritime Research Institute Netherlands; NREL = National Renewable Energy Laboratory; EXP = experiment.</p> Full article ">Figure 5
<p>Regression analyses extracting the surge-damping coefficients from (<b>a</b>) the CFD simulations performed by ABS, MARIN, and NREL (note that the NREL simulation is based on the baseline numerical setup of <a href="#sec3-energies-15-00389" class="html-sec">Section 3</a>) and (<b>b</b>) the experimental measurement. The symbols are the data points from the surge free-decay motion of the platform, and the lines or curve are the best fits of the data points. In (<b>a</b>), the fits are of the form given by Equation (9), which only considers linear and quadratic damping. In (<b>b</b>), the fit is given by Equation (11), which also includes a constant Coulomb-friction-like damping force.</p> Full article ">Figure 6
<p>Comparison of the MARIN CFD solutions for surge decay (LC 4.2) with and without <math display="inline"><semantics> <mrow> <msub> <mi>B</mi> <mn>0</mn> </msub> <mo>=</mo> <mn>2.3</mn> </mrow> </semantics></math> kN full scale. The experimental measurement (EXP) is included for reference. (<b>a</b>) Surge time series and (<b>b</b>) regression analysis for extracting the surge-damping coefficients.</p> Full article ">Figure 7
<p>Regression analyses extracting the heave-damping coefficients from (<b>a</b>) the CFD simulations performed by ABS, MARIN, and NREL (note that the NREL simulation is based on the baseline numerical setup of <a href="#sec3-energies-15-00389" class="html-sec">Section 3</a>) and (<b>b</b>) the experimental measurement. The symbols are the data points from the heave free-decay motion of the platform, and the lines are the best fits given by Equation (9).</p> Full article ">Figure 8
<p>Regression analyses extracting the pitch-damping coefficients from (<b>a</b>) the CFD simulations performed by ABS, MARIN, and NREL (note that the NREL simulation is based on the baseline numerical setup of <a href="#sec3-energies-15-00389" class="html-sec">Section 3</a>) and (<b>b</b>) the experimental measurement. The symbols are the data points from the pitch free-decay motion of the platform, and the lines are the best fits given by Equation (9).</p> Full article ">Figure 9
<p>Unnormalized root-mean-square (RMS) residual of the <math display="inline"><semantics> <mi>x</mi> </semantics></math>-moment equation at the end of each time step.</p> Full article ">Figure 10
<p>Time series of (<b>a</b>) the surge-decay motion and (<b>b</b>) the heave-decay motion obtained from the CFD simulations with different numbers of SIMPLE iterations per time step.</p> Full article ">Figure 10 Cont.
<p>Time series of (<b>a</b>) the surge-decay motion and (<b>b</b>) the heave-decay motion obtained from the CFD simulations with different numbers of SIMPLE iterations per time step.</p> Full article ">Figure 11
<p>Time series of (<b>a</b>) the surge-decay motion and (<b>b</b>) the heave-decay motion obtained from the CFD simulations with the four different levels of numerical refinement described in <a href="#energies-15-00389-t011" class="html-table">Table 11</a>.</p> Full article ">Figure 12
<p>Convergence of (<b>a</b>) the linear damping coefficient, (<b>b</b>) quadratic damping coefficient, and (<b>c</b>) equivalent linear damping ratio in surge with simultaneous time-step and grid refinement. The crosses are the CFD solutions computed with the four different refinement ratios in <a href="#energies-15-00389-t011" class="html-table">Table 11</a>, and the estimated discretization uncertainties are shown as symmetric uncertainty bands attached to the crosses.</p> Full article ">Figure 13
<p>Convergence of (<b>a</b>) the linear damping coefficient and (<b>b</b>) the quadratic damping coefficient in heave with simultaneous time-step and grid refinement. The crosses are the CFD solutions computed with the four different refinement ratios in <a href="#energies-15-00389-t011" class="html-table">Table 11</a>, and the estimated discretization uncertainties are shown as symmetric uncertainty bands attached to the crosses.</p> Full article ">Figure 14
<p>Periods of free-decay motions in surge, heave, and pitch from the experiment (EXP), the CFD simulations, and the potential-flow simulation (TUHH). For interpretation of the legends, which denote different participants of the OC6 Phase Ia project, please refer to the caption of <a href="#energies-15-00389-f004" class="html-fig">Figure 4</a>. The four NREL solutions correspond to the four different numerical setups used in the convergence study listed in <a href="#energies-15-00389-t011" class="html-table">Table 11</a>.</p> Full article ">Figure 15
<p>Comparison of the linear and quadratic damping in surge, characterized by the values of <math display="inline"><semantics> <mi>P</mi> </semantics></math> and <math display="inline"><semantics> <mi>Q</mi> </semantics></math>, respectively, and the equivalent linear damping ratio, <math display="inline"><semantics> <mi>ζ</mi> </semantics></math>, from the experiment (EXP), the CFD simulations, and the potential-flow simulation (TUHH). The <math display="inline"><semantics> <mi>P</mi> </semantics></math> and <math display="inline"><semantics> <mi>Q</mi> </semantics></math> values are calculated from the motion time series using the <math display="inline"><semantics> <mrow> <mi>P</mi> <mi>Q</mi> </mrow> </semantics></math> analysis discussed in <a href="#sec5-energies-15-00389" class="html-sec">Section 5</a> and are proportional to the linear and quadratic damping coefficients, <math display="inline"><semantics> <mrow> <msub> <mi>B</mi> <mn>1</mn> </msub> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <msub> <mi>B</mi> <mn>2</mn> </msub> </mrow> </semantics></math>, respectively, following Equation (10). The equivalent linear damping ratio, <math display="inline"><semantics> <mi>ζ</mi> </semantics></math>, is calculated using Equation (13). The amplitude factor <math display="inline"><semantics> <mrow> <msub> <mover accent="true"> <mi>F</mi> <mo>˜</mo> </mover> <mi>A</mi> </msub> </mrow> </semantics></math> used to normalize <math display="inline"><semantics> <mi>Q</mi> </semantics></math> is 2.8 m. For interpretation of the legends, which denote different participants of the OC6 Phase Ia project, please refer to the caption of <a href="#energies-15-00389-f004" class="html-fig">Figure 4</a>. The four NREL solutions correspond to the four different numerical setups used in the convergence study listed in <a href="#energies-15-00389-t011" class="html-table">Table 11</a>. The uncertainty bands attached to the NREL solutions are the numerical discretization uncertainties estimated in <a href="#sec6dot2-energies-15-00389" class="html-sec">Section 6.2</a>.</p> Full article ">Figure 16
<p>Comparison of the linear and quadratic damping in heave, characterized by the values of <math display="inline"><semantics> <mi>P</mi> </semantics></math> and <math display="inline"><semantics> <mi>Q</mi> </semantics></math>, respectively, and the equivalent linear damping ratio, <math display="inline"><semantics> <mi>ζ</mi> </semantics></math>, from the experiment (EXP), the CFD simulations, and the potential-flow simulation (TUHH). The <math display="inline"><semantics> <mi>P</mi> </semantics></math> and <math display="inline"><semantics> <mi>Q</mi> </semantics></math> values are calculated from the motion time series using the <math display="inline"><semantics> <mrow> <mi>P</mi> <mi>Q</mi> </mrow> </semantics></math> analysis discussed in <a href="#sec5-energies-15-00389" class="html-sec">Section 5</a> and are proportional to the linear and quadratic damping coefficients, <math display="inline"><semantics> <mrow> <msub> <mi>B</mi> <mn>1</mn> </msub> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <msub> <mi>B</mi> <mn>2</mn> </msub> </mrow> </semantics></math>, respectively, following Equation (10). The equivalent linear damping ratio, <math display="inline"><semantics> <mi>ζ</mi> </semantics></math>, is calculated using Equation (13). The amplitude factor <math display="inline"><semantics> <mrow> <msub> <mover accent="true"> <mi>F</mi> <mo>˜</mo> </mover> <mi>A</mi> </msub> </mrow> </semantics></math> used to normalize <math display="inline"><semantics> <mi>Q</mi> </semantics></math> is 0.48 m. For interpretation of the legends, which denote different participants of the OC6 Phase Ia project, please refer to the caption of <a href="#energies-15-00389-f004" class="html-fig">Figure 4</a>. The four NREL solutions correspond to the four different numerical setups used in the convergence study listed in <a href="#energies-15-00389-t011" class="html-table">Table 11</a>. The uncertainty bands attached to the NREL solutions are the numerical discretization uncertainties estimated in <a href="#sec6dot2-energies-15-00389" class="html-sec">Section 6.2</a>.</p> Full article ">Figure 17
<p>Comparison of the linear and quadratic damping in pitch, characterized by the values of <math display="inline"><semantics> <mi>P</mi> </semantics></math> and <math display="inline"><semantics> <mi>Q</mi> </semantics></math>, respectively, and the equivalent linear damping ratio, <math display="inline"><semantics> <mi>ζ</mi> </semantics></math>, from the experiment (EXP), the CFD simulations, and the potential-flow simulation (TUHH). The <math display="inline"><semantics> <mi>P</mi> </semantics></math> and <math display="inline"><semantics> <mi>Q</mi> </semantics></math> values are calculated from the motion time series using the <math display="inline"><semantics> <mrow> <mi>P</mi> <mi>Q</mi> </mrow> </semantics></math> analysis discussed in <a href="#sec5-energies-15-00389" class="html-sec">Section 5</a> and are proportional to the linear and quadratic damping coefficients, <math display="inline"><semantics> <mrow> <msub> <mi>B</mi> <mn>1</mn> </msub> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <msub> <mi>B</mi> <mn>2</mn> </msub> </mrow> </semantics></math>, respectively, following Equation (10). The equivalent linear damping ratio, <math display="inline"><semantics> <mi>ζ</mi> </semantics></math>, is calculated using Equation (13). The amplitude factor <math display="inline"><semantics> <mrow> <msub> <mover accent="true"> <mi>F</mi> <mo>˜</mo> </mover> <mi>A</mi> </msub> </mrow> </semantics></math> used to normalize <math display="inline"><semantics> <mi>Q</mi> </semantics></math> is 0.053 radian. For interpretation of the legends, which denote different participants of the OC6 Phase Ia project, please refer to the caption of <a href="#energies-15-00389-f004" class="html-fig">Figure 4</a>.</p> Full article ">
38 pages, 6700 KiB  
Review
A Review of Modelling of the FCC Unit—Part II: The Regenerator
by Thabang W. Selalame, Raj Patel, Iqbal M. Mujtaba and Yakubu M. John
Energies 2022, 15(1), 388; https://doi.org/10.3390/en15010388 - 5 Jan 2022
Cited by 8 | Viewed by 3323
Abstract
Heavy petroleum industries, including the Fluid Catalytic Cracking (FCC) unit, are among some of the biggest contributors to global greenhouse gas (GHG) emissions. The FCC unit’s regenerator is where these emissions originate mostly, meaning the operation of FCC regenerators has come under scrutiny [...] Read more.
Heavy petroleum industries, including the Fluid Catalytic Cracking (FCC) unit, are among some of the biggest contributors to global greenhouse gas (GHG) emissions. The FCC unit’s regenerator is where these emissions originate mostly, meaning the operation of FCC regenerators has come under scrutiny in recent years due to the global mitigation efforts against climate change, affecting both current operations and the future of the FCC unit. As a result, it is more important than ever to develop models that are accurate and reliable at predicting emissions of various greenhouse gases to keep up with new reporting guidelines that will help optimise the unit for increased coke conversion and lower operating costs. Part 1 of this paper was dedicated to reviewing the riser section of the FCC unit. Part 2 reviews traditional modelling methodologies used in modelling and simulating the FCC regenerator. Hydrodynamics and kinetics of the regenerator are discussed in terms of experimental data and modelling. Modelling of constitutive parts that are important to the FCC unit, such as gas–solid cyclones and catalyst transport lines, are also considered. This review then identifies areas where the current generation of models of the regenerator can be improved for the future. Parts 1 and 2 are such that a comprehensive review of the literature on modelling the FCC unit is presented, showing the guidance and framework followed in building models for the unit. Full article
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<p>Axial solid profile in FCC regenerator (redrawn from [<a href="#B3-energies-15-00388" class="html-bibr">3</a>]).</p> Full article ">Figure 2
<p>Displacement caused by a single rising bubble through a three-dimensional bed [<a href="#B86-energies-15-00388" class="html-bibr">86</a>].</p> Full article ">Figure 3
<p>Summary of Regenerator modelling and key hydrodynamic assumptions.</p> Full article ">Figure 4
<p>Comparison of predictions from FCC regenerator models in the literature against plant/experimental data for (<b>a</b>) axial profiles of carbon dioxide, (<b>b</b>) axial profiles of oxygen, (<b>c</b>) axial profiles of water vapor and (<b>d</b>) axial profiles of temperature, along the regenerator. Predictions from [<a href="#B18-energies-15-00388" class="html-bibr">18</a>,<a href="#B131-energies-15-00388" class="html-bibr">131</a>,<a href="#B132-energies-15-00388" class="html-bibr">132</a>,<a href="#B134-energies-15-00388" class="html-bibr">134</a>], and plant/experimental data from [<a href="#B19-energies-15-00388" class="html-bibr">19</a>,<a href="#B132-energies-15-00388" class="html-bibr">132</a>,<a href="#B144-energies-15-00388" class="html-bibr">144</a>].</p> Full article ">Figure 4 Cont.
<p>Comparison of predictions from FCC regenerator models in the literature against plant/experimental data for (<b>a</b>) axial profiles of carbon dioxide, (<b>b</b>) axial profiles of oxygen, (<b>c</b>) axial profiles of water vapor and (<b>d</b>) axial profiles of temperature, along the regenerator. Predictions from [<a href="#B18-energies-15-00388" class="html-bibr">18</a>,<a href="#B131-energies-15-00388" class="html-bibr">131</a>,<a href="#B132-energies-15-00388" class="html-bibr">132</a>,<a href="#B134-energies-15-00388" class="html-bibr">134</a>], and plant/experimental data from [<a href="#B19-energies-15-00388" class="html-bibr">19</a>,<a href="#B132-energies-15-00388" class="html-bibr">132</a>,<a href="#B144-energies-15-00388" class="html-bibr">144</a>].</p> Full article ">Figure 5
<p>(<b>a</b>) vortex flow patterns inside a tangential inlet cyclone [<a href="#B158-energies-15-00388" class="html-bibr">158</a>], (<b>b</b>) a basic vortex quick separation showing a multi-cyclone system for FCC reactor termination [<a href="#B159-energies-15-00388" class="html-bibr">159</a>].</p> Full article ">
24 pages, 3254 KiB  
Review
Prospects for the Development of the Russian Rare-Earth Metal Industry in View of the Global Energy Transition—A Review
by Alexey Cherepovitsyn and Victoria Solovyova
Energies 2022, 15(1), 387; https://doi.org/10.3390/en15010387 - 5 Jan 2022
Cited by 21 | Viewed by 5019
Abstract
Global energy transition trends are reflected not only in oil and gas market dynamics, but also in the development of related sectors. They influence the demand for various types of metals and minerals. It is well-known that clean technologies require far more metals [...] Read more.
Global energy transition trends are reflected not only in oil and gas market dynamics, but also in the development of related sectors. They influence the demand for various types of metals and minerals. It is well-known that clean technologies require far more metals than their counterparts relying on fossil fuels. Nowadays, rare-earth metals (REMs) have become part and parcel of green technologies as they are widely used in wind turbine generators, motors for electric vehicles, and permanent magnet generators, and there are no materials to substitute them. Consequently, growth in demand for this group of metals can be projected in the near future. The topic discussed is particularly relevant for Russia. On the one hand, current trends associated with the global energy transition affect the country’s economy, which largely depends on hydrocarbon exports. On the other hand, Russia possesses huge REM reserves, which may take the country on a low-carbon development path. However, they are not being exploited. The aim of this study is to investigate the prospects for the development of Russia’s rare-earth metal industry in view of the global energy transition. The study is based on an extensive list of references. The methods applied include content analysis, strategic management methods and instruments, as well as planning and forecasting. The article presents a comprehensive analysis of the global energy sector’s development, identifies the relationship between the REM market and modern green technologies, and elaborates the conceptual framework for the development of the REM industry in the context of the latest global tendencies. It also contains a critical analysis of the current trends in the Russian energy sector and the plans to develop the industry of green technologies, forecasts future trends in metal consumption within based on existing plans, and makes conclusions on future prospects for the development of the REM industry in Russia. Full article
(This article belongs to the Special Issue Sources and Markets of New Energy Minerals for Renewable Energy Generation and Storage)
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<p>Algorithm of the research.</p> Full article ">Figure 2
<p>Approaches to defining «energy transition». Source: compiled by the authors based on [<a href="#B5-energies-15-00387" class="html-bibr">5</a>,<a href="#B41-energies-15-00387" class="html-bibr">41</a>,<a href="#B42-energies-15-00387" class="html-bibr">42</a>].</p> Full article ">Figure 3
<p>Changes in oil prices and total investments in the global energy transition. Source: compiled by the authors based on [<a href="#B45-energies-15-00387" class="html-bibr">45</a>,<a href="#B46-energies-15-00387" class="html-bibr">46</a>].</p> Full article ">Figure 4
<p>Conceptual framework for the development of the rare-earth metal industry in the context of global energy transition trends.</p> Full article ">Figure 5
<p>Oil and coal production scenarios according to the Energy Strategy of the Russian Federation for the period up to 2035. Source: compiled by the authors based on [<a href="#B83-energies-15-00387" class="html-bibr">83</a>,<a href="#B84-energies-15-00387" class="html-bibr">84</a>].</p> Full article ">Figure 6
<p>Forecasted REM consumption (<b>a</b>) in the implementation of the plans announced by the state for the production of electric vehicles; (<b>b</b>) in the implementation of the plans announced by the state for the production of electric vehicles without taking into account the ZETTA electric vehicle that does not require REMs.</p> Full article ">Figure 7
<p>Comparison of planned and actual indicators of wind production capacities in Russia with an assessment of potential requirements for rare-earth materials.</p> Full article ">Figure 8
<p>Total demand for key REMs (cumulative total).</p> Full article ">Figure 9
<p>Forecasts for the increase in demand compared to the baseline indicator (if the plans associated with wind farms and electric vehicles are fulfilled), tons TREO.</p> Full article ">
16 pages, 4789 KiB  
Article
A Comparative Study of Equivalent Circuit Models for Electro-Chemical Impedance Spectroscopy Analysis of Proton Exchange Membrane Fuel Cells
by Lei Zhao, Haifeng Dai, Fenglai Pei, Pingwen Ming, Xuezhe Wei and Jiangdong Zhou
Energies 2022, 15(1), 386; https://doi.org/10.3390/en15010386 - 5 Jan 2022
Cited by 21 | Viewed by 4056
Abstract
Electrochemical impedance spectroscopy is one of the important tools for the performance analysis and diagnosis of proton exchange membrane fuel cells. The equivalent circuit model is an effective method for electrochemical impedance spectroscopy resolution. In this paper, four typical equivalent circuit models are [...] Read more.
Electrochemical impedance spectroscopy is one of the important tools for the performance analysis and diagnosis of proton exchange membrane fuel cells. The equivalent circuit model is an effective method for electrochemical impedance spectroscopy resolution. In this paper, four typical equivalent circuit models are selected to comprehensively compare and analyze the difference in the fitting results of the models for the electrochemical impedance spectroscopy under different working conditions (inlet pressure, stoichiometry, and humidity) from the perspective of the fitting accuracy, change trend of the model parameters, and the goodness of fit. The results show that the fitting accuracy of the model with the Warburg element is the best for all under each working condition. When considering the goodness of fit, the model with constant phase components is the best choice for fitting electrochemical impedance spectroscopy under different inlet pressure and air stoichiometry. However, under different air humidity, the model with the Warburg element is best. This work can help to promote the development of internal state analysis, estimation, and diagnosis of the fuel cell based on the equivalent circuit modeling of electrochemical impedance spectroscopy. Full article
(This article belongs to the Collection Batteries, Fuel Cells and Supercapacitors Technologies)
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<p>Connection diagram of the fuel cell test system.</p> Full article ">Figure 2
<p>Nyquist diagram of the test fuel cell at 0.6 A/cm<sup>2</sup>.</p> Full article ">Figure 3
<p>Typical equivalent circuit models used to fit the EIS data of PEMFCs: (<b>a</b>) the model with constant phase elements; (<b>b</b>) the model with the Warburg element; (<b>c</b>) the model with capacitances; (<b>d</b>) the model with the constant phase element and capacitance.</p> Full article ">Figure 4
<p>The model-fitting results under different inlet pressure: (<b>a</b>) the fitting result of the model A; (<b>b</b>) the fitting result of the model B; (<b>c</b>) the fitting result of the model C; (<b>d</b>) the fitting result of the model D.</p> Full article ">Figure 5
<p>The model-fitting results under different air stoichiometry: (<b>a</b>) the fitting result of the model A; (<b>b</b>) the fitting result of the model B; (<b>c</b>) the fitting result of the model C; (<b>d</b>) the fitting result of the model D.</p> Full article ">Figure 6
<p>The model-fitting results under different air humidity: (<b>a</b>) the fitting result of the model A; (<b>b</b>) the fitting result of the model B; (<b>c</b>) the fitting result of the model C; (<b>d</b>) the fitting result of the model D.</p> Full article ">Figure 7
<p>The Changing trend of the model parameters under different inlet pressure: (<b>a</b>) the parameter variations of model A; (<b>b</b>) the parameter variations of model B; (<b>c</b>) the parameter variations of model C; (<b>d</b>) the parameter variations of model D.</p> Full article ">Figure 8
<p>The Changing trend of the model parameters under different air stoichiometry: (<b>a</b>) the parameter variations of model A; (<b>b</b>) the parameter variations of model B; (<b>c</b>) the parameter variations of model C; (<b>d</b>) the parameter variations of model D.</p> Full article ">Figure 9
<p>The Changing trend of the model parameters under different air humidity: (<b>a</b>) the parameter variations of model A; (<b>b</b>) the parameter variations of model B; (<b>c</b>) the parameter variations of model C; (<b>d</b>) the parameter variations of model D.</p> Full article ">
21 pages, 2798 KiB  
Review
Bio-Based Waste’ Substrates for Degraded Soil Improvement—Advantages and Challenges in European Context
by Malgorzata Kacprzak, Iwona Kupich, Anna Jasinska and Krzysztof Fijalkowski
Energies 2022, 15(1), 385; https://doi.org/10.3390/en15010385 - 5 Jan 2022
Cited by 23 | Viewed by 3202
Abstract
The area of degraded sites in the world is constantly expanding and has been a serious environmental problem for years. Such terrains are not only polluted, but also due to erosion, devoid of plant cover and organic matter. The degradation trends can be [...] Read more.
The area of degraded sites in the world is constantly expanding and has been a serious environmental problem for years. Such terrains are not only polluted, but also due to erosion, devoid of plant cover and organic matter. The degradation trends can be reversed by supporting remediation/reclamation processes. One of the possibilities is the introduction of biodegradable waste/biowaste substrates into the soil. The additives can be the waste itself or preformed substrates, such composts, mineral-organic fertilizers or biochar. In EU countries average value of compost used for land restoration and landfill cover was equal 4.9%. The transformation of waste in valuable products require the fulfillment of a number of conditions (waste quality, process conditions, law, local circumstances). Application on degraded land surface bio-based waste substrates has several advantages: increase soil organic matter (SOM) and nutrient content, biodiversity and activity of microbial soil communities and change of several others physical and chemical factors including degradation/immobilization of contaminants. The additives improve the water ratio and availability to plants and restore aboveground ecosystem. Due to organic additives degraded terrains are able to sequestrate carbon and climate mitigate. However, we identified some challenges. The application of waste to soil must comply with the legal requirements and meet the end of use criteria. Moreover, shorter or long-term use of bio-waste based substrate lead to even greater soil chemical or microbial contamination. Among pollutants, “emerging contaminants” appear more frequently, such microplastics, nanoparticles or active compounds of pharmaceuticals. That is why a holistic approach is necessary for use the bio-waste based substrate for rehabilitation of soil degraded ecosystems. Full article
(This article belongs to the Special Issue Biodegradable Waste as an Element of the Circular Economy–Smart Solutions)
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<p>The samples of valuable compounds from biodegradable waste that can be used for degraded soil remediation/revitalization.</p> Full article ">Figure 2
<p>The use (as % of total mass) of sewage sludge for reclamation purposes between years of 2000 and 2019, performed their own study based on Statistics Poland data, (<a href="https://stat.gov.pl/en" target="_blank">https://stat.gov.pl/en</a>, accessed on 28 November 2021) [<a href="#B16-energies-15-00385" class="html-bibr">16</a>].</p> Full article ">Figure 3
<p>Materials used in the composting process [<a href="#B18-energies-15-00385" class="html-bibr">18</a>,<a href="#B19-energies-15-00385" class="html-bibr">19</a>,<a href="#B20-energies-15-00385" class="html-bibr">20</a>,<a href="#B21-energies-15-00385" class="html-bibr">21</a>,<a href="#B22-energies-15-00385" class="html-bibr">22</a>,<a href="#B23-energies-15-00385" class="html-bibr">23</a>].</p> Full article ">Figure 4
<p>Carbon-rich materials used in the composting process (<b>a</b>) and potential nitrogen sources for compost mixes (<b>b</b>) [<a href="#B25-energies-15-00385" class="html-bibr">25</a>,<a href="#B26-energies-15-00385" class="html-bibr">26</a>,<a href="#B27-energies-15-00385" class="html-bibr">27</a>,<a href="#B28-energies-15-00385" class="html-bibr">28</a>,<a href="#B29-energies-15-00385" class="html-bibr">29</a>].</p> Full article ">Figure 5
<p>A schematic diagram showing the mechanisms of sorption of organic and inorganic pollutants on biocarbons produced at high and low temperatures [<a href="#B48-energies-15-00385" class="html-bibr">48</a>], modified.</p> Full article ">Figure 6
<p>Methods of increasing carbon deposit in the soil [<a href="#B66-energies-15-00385" class="html-bibr">66</a>,<a href="#B67-energies-15-00385" class="html-bibr">67</a>].</p> Full article ">Figure 7
<p>Mycorrhized Scots pine growing in a plot in the field growing on control soil (<b>a</b>) and on soil enriched with sewage sludge (<b>b</b>), (photo M. Kacprzak).</p> Full article ">
22 pages, 1299 KiB  
Review
Waste Heat Recovery Technologies Revisited with Emphasis on New Solutions, Including Heat Pipes, and Case Studies
by Paul Christodoulides, Rafaela Agathokleous, Lazaros Aresti, Soteris A. Kalogirou, Savvas A. Tassou and Georgios A. Florides
Energies 2022, 15(1), 384; https://doi.org/10.3390/en15010384 - 5 Jan 2022
Cited by 26 | Viewed by 6009
Abstract
Industrial processes are characterized by energy losses, such as heat streams rejected to the environment in the form of exhaust gases or effluents occurring at different temperature levels. Hence, waste heat recovery (WHR) has been a challenge for industries, as it can lead [...] Read more.
Industrial processes are characterized by energy losses, such as heat streams rejected to the environment in the form of exhaust gases or effluents occurring at different temperature levels. Hence, waste heat recovery (WHR) has been a challenge for industries, as it can lead to energy savings, higher energy efficiency, and sustainability. As a consequence, WHR methods and technologies have been used extensively in the European Union (EU) (and worldwide for that matter). The current paper revisits and reviews conventional WHR technologies, their use in all types of industry, and their limitations. Special attention is given to alternative “new” technologies, which are discussed for parameters such as projected energy and cost savings. Finally, an extended review of case studies regarding applications of WHR technologies is presented. The information presented here can also be used to determine target energy performance, as well as capital and installation costs, for increasing the attractiveness of WHR technologies, leading to the widespread adoption by industry. Full article
(This article belongs to the Special Issue Applications and New Technologies of Waste Heat Recovery)
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<p>Heat recovery range and technologies in I-ThERM.</p> Full article ">Figure 2
<p>Flat heat pipe application schematic (adapted from [<a href="#B38-energies-15-00384" class="html-bibr">38</a>]).</p> Full article ">Figure 3
<p>Schematic representation of a condensing economizer.</p> Full article ">Figure 4
<p>Schematic representation of the trilateral flush cycle.</p> Full article ">Figure 5
<p>Schematic representation of the supercritical carbon dioxide cycle.</p> Full article ">
13 pages, 2150 KiB  
Article
Numerical Simulation of Operating Parameters of the Ground Source Heat Pump
by Filip Bartyzel, Tomasz Wegiel, Magdalena Kozień-Woźniak and Marek Czamara
Energies 2022, 15(1), 383; https://doi.org/10.3390/en15010383 - 5 Jan 2022
Cited by 2 | Viewed by 4577
Abstract
Due to the growing demand for new ecological, low-emission heat sources, there is a need to develop new tools for simulating the operating parameters and costs of the implemented solutions. The article analyses the existing solutions for the simulation of heat pump operation [...] Read more.
Due to the growing demand for new ecological, low-emission heat sources, there is a need to develop new tools for simulating the operating parameters and costs of the implemented solutions. The article analyses the existing solutions for the simulation of heat pump operation parameters, describes the requirements for a modern building—nZEB and proposes a simulation tool based on thermodynamic parameters of the refrigerant. The script allows for deriving simple linear equations that can be used for the overall simulation of a system in which the heat pump is a key part and the efficiency of the entire system depends on its performance. The developed numerical script allows for reproducing the Linde refrigeration cycle and the parameters of its characteristic points. To calibrate the simulation, historical data obtained from the SOPSAR system were used. These data were pre-cleaned (peaks and other obvious measurement errors were removed). The obtained numerical model in combination with ground and air temperatures, anticipated hot water consumption and energy losses of the building can be used to simulate the annual performance and energy consumption of the heat pump. The obtained linear models have an RSMD error of 8% compared to historical data from SOPSAR system for all sets of simulated temperatures. Full article
(This article belongs to the Special Issue Computational Thermal, Energy, and Environmental Engineering)
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<p>Log T-s diagram of the vapour-compression refrigeration cycle. Reprinted with permission from ref. [<a href="#B19-energies-15-00383" class="html-bibr">19</a>]. 2017 Duarte et al.</p> Full article ">Figure 2
<p>Log p-h diagram of the vapour-compression refrigeration cycle. Reprinted with permission from ref. [<a href="#B19-energies-15-00383" class="html-bibr">19</a>]. 2017 Duarte et al.</p> Full article ">Figure 3
<p>Schematics of the vapour-compression device. Reprinted with permission from ref. [<a href="#B19-energies-15-00383" class="html-bibr">19</a>]. 2017 Duarte et al.</p> Full article ">Figure 4
<p>Schematics of RESHeat system. Reprinted with permission from ref. [<a href="#B23-energies-15-00383" class="html-bibr">23</a>]. 2021 Ocłoń.</p> Full article ">Figure 5
<p>Characteristic points for R410A refrigerant cycle generated by the Python script for source temperature equal to 5 °C and sink temperature of 45 °C.</p> Full article ">Figure 6
<p>Elements of existing SOPSAR system, solar tracked collectors manufactured by the Elfran company (<b>top left corner</b>), solar tracked PV-T panels manufactured by the Elfran company (<b>top right corner</b>), underground heat storage tanks (<b>bottom left corner</b>), and heat pump (<b>bottom right corner</b>). Reprinted with permission from ref. [<a href="#B23-energies-15-00383" class="html-bibr">23</a>]. 2021 Ocłoń.</p> Full article ">Figure 7
<p>COP results for sink temperature = 45 °C.</p> Full article ">Figure 8
<p>COP results for sink temperature = 50 °C.</p> Full article ">
19 pages, 5607 KiB  
Article
Chlorine Corrosion in a Low-Power Boiler Fired with Agricultural Biomass
by Danuta Król, Przemysław Motyl and Sławomir Poskrobko
Energies 2022, 15(1), 382; https://doi.org/10.3390/en15010382 - 5 Jan 2022
Cited by 15 | Viewed by 2459
Abstract
The selection of appropriate heat-resistant materials which are at the same time resistant to atmospheres rich in chlorine and its compounds is one of the most important current construction problems in steel boiler elements when using biomass fuels of agricultural origin. In the [...] Read more.
The selection of appropriate heat-resistant materials which are at the same time resistant to atmospheres rich in chlorine and its compounds is one of the most important current construction problems in steel boiler elements when using biomass fuels of agricultural origin. In the research presented here, an area was identified in the furnace of a 10 kW boiler where there was a potential risk of chlorine corrosion. This zone was determined based on numerical analysis of the combustion process; it is the zone with the highest temperatures and where the gas atmosphere conducive to the formation of chlorine corrosion centers. Subsequently, tests were carried out in the process environment of the combustion chamber of a 10 kW boiler (the fuel was barley straw) by placing samples of eight construction materials in a numerically-designated zone. These included samples of steel (coal boiler St41K, heat-resistant H25T and H24JS, and heat-resistant valve 50H21G9N4) as well as intermetallic materials based on phases (FeAl, Fe3Al, NiAl, and Ni3Al). The samples remained in the atmosphere of the boiler furnace for 1152 h at a temperature of 750–900 °C. After this time, the surfaces of the samples were subjected to SEM microscopy and scanning analysis. The results showed that the St41K boiler steel was not suitable for operation under the assumed conditions, and that a thick layer of complex corrosion products was visible on its surface. The least amount of corrosion damage was observed for the samples of 50H21G9N4 steel and intermetallic materials. Full article
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<p>Barley straw pellets.</p> Full article ">Figure 2
<p>Temperature distribution [K].</p> Full article ">Figure 3
<p>(<b>a</b>) O<sub>2</sub> concentration [%]; (<b>b</b>) CO concentration [%].</p> Full article ">Figure 4
<p>Temperature distribution [K].</p> Full article ">Figure 5
<p>(<b>a</b>) O<sub>2</sub> concentration [%]; (<b>b</b>) CO concentration [%].</p> Full article ">Figure 6
<p>View of the boiler: (<b>a</b>) The boiler on the test stand; (<b>b</b>) Combustion chamber with marked key levels for further analysis of the results.</p> Full article ">Figure 7
<p>Dimensions of steel samples.</p> Full article ">Figure 8
<p>Photos of samples of the St41K boiler steel after exposure in the combustion chamber of the boiler: (<b>a</b>) a layer of porous corrosion products; (<b>b</b>) exposure of the substrate.</p> Full article ">Figure 9
<p>Photo of the 50H21G9N4 steel sample after exposure in the boiler combustion chamber.</p> Full article ">Figure 10
<p>Photo of a sample of H24JS steel after exposure in the boiler combustion chamber.</p> Full article ">Figure 11
<p>Photo of the H25T steel sample after exposure in the boiler combustion chamber.</p> Full article ">Figure 12
<p>Photo of the FeAl intermetal sample after exposure in the boiler combustion chamber.</p> Full article ">Figure 13
<p>Photo of the Fe3Al intermetal sample after exposure in the boiler combustion chamber.</p> Full article ">Figure 14
<p>Photo of the NiAl intermetal sample after exposure in the boiler combustion chamber.</p> Full article ">Figure 15
<p>Photo of the Ni3Al intermetal sample after exposure in the boiler combustion chamber.</p> Full article ">Figure 16
<p>(<b>a</b>) The chemical composition of the surface of the St41K boiler steel in the planes pt1, pt2 and pt3 on the microscopic photo; (<b>b</b>) microscopic photo (SEM) of the surface of the St41K boiler steel.</p> Full article ">Figure 17
<p>(<b>a</b>) The chemical composition of the 50H21G9N4 valve steel surface in the pt1 surface in the microscopic photo; (<b>b</b>) microscopic photo (SEM) of the surface of the St41K boiler steel.</p> Full article ">Figure 18
<p>(<b>a</b>) Chemical composition of the surface of heat-resistant steel H24JS in planes pt1, pt2 and pt3; (<b>b</b>) microscopic photo (SEM) of the surface of H24JS heat-resistant steel.</p> Full article ">Figure 19
<p>(<b>a</b>) Chemical composition of the surface of heat-resistant steel H25T in planes pt1 and pt2; (<b>b</b>) microscopic photo (SEM) of the surface of H25T heat-resistant steel.</p> Full article ">Figure 20
<p>(<b>a</b>) Chemical composition of the FeAl intermetal surface in the pt1 and pt2 surfaces; (<b>b</b>) microscopic photo (SEM) of the FeAl intermetal surface.</p> Full article ">Figure 21
<p>(<b>a</b>) Chemical composition of the Fe Al intermetal surface in the pt1 and pt2 planes; (<b>b</b>) microscopic photo (SEM) of the Fe<sub>3</sub>Al intermetal surface.</p> Full article ">Figure 22
<p>(<b>a</b>) Chemical composition of the NiAl intermetal surface in planes pt1, pt2, pt3 and pt4; (<b>b</b>) microscopic photo (SEM) of NiAl intermetal surface.</p> Full article ">Figure 23
<p>(<b>a</b>) Chemical composition of the Ni<sub>3</sub>Al intermetal surface in planes pt1, pt2 and pt3; (<b>b</b>) microscopic photo (SEM) of the Ni<sub>3</sub>Al.</p> Full article ">
14 pages, 4047 KiB  
Article
Prediction and Optimization of the Cost of Energy Resources in Greek Public Hospitals
by Paraskevi N. Zaza, Anastasios Sepetis and Pantelis G. Bagos
Energies 2022, 15(1), 381; https://doi.org/10.3390/en15010381 - 5 Jan 2022
Cited by 7 | Viewed by 2860
Abstract
The continuous operation and the specialized conditions needed for safely delivering healthcare services make hospitals among the most expensive buildings. Several studies in different countries have investigated the potential role and contribution of macroscopic indices of hospitals in total energy requirements. In this [...] Read more.
The continuous operation and the specialized conditions needed for safely delivering healthcare services make hospitals among the most expensive buildings. Several studies in different countries have investigated the potential role and contribution of macroscopic indices of hospitals in total energy requirements. In this work, we tried to investigate the energy requirements of Greek hospitals in terms of cost. We collected data from all public hospitals in Greece over a 2 year period (2018–2019) and evaluated the contribution of various factors in the total energy cost. The data revealed large variability by region and by hospital, even regarding structures of the same category and size. The analysis also showed that structural and operational data of each hospital differently influence the hospitals’ energy requirements. Using regression methods, we developed two models for calculating annual energy costs. One only contains hospital structural data (number of beds, type of hospital, number of employees, and the non/use of alternative energy sources such as natural gas), and it reached an R² of 0.84. The second model contains not only structural but also operational data from each hospital (number of the internal patients, number of surgeries and number of medical imaging tests), and it reached an R² of 0.87. The former model is easier to compute since it only relies on data that can be easily gathered, but the latter has slightly better performance. These tools can help the Ministry of Health and hospitals’ management to identify the factors that contribute to the energy cost in order to plan targeted interventions, be well-prepared regarding budgeting, and be able to progressively measure, monitor, and improve the environmental footprint of hospitals by investing in renewable energy resources. Full article
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>The hospital cost of energy resources vs. the number of beds.</p> Full article ">Figure 2
<p>The hospital cost of energy resources vs. the number of employees.</p> Full article ">Figure 3
<p>Box plots for cost of energy resources by hospital location.</p> Full article ">Figure 4
<p>Box plots for cost of energy resources by hospital type.</p> Full article ">Figure 5
<p>The hospital cost of energy resources vs. the number of the medical imaging tests performed per year.</p> Full article ">Figure 6
<p>Energy cost projections for hospitals with different numbers of beds with/without a natural gas supply.</p> Full article ">Figure 7
<p>Energy cost projections for hospitals with different numbers of beds with/without a natural gas supply.</p> Full article ">
16 pages, 3027 KiB  
Article
Self-Heating of Biochar during Postproduction Storage by O2 Chemisorption at Low Temperatures
by Aekjuthon Phounglamcheik, Nils Johnson, Norbert Kienzl, Christoph Strasser and Kentaro Umeki
Energies 2022, 15(1), 380; https://doi.org/10.3390/en15010380 - 5 Jan 2022
Cited by 3 | Viewed by 3430
Abstract
Biochar is attracting attention as an alternative carbon/fuel source to coal in the process industry and energy sector. However, it is prone to self-heating and often leads to spontaneous ignition and thermal runaway during storage, resulting in production loss and health risks. This [...] Read more.
Biochar is attracting attention as an alternative carbon/fuel source to coal in the process industry and energy sector. However, it is prone to self-heating and often leads to spontaneous ignition and thermal runaway during storage, resulting in production loss and health risks. This study investigates biochar self-heating upon its contact with O2 at low temperatures, i.e., 50–300 °C. First, kinetic parameters of O2 adsorption and CO2 release were measured in a thermogravimetric analyzer using biochar produced from a pilot-scale pyrolysis process. Then, specific heat capacity and heat of reactions were measured in a differential scanning calorimeter. Finally, a one-dimensional transient model was developed to simulate self-heating in containers and gain insight into the influences of major parameters. The model showed a good agreement with experimental measurement in a closed metal container. It was observed that char temperature slowly increased from the initial temperature due to heat released during O2 adsorption. Thermal runaway, i.e., self-ignition, was observed in some cases even at the initial biochar temperature of ca. 200 °C. However, if O2 is not permeable through the container materials, the temperature starts decreasing after the consumption of O2 in the container. The simulation model was also applied to examine important factors related to self-heating. The results suggested that self-heating can be somewhat mitigated by decreasing the void fraction, reducing storage volume, and lowering the initial char temperature. This study demonstrated a robust way to estimate the cooling demands required in the biochar production process. Full article
(This article belongs to the Special Issue Advances in Solid Fuels Conversion to Enable the Global Energy Transitions)
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<p>The closed metal container and the thermocouple positions.</p> Full article ">Figure 2
<p>Discretization and the boundary conditions.</p> Full article ">Figure 3
<p>TGA-DSC result in comparison with the models for: (<b>a</b>) mass; and (<b>b</b>) heat.</p> Full article ">Figure 4
<p>Temperatures as a function of time at different locations in the container (Conditions: T<sub>0</sub> = 33 °C, T<sub>ambient</sub> = 25 °C, <math display="inline"><semantics> <mrow> <msub> <mi>ρ</mi> <mrow> <mi>c</mi> <mo>,</mo> <mn>0</mn> </mrow> </msub> </mrow> </semantics></math> = 200 kg m<sup>−3</sup>, H<sub>container</sub> = 1 m): (<b>a</b>) Experimental results; (<b>b</b>) Simulation results with and without an effectiveness factor.</p> Full article ">Figure 5
<p>Evolution of local properties over time with the interval of 100 min (Conditions: T<sub>0</sub> = 33 °C, T<sub>ambient</sub> = 25 °C, <math display="inline"><semantics> <mrow> <msub> <mi>ρ</mi> <mrow> <mi>c</mi> <mo>,</mo> <mn>0</mn> </mrow> </msub> </mrow> </semantics></math> = 200 kg m<sup>−3</sup>, and H<sub>container</sub> = 1 m): (<b>a</b>) Local temperature; (<b>b</b>) char density; (<b>c</b>) O<sub>2</sub> mass fraction; (<b>d</b>) CO<sub>2</sub> mass fraction.</p> Full article ">Figure 6
<p>Effects of bed void fraction on the temperature at the center of a closed container. (Condition: T<sub>0</sub> = 33 °C, T<sub>ambient</sub> = 25 °C, H<sub>container</sub> = 1 m).</p> Full article ">Figure 7
<p>Effect of container size on the temperature at the center of the container with the conditions of T<sub>ambient</sub> = 25 °C, <math display="inline"><semantics> <mrow> <msub> <mi>ρ</mi> <mrow> <mi>c</mi> <mo>,</mo> <mn>0</mn> </mrow> </msub> </mrow> </semantics></math> = 200 kg m<sup>−3</sup>: (<b>a</b>) initial char temperatures of 33 °C; (<b>b</b>) initial char temperatures of 230 °C.</p> Full article ">Figure 8
<p>Effects of ambient temperature on the temperature at the center of the container with the storage conditions of <math display="inline"><semantics> <mrow> <msub> <mi>ρ</mi> <mrow> <mi>c</mi> <mo>,</mo> <mn>0</mn> </mrow> </msub> </mrow> </semantics></math> = 200 kg m<sup>−3</sup> and H<sub>container</sub> = 1 m: (<b>a</b>) initial char temperatures of 33 °C; (<b>b</b>) initial char temperatures of 230 °C.</p> Full article ">Figure 9
<p>Effects of char initial temperature with the strorage condition of T<sub>ambient</sub> = 25 °C, <math display="inline"><semantics> <mrow> <msub> <mi>ρ</mi> <mrow> <mi>c</mi> <mo>,</mo> <mn>0</mn> </mrow> </msub> </mrow> </semantics></math> = 200 kg m<sup>−3</sup>, and H<sub>container</sub> = 1 m: (<b>a</b>) on thermal runaway represented by the average char temperature; (<b>b</b>) on average char density.</p> Full article ">Figure 10
<p>Local profiles inside the storage container after 12 h (storage condition: T<sub>0</sub> = 210 °C, T<sub>ambient</sub> = 25 °C, <math display="inline"><semantics> <mrow> <msub> <mi>ρ</mi> <mrow> <mi>c</mi> <mo>,</mo> <mn>0</mn> </mrow> </msub> </mrow> </semantics></math> = 200 kg m<sup>−3</sup>, and H<sub>container</sub> = 1 m): (<b>a</b>) char temperature; (<b>b</b>) char density.</p> Full article ">Figure 11
<p>The safe biochar temperatures for safe storage in different types of containers. (storage condition: <math display="inline"><semantics> <mrow> <msub> <mi>ρ</mi> <mrow> <mi>c</mi> <mo>,</mo> <mn>0</mn> </mrow> </msub> </mrow> </semantics></math> = 200 kg m<sup>−3</sup>, H<sub>container</sub> = 1 m, t = 8 h).</p> Full article ">
18 pages, 16864 KiB  
Article
Simulation and Flow Analysis of the Hole Diaphragm Labyrinth Seal at Several Whirl Frequencies
by Xiang Zhang, Yinghou Jiao, Xiuquan Qu, Guanghe Huo and Zhiqian Zhao
Energies 2022, 15(1), 379; https://doi.org/10.3390/en15010379 - 5 Jan 2022
Cited by 6 | Viewed by 2486
Abstract
The seal is designed to reduce leakage and improve the efficiency of gas turbine machines, and is an important technology that needs to be studied in gas turbine design. A series of seals were proposed to try to achieve this goal. However, due [...] Read more.
The seal is designed to reduce leakage and improve the efficiency of gas turbine machines, and is an important technology that needs to be studied in gas turbine design. A series of seals were proposed to try to achieve this goal. However, due to the complex fluid dynamic performance of the seal-rotor system, the seal structure can obtain both the best leakage performance and best rotordynamic performance. This paper presents a detailed flow analysis of the hole diaphragm labyrinth seal (HDLS) at several whirl frequencies and several rotation speeds. The pressure drop, velocity, turbulence kinetic energy and leakage performance of the HDLS were discussed by simulations. An interesting exponential–type relationship between rotation speeds and leakage flow at different whirl frequencies was observed by curve fitting technology. A reverse flow rate was proposed to describe such an unusual phenomenon. Such a relationship can be used to further establish the leakage model of the HDLS and other similar seals. Full article
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<p>Sectional drawing of traditional LS structure.</p> Full article ">Figure 2
<p>Schematic diagram of the hole diaphragm labyrinth seal (HDLS).</p> Full article ">Figure 3
<p>Analysis panels and lines setting.</p> Full article ">Figure 4
<p>Meshing diagram of +y+z 45 degrees panel.</p> Full article ">Figure 5
<p>Schematic diagram of the quasi-steady-state model.</p> Full article ">Figure 6
<p>Simulation reliability validation.</p> Full article ">Figure 7
<p>Leakage performance of different elements meshing.</p> Full article ">Figure 8
<p>Pressure in the positive y-direction at different whirl frequencies (<math display="inline"><semantics> <mi>ω</mi> </semantics></math> = 5000 rpm).</p> Full article ">Figure 9
<p>Pressure comparison of different circumferential directions (<math display="inline"><semantics> <mi mathvariant="sans-serif">Ω</mi> </semantics></math> = 300 Hz).</p> Full article ">Figure 10
<p>Pressure drop in the positive y-direction.</p> Full article ">Figure 11
<p>Velocity curves in different directions with different whirl frequencies (<math display="inline"><semantics> <mi>ω</mi> </semantics></math> = 5000 rpm).</p> Full article ">Figure 12
<p>Circumferential direction velocity isopleth diagram in the first, fifth, and ninth cavities (<math display="inline"><semantics> <mi>ω</mi> </semantics></math> = 5000 rpm, <math display="inline"><semantics> <mi mathvariant="sans-serif">Ω</mi> </semantics></math> = 50 Hz).</p> Full article ">Figure 13
<p>Circumferential direction velocity isopleth diagram in the first, fifth, and ninth cavities (<math display="inline"><semantics> <mi>ω</mi> </semantics></math> = 5000 rpm, <math display="inline"><semantics> <mi mathvariant="sans-serif">Ω</mi> </semantics></math> = 300 Hz).</p> Full article ">Figure 14
<p>Streamlines form eight panels of HDLS (<math display="inline"><semantics> <mi>ω</mi> </semantics></math> = 5000 rpm, <math display="inline"><semantics> <mi mathvariant="sans-serif">Ω</mi> </semantics></math> = 50 Hz).</p> Full article ">Figure 15
<p>Surface streamline and velocity contour of HDLS (<math display="inline"><semantics> <mi>ω</mi> </semantics></math> = 5000 rpm, <math display="inline"><semantics> <mi mathvariant="sans-serif">Ω</mi> </semantics></math> = 50 Hz).</p> Full article ">Figure 16
<p>Turbulence kinetic energy contour of HDLS (<math display="inline"><semantics> <mi>ω</mi> </semantics></math> = 5000 rpm, <math display="inline"><semantics> <mi mathvariant="sans-serif">Ω</mi> </semantics></math> = 50 Hz).</p> Full article ">Figure 17
<p>Turbulence kinetic energy in the positive y-direction (<math display="inline"><semantics> <mi>ω</mi> </semantics></math> = 5000 rpm).</p> Full article ">Figure 18
<p>Turbulence kinetic energy with different positions and whirl frequencies (<math display="inline"><semantics> <mi>ω</mi> </semantics></math> = 5000 rpm).</p> Full article ">Figure 19
<p>Eddy viscosity of HDLS (<math display="inline"><semantics> <mi>ω</mi> </semantics></math> = 5000 rpm, <math display="inline"><semantics> <mi mathvariant="sans-serif">Ω</mi> </semantics></math> = 50 Hz).</p> Full article ">Figure 20
<p>Comparison of leakage performance at a 50 Hz whirl frequency between HDLS and traditional LS in Ref [<a href="#B9-energies-15-00379" class="html-bibr">9</a>].</p> Full article ">Figure 21
<p>Leakage performance of HDLS at different whirl frequencies.</p> Full article ">Figure 22
<p>Nonlinear curve fittings of leakage flow at different whirl frequencies.</p> Full article ">
20 pages, 351 KiB  
Article
On the Assessment of e-Banking Websites Supporting Sustainable Development Goals
by Witold Chmielarz and Marek Zborowski
Energies 2022, 15(1), 378; https://doi.org/10.3390/en15010378 - 5 Jan 2022
Cited by 7 | Viewed by 2356
Abstract
The main aim of this article was to test the authors’ proprietary method (i.e., the conversion method applied to evaluate e-banking services that support sustainable development goals in households, communities, and society). The authors’ conversion method can be applied with the aim of [...] Read more.
The main aim of this article was to test the authors’ proprietary method (i.e., the conversion method applied to evaluate e-banking services that support sustainable development goals in households, communities, and society). The authors’ conversion method can be applied with the aim of maintaining a balance between households, producers, and public administration services in line with the principles of sustainable development of the information society in Poland. To achieve this goal, the authors identified the differences between the results obtained using the conversion method and the results produced by other methods such as TOPSIS, Promethee II, and PROSA involving the same group of respondents. A hypothesis was made about the existence of significant differences in the results obtained as part of the studies. The research was carried out on a sample of nearly 830 ratings concerning the 27 most popular electronic banks in Poland. As part of the survey, the respondents assessed 18 characteristics (attributes) of the selected banks using a simplified Likert scale. The study was conducted during the pandemic in Poland in 2020. The authors compared the results achieved in the case of the TOPSIS, Promethee II, and PROSA methods and the ones obtained with the application of the conversion method. Then, the ratings of the e-banking websites were arranged in descending order, and the distances between the positions in the rankings obtained by the conversion method and other methods were calculated. In addition, the R2 correlation coefficients were calculated for all combinations of the results received using individual methods. The results showed the greatest differences both in the absolute distances between the positions obtained in the ranking and the lowest value of the R2 correlation coefficient in the case of the conversion method in relation to the other methods. The limitation of the present research resulted from the fact that the study sample included respondents who were all members of the academic environment. The students analyzed in the study were part of a group supporting globalization processes where e-business solutions are widely used. However, the purchases of goods and services both local and foreign made by this group were often limited in scope and value due to a lack of funds. The research results indicate a potential need for improvement of the conversion method. Full article
(This article belongs to the Special Issue Sustainable Development: Policies, Challenges, and Further)
13 pages, 1423 KiB  
Article
Biogas Generation from Maize and Cocksfoot Growing in Degraded Soil Enriched with New Zeolite Substrate
by Mariola Chomczyńska, Małgorzata Pawłowska, Oliwia Szczepaniak and Ewelina Duma
Energies 2022, 15(1), 377; https://doi.org/10.3390/en15010377 - 5 Jan 2022
Cited by 2 | Viewed by 1732
Abstract
Degraded lands are potential areas for obtaining biomass which can serve as an energy source after its conversion into biogas. Thus, the studies on biogas production from maize and cocksfoot biomasses obtained from degraded soil supplemented with additions of new zeolite substrate (Z-ion [...] Read more.
Degraded lands are potential areas for obtaining biomass which can serve as an energy source after its conversion into biogas. Thus, the studies on biogas production from maize and cocksfoot biomasses obtained from degraded soil supplemented with additions of new zeolite substrate (Z-ion as the nutrient carrier) and on arable soil (reference soil) were carried out during batch digestion tests. It was found that the biogas and biomethane potentials and specific energy of the test species growing in degraded soil enriched with Z-ion additions (1% and 5% v/v in the cases of cocksfoot and maize, respectively) did not differ significantly from the values of these parameters that were found for the plants growing in arable soil. The application of Z-ion to the degraded soil (especially in a dose of 5% v/v) resulted in an increase in the nitrogen content and decrease (below the lower optimum value) in the C/N ratio in the plant biomass. However, these changes did not negatively influence the final values of the biogas or methane potentials or the specific energy found for the maize biomass. Therefore, the study results indicated the usefulness of Z-ion substrate for improving the growth conditions for energy crops in degraded soils and, as a consequence, obtaining a plant feedstock suitable for the digestion process. Full article
(This article belongs to the Topic Anaerobic Digestion Processes)
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<p>Daily biogas production for (<b>a</b>) the cocksfoot biomass obtained in arable soil and degraded soil supplemented with a 1% Z-ion addition, and (<b>b</b>) the maize biomass obtained in arable soil and degraded soil supplemented with a 5% Z-ion addition (values presented as means, <span class="html-italic">n</span> = 3).</p> Full article ">Figure 2
<p>Cumulative biogas production for (<b>a</b>) the cocksfoot biomass obtained in arable soil and degraded soil supplemented with a 1% Z-ion addition and (<b>b</b>) the maize biomass obtained in arable soil and degraded soil supplemented with a 5% Z-ion addition (values presented as means, <span class="html-italic">n</span> = 3).</p> Full article ">
15 pages, 3574 KiB  
Article
Experimental Validation of a Hydrostatic Transmission for Community Wind Turbines
by Biswaranjan Mohanty and Kim A. Stelson
Energies 2022, 15(1), 376; https://doi.org/10.3390/en15010376 - 5 Jan 2022
Cited by 11 | Viewed by 2225
Abstract
Hydrostatic transmissions are commonly used in heavy-duty equipment for their design flexibility and superior power density. Compared to a conventional wind turbine transmission, a hydrostatic transmission (HST) is a lighter, more reliable, cheaper, continuously variable alternative for a wind turbine. In this paper, [...] Read more.
Hydrostatic transmissions are commonly used in heavy-duty equipment for their design flexibility and superior power density. Compared to a conventional wind turbine transmission, a hydrostatic transmission (HST) is a lighter, more reliable, cheaper, continuously variable alternative for a wind turbine. In this paper, for the first time, a validated dynamical model and controlled experiment have been used to analyze the performance of a hydrostatic transmission with a fixed-displacement pump and a variable-displacement motor for community wind turbines. From the dynamics of the HST, a pressure control strategy is designed to maximize the power capture. A hardware-in-the-loop simulation is developed to experimentally validate the performance and efficiency of the HST drive train control in a 60 kW virtual wind turbine environment. The HST turbine is extensively evaluated under steady and time-varying wind on a state-of-the-art power regenerative hydrostatic dynamometer. The proposed controller tracks the optimal tip-speed ratio to maximize power capture. Full article
(This article belongs to the Special Issue Advancement in Wind Turbine Technology)
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<p>HST wind turbine schematic.</p> Full article ">Figure 2
<p>A 100 kW power regenerative hydrostatic dynamometer.</p> Full article ">Figure 3
<p>Schematic of the HST wind turbine control.</p> Full article ">Figure 4
<p>Schematic of the hardware-in-the-loop test on the power regenerative dynamometer.</p> Full article ">Figure 5
<p>Power coefficient curve of a 60 kW wind turbine.</p> Full article ">Figure 6
<p>Wind inputs. (<b>A</b>) Step wind. (<b>B</b>) Guest wind. (<b>C</b>) Turbulent wind.</p> Full article ">Figure 7
<p>Performance of the HST wind turbine to a step wind.</p> Full article ">Figure 8
<p>Performance of the HST wind turbine to a gust wind.</p> Full article ">Figure 9
<p>Performance of the HST wind turbine to a turbulent wind.</p> Full article ">Figure 10
<p>Effect of rotor inertia on the rotor speed (<b>Top</b>: HIL simulated rotor speed; <b>Bottom</b>: Measured rotor speed).</p> Full article ">Figure 11
<p>Rotor power at steady wind measured on the dynamometer.</p> Full article ">Figure 12
<p>Efficiency of the HST wind turbine.</p> Full article ">Figure 13
<p>Generator torque and speed to a wind gust.</p> Full article ">
27 pages, 3409 KiB  
Review
Methods of Thermal Treatment of Radioactive Waste
by Leon Fuks, Irena Herdzik-Koniecko, Katarzyna Kiegiel, Agnieszka Miskiewicz and Grazyna Zakrzewska-Koltuniewicz
Energies 2022, 15(1), 375; https://doi.org/10.3390/en15010375 - 5 Jan 2022
Cited by 12 | Viewed by 4420
Abstract
Throughout the world, and especially in the European Union, numerous technologies for the thermal treatment of radioactive waste are available or being developed. These technologies can be applied to a large range of different radioactive waste streams, including non-standard types of waste that [...] Read more.
Throughout the world, and especially in the European Union, numerous technologies for the thermal treatment of radioactive waste are available or being developed. These technologies can be applied to a large range of different radioactive waste streams, including non-standard types of waste that present specific waste management challenges. Thermal treatment can result in a significant reduction in volume and hazard, which are beneficial for safe storage and disposal. Thermal treatment also removes organic material that can form complexing agents and increase the mobility of radionuclides in the landfill. In the paper, basic thermal techniques are presented, and some examples of the installations are shown. Common knowledge of these methods may result in an increased public acceptance of nuclear energy in a country just introducing it, as Poland is. Full article
(This article belongs to the Special Issue Storage and Disposal Options for Nuclear Waste)
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<p>Schematic presentation of: (<b>A</b>) combustion, gasification, or pyrolysis processes; (<b>B</b>) column distillation of wastewater.</p> Full article ">Figure 2
<p>(<b>A</b>) Technological scheme of converting high-level nuclear waste into solids in pot calcination (adapted from Ref. [<a href="#B10-energies-15-00375" class="html-bibr">10</a>]); (<b>B</b>) calcination vessel (adapted from Ref. [<a href="#B14-energies-15-00375" class="html-bibr">14</a>]).</p> Full article ">Figure 3
<p>(<b>A</b>,<b>B</b>) Scheme of the co-current and counter current rotary kilns; (<b>C</b>) secondary chamber in thermal process; (<b>D</b>) schematic illustration of the French two-step calciner, plus hot crucible vitrification process.</p> Full article ">Figure 4
<p>(<b>A</b>) Flowchart of a fluidized bed calcining system (adapted from Ref. [<a href="#B18-energies-15-00375" class="html-bibr">18</a>]); (<b>B</b>) schematic of a fluidized bed calciner (adapted from Ref. [<a href="#B19-energies-15-00375" class="html-bibr">19</a>]).</p> Full article ">Figure 5
<p>Schematic flowsheet of the WCF in the Idaho Chemical Processing Plant (adapted from Ref. [<a href="#B22-energies-15-00375" class="html-bibr">22</a>]).</p> Full article ">Figure 6
<p>(<b>A</b>) The process diagram of incinerator Pierrelatte (COGEMA) (adapted from Ref. [<a href="#B26-energies-15-00375" class="html-bibr">26</a>]); (<b>B</b>) simplified scheme of the COGEMA calciner skeleton (adapted from Ref. [<a href="#B26-energies-15-00375" class="html-bibr">26</a>]).</p> Full article ">Figure 7
<p>Process flow diagram of the Pyrolab Pilot process used at the La Hague plant (adapted from Ref. [<a href="#B29-energies-15-00375" class="html-bibr">29</a>]).</p> Full article ">Figure 8
<p>Schematic presentation of a fractional distillation of wastewater.</p> Full article ">Figure 9
<p>Schematic presentation of an installation for the recovery of boric acid by volatilization during evaporation (PC: pressure control; LC: level control; pH: pH control; QI: throughput indication) (adapted from Ref. [<a href="#B37-energies-15-00375" class="html-bibr">37</a>]).</p> Full article ">Figure 10
<p>Simplified diagram of the batch bituminization installation operating in the reprocessing plant at SCK CEN, Mol, Belgium (adapted from Ref. [<a href="#B40-energies-15-00375" class="html-bibr">40</a>]).</p> Full article ">Figure 11
<p>Simplified diagram of (continuous) extruder-type bituminization made in Marcoule, France (adapted from Ref. [<a href="#B19-energies-15-00375" class="html-bibr">19</a>]).</p> Full article ">Figure 12
<p>Schematic of a vitrification process (adapted from Ref. [<a href="#B21-energies-15-00375" class="html-bibr">21</a>]).</p> Full article ">Figure 13
<p>Scheme of the Synroc process using the Sandia method (adapted from Ref. [<a href="#B59-energies-15-00375" class="html-bibr">59</a>]).</p> Full article ">
22 pages, 11806 KiB  
Article
Extending DC Bus Utilization for Induction Motors with Stator Flux Oriented Direct Torque Control
by Tomas Esparza Sola, Huang-Jen Chiu, Yu-Chen Liu and Arief Noor Rahman
Energies 2022, 15(1), 374; https://doi.org/10.3390/en15010374 - 5 Jan 2022
Cited by 9 | Viewed by 2068
Abstract
This paper presents a method to extend the DC bus utilization on an induction motor (IM) by using a combination of Space-Vector Modulated Direct Torque Control (DTC–SVM) and conventional DTC. The scheme proposed in this paper exploits the advantages of both control methods. [...] Read more.
This paper presents a method to extend the DC bus utilization on an induction motor (IM) by using a combination of Space-Vector Modulated Direct Torque Control (DTC–SVM) and conventional DTC. The scheme proposed in this paper exploits the advantages of both control methods. During the linear region, it allows for a low torque ripple and low current harmonic distortion (THD). During the overmodulation region, it allows for the fastest torque response up to the six-step operation region. In both regions, there is complete independence of the motor parameters. The paper describes a way to provide a smooth transition between the two control schemes. Non-linearities affect the stator flux angle estimation, which leads to the inability to decouple torque and flux. To overcome this problem, a novel PI-based control scheme as well as a simplification on the decoupling terms’ calculation are proposed. Simulation and experimental results are presented to verify the feasibility of the proposed method. Full article
(This article belongs to the Special Issue Design and Control of Electrical Motor Drives II)
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<p>Conventional DTC principle: (<b>a</b>) control scheme; (<b>b</b>) flux hysteretic cycle; (<b>c</b>) torque hysteretic cycle.</p> Full article ">Figure 2
<p>Voltage vectors in conventional DTC.</p> Full article ">Figure 3
<p>DTC–SVM scheme operated in stator flux cartesian coordinates.</p> Full article ">Figure 4
<p>Stator flux block diagram.</p> Full article ">Figure 5
<p>Torque–speed curve of an induction motor.</p> Full article ">Figure 6
<p>Torque block diagram.</p> Full article ">Figure 7
<p>Modified integrator with a saturable feedback.</p> Full article ">Figure 8
<p>Stator flux ideally aligned with <span class="html-italic">d</span>-axis.</p> Full article ">Figure 9
<p>Misalignment in the stator flux: (<b>a</b>) <span class="html-italic">d</span>-axis lagging behind; (<b>b</b>) <span class="html-italic">d</span>-axis ahead.</p> Full article ">Figure 10
<p>Stator flux angle compensation block diagram.</p> Full article ">Figure 11
<p>DTC–SVM and conventional DTC working regions.</p> Full article ">Figure 12
<p>DTC–SVM combined with conventional DTC.</p> Full article ">Figure 13
<p>Control structure in detail: (<b>a</b>) DTC–SVM, (<b>b</b>) transition from conventional DTC to DTC–SVM and (<b>c</b>) conventional DTC.</p> Full article ">Figure 14
<p>Control mode selection algorithm.</p> Full article ">Figure 15
<p>Photograph of the applied IMs.</p> Full article ">Figure 16
<p>PI controller response for the no-load condition: (<b>a</b>) without correction of <math display="inline"><semantics> <mrow> <msub> <mi mathvariant="sans-serif">θ</mi> <mrow> <msub> <mi mathvariant="sans-serif">ψ</mi> <mi mathvariant="normal">s</mi> </msub> </mrow> </msub> </mrow> </semantics></math>, (<b>b</b>) with correction <math display="inline"><semantics> <mrow> <msub> <mi mathvariant="sans-serif">θ</mi> <mrow> <msub> <mi mathvariant="sans-serif">ψ</mi> <mi mathvariant="normal">s</mi> </msub> </mrow> </msub> </mrow> </semantics></math>.</p> Full article ">Figure 17
<p>PI controller response for the rated torque condition: (<b>a</b>) without correction of <math display="inline"><semantics> <mrow> <msub> <mi mathvariant="sans-serif">θ</mi> <mrow> <msub> <mi mathvariant="sans-serif">ψ</mi> <mi mathvariant="normal">s</mi> </msub> </mrow> </msub> </mrow> </semantics></math>, (<b>b</b>) with correction of <math display="inline"><semantics> <mrow> <msub> <mi mathvariant="sans-serif">θ</mi> <mrow> <msub> <mi mathvariant="sans-serif">ψ</mi> <mi mathvariant="normal">s</mi> </msub> </mrow> </msub> </mrow> </semantics></math>.</p> Full article ">Figure 18
<p>PI controller response for a step change in the load at constant speed: (<b>a</b>) without correction of <math display="inline"><semantics> <mrow> <msub> <mi mathvariant="sans-serif">θ</mi> <mrow> <msub> <mi mathvariant="sans-serif">ψ</mi> <mi mathvariant="normal">s</mi> </msub> </mrow> </msub> </mrow> </semantics></math>, (<b>b</b>) with correction of <math display="inline"><semantics> <mrow> <msub> <mi mathvariant="sans-serif">θ</mi> <mrow> <msub> <mi mathvariant="sans-serif">ψ</mi> <mi mathvariant="normal">s</mi> </msub> </mrow> </msub> </mrow> </semantics></math>.</p> Full article ">Figure 19
<p>Flux and torque decoupling terms behavior.</p> Full article ">Figure 20
<p>Transition between control modes for no-load condition: (<b>a</b>) whole operation region, (<b>b</b>) transition from DTC–SVM to conventional DTC and (<b>c</b>) transition from conventional DTC to DTC–SVM.</p> Full article ">Figure 21
<p>Transition between control modes at constant speed: (<b>a</b>) whole operation region for an increase on the load, (<b>b</b>) whole operation region for a reduction on the load, (<b>c</b>) zoom at the transition for an increase on the load and (<b>d</b>) zoom at the transition when the load is reduced.</p> Full article ">
24 pages, 2032 KiB  
Article
Multi-Agent Real-Time Advanced Metering Infrastructure Based on Fog Computing
by Ivan Popović, Aleksandar Rakić and Ivan D. Petruševski
Energies 2022, 15(1), 373; https://doi.org/10.3390/en15010373 - 5 Jan 2022
Cited by 10 | Viewed by 3247
Abstract
This effort to make the power grid more intelligent is tightly coupled with the deployment of advanced metering infrastructure (AMI) as an integral part of the future vision of smart grid. The goal of AMI is to provide necessary information for the consumers [...] Read more.
This effort to make the power grid more intelligent is tightly coupled with the deployment of advanced metering infrastructure (AMI) as an integral part of the future vision of smart grid. The goal of AMI is to provide necessary information for the consumers and utilities to accurately monitor and manage energy consumption and pricing in real time. Immediate benefits are enhanced transparency and efficiency of energy usage and the improvement of customer services. Although the road map toward successful AMI deployment is clearly defined, many challenges and issues are to be solved regarding the design of AMI. In this paper, a multi-agent AMI based on the fog-computing approach is presented. Architecture follows structural decomposition of AMI functionalities encapsulated in a form of local and area-specific service components that reside at the different tiers of hierarchically organized AMI deployment. Fog computing concepts provide the framework to effectively solve the problems of creating refined and scalable solutions capable of meeting the requirements of the AMI as a part of future smart grid. On the other hand, agent-based design enables concurrent execution of AMI operations across the distributed system architecture, in the same time improving performance of its execution and preserving the scalability of the AMI solution. The real-time performance of the proposed AMI solution, related to the periodic and on-demand acquisition of metering data from the connected electricity meters, was successfully verified during one year of pilot project operation. The detailed analysis of the performance of AMI operation regarding data collection, communication and data availability across the deployed pilot AMI, covering several transformer station areas with diverse grid topologies, is also presented. Full article
(This article belongs to the Special Issue Challenges and Research Trends of Smart Grids and Distribution Network)
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<p>Tiered AMI architecture based on fog computing.</p> Full article ">Figure 2
<p>Deployment of AMI services with the details of command execution data flow (red arrows—automatic operations, green arrows—on-demand commands).</p> Full article ">Figure 3
<p>AMI deployment in pilot project covering tree transformer station areas with different grid topologies.</p> Full article ">Figure 4
<p>Time distribution of load profile data availability at the MDC tier.</p> Full article ">Figure 5
<p>Timing analysis along the EM to MDC data path during the periodic acquisition of load profile data.</p> Full article ">Figure 6
<p>Time distribution of the data availability at the MDC tier during the acquisition of load profile data given for different TSC areas.</p> Full article ">Figure 7
<p>TCS area-specific distribution of the inter-node data availability time of load profile data along: (<b>a</b>) TSC-LMC data path; (<b>b</b>) LMC-EM data path.</p> Full article ">Figure 8
<p>Averaged time of on-demand readout command execution performed on a unified group of vendor-type specific EMs connected to single LMCs.</p> Full article ">
19 pages, 3753 KiB  
Article
The Impact of Alumina Nanofluids on Pool Boiling Performance on Biphilic Surfaces for Cooling Applications
by Ricardo Santos, Ana Sofia Moita, Ana Paula C. Ribeiro and António Luís N. Moreira
Energies 2022, 15(1), 372; https://doi.org/10.3390/en15010372 - 5 Jan 2022
Cited by 6 | Viewed by 1605
Abstract
This work aims to study the impact of nanofluids with alumina particles on pool boiling performance. Unlike most studies, which use a trial-and-error approach to improve boiling performance parameters, this study details the possible effects of nanoparticles on the effective mechanisms of boiling [...] Read more.
This work aims to study the impact of nanofluids with alumina particles on pool boiling performance. Unlike most studies, which use a trial-and-error approach to improve boiling performance parameters, this study details the possible effects of nanoparticles on the effective mechanisms of boiling and heat transfer. For this purpose, biphilic surfaces (hydrophilic surfaces with superhydrophobic spots) were used, which allow the individual analysis of bubbles. Surfaces with different configurations of superhydrophobic regions were used. The thermophysical properties of fluids only vary slightly with increasing nanoparticle concentration. The evolution of the dissipated heat flux and temperature profiles for a nucleation time frame is independent of the fluid and imposed heat flux. It can be concluded that the optimal concentration of nanoparticles is 3 wt%. Using this nanoparticle concentration leads to lower surface temperature values than those obtained with water, the reference fluid. This is due to the changes in the balance of forces in the triple line, induced by increased wettability as a consequence of the deposited particles. Wherefore, smaller and more frequent bubbles are formed, resulting in higher heat transfer coefficients. This effect, although relevant, is still of minor importance when compared to that of the use of biphilic surfaces. Full article
(This article belongs to the Special Issue Industrial Applications of Nanofluids in the Energy Sector)
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<p>Schematic view of the experimental setup: (1) boiling chamber, (2) funnel, (3) condensed fluid recipient, (4) computer, (5) tank base, (6) DC power supply, (7) high-speed camera, (8) infrared camera, (9) LED, and (10) Personal computer.</p> Full article ">Figure 2
<p>Test surface: (<b>a</b>) clean; (<b>b</b>) with deposited nanoparticles, after the experiment with 3 wt% concentration nanofluid.</p> Full article ">Figure 3
<p>Temporal evolution of the: (<b>a</b>) dissipated heat flux, (<b>b</b>) mean surface temperature. The interest area has a diameter of 3 mm, the fluid is water, and the imposed heat flux is 1290 W/m<sup>2</sup>.</p> Full article ">Figure 4
<p>Average dissipated heat flux for a nucleation time frame, for different imposed heat fluxes, using water and 3 wt% concentration Al<sub>2</sub>O<sub>3</sub>/water nanofluid. The superhydrophobic region is 1.5 mm in diameter. (<b>a</b>) 1290 W/m<sup>2</sup> (7 A). (<b>b</b>) 2132 W/m<sup>2</sup> (9 A). (<b>c</b>) 3790 W/m<sup>2</sup> (12 A).</p> Full article ">Figure 5
<p>Mean surface temperature profiles for all working fluids. The superhydrophobic region is 1.5 mm diameter. The imposed heat fluxes are: (<b>a</b>) 1290 W/m<sup>2</sup> (7 A), (<b>b</b>) 2132 W/m<sup>2</sup> (9 A), and (<b>c</b>) 3790 W/m<sup>2</sup> (12 A).</p> Full article ">Figure 6
<p>Wall superheat versus dissipated heat flux. The superhydrophobic region is 1.5 mm in diameter.</p> Full article ">Figure 7
<p>Dissipated heat flux versus heat transfer coefficient. The superhydrophobic region is 1.5 mm in diameter.</p> Full article ">Figure 8
<p>Average dissipated heat flux for a nucleation time frame, for different imposed heat fluxes, using water and 3 wt% concentration Al<sub>2</sub>O<sub>3</sub>/water nanofluid. Multiple superhydrophobic spots configuration. (<b>a</b>) 1290 W/m<sup>2</sup> (7 A). (<b>b</b>) 2132 W/m<sup>2</sup> (9 A). (<b>c</b>) 3790 W/m<sup>2</sup> (12 A).</p> Full article ">Figure 9
<p>Mean surface temperature profiles. Septuple superhydrophobic region with 1.5 mm diameter spots. The imposed heat fluxes are: (<b>a</b>) 1290 W/m<sup>2</sup> (7 A), (<b>b</b>) 2132 W/m<sup>2</sup> (9 A), and (<b>c</b>) 3790 W/m<sup>2</sup> (12 A).</p> Full article ">Figure 10
<p>Wall superheat versus dissipated heat flux. Septuple superhydrophobic region with 1.5 mm diameter spots.</p> Full article ">Figure 11
<p>Dissipated heat flux versus heat transfer coefficient. Septuple superhydrophobic region with 1.5 mm diameter spots.</p> Full article ">
31 pages, 13954 KiB  
Article
A Smart Energy Recovery System to Avoid Preheating in Gas Grid Pressure Reduction Stations
by Piero Danieli, Massimo Masi, Andrea Lazzaretto, Gianluca Carraro and Gabriele Volpato
Energies 2022, 15(1), 371; https://doi.org/10.3390/en15010371 - 5 Jan 2022
Cited by 6 | Viewed by 2412
Abstract
Preheating is often required to prevent hydrate formation during the pressure reduction process in a natural gas distribution network’s pressure reduction station. This paper examines an energy recovery method to avoid the cost and energy consumption of this preheating. The primary aim is [...] Read more.
Preheating is often required to prevent hydrate formation during the pressure reduction process in a natural gas distribution network’s pressure reduction station. This paper examines an energy recovery method to avoid the cost and energy consumption of this preheating. The primary aim is to assess the techno-economic feasibility of an energy recovery system based on the Ranque–Hilsch vortex tube coupled to a heat exchanger for large-scale application to the gas grid. To this end, a techno-economic model of the entire energy recovery system was included in an optimisation procedure. The resulting design minimises the payback period (PP) when the system is applied to the pressure reduction stations belonging to a particular gas grid. The pressure reduction stations always operate at an outlet pressure above atmospheric pressure. However, available performance models for the Ranque–Hilsch vortex tube do not permit prediction at backpressure operation. Therefore, a novel empirical model of the device is proposed, and a cost function derived from several manufacturer quotations is introduced for the first time, to evaluate the price of the Ranque–Hilsch vortex tubes. Finally, a nearly complete set of pressure reduction stations belonging to the Italian natural gas grid was chosen as a case study using actual operating parameters collected by each station’s grid manager. The results indicate that the environmental temperature strongly affects the technical and economic feasibility of the proposed energy recovery system. In general, pressure reduction stations operating at an ambient temperature above 0 °C are economically desirable candidates. In addition, the higher the energy recovery system convenience, the higher the flow rate and pressure drop managed by the station. In the Italian case study, 95% of preheating costs could be eliminated with a PP of fewer than 20 years. A 40% preheating cost saving is still possible if the maximum PP is limited to 10 years, and a small but non-negligible 3% of preheating costs could be eliminated with a PP of fewer than 4.5 years. Full article
(This article belongs to the Special Issue Advances in Natural Gas Engineering)
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<p>(<b>a</b>) Standard isothermal expansion within a PRS with a preheating system; (<b>b</b>) comparison between a gas expansion performed by the Ranque–Hilsch vortex tube (on the right) and a throttling valve (on the left); (<b>c</b>) isothermal expansion performed by the RHVT + HE system.</p> Full article ">Figure 2
<p>Heating and cooling effects of the Ranque–Hilsch vortex tube against expansion ratio and mass flow rate split as obtained from experimental data for (<b>a</b>) air and (<b>b</b>) predicted for methane.</p> Full article ">Figure 3
<p>(<b>a</b>) Index Z against expansion ratio for x ranging from 0.2 to 0.8; (<b>b</b>) heating and cooling efficiencies against expansion ratio for x ranging from 0.2 to 0.8.</p> Full article ">Figure 4
<p>Procedure to calculate the performance of RHVT for <span class="html-italic">p<sub>out</sub> &gt; p<sub>amb</sub></span>.</p> Full article ">Figure 5
<p>Comparison between experimental and predicted performance for the expansion of (<b>a</b>) methane and (<b>b</b>) air to <span class="html-italic">p<sub>out</sub> &gt; p<sub>amb</sub></span>.</p> Full article ">Figure 6
<p>Cost of RHVT vs. inlet pressure for a constant standard volumetric flow rate (100,000 Sm<sup>3</sup>/h).</p> Full article ">Figure 7
<p>Temperature correction of the hot fluid at the ‘cold side’ of the HE to account for possible ice formation and no forced convection (only natural convection) on the shell side.</p> Full article ">Figure 8
<p>Heat exchanger investment cost function.</p> Full article ">Figure 9
<p>Dimensionless annual trend of the PRS mass flow rate.</p> Full article ">Figure 10
<p>Cumulative percentage distribution of the 7142 PRSs with a preheating system installed in Italy against the annual averaged volume flow rate processed by the entire set of PRSs.</p> Full article ">Figure 11
<p>Block scheme of the methodology used to calculate the preheating costs.</p> Full article ">Figure 12
<p>Annual preheating cost against outlet pressure for PRSs expanding 100,000 Sm<sup>3</sup>/h of NG for several inlet pressures values.</p> Full article ">Figure 13
<p>Cumulative percentage distribution of preheating costs associated with the operation of 7142 PRSs installed in Italy against the annual averaged volume flow rate of gas processed.</p> Full article ">Figure 14
<p>Flowchart of the design optimisation procedure.</p> Full article ">Figure 15
<p>Technically feasible (blue) and unfeasible (red) inlet/outlet pressure pairs at ambient temperatures of (<b>a</b>) −5 °C and (<b>b</b>) −10 °C.</p> Full article ">Figure 16
<p>PP, percentage of PRSs with preheating systems, and preheating cost savings of the proposed system vs. annual averaged volume flow rate of the PRSs. Ambient temperature equal to (<b>a</b>) 10 °C, (<b>b</b>) 5 °C, (<b>c</b>) 0 °C, (<b>d</b>) −5 °C, and (<b>e</b>) −10 °C.</p> Full article ">Figure 16 Cont.
<p>PP, percentage of PRSs with preheating systems, and preheating cost savings of the proposed system vs. annual averaged volume flow rate of the PRSs. Ambient temperature equal to (<b>a</b>) 10 °C, (<b>b</b>) 5 °C, (<b>c</b>) 0 °C, (<b>d</b>) −5 °C, and (<b>e</b>) −10 °C.</p> Full article ">Figure A1
<p>PP vs. outlet pressure for various inlet pressures. Average volume flow rate of 100,000 Sm<sup>3</sup>/h and ambient temperature of 10 °C.</p> Full article ">Figure A2
<p>Cost of RHVT + HE vs. outlet pressure for different inlet pressures.</p> Full article ">Figure A3
<p>Flow rate split ratio vs. outlet pressure for different inlet pressures.</p> Full article ">Figure A4
<p>PP vs. outlet pressure for different inlet pressures. Averaged volume flow rate of (<b>a</b>) 5000 and (<b>b</b>) 100 Sm<sup>3</sup>/h and ambient temperature of 10 °C.</p> Full article ">Figure A5
<p>Cost of RHVT + HE vs. outlet pressure for different inlet pressures. Averaged volume flow rate of (<b>a</b>) 5000 Sm<sup>3</sup>/h and (<b>b</b>) 100 Sm<sup>3</sup>/h.</p> Full article ">Figure A6
<p>PP vs. outlet pressure for different inlet pressures. Averaged volume flow rate of 100,000 Sm<sup>3</sup>/h and ambient temperature of (<b>a</b>) 5 °C, (<b>b</b>) 0 °C, (<b>c</b>) −5 °C, and (<b>d</b>) −10 °C.</p> Full article ">Figure A7
<p>Cost of RHVT + HE vs. outlet pressure for different inlet pressures. Large size PRS (100,000 Sm<sup>3</sup>/h) and ambient temperature of (<b>a</b>) 5 °C, (<b>b</b>) 0 °C, (<b>c</b>) −5 °C, and (<b>d</b>) −10 °C.</p> Full article ">Figure A8
<p>PP vs. outlet pressure for different inlet pressures. Averaged volume flow rate of 5000 Sm<sup>3</sup>/h and ambient temperature of (<b>a</b>) 5 °C, (<b>b</b>) 0 °C, (<b>c</b>) −5 °C, and (<b>d</b>) −10 °C.</p> Full article ">Figure A9
<p>PP vs. outlet pressure for different inlet pressure. Averaged volume flow rate of 100 Sm<sup>3</sup>/h and ambient temperature of (<b>a</b>) 5 °C, (<b>b</b>) 0 °C, (<b>c</b>) −5 °C, and (<b>d</b>) −10 °C.</p> Full article ">Figure A9 Cont.
<p>PP vs. outlet pressure for different inlet pressure. Averaged volume flow rate of 100 Sm<sup>3</sup>/h and ambient temperature of (<b>a</b>) 5 °C, (<b>b</b>) 0 °C, (<b>c</b>) −5 °C, and (<b>d</b>) −10 °C.</p> Full article ">Figure A10
<p>Cost of RHVT + HE vs. outlet pressure for different inlet pressures. Medium size PRS (5000 Sm<sup>3</sup>/h) and ambient temperature (<b>a</b>) 5 °C, (<b>b</b>) 0 °C, (<b>c</b>) −5 °C, and (<b>d</b>) −10 °C.</p> Full article ">Figure A11
<p>Cost of RHVT + HE vs. outlet pressure for different inlet pressures. Small size PRS (100 Sm<sup>3</sup>/h) and ambient temperature (<b>a</b>) 5 °C, (<b>b</b>) 0 °C, (<b>c</b>) −5 °C, and (<b>d</b>) −10 °C.</p> Full article ">
18 pages, 447 KiB  
Review
Forecasting of Wind and Solar Farm Output in the Australian National Electricity Market: A Review
by John Boland, Sleiman Farah and Lei Bai
Energies 2022, 15(1), 370; https://doi.org/10.3390/en15010370 - 5 Jan 2022
Cited by 2 | Viewed by 2669
Abstract
Accurately forecasting the output of grid connected wind and solar systems is critical to increasing the overall penetration of renewables on the electrical network. This is especially the case in Australia, where there has been a massive increase in solar and wind farms [...] Read more.
Accurately forecasting the output of grid connected wind and solar systems is critical to increasing the overall penetration of renewables on the electrical network. This is especially the case in Australia, where there has been a massive increase in solar and wind farms in the last 15 years, as well as in roof top solar, both domestic and commercial. For example, in 2020, 27% of the electricity in Australia was from renewable sources, and in South Australia almost 60% was from wind and solar. In the literature, there has been extensive research reported on solar and wind resource, entailing both point and interval forecasts, but there has been much less focus on the forecasting of output from wind and solar systems. In this review, we canvass both what has been reported and also what gaps remain. In the case of the latter topic, there are numerous aspects that are not well dealt with in the literature. We have added discussion on the value of forecasts, rather than just focusing on forecast skill. Further, we present a section on how to deal with conditionally changing variance, a topic that has little focus in the literature. One other topic may be particularly important in Australia at the moment, but may become more widespread. This is how to deal with the concept of a clear sky output from a solar farm when the field is oversized compared to the inverter capacity, resulting in a plateau for the output. Full article
(This article belongs to the Special Issue Advances in Wind and Solar Farm Forecasting)
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<p>Clear day output in Broken Hill. Time is in 5 min intervals, with 288 intervals per day.</p> Full article ">Figure 2
<p>Clear day output in Broken Hill.</p> Full article ">Figure 3
<p>Exponentially weighted moving variance. Time is in 5 min intervals.</p> Full article ">Figure 4
<p>Histogram of wind farm output noise with normal curve overlaid.</p> Full article ">
17 pages, 60236 KiB  
Article
Improving Energy Efficiency by Utilizing Wetted Cellulose Pads in Passive Cooling Systems
by Ebrahim Morady, Madjid Soltani, Farshad Moradi Kashkooli, Masoud Ziabasharhagh, Armughan Al-Haq and Jatin Nathwani
Energies 2022, 15(1), 369; https://doi.org/10.3390/en15010369 - 5 Jan 2022
Cited by 4 | Viewed by 2291
Abstract
The effectiveness of using wetted cellulose pads on improving the performance of two conventional passive cooling systems has been evaluated. First, an experimental design was developed to determine the impact of using a wetted cellulose pad on the temperature and velocity of the [...] Read more.
The effectiveness of using wetted cellulose pads on improving the performance of two conventional passive cooling systems has been evaluated. First, an experimental design was developed to determine the impact of using a wetted cellulose pad on the temperature and velocity of the airflow. A cellulose pad (7090 model) with a cross-sectional area of 0.5 × 0.5 m2 and three different thicknesses of 10, 15, and 30 cm were selected and tested. The results indicated that using wetted cellulose pads with thicknesses ranging from 10–30 cm decreased the outlet airflow temperature from 11.3 to 13.7 °C on average. For free airflow at velocity 3.5 m/s, the outlet airflow velocity from the wetted cellulose pad decreased to 0.9, 0.7 and 0.6 m/s, respectively, for cellulose pads with thicknesses of 10, 15, and 30 cm. By applying experimental results on a psychrometric chart, the humidity ratio of outlet airflow was obtained between 40–70%. The study established airflow velocity as the critical parameter in passive cooling systems. With the novel concept of combining wetted cellulose pads for passive cooling systems (i.e., wind catchers and induced ventilation), there is good potential to reduce the energy requirements for thermal comfort in buildings in regions with a hot and arid climate. Full article
(This article belongs to the Section A3: Wind, Wave and Tidal Energy)
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<p>A view of one-sided wind catchers in Kashan city, Isfahan province, Iran.</p> Full article ">Figure 2
<p>A view of a different types of wind catcher. (<b>a</b>) One-sided wind catcher, Kashan city, Esfahan province, Iran. (<b>b</b>) Two-sided wind catcher [<a href="#B14-energies-15-00369" class="html-bibr">14</a>]. (<b>c</b>) A cylindrical wind catcher [<a href="#B14-energies-15-00369" class="html-bibr">14</a>]. (<b>d</b>) A four-sided wind catcher [<a href="#B14-energies-15-00369" class="html-bibr">14</a>].</p> Full article ">Figure 2 Cont.
<p>A view of a different types of wind catcher. (<b>a</b>) One-sided wind catcher, Kashan city, Esfahan province, Iran. (<b>b</b>) Two-sided wind catcher [<a href="#B14-energies-15-00369" class="html-bibr">14</a>]. (<b>c</b>) A cylindrical wind catcher [<a href="#B14-energies-15-00369" class="html-bibr">14</a>]. (<b>d</b>) A four-sided wind catcher [<a href="#B14-energies-15-00369" class="html-bibr">14</a>].</p> Full article ">Figure 3
<p>A schematic of (<b>a</b>) the laboratory prototype; (1) fan; electrical element and primary channel; (2) probe; (3) cellulose pad; (4) water storage tank with circulation pump; (5) holder; (6) secondary channel; (7) monitor; (8) calibrated rod. (<b>b</b>) Diagram of the sensor arrangement—measuring points—in the inlet and outlet section.</p> Full article ">Figure 4
<p>Different parts of the laboratory prototype of the present study; (<b>a</b>) pad with maximum thickness; (<b>b</b>) electrical elements; (<b>c</b>) top water distributor tray; (<b>d</b>) bottom water collector tray; (<b>e</b>) measurement probe.</p> Full article ">Figure 5
<p>Maximum distance and angle of placement of the cellulose pads.</p> Full article ">Figure 6
<p>Turbine anemometer.</p> Full article ">Figure 7
<p>Experimental results for outlet airflow velocity (from 7090 cellulose pad model).</p> Full article ">Figure 8
<p>Experimental results for outlet air temperature (from 7090 cellulose pad model).</p> Full article ">Figure 9
<p>Effectiveness of 7090 cellulose pad model.</p> Full article ">Figure 10
<p>The rate of evaporated water for 7090 cellulose pad model.</p> Full article ">Figure 11
<p>Evaporative cooling process for different pad thicknesses. (<b>a</b>) 10 cm. (<b>b</b>) 15 cm. (<b>c</b>) 30 cm.</p> Full article ">Figure 11 Cont.
<p>Evaporative cooling process for different pad thicknesses. (<b>a</b>) 10 cm. (<b>b</b>) 15 cm. (<b>c</b>) 30 cm.</p> Full article ">Figure 12
<p>A schematic of using wetted cellulose pad in the inflow section of the wind catcher: (1) cellulose pad; (2) wind catcher; (3) wind vane; (4) feed water pipe; (5) return pipe; (6) water circulation pump; (7) vent; (8) water reservoir tank; and (9) roof.</p> Full article ">Figure 13
<p>A schematic of (<b>a</b>) a high-rise tower with induced ventilation as a passive cooling method; (<b>b</b>) a floor of a high-rise tower with induced ventilation as a passive cooling method; (<b>c</b>) whole passive cooling process; and (<b>d</b>) an opening with cellulose pad and piping lines.</p> Full article ">Figure 13 Cont.
<p>A schematic of (<b>a</b>) a high-rise tower with induced ventilation as a passive cooling method; (<b>b</b>) a floor of a high-rise tower with induced ventilation as a passive cooling method; (<b>c</b>) whole passive cooling process; and (<b>d</b>) an opening with cellulose pad and piping lines.</p> Full article ">
15 pages, 3841 KiB  
Article
Possibility of Advanced Modified-Silica-Based Porous Materials Utilisation in Water Adsorption Processes—A Comparative Study
by Karol Sztekler, Agata Mlonka-Mędrala, Nezar H. Khdary, Wojciech Kalawa, Wojciech Nowak and Łukasz Mika
Energies 2022, 15(1), 368; https://doi.org/10.3390/en15010368 - 5 Jan 2022
Cited by 6 | Viewed by 2215
Abstract
Due to a high risk of power outages, a heat-driven adsorption chillers are gaining the attention. To increase the efficiency of the chiller, new adsorbents must be produced and examined. In this study, four newly developed silica–based porous materials were tested and compared [...] Read more.
Due to a high risk of power outages, a heat-driven adsorption chillers are gaining the attention. To increase the efficiency of the chiller, new adsorbents must be produced and examined. In this study, four newly developed silica–based porous materials were tested and compared with silica gel, an adsorber commonly paired with water. Extended sorption tests using mercury intrusion porosimetry, gas adsorption, and dynamic vapor sorption were performed. The morphology of the samples was determined using a scanning electron microscope. The thermal properties were defined using simultaneous thermal analysis and a laser flash method. Metal organic silica (MOS) nanocomposites analysed in this study had thermal properties similar to those of commonly used silica gel. MOS samples have a thermal diffusivity coefficient in the range of 0.17–0.25 mm2/s, whereas silica gel of about 0.2 mm2/s. The highest water adsorption capacity was measured for AFSMo-Cu and equal to 33–35%. For narrow porous silica gel mass uptake was equal about 25%. In the case of water adsorption, it was observed that the pore size of the sorbent is essential, and adsorbents with pore sizes higher than 5 nm, are most recommended in working pairs with water. Full article
(This article belongs to the Special Issue Adsorption Desalination and Cooling Systems: Advances in Design, Modeling and Performance)
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<p>Photographs of the samples analysed in the study.</p> Full article ">Figure 2
<p>Morphology analysis of adsorbents analysed in this study.</p> Full article ">Figure 3
<p>Pore distribution determined using mercury intrusion porosimetry.</p> Full article ">Figure 4
<p>Cumulative pore volume determined using mercury intrusion porosimetry.</p> Full article ">Figure 5
<p>Thermal diffusivity coefficient of selected samples measured at four process temperatures (30, 40, 50, 60 °C).</p> Full article ">Figure 6
<p>Adsorption and desorption isotherms for the AFSMo-Cu sample, at 30, 40, 50, and 60 °C.</p> Full article ">Figure 7
<p>Adsorption and desorption isotherms for the AFSPd-Cu sample, at 30, 40, 50, and 60 °C.</p> Full article ">Figure 8
<p>Adsorption and desorption isotherms for AFSPd-Cu (NP) sample, at 30, 40, 50 and 60 °C.</p> Full article ">Figure 9
<p>Adsorption and desorption isotherms for MPSilica samples, at 30, 40, 50 and 60 °C.</p> Full article ">Figure 10
<p>Adsorption and desorption isotherms for Silica gel samples, at 40, 50 and 60 °C.</p> Full article ">Figure 11
<p>Thermal behaviour of analysed sorbents up to 300 °C in oxidising atmosphere.</p> Full article ">
20 pages, 8634 KiB  
Article
Development and Test of a Novel Electronic Radiator Thermostat with a Return Temperature Limiting Function
by Michele Tunzi, Dorte Skaarup Østergaard and Svend Svendsen
Energies 2022, 15(1), 367; https://doi.org/10.3390/en15010367 - 5 Jan 2022
Cited by 3 | Viewed by 1905
Abstract
Automated hydronic balancing in space heating systems is crucial for the fourth-generation district heating transition. The current manual balancing requires labor- and time-consuming activities. This article presents the field results of an innovative electronic radiator thermostat tested on two Danish multi-family buildings. The [...] Read more.
Automated hydronic balancing in space heating systems is crucial for the fourth-generation district heating transition. The current manual balancing requires labor- and time-consuming activities. This article presents the field results of an innovative electronic radiator thermostat tested on two Danish multi-family buildings. The prototypes had an additional return temperature sensor on each radiator and an algorithm was used to accurately control valve opening to ensure automated hydronic balancing. The results highlighted that the new thermostat performed as expected and helped secure the cooling of district heating temperatures —defined as the difference between supply and return temperature—4–12 °C higher during the test compared to results obtained in 2020, when the prototypes were replaced with state-of-the-art thermostats in the first building. The measurements from the other building illustrated how only two uncontrolled radiators out of 175 could contaminate the overall return temperature. The remote connection of the thermostats helped pinpoint the faults in the heating system, although the end-users were not experiencing any discomfort, and secure, after fixing the problems, a return temperature of 35 °C. Future designs may consider integrating a safety functionality to close the valve or limit the flow in case of damage or malfunction to avoid a few radiators compromising the low-temperature operation of an entire building before the cause of the problem has been identified. Full article
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<p>Pictures of the two test buildings: Building A (<b>left</b>) and Building B (<b>right</b>).</p> Full article ">Figure 2
<p>Measurements of energy consumption for domestic hot water and space heating in Building A (in the two staircases) and Building B during the period where the prototypes were tested.</p> Full article ">Figure 3
<p>Building A plan and schematic view of the pipelines and risers; temperature sensors are installed on each return riser.</p> Full article ">Figure 4
<p>Building B section of the pipelines, risers and radiators; temperature sensors are installed on each return riser.</p> Full article ">Figure 5
<p>Pictures of the prototype thermostat and return temperature sensor and how they were installed on the supply (<b>left</b>) and on the side of the radiator (<b>right</b>) in the test buildings.</p> Full article ">Figure 6
<p>Monthly average district heating temperature difference during the past five years in Building A including timeline for adjustments.</p> Full article ">Figure 7
<p>Space heating supply and return temperatures vs. outdoor temperature during the prototype test and during the reference period afterward.</p> Full article ">Figure 8
<p>Comparison of the measured hourly average flow rates in the space heating system during the test and in the reference period afterward.</p> Full article ">Figure 9
<p>Supply and return temperatures in the space heating system during the test of prototype version 1.</p> Full article ">Figure 10
<p>Supply and return temperatures in the space heating system of the test staircase and from the main district heating meter during a period where string balancing valves are opened up.</p> Full article ">Figure 11
<p>Monthly average cooling of district heating temperatures during the past five years in Building B, including timeline for adjustments.</p> Full article ">Figure 12
<p>Hourly measurements of supply and return temperatures in the space heating system during the test of prototype 1 in February 2020.</p> Full article ">Figure 13
<p>Daily average measurements of supply and return temperatures in the space heating system during the test of prototype 1 in April 2020, where the supply temperature was reduced.</p> Full article ">Figure 14
<p>Hourly measurements of supply and return temperatures in the space heating system during the test of prototype 2.</p> Full article ">Figure 15
<p>Return temperature measurements from all risers in Building B, 14/11/2020–19/11/2020.</p> Full article ">Figure 16
<p>Return temperature measurements from the radiators connected to risers 1 and 10.</p> Full article ">
18 pages, 2947 KiB  
Article
Modeling Multivalued Dynamic Series of Financial Indexes on the Basis of Minimax Approximation
by Zahid Mamedov, Irina Vygodchikova, Ayaz Aliev, Lira Gurieva and Natalia Rud
Energies 2022, 15(1), 366; https://doi.org/10.3390/en15010366 - 5 Jan 2022
Cited by 1 | Viewed by 1779
Abstract
In this article, the problem of modeling a time series using the Minimax method is considered. The expediency of using Minimax to identify points of change in trends and the range of changes in the graphical figures of technical analysis is justified. Spline [...] Read more.
In this article, the problem of modeling a time series using the Minimax method is considered. The expediency of using Minimax to identify points of change in trends and the range of changes in the graphical figures of technical analysis is justified. Spline approximation of the dynamic process with range constraints was performed to improve the quality of the model. Investors are advised to refrain from making hasty decisions in favor of holding reliable shares (such as PJSC Novatek shares), rather than selling them. The purchase of new shares should be carefully analyzed. Through an approximation of the dynamic number of the applicable optimization problem of minimizing the maximum Hausdorff distances between the ranges of the dynamic series and the values of the approximating function, the applied approach can provide reliable justification for signals to buy shares. Energy policy occupies the highest place in the list of progress ratings according to news analytics of businesses related to the energy sector of the economy. At the same time, statistical indicators and technologies of expert developments in this field, including intellectual analysis, can become an important basis for the development of a robotic knowledge program in the field under study, an organic addition to which is the authors’ methodology of development in energy economics as in energy policy. This paper examines the model of approximation of the multivalued time series of PJSC Novatek, represented as a series of ranges of numerical values of the indicators of financial markets, with constraints on the approximating function. The authors consider it advisable for promising companies to apply this approach for successful long-term investment. Full article
(This article belongs to the Special Issue Innovative Economic Technologies and Policies in the Energy Sector)
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<p>DSS. Justification for using Minimax presented in Figures 5–7 and Table 1.</p> Full article ">Figure 2
<p>Spline joining points, selection (approximation error 10%).</p> Full article ">Figure 3
<p>First approximation by model (2), approximation error 5%.</p> Full article ">Figure 4
<p>Second approximation by model (2), approximation error 5%.</p> Full article ">Figure 5
<p>Improving the approximative properties of splines by using model (3), approximation error 3–6%, 3% at last period.</p> Full article ">Figure 6
<p>Minimax and OLS approximation (<span class="html-italic">n</span> = 1, line).</p> Full article ">Figure 7
<p>Spline (<span class="html-italic">n</span> = 2) and OLS approximation (<span class="html-italic">n</span> = 4).</p> Full article ">
18 pages, 5822 KiB  
Article
Mixed H2/H∞ Optimal Voltage Control Design for Smart Transformer Low-Voltage Inverter
by Wei Hu, Yu Shen, Zhichun Yang and Huaidong Min
Energies 2022, 15(1), 365; https://doi.org/10.3390/en15010365 - 5 Jan 2022
Cited by 2 | Viewed by 1659
Abstract
The smart transformer has been widely applied for the integration of renewables and loads. For the smart transformer application, the voltage control of low-voltage inverter is important for feeding the load. In this paper, a multi-objective optimization control design approach which comprehensively considers [...] Read more.
The smart transformer has been widely applied for the integration of renewables and loads. For the smart transformer application, the voltage control of low-voltage inverter is important for feeding the load. In this paper, a multi-objective optimization control design approach which comprehensively considers all aspects of indexes, such as linear quadratic (LQ) index, H∞ norm, and closed-loop poles placement, is proposed based on the linear matrix inequality (LMI) solution. The proposed approach is able to alleviate the weight of the designer from the tedious design process of the multiple resonant controllers and the selection of the weighting matrix for the LQ control. Besides that, some excellent performances such as fast recovering time, low total harmonic distortion (THD) and high robustness are achieved by the proposed approach. The THD are 0.5% and 1.7% for linear and non-linear loads, respectively. The voltage drop for linear load step is reduced to 10 V. The proposed approach is applied to a 5 kVA three-phase inverter to yield an optimal control law. Results from the simulation and experiment presented herein will illustrate and validate the proposed approach. Full article
(This article belongs to the Special Issue Smart Transformers and Their Role in Smart Grids)
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<p>Structure of the simple inverter system.</p> Full article ">Figure 2
<p>State space structure of the complex variable resonant controller (CVRC).</p> Full article ">Figure 3
<p>Closed-loop control structure of the system.</p> Full article ">Figure 4
<p>Region D in complex plane.</p> Full article ">Figure 5
<p>The schematic of the studied system.</p> Full article ">Figure 6
<p>Simulation results of the proposed optimal control law with different LC filter parameters: (<b>a</b>) 1 mH, 30 μF; (<b>b</b>) 2 mH, 15 μF; (<b>c</b>) 2 mH, 30 μF (nominal); (<b>d</b>) 2 mH, 60 μF.</p> Full article ">Figure 7
<p>Non-linear load circuit with a three-phase diode rectifier for (<b>a</b>) simulation and (<b>b</b>) experiment.</p> Full article ">Figure 8
<p>Steady waveforms and the total harmonic distortion (THD) of the proposed optimal control law under nominal LC filter parameters (2 mH, 30 μF): (<b>a</b>) linear load, (<b>b</b>) non-linear load.</p> Full article ">Figure 9
<p>Dynamic waveforms of the proposed optimal control law with different LC filter parameters: (<b>a</b>) 1 mH, 30 μF; (<b>b</b>) 2 mH, 15 μF; (<b>c</b>) 2 mH, 30 μF (nominal); (<b>d</b>) 2 mH, 60 μF.</p> Full article ">Figure 10
<p>Dynamic waveforms of the method proposed in 26 with different LC filter parameters: (<b>a</b>) 2 mH, 30 μF (nominal); (<b>b</b>) 2 mH, 60 μF.</p> Full article ">Figure 11
<p>Dynamic waveforms of the conventional linear quadratic regulation (LQR) with different LC filter parameters: (<b>a</b>) 2 mH, 30 μF (nominal); (<b>b</b>) 2 mH, 60 μF.</p> Full article ">
15 pages, 12654 KiB  
Article
Bio-Crude Production from Protein-Extracted Grass Residue through Hydrothermal Liquefaction
by Saqib Sohail Toor, Ayaz Ali Shah, Kamaldeep Sharma, Tahir Hussain Seehar, Thomas Helmer Pedersen and Lasse Aistrup Rosendahl
Energies 2022, 15(1), 364; https://doi.org/10.3390/en15010364 - 5 Jan 2022
Cited by 8 | Viewed by 2549
Abstract
In the present study, the protein-extracted grass residue (press cake) was processed through hydrothermal liquefaction under sub and supercritical temperatures (300, 350 and 400 °C) with and without using a potassium carbonate catalyst. The results revealed that bio-crude yield was influenced by both [...] Read more.
In the present study, the protein-extracted grass residue (press cake) was processed through hydrothermal liquefaction under sub and supercritical temperatures (300, 350 and 400 °C) with and without using a potassium carbonate catalyst. The results revealed that bio-crude yield was influenced by both temperature and the catalyst. The catalyst was found to be effective at 350 °C (350 Cat) for enhancing the bio-crude yield, whereas supercritical state in both catalytic and non-catalytic conditions improved the quality of bio-crude with reasonable HHVs (33 to 36 MJ/kg). The thermal behaviour of bio-crude was analysed and higher volatile contents (more than 50% under the range of 350 °C) were found at supercritical conditions. The overall TOC values in the residual aqueous phase varied from 22 to 38 g/L. Higher carbon loss was noticed in the aqueous phase in supercritical conditions. Furthermore, GCMS analysis showed ketones, acids and ester, aromatics and hydrocarbon with negligible nitrogen-containing compounds in bio-crude. In conclusion, the catalytic conversion of grass residue under subcritical conditions (350 Cat) is favourable in terms of high bio-crude yield, however, supercritical conditions promote the deoxygenation of oxygen-containing compounds in biomass and thus improve HHVs of bio-crude. Full article
(This article belongs to the Special Issue Hydrothermal Liquefaction for Aviation and Maritime Sustainable Fuels)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>BioRefinery process stages.</p> Full article ">Figure 2
<p>Volatility of grass residue.</p> Full article ">Figure 3
<p>Product yield at Sub-Supercritical conditions.</p> Full article ">Figure 4
<p>Volatility curves of bio-crudes.</p> Full article ">Figure 5
<p>Distribution of Organic Compounds.</p> Full article ">Figure 6
<p>TOC, TN and pH of the aqueous phase.</p> Full article ">Figure 7
<p>Carbon recovery in HTL products.</p> Full article ">
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