Biraj Singh Thapa
Kathmandu University, Mechanical Engineering, Faculty Member
The study incorporates an overview of the green hydrogen-production potential from wind energy in the USA, its application in power generation and the scope of substituting grey and blue hydrogen for industrial usage. Over 10 million... more
The study incorporates an overview of the green hydrogen-production potential from wind energy in the USA, its application in power generation and the scope of substituting grey and blue hydrogen for industrial usage. Over 10 million metric tons of grey and blue hydrogen is produced in the USA annually to fulfil the industrial demand, whereas, for 1 million metric tons of hydrogen generated, 13 million metric tons of CO2 are released into the atmosphere. The research aims to provide a state-of-the-art review of the green hydrogen technology value chain and a case study on the production of green hydrogen from an 8-MW wind turbine installed in the southern plain region of Texas. This research estimates that the wind-farm capacity of 130 gigawatt-hours is required to substitute grey and blue hydrogen for fulfilling the current US annual industrial hydrogen demand of 10 million metric tons. The study investigates hydrogen-storage methods and the scope of green hydrogen-based storage fa...
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Pumps are widely used machinery in various applications. Mostly now, a day in importance is seen from household applications to different industrial level. Various types of pumps are available in the market according to their applications... more
Pumps are widely used machinery in various applications. Mostly now, a day in importance is seen from household applications to different industrial level. Various types of pumps are available in the market according to their applications and centrifugal pumps are one of most common types among them. In the course of time, pumps faces various problems and repairing is required. Among them wear is one of the most common problem for reduction in pump performance. Cavitation, corrosion, erosion, fatigue are the common wear mechanisms faced by the centrifugal pumps. In order to minimize such problems frequent maintenance strategies are required. Various researchers have purposed different methodologies. Material properties, coatings in design and optimizing hydraulic and mechanical design for such challenges has been now a major topic of research. In this study, the different wear mechanisms and their causes with reference to various research paper is presented. Different effects for su...
Sediment erosion in hydraulic turbines are severe in case of hydropower plants operating in Himalayan Rivers of Nepal. Francis turbine components are heavily eroded while hard particles as quartz flow along with water through the water... more
Sediment erosion in hydraulic turbines are severe in case of hydropower plants operating in Himalayan Rivers of Nepal. Francis turbine components are heavily eroded while hard particles as quartz flow along with water through the water conduit in power plant. In Francis turbines, the runner blades where significant portion of hydraulic energy converts in mechanical energy are heavily eroded. This is due to complexity in fluid flow while operated at different operating conditions with sediment contained water. Conventional design of Francis turbines has overlooked on the effects of sediment erosion while considering optimum efficiency at all operating conditions. This paper examines multi-objective optimization of a reference 92 kW model Francis runner for minimizing sediment erosion effects. The model turbine studied in this paper is a scale down model turbine of Jhimruk Hydropower Plant, Nepal that is severely affected by sediment erosion. It was found that sediment erosion was red...
Cavitation is one of the major challenges in the Himalayan rivers of Nepal that cause damage and degradation of the performance of hydraulic turbine components. Numerical analysis has been performed to investigate the cavitation effect in... more
Cavitation is one of the major challenges in the Himalayan rivers of Nepal that cause damage and degradation of the performance of hydraulic turbine components. Numerical analysis has been performed to investigate the cavitation effect in the Francis turbine. For detection of cavitation, the SST turbulence model using Rayleigh plesset equation has been used in ANSYS-CFX. The turbine is investigated for three different operating conditions i.e. part load, BEP and full load under cavitation and without cavitation. The results are shown based on efficiency, pressure fluctuation, vortex rope and vapor volume fraction. It has been observed that changes in efficiency and pressure distribution are found to be minimal between cavitation and without cavitation conditions at rated discharge and head. Under part load condition, turbine efficiency loss and vapor bubbles formation at the leading edge of the runner blade is found to be maximum.
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Erosion on hydro turbine mostly depends on impingement velocity, angle of impact, concentration, shape, size and distribution of erodent particle and substrate material. In the case of Francis turbines, the sediment particles tend to... more
Erosion on hydro turbine mostly depends on impingement velocity, angle of impact, concentration, shape, size and distribution of erodent particle and substrate material. In the case of Francis turbines, the sediment particles tend to erode more in the off-designed conditions than at the best efficiency point. Previous studies focused on the optimized runner blade design to reduce erosion at the designed flow. However, the effect of the change in the design on other operating conditions was not studied. This paper demonstrates the performance of optimized Francis turbine exposed to sediment erosion in various operating conditions. Comparative study has been carryout among the five different shapes of runner, different set of guide vane and stay vane angles. The effect of erosion is studied in terms of average erosion density rate on optimized design Francis runner with Lagrangian particle tracking method in CFD analysis. The numerical sensitivity of the results are investigated by comparing two turbulence models. Numerical results are validated from the velocity measurements carried out in the actual turbine. Results show that runner blades are susceptible to more erosion at part load conditions compared to BEP, whereas for the case of guide vanes, more erosion occurs at full load conditions. Out of the five shapes compared, Shape 5 provides an optimum combination of efficiency and erosion on the studied operating conditions.
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Clearance gaps between guide vanes and cover plates of Francis turbines tend to increase in size due to simultaneous effect of secondary flow and erosion in sediment affected hydropower plants. The pressure difference between the two... more
Clearance gaps between guide vanes and cover plates of Francis turbines tend to increase in size due to simultaneous effect of secondary flow and erosion in sediment affected hydropower plants. The pressure difference between the two sides of the guide vane induces leakage flow through the gap. This flow enters into the suction side with high acceleration, disturbing the primary flow and causing more erosion and losses in downstream turbine components. A cascade rig containing a single guide vane passage has been built to study the effect of the clearance gap using pressure sensors and PIV (Particle Image Velocimetry) technique. This study focuses on developing a numerical model of the test rig, validating the results with experiments and investigating the behavior of leakage flow numerically. It was observed from both CFD and experiment that the leakage flow forms a passage vortex, which shifts away from the wall while travelling downstream. The streamlines contributing to the form...
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Guide vanes of Francis turbines convey a significant influence on the flow field at the inlet of the runner. This influence is in the form of pressure pulsation, caused due to rotor-stator-interaction. A guide vane cascade containing a... more
Guide vanes of Francis turbines convey a significant influence on the flow field at the inlet of the runner. This influence is in the form of pressure pulsation, caused due to rotor-stator-interaction. A guide vane cascade containing a single blade passage was developed to predict the flow field experimentally. Firstly, this paper investigates flow phenomena around the guide vane cascade through computational techniques. A numerical model is prepared with three different turbulence models. The velocity distribution obtained from these models are compared with experimental results at two circumferential midspan locations. Secondly, the influence of increasing the clearance gap on the flow is studied. Such gaps are expected to increase when the flow containing eroding particles passes through the turbine. This paper also shows that the pressure difference between the pressure and the suction side of guide vane influences the leakage flow through the gap. Hence, reduction of the pressure gradient will reduce leakages through clearance gaps, hereby condensing the subsequent effect of pressure pulsations and erosion. This study also shows that the effect of the gap is prominent in the near wall regions which are close to the gap, whereas it dissipates gradually towards the midspan.
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ABSTRACT Kathmandu University (KU) is one of the leading educational institutes in Nepal with a decade long experience with R&D of micro-hydro turbines. With a technical collaboration with Norwegian University of Science and... more
ABSTRACT Kathmandu University (KU) is one of the leading educational institutes in Nepal with a decade long experience with R&D of micro-hydro turbines. With a technical collaboration with Norwegian University of Science and Technology (NTNU), KU has also conducted several studies related to sediment erosion in hydro turbine.In the presented study a new program has been developed to create and optimize the design of Francis runners. The program is also featured to compare erosion in runner blades for different design cases. The final design can be exported to Computational Fluid Dynamics (CFD) and Fluid Structure Interaction (FSI) for further analysis. Parametric survey was carried out with this program to evaluate the relative effect of each design parameter on sediment erosion. Several optimized designs were developed and analyzed with CFD tools to fulfill the desired condition of minimum erosion and maximum efficiency.This paper summaries the problem of sediment erosion of hydro turbines in South Asia region. Some of the important achievements in R&D of hydro turbine and sediment erosion at KU are also presented. The findings of design optimization of Francis turbine for effective reduction in sediment erosion is discussed in details.
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Nepal has huge potential for hydropower due to glaciers in the Himalayas, regular monsoon rain and local topography. Most of the hydropower plants in the Himalayan Rivers are affected by excessive sediment which decrease the capacity of... more
Nepal has huge potential for hydropower due to glaciers in the Himalayas, regular monsoon rain and local topography. Most of the hydropower plants in the Himalayan Rivers are affected by excessive sediment which decrease the capacity of reservoir and cause erosion of turbine components. The erosion of hydraulic machinery depends on operating environment, properties of eroding particles and substrates. The shape, size and mineral content of sediment vary at different locations of the same river system, depending on distance traversed by particles, gradient of the river and the geological formation of the river course and catchments area. Khimti hydropower project, Nepal represents typical high head power plant in the Himalayan River which is affected by river sediment. The laboratory erosion tests of turbine material revealed the dependence of erosion rate with respect to mineral content. Sediments in the hydro power projects are normally considered as burden, but there is a scope of...
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Growth in global demand of clean energy has also increased hydropower development activities. This has also increased the necessity of overall efficiency improvements in hydropower plants for producing larger power with same site... more
Growth in global demand of clean energy has also increased hydropower development activities. This has also increased the necessity of overall efficiency improvements in hydropower plants for producing larger power with same site conditions. Efficiency improvement by design optimization of turbines is primary task in elevating performance of any hydropower projects. Institutional laboratory test facilities, which are expensive and demand high level of proficiency, are needed to certify performance of turbines. Due to the lack of well equipped and standard test facilities at South Asia region, efficiency measurement of turbines is mostly done at project sites. Kathmandu University (KU) is an autonomous, not-for-profit, non government institution dedicated to maintain high standards of academic excellence. With technical support from Norwegian Institute of Science and Technology (NTNU), KU has been upgrading its competency to support the ambitious plan of Government of Nepal (2010) to...
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Designing and manufacturing site-specific turbines for small hydropower is not economical. Using abundantly available Pump, from the market, as Turbine (PAT) instead of designing a completely different turbine can be much more economical... more
Designing and manufacturing site-specific turbines for small hydropower is not economical. Using abundantly available Pump, from the market, as Turbine (PAT) instead of designing a completely different turbine can be much more economical for small-scale hydropower. Lot of research have been going throughout the world on this and has already proven its effectiveness. In Nepalese hydropower, including the ones already developed and the ones that will be developed in the future, Francis turbines are supposedly the suitable turbine of choice. However, designing and manufacturing Francis turbine is a tedious task and the local manufacturers, who are expert in manufacturing Cross-flow turbines; do not have the technology and competence to manufacture the modern Francis turbines. Sediment in Himalayan rivers are the major hurdles of operation as they reduce the lifetime of the turbine by a very large factor, shooting up the maintenance cost of the hydropower. The operational region of Fran...
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Design of hydraulic turbines involves several stages of iterative calculations. The operational challenges of these turbines are unique to each site conditions. This makes the R&D of the hydraulic turbines a complicated and time consuming... more
Design of hydraulic turbines involves several stages of iterative calculations. The operational challenges of these turbines are unique to each site conditions. This makes the R&D of the hydraulic turbines a complicated and time consuming work. Recent advancements in computational tools and processors have added advantages to the R&D process of hydraulic turbines. These tools are able not only to compute solutions for the complex design equations but also provide the user friendly virtual environment for performance test and design optimization. This study is conducted tosimulate the design and operational problems of Francis and Pelton turbines by the application of computational tools. A new program is developed to optimize designs of Francis runners for sediment erosion problems and CFD analysis of some new design conditions is done. T rue size Pelton runner model is developed by using SolidWorksfor stress and fatigue analysis by using CosmosWorksin its operating conditions. It w...
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Sediment erosion is a major challenge for run-of-river power plants, especially during flood periods. Due to the high content of hard minerals such as quartz and feldspar carried in the river, substantial damage is observed on the turbine... more
Sediment erosion is a major challenge for run-of-river power plants, especially during flood periods. Due to the high content of hard minerals such as quartz and feldspar carried in the river, substantial damage is observed on the turbine components. Material is gradually removed, thus the efficiency of the turbine decreases and the operating time of the turbine reduces. Hydro power plants situated in areas with high sediment concentration suffer under hard conditions, where turbine components could be worn out after only a short period of three months. This short life expectation causes trouble for energy production since the replacement of new turbine parts is a time consuming and costly procedure. It is desirable to design a Francis runner which will withstand sediment erosion better than the traditional designs. The literature states that an expression for erosion is velocity to the power of three. By reducing the relative velocities in the runner by 10%, the erosion will decrea...
Large amounts of sediment in the Himalayan rivers causes severe silt erosion to the hydraulic machinery operating along these rivers. In this study, the effects of silt characteristics on the silt-erosion characteristics of a... more
Large amounts of sediment in the Himalayan rivers causes severe silt erosion to the hydraulic machinery operating along these rivers. In this study, the effects of silt characteristics on the silt-erosion characteristics of a double-suction centrifugal pump was studied and the anti-erosion property of bionic convex domes on silt erosion under these conditions was explored by using computational-fluid-dynamics methods, partly supported by a painted-blade erosion experiment. The results show that the silt size affects the erosion position and erosion strength, whereas the silt concentration mainly affects the erosion strength for the studied range. The bionic convex domes provide an effective solution to improve the silt erosion for most of the investigated silt-laden conditions by decreasing the erosion rate and the erosion area of the blade. The anti-erosion mechanism was studied combined with large eddy simulation. The analysis shows that the relative velocity of water around the b...
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The aim of this study was comparative analysis of sediment-induced erosion on optimized design and traditional design of Francis runner blade. The analysis was conducted through laboratory experiments in a test rig called Rotating Disc... more
The aim of this study was comparative analysis of sediment-induced erosion on optimized design and traditional design of Francis runner blade. The analysis was conducted through laboratory experiments in a test rig called Rotating Disc Apparatus. The results showed that the extent of erosion was significantly less in the optimized design when compared based on the material loss. It was observed that the optimized design could reduce sediment erosion by about 14.4% if it was used in place of the reference design for entire duration of the experiment. Based on the observations and results obtained, it has been concluded that the optimization of hydraulic design of blade profile of Francis runner can significantly reduce the effect of sediment-induced erosion.
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ABSTRACT Sediment erosion in hydraulic turbines has been a major challenge in development of hydropower projects in Nepal. The hard abrasive material present in the river water of this region cause rapid erosion of turbine components and... more
ABSTRACT Sediment erosion in hydraulic turbines has been a major challenge in development of hydropower projects in Nepal. The hard abrasive material present in the river water of this region cause rapid erosion of turbine components and affect the performance of turbines, which in turn decreases the efficiency, reliability and operating life of such projects. There is a need of a new design methodology to develop turbines to resist erosion in high sediment conditions. The first step towards such development would be to investigate different design options in laboratory, which needs a standard methodology to carry out sediment erosion test in controlled environment. This study is focused on design and development of a laboratory test setup suitable for carrying out sediment erosion test in Francis runner blades. A test rig called rotating disc apparatus has been developed and installed in Turbine Testing Laboratory, Kathmandu University, Nepal, which uses Francis runner blades as test specimens. The test carried out in this setup has shown that the Francis turbines designed with traditional design methodology is highly prone to loss of material due to sediment erosion. © 2013 Elsevier B.V.
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Climate and energy crises are increasing worldwide. Community-led humanitarian engineering interventions for localized sustainable development and disaster resilience could support populations at risk. This article presents findings from... more
Climate and energy crises are increasing worldwide. Community-led humanitarian engineering interventions for localized sustainable development and disaster resilience could support populations at risk. This article presents findings from a study that investigated flood response and energy needs of two riparian communities in Greece and Nepal. The findings indicate that the co-development of a hybrid unit for hydropower generation and flood warning is most preferred. This prototype could find applications in different riparian areas as either a main or supplementary system.
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Erosion wear is a major problem for hydraulic turbines operating on rivers from the Himalaya Mountains. The runner is the most important energy conversion component but it suffers heavy damage due to direct contact with the sediment-laden... more
Erosion wear is a major problem for hydraulic turbines operating on rivers from the Himalaya Mountains. The runner is the most important energy conversion component but it suffers heavy damage due to direct contact with the sediment-laden water. In this research, the runner's physical erosion wear mechanism is revealed using numerical simulations and the results are compared with damaged runners from Francis turbines in the Jhimruk Hydroelectric Center (JHC). Simulations show that high erosive wear occurs near the blade outlet on the suction side, which is consistent with site observations. Because of the high relative velocity at the runner outlet, the high accretion rate appears to be directly responsible for the heavy erosion rate. The adjustment of the guide vanes is the main action available in real situation to change the operation condition of turbine and flow separation can easily occur under off-design conditions, causing interblade vortex production. The vortex guides ...