Adsorption cooling is considered as attractive heat powered cooling technology suitable for vario... more Adsorption cooling is considered as attractive heat powered cooling technology suitable for various applications. Commercially available systems use water/silica gel, water/zeolite and ammonia/ chloride salts working pairs. The water based pairs are limited to work above 0 °C due to the water high freezing temperature, while ammonia has the disadvantage of being toxic. This work experimentally investigates the ethanol adsorption characteristics for a wide range of activated carbon materials using gravimetric analysis method. Numerical simulation of the adsorption process was carried out to investigate the effect of adsorbent material thickness on the cycle uptake.
This paper presents the integrated modelling and multi-objective optimization of ORC based on rad... more This paper presents the integrated modelling and multi-objective optimization of ORC based on radial inflow turbine. With this approach it is possible to replace the constant turbine efficiency with a dynamic efficiency that is unique for each set of cycle operating conditions and working fluid properties. This allows overcoming any arbitrary assumption of the turbine efficiency, unlike the previous literature, and providing a more realistic estimation of the cycle performance. Parametric studies were conducted utilizing the developed model to identify the key input variables that have significant effects on the critical turbine-ORC performance indicators. These variables were then included in the optimization process using DIRECT algorithm to optimize two objective functions as the cycle thermal efficiency and the turbine overall size for five organic fluids. Optimization results predicted that isobutane exhibited the best performance with the maximum cycle thermal efficiency of 13.21% and turbine overall size of 0.1434m while having relatively high turbine isentropic efficiency of 77.03 %.
Organic Rankine Cycle converts low grade heat sources into power utilizing organic fluids with lo... more Organic Rankine Cycle converts low grade heat sources into power utilizing organic fluids with low boiling temperature and pressure. In this cycle the design and performance of the expander has a significant impact on the cycle's overall efficiency. This work presents an integrated mathematical approach for the development of an efficient and compact small-scale radial turbine. This mathematical approach integrates the mean-line modelling with real gas formulation and GA(genetic algorithm) optimisation technique. In this methodology, the mean-line modelling coupled with real gas formulation is employed to perform parametric studies to identify the key variables that have significant effect on the turbine efficiency. Such variables are then used in the GA to optimise the turbine performance. Eight organic fluids are investigated to optimise the performance of the small-scale radial turbine in terms of efficiency. Results showed that the achieved radial turbine efficiencies vary from 82.9% to 84%; which is higher than the reported efficiency values of other types of expanders. R152a showed the highest efficiency of 84% with seven degrees (K) of superheating. However, if the superheating is to be avoided, isobutane exhibited the most favourable characteristics in terms of efficiency (83.82%), rotor size (66.3 mm) and inlet temperature (89.2 °C).
In most of the organic Rankine cycle (ORC) studies, constant expander efficiency is considered fo... more In most of the organic Rankine cycle (ORC) studies, constant expander efficiency is considered for a wide range of cycle operating conditions and for various working fluids. This study presents an optimized modelling approach for the ORC based on radial inflow turbine, where the constant expander efficiency is replaced by dynamic efficiency that is unique for each set of cycle operating conditions and working fluid properties. Considering the size and performance of the ORC, the model was used to identify the key input variables that have significant effects on the turbine overall size and the cycle net electric power output. These parameters were then included in the optimization process using the DIRECT algorithm to maximize the ratio of cycle net electric power output to the turbine overall size (objective function) for six organic fluids. Results showed that, dynamic efficiency approach predicted considerable differences in the turbine efficiencies of various working fluids. The maximum difference of 6.13% between the turbine efficiencies of R245fa and isobutane was predicted. Also the optimization results showed that, the maximum objective function of 0.5748 kW/mm was achieved by isobutane with the cycle net electric power output and the turbine overall size of 90.3 kW and 157.2 mm respectively. Such results are better than the other studies and highlight the potential of the optimization technique to further improve the performance and reduce the size of the ORC based on small-scale radial turbines.
ABSTRACT This paper experimentally investigates the effects of tube and coil diameters on flow bo... more ABSTRACT This paper experimentally investigates the effects of tube and coil diameters on flow boiling heat transfer coefficients inside small diameter (<3 mm) helically coiled tubes. Four different helical coils with coil diameters ranging from 30 mm to 60 mm were studied using tube diameters ranging from 1.1 to 2.8 mm. The heat flux varied from 2500 to 12,000 Wm−2 and mass velocities from 100 to 450 kgm−2s−1. Results have shown that decreasing the tube diameter improved the heat transfer coefficient by up to 63% but early dryout (vapour quality as low as 0.4) was observed especially at high heat fluxes (q = 12,000 Wm−2). Also, decreasing the coil diameter improves the heat transfer coefficient by up to 150%. New correlation for the boiling heat transfer coefficient inside small tube diameter helical coils was developed which predicted the 227 data points used with mean absolute relative error (MARE) of 16%.
International Journal of Heat and Mass Transfer, 2012
ABSTRACT Silica gel/water adsorption cooling systems suffer from size, performance and cost limit... more ABSTRACT Silica gel/water adsorption cooling systems suffer from size, performance and cost limitations. Therefore, there is a need for new adsorbent materials that outperform silica gel. Metal organic frameworks (MOFs) are new micro-porous materials that have extraordinary porosity and uniform structure. Due to the lack of published data that characterise MOF/water adsorption, this paper experimentally investigates the adsorption characteristics of HKUST-1 (Cu-BTC (copper benzene-1,3,5-tricarboxylate), C18H6Cu3O12) and MIL-100 (Fe-BTC (Iron 1,3,5-benzenetricarboxylate), C9H3FeO6) MOFs compared to silica gel RD-2060. The adsorption characteristics of Silica gel RD-2060, HKUST-1 and MIL-100 were determined using an advanced gravimetric dynamic vapour sorption analyser (DVS). Results showed that HKUST-1 performed better than silica gel RD-2060 with an increase of water uptake of 93.2%, which could lead to a considerable increase in refrigerant flow rate, cooling capacity and/or reducing the size of the adsorption system. However, MIL-100 MOF showed reduced water uptake comparable to silica gel RD-2060 for water chilling applications with evaporation at 5 0C. These results highlight the potential of using MOF materials to improve the efficiency of water adsorption cooling systems.
ABSTRACT Recently interest in adsorption cooling systems has increased due to their capability to... more ABSTRACT Recently interest in adsorption cooling systems has increased due to their capability to utilise low grade heat sources and environmentally friendly refrigerants. Currently, most of the commercially available adsorption cooling systems utilise granular packed adsorbent beds. Enhancing the heat transfer process inside the adsorbent bed will improve the overall efficiency of the adsorption system. Using recently developed empirical lumped analytical simulation model for a 450 kW two-bed silica gel/water adsorption chiller, this paper theoretically investigates the effects of various adsorbent bed heat transfer enhancement techniques on the adsorption system cooling capacity. Firstly, coating the first adsorbent layer to the metal part and packing the rest of adsorbent granules to eliminate the thermal contact resistance between heat exchanger metal and granules while keeping the same level of permeability. Secondly, adding metal particles to the adsorbent in order to enhance the granules thermal conductivity. The effective thermal conductivity of adsorbent/metal mixtures were determined and validated by comparing it with published experimental data. Also, the combined effect of using both techniques simultaneously was investigated. All these investigations were carried out at various adsorption bed fin spacing. Results of the combined techniques showed that the enhancement in the cooling capacity and system coefficient of performance (COP) increased with increasing the fin spacing ratio to reach maximum of 25% and 10% respectively at fin spacing ratio of 2.
Adsorption cooling is considered as attractive heat powered cooling technology suitable for vario... more Adsorption cooling is considered as attractive heat powered cooling technology suitable for various applications. Commercially available systems use water/silica gel, water/zeolite and ammonia/ chloride salts working pairs. The water based pairs are limited to work above 0 °C due to the water high freezing temperature, while ammonia has the disadvantage of being toxic. This work experimentally investigates the ethanol adsorption characteristics for a wide range of activated carbon materials using gravimetric analysis method. Numerical simulation of the adsorption process was carried out to investigate the effect of adsorbent material thickness on the cycle uptake.
This paper presents the integrated modelling and multi-objective optimization of ORC based on rad... more This paper presents the integrated modelling and multi-objective optimization of ORC based on radial inflow turbine. With this approach it is possible to replace the constant turbine efficiency with a dynamic efficiency that is unique for each set of cycle operating conditions and working fluid properties. This allows overcoming any arbitrary assumption of the turbine efficiency, unlike the previous literature, and providing a more realistic estimation of the cycle performance. Parametric studies were conducted utilizing the developed model to identify the key input variables that have significant effects on the critical turbine-ORC performance indicators. These variables were then included in the optimization process using DIRECT algorithm to optimize two objective functions as the cycle thermal efficiency and the turbine overall size for five organic fluids. Optimization results predicted that isobutane exhibited the best performance with the maximum cycle thermal efficiency of 13.21% and turbine overall size of 0.1434m while having relatively high turbine isentropic efficiency of 77.03 %.
Organic Rankine Cycle converts low grade heat sources into power utilizing organic fluids with lo... more Organic Rankine Cycle converts low grade heat sources into power utilizing organic fluids with low boiling temperature and pressure. In this cycle the design and performance of the expander has a significant impact on the cycle's overall efficiency. This work presents an integrated mathematical approach for the development of an efficient and compact small-scale radial turbine. This mathematical approach integrates the mean-line modelling with real gas formulation and GA(genetic algorithm) optimisation technique. In this methodology, the mean-line modelling coupled with real gas formulation is employed to perform parametric studies to identify the key variables that have significant effect on the turbine efficiency. Such variables are then used in the GA to optimise the turbine performance. Eight organic fluids are investigated to optimise the performance of the small-scale radial turbine in terms of efficiency. Results showed that the achieved radial turbine efficiencies vary from 82.9% to 84%; which is higher than the reported efficiency values of other types of expanders. R152a showed the highest efficiency of 84% with seven degrees (K) of superheating. However, if the superheating is to be avoided, isobutane exhibited the most favourable characteristics in terms of efficiency (83.82%), rotor size (66.3 mm) and inlet temperature (89.2 °C).
In most of the organic Rankine cycle (ORC) studies, constant expander efficiency is considered fo... more In most of the organic Rankine cycle (ORC) studies, constant expander efficiency is considered for a wide range of cycle operating conditions and for various working fluids. This study presents an optimized modelling approach for the ORC based on radial inflow turbine, where the constant expander efficiency is replaced by dynamic efficiency that is unique for each set of cycle operating conditions and working fluid properties. Considering the size and performance of the ORC, the model was used to identify the key input variables that have significant effects on the turbine overall size and the cycle net electric power output. These parameters were then included in the optimization process using the DIRECT algorithm to maximize the ratio of cycle net electric power output to the turbine overall size (objective function) for six organic fluids. Results showed that, dynamic efficiency approach predicted considerable differences in the turbine efficiencies of various working fluids. The maximum difference of 6.13% between the turbine efficiencies of R245fa and isobutane was predicted. Also the optimization results showed that, the maximum objective function of 0.5748 kW/mm was achieved by isobutane with the cycle net electric power output and the turbine overall size of 90.3 kW and 157.2 mm respectively. Such results are better than the other studies and highlight the potential of the optimization technique to further improve the performance and reduce the size of the ORC based on small-scale radial turbines.
ABSTRACT This paper experimentally investigates the effects of tube and coil diameters on flow bo... more ABSTRACT This paper experimentally investigates the effects of tube and coil diameters on flow boiling heat transfer coefficients inside small diameter (<3 mm) helically coiled tubes. Four different helical coils with coil diameters ranging from 30 mm to 60 mm were studied using tube diameters ranging from 1.1 to 2.8 mm. The heat flux varied from 2500 to 12,000 Wm−2 and mass velocities from 100 to 450 kgm−2s−1. Results have shown that decreasing the tube diameter improved the heat transfer coefficient by up to 63% but early dryout (vapour quality as low as 0.4) was observed especially at high heat fluxes (q = 12,000 Wm−2). Also, decreasing the coil diameter improves the heat transfer coefficient by up to 150%. New correlation for the boiling heat transfer coefficient inside small tube diameter helical coils was developed which predicted the 227 data points used with mean absolute relative error (MARE) of 16%.
International Journal of Heat and Mass Transfer, 2012
ABSTRACT Silica gel/water adsorption cooling systems suffer from size, performance and cost limit... more ABSTRACT Silica gel/water adsorption cooling systems suffer from size, performance and cost limitations. Therefore, there is a need for new adsorbent materials that outperform silica gel. Metal organic frameworks (MOFs) are new micro-porous materials that have extraordinary porosity and uniform structure. Due to the lack of published data that characterise MOF/water adsorption, this paper experimentally investigates the adsorption characteristics of HKUST-1 (Cu-BTC (copper benzene-1,3,5-tricarboxylate), C18H6Cu3O12) and MIL-100 (Fe-BTC (Iron 1,3,5-benzenetricarboxylate), C9H3FeO6) MOFs compared to silica gel RD-2060. The adsorption characteristics of Silica gel RD-2060, HKUST-1 and MIL-100 were determined using an advanced gravimetric dynamic vapour sorption analyser (DVS). Results showed that HKUST-1 performed better than silica gel RD-2060 with an increase of water uptake of 93.2%, which could lead to a considerable increase in refrigerant flow rate, cooling capacity and/or reducing the size of the adsorption system. However, MIL-100 MOF showed reduced water uptake comparable to silica gel RD-2060 for water chilling applications with evaporation at 5 0C. These results highlight the potential of using MOF materials to improve the efficiency of water adsorption cooling systems.
ABSTRACT Recently interest in adsorption cooling systems has increased due to their capability to... more ABSTRACT Recently interest in adsorption cooling systems has increased due to their capability to utilise low grade heat sources and environmentally friendly refrigerants. Currently, most of the commercially available adsorption cooling systems utilise granular packed adsorbent beds. Enhancing the heat transfer process inside the adsorbent bed will improve the overall efficiency of the adsorption system. Using recently developed empirical lumped analytical simulation model for a 450 kW two-bed silica gel/water adsorption chiller, this paper theoretically investigates the effects of various adsorbent bed heat transfer enhancement techniques on the adsorption system cooling capacity. Firstly, coating the first adsorbent layer to the metal part and packing the rest of adsorbent granules to eliminate the thermal contact resistance between heat exchanger metal and granules while keeping the same level of permeability. Secondly, adding metal particles to the adsorbent in order to enhance the granules thermal conductivity. The effective thermal conductivity of adsorbent/metal mixtures were determined and validated by comparing it with published experimental data. Also, the combined effect of using both techniques simultaneously was investigated. All these investigations were carried out at various adsorption bed fin spacing. Results of the combined techniques showed that the enhancement in the cooling capacity and system coefficient of performance (COP) increased with increasing the fin spacing ratio to reach maximum of 25% and 10% respectively at fin spacing ratio of 2.
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