Abstract The objective of the present work is to investigate the feasibility and the eventual imp... more Abstract The objective of the present work is to investigate the feasibility and the eventual improvement in performance of an ejector powered water/lithium bromide double-effect absorption/recompression refrigeration cycle driven by high temperature heat sources. The results show that the cycle performance parameters are significantly affected by the presence of the ejector and its characteristics. Further, the COP responses to variation of working conditions are different from those observed for the conventional double-effect absorption refrigeration cycles. The maximum COP values of the ejector cycle occur at HP-generator temperatures lower by 20 °C to 25 °C than those of the conventional double-effect absorption cycle. The enhancement factor of the COP varies between 1.34 and 1.70 at a driving steam temperature ranging from 240 °C to 340 °C. As regards the ejector design, the ratio of HP-generator pressure and driving steam pressure should be kept as low as possible. The geometry of the design should allow for the maximum entrainment ratio feasible.
In this paper, a hybrid ejector single-effect lithium-bromide water cycle is theoretically invest... more In this paper, a hybrid ejector single-effect lithium-bromide water cycle is theoretically investigated. The system is a conventional single-effect cycle activated by an external steam-ejector loop. A mathematical model of the whole system is developed. Simulations are carried out to study the effect of the major parameters of the hybrid cycle on its performances and in comparison with the conventional cycle. The ejector performance is also investigated. Results show that the entrainment ratio rises with steam pressure and condenser temperature, while it decreases with increasing generator temperature. The effect of the evaporator temperature on ejector performance is negligible. It is shown also that the hybrid cycle exhibits better performances than the corresponding basic cycle. However, the performance improvement is limited to a specific range of the operating parameters. Outside this range, the hybrid system behaves similar to a conventional cycle. Inside this range, the COP i...
The objective of this paper is to investigate theoretically a solar driven 60 kW absorption cooli... more The objective of this paper is to investigate theoretically a solar driven 60 kW absorption cooling system. The system is constituted of a combined ejector single-effect absorption cycle coupled with a linear Fresnel solar concentrator and using water/lithium bromide as working fluid. The combined ejector single-effect absorption cycle exhibits high performances, almost equal to that of double-effect absorption device. However, higher driving heat temperatures are required than in the case of conventional single-effect machines. A mathematical model is set up to analyze the optical performance of the linear Fresnel concentrator. Simulations are carried out to study the overall system performance COPsystem and the performances of the combined absorption machine COPcycle for generator driving temperatures and pressures in the ranges 180°C – 210°C and 198 kPa – 270 kPa, respectively. Further, the effect of operating parameters such as the cooling medium and chilled water temperatures i...
2016 7th International Renewable Energy Congress (IREC), 2016
— In this paper a comparative exergy analysis of an air-cooled vapor compression chilled water (V... more — In this paper a comparative exergy analysis of an air-cooled vapor compression chilled water (VCCW) using an alternative refrigerant HFO-1234ze to HFC-134a is presented. A computer model has been developed to calculate the thermodynamic properties of all state points, heat flow rates, exergy losses in each component of the system. The system performance based on coefficient of performance as well as exergetic efficiency was evaluated. A parametric study was done to examine the influence of different parameters on the coefficient of performance and the exergy efficiency of the system.
The objective of this work, based on a theoretical and experimental study, is to investigate the ... more The objective of this work, based on a theoretical and experimental study, is to investigate the energy and economic performance of a totally solar drying unit with storage for aromatic and medicinal plants, to satisfy a dimensioning already carried out on a macroscopic scale for an energy request well defined: to dry a quantity of a given agricultural products during 1 day of harvest season, so between September and May, with a heat storage which relays at night. Drying experiments were conducted for spearmint grown in Tunisia. Mathematical formulation of the physical process of this solar drying unit based on conventional heat and mass transfer equations showed a certain agreement with the experimental results under climatic conditions of Tunis (Tunisia). All the experimental drying curves showed only a falling drying rate period. The main factor in controlling the drying rate was found to be the drying air temperature. It was observed that this unit is able to dry more than 2.5 k...
RESUME. Les paramètres hydrauliques d’un milieu poreux non saturés sont déterminés à partir des d... more RESUME. Les paramètres hydrauliques d’un milieu poreux non saturés sont déterminés à partir des différents tests. Dans ce papier, on montre la possibilité d’identification de tous les paramètres hydrauliques du sable en utilisant un test en colonne. Le test considéré est un essai de drainage gravitaire dont seule l’évolution temporelle du débit est mesurée. Différents tensiomètres ont été installés le long de la colonne pour mesurer la pression au sein de l’échantillon. Dans cette étude, une analyse inverse est adoptée pour la résolution des problèmes fortement non linéaires. L'identification de ces paramètres est validée en utilisant des tests conventionnels, comme l’essai de drainage à pas de pression multiple et la mesure de conductivité hydraulique à la saturation. ABSTRACT. There are different tests to estimate the hydraulic parameters of the van Genuchten-Mualem model needed to simulate the flow in unsaturated porous media. In this paper it is shown that it is possible to ...
ABSTRACT Using the PC-SAFT equation of state to the correlation and prediction of the phase equil... more ABSTRACT Using the PC-SAFT equation of state to the correlation and prediction of the phase equilibria of associating systems, the vapor-liquid, the liquid-liquid and the vapor-liquid-liquid equilibria of binary and ternary mixtures were investigated. In this equation of state five pure-component parameters are required for each associating substance, two of which characterize the association interactions. Pure-component parameters for 23 self-associating and 6 non-associating substances are identified by correlating vapor pressure and liquid density data. A comparison of calculated values to literature data shows a good agreement for pure fluids. Binary systems with two self-associating compounds and others with one self-associating component and another non-self associating but can have cross-associating interactions with the first component are investigated. Binary parameters correcting the cross-dispersive interactions, kij, and the cross-associating interactions, υij and λij, are fitted to the phase equilibrium data. In addition, when a simple non-self associating pure fluid is a part of a binary system and can have cross-associating interactions with the other component, its association fictive volume and energy are regressed simultaneously with the binary interaction parameters to the phase equilibrium data. The found results have shown that the PC-SAFT equation of state demonstrates high potential of correlation and prediction of vapor-liquid, liquid-liquid and vapor-liquid-liquid phase equilibria of 38 binary systems of associating fluids. The same observations are made for the phase behavior prediction of 22 ternary mixtures of associating fluids. The PC-SAFT equation of state with its theoretical base represents a great tool for modeling and prediction of phase equilibria and thermodynamic properties of mixtures of associating fluids.
Abstract The objective of the present work is to investigate the feasibility and the eventual imp... more Abstract The objective of the present work is to investigate the feasibility and the eventual improvement in performance of an ejector powered water/lithium bromide double-effect absorption/recompression refrigeration cycle driven by high temperature heat sources. The results show that the cycle performance parameters are significantly affected by the presence of the ejector and its characteristics. Further, the COP responses to variation of working conditions are different from those observed for the conventional double-effect absorption refrigeration cycles. The maximum COP values of the ejector cycle occur at HP-generator temperatures lower by 20 °C to 25 °C than those of the conventional double-effect absorption cycle. The enhancement factor of the COP varies between 1.34 and 1.70 at a driving steam temperature ranging from 240 °C to 340 °C. As regards the ejector design, the ratio of HP-generator pressure and driving steam pressure should be kept as low as possible. The geometry of the design should allow for the maximum entrainment ratio feasible.
In this paper, a hybrid ejector single-effect lithium-bromide water cycle is theoretically invest... more In this paper, a hybrid ejector single-effect lithium-bromide water cycle is theoretically investigated. The system is a conventional single-effect cycle activated by an external steam-ejector loop. A mathematical model of the whole system is developed. Simulations are carried out to study the effect of the major parameters of the hybrid cycle on its performances and in comparison with the conventional cycle. The ejector performance is also investigated. Results show that the entrainment ratio rises with steam pressure and condenser temperature, while it decreases with increasing generator temperature. The effect of the evaporator temperature on ejector performance is negligible. It is shown also that the hybrid cycle exhibits better performances than the corresponding basic cycle. However, the performance improvement is limited to a specific range of the operating parameters. Outside this range, the hybrid system behaves similar to a conventional cycle. Inside this range, the COP i...
The objective of this paper is to investigate theoretically a solar driven 60 kW absorption cooli... more The objective of this paper is to investigate theoretically a solar driven 60 kW absorption cooling system. The system is constituted of a combined ejector single-effect absorption cycle coupled with a linear Fresnel solar concentrator and using water/lithium bromide as working fluid. The combined ejector single-effect absorption cycle exhibits high performances, almost equal to that of double-effect absorption device. However, higher driving heat temperatures are required than in the case of conventional single-effect machines. A mathematical model is set up to analyze the optical performance of the linear Fresnel concentrator. Simulations are carried out to study the overall system performance COPsystem and the performances of the combined absorption machine COPcycle for generator driving temperatures and pressures in the ranges 180°C – 210°C and 198 kPa – 270 kPa, respectively. Further, the effect of operating parameters such as the cooling medium and chilled water temperatures i...
2016 7th International Renewable Energy Congress (IREC), 2016
— In this paper a comparative exergy analysis of an air-cooled vapor compression chilled water (V... more — In this paper a comparative exergy analysis of an air-cooled vapor compression chilled water (VCCW) using an alternative refrigerant HFO-1234ze to HFC-134a is presented. A computer model has been developed to calculate the thermodynamic properties of all state points, heat flow rates, exergy losses in each component of the system. The system performance based on coefficient of performance as well as exergetic efficiency was evaluated. A parametric study was done to examine the influence of different parameters on the coefficient of performance and the exergy efficiency of the system.
The objective of this work, based on a theoretical and experimental study, is to investigate the ... more The objective of this work, based on a theoretical and experimental study, is to investigate the energy and economic performance of a totally solar drying unit with storage for aromatic and medicinal plants, to satisfy a dimensioning already carried out on a macroscopic scale for an energy request well defined: to dry a quantity of a given agricultural products during 1 day of harvest season, so between September and May, with a heat storage which relays at night. Drying experiments were conducted for spearmint grown in Tunisia. Mathematical formulation of the physical process of this solar drying unit based on conventional heat and mass transfer equations showed a certain agreement with the experimental results under climatic conditions of Tunis (Tunisia). All the experimental drying curves showed only a falling drying rate period. The main factor in controlling the drying rate was found to be the drying air temperature. It was observed that this unit is able to dry more than 2.5 k...
RESUME. Les paramètres hydrauliques d’un milieu poreux non saturés sont déterminés à partir des d... more RESUME. Les paramètres hydrauliques d’un milieu poreux non saturés sont déterminés à partir des différents tests. Dans ce papier, on montre la possibilité d’identification de tous les paramètres hydrauliques du sable en utilisant un test en colonne. Le test considéré est un essai de drainage gravitaire dont seule l’évolution temporelle du débit est mesurée. Différents tensiomètres ont été installés le long de la colonne pour mesurer la pression au sein de l’échantillon. Dans cette étude, une analyse inverse est adoptée pour la résolution des problèmes fortement non linéaires. L'identification de ces paramètres est validée en utilisant des tests conventionnels, comme l’essai de drainage à pas de pression multiple et la mesure de conductivité hydraulique à la saturation. ABSTRACT. There are different tests to estimate the hydraulic parameters of the van Genuchten-Mualem model needed to simulate the flow in unsaturated porous media. In this paper it is shown that it is possible to ...
ABSTRACT Using the PC-SAFT equation of state to the correlation and prediction of the phase equil... more ABSTRACT Using the PC-SAFT equation of state to the correlation and prediction of the phase equilibria of associating systems, the vapor-liquid, the liquid-liquid and the vapor-liquid-liquid equilibria of binary and ternary mixtures were investigated. In this equation of state five pure-component parameters are required for each associating substance, two of which characterize the association interactions. Pure-component parameters for 23 self-associating and 6 non-associating substances are identified by correlating vapor pressure and liquid density data. A comparison of calculated values to literature data shows a good agreement for pure fluids. Binary systems with two self-associating compounds and others with one self-associating component and another non-self associating but can have cross-associating interactions with the first component are investigated. Binary parameters correcting the cross-dispersive interactions, kij, and the cross-associating interactions, υij and λij, are fitted to the phase equilibrium data. In addition, when a simple non-self associating pure fluid is a part of a binary system and can have cross-associating interactions with the other component, its association fictive volume and energy are regressed simultaneously with the binary interaction parameters to the phase equilibrium data. The found results have shown that the PC-SAFT equation of state demonstrates high potential of correlation and prediction of vapor-liquid, liquid-liquid and vapor-liquid-liquid phase equilibria of 38 binary systems of associating fluids. The same observations are made for the phase behavior prediction of 22 ternary mixtures of associating fluids. The PC-SAFT equation of state with its theoretical base represents a great tool for modeling and prediction of phase equilibria and thermodynamic properties of mixtures of associating fluids.
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Papers by Ahmed Bellagi