L. Kairouani is a professor at Tunis El Manar University, National Engineering School of Tunis. He teaches Heat transfer, Applied Thermodynamics, His research activities focus on refrigeration, efficient use of energy, energy systems, renewable energies and their applications in refrigeration by absorption and the production of mechanical energy by Rankine cycles, Kalina. He is the author of 2 books in applied thermodynamics and refrigeration and several scientific articles. He leads the research Laboratory "Energy
Abstract Natural substances are becoming very promising for long term alternative for refrigerati... more Abstract Natural substances are becoming very promising for long term alternative for refrigeration purposes. In this paper, two natural refrigerants have been proposed and analyzed for a novel ejector expansion transcritical cascade refrigeration (NEETCR) system. Nitrous oxide (N2O) is used in the low temperature circuit (LTC) whereas carbon dioxide (CO2) is used in the high temperature circuit (HTC) of the NEETCR system. The reject of refrigerant vapor heat in the HTC is carried out through the use of transcritical carbon dioxide Rankine cycle. This produces work, which will be used to reduce the consumption work of compressors and feed pump thereby resulting in the improvement of the energy efficiency of the whole system. The simulation results were obtained by a computer FORTRAN program, where REFPROP 9 database was used to get the refrigerant thermodynamic properties. The simulation results showed that the (NEETCR) system had higher coefficient of performance and higher system second law efficiency compared to the EETCR system. An enhancement more than 9% in the COP and exergy efficiency of NEETCR system was found in comparison with EETCR system, when the cooling capacity and operating conditions of the two systems were the same. The increase of COP of NEETCR system and its efficiency along with the reduction of power consumption make it more practical for the use in cooling applications.
Waste heat from the gas cooler is a form of free energy, which can be utilized to drive an ejecto... more Waste heat from the gas cooler is a form of free energy, which can be utilized to drive an ejector cooling cycle. This paper presents a new CO2 ejector-cascade refrigeration cycle. The effects of important parameters on the thermodynamic performance of the new cycle are theoretically investigated based on energetic and exergetic analyses. Furthermore, the performance comparison of the proposed cycle and conventional cycle is carried out. The theoretical study shows that the new cycle exhibits a reasonable value of COP (coefficient of performance) and system second law efficiency. For the same cooling capacity, the improvements of the maximum COP and second law efficiency could reach 37% and 12%, respectively, over those of the conventional cascade cycle under the given operating conditions and at the optimum gas cooler pressure.
The objectives of this paper are to develop a novel combined refrigeration system, and to discuss... more The objectives of this paper are to develop a novel combined refrigeration system, and to discuss the thermodynamic analysis of the cycle and the feasibility of its practical development. The aim of this work was to study the possibility of using geothermal energy to supply vapour ...
Multistage flash (MSF) desalination plants are energy intensive and it is, therefore, important t... more Multistage flash (MSF) desalination plants are energy intensive and it is, therefore, important to use operating parameters that lead to reduction of energy consumption and consequently reduction of fresh water production cost. In this study, an optimization of operating parameters of an actual MSFBR desalination plant was performed using as objective the improvement of the main plant performance indicators. Four decision variables related to the operating conditions were chosen for optimization, i.e., the temperature of the heating steam, the cooling seawater flow rate, the brine recycle flow rate, and the make-up flow rate. These decision variables were subjected to constraints to ensure that maximum and minimum bounds were adhered. A multiobjective function that consists of the main plant performance indicators, i.e., the thermal performance ratio, the specific cooling water flow rate, the specific recirculating brine flow rate, and the specific feed flow rate, were used in the o...
Información del artículo Ciclo de compresión/eyección para refrigeración doméstica: análisis del ... more Información del artículo Ciclo de compresión/eyección para refrigeración doméstica: análisis del rendimiento.
Abstract Three different refrigeration cycles, namely the vapor compression cycle, the combined r... more Abstract Three different refrigeration cycles, namely the vapor compression cycle, the combined refrigeration cycle and the new combined refrigeration cycle for power and cold, are investigated. The principles of mass and energy conservation are applied to every component of the systems, and the resulted linear system of equations was numerically solved. It was found that the new proposed cycle had a lower optimum gas cooler pressure than other refrigeration cycles, and this would enhance the lifetime and safety of the system. Besides, it was found that the coefficient of performance of the new cycle is higher than that of the vapor compression and combined refrigeration cycles 110% and 50%, respectively. The exergy efficiency was approximately 78% and 58% higher than that of the vapor and combined refrigeration cycles, respectively. Furthermore, the exergoeconomic results of the new cycle showed that the total unit cost was lower by 16.6% and 13% than that for the vapor compression and combined refrigeration cycles, respectively.
Abstract This paper presents a theoretical thermodynamic analysis of a novel Ejector Enhanced Vap... more Abstract This paper presents a theoretical thermodynamic analysis of a novel Ejector Enhanced Vapor Compression Refrigeration (EEVCR) cycle using zeotropic mixture of propane and isobutane (R290/R600a) as a refrigerant to replace R134a in domestic refrigerators/freezers. 1 D thermodynamic model for a constant area mixing ejector is used to estimate the cycle performance under the condition of optimal operating regime. The Coefficient of Performance (COP), the Volumetric Cooling Capacity (VCC), Qv and the compressor pressure ratio are studied for the novel EEVCR cycle and the results are compared to the conventional cycle using pure fluid R134a and zeotropic mixture R290/R600a. A comparative study was carried out to determine the propane mass fraction, z in the zeotropic mixture that would be a suitable replacement for R134a. The results indicated that the cycle COP and Qv could be improved by 23% and 62.71%, respectively. In addition, the cycle COP and Qv for the proposed EEVCR cycle were higher by 70% than those for a modified ejector expansion cycle. Finally, the propane mass fraction of 60% in the zeotropic R290/R600a mixture was found to have similar saturation pressure as R134a and the cycle COP and Qv were found similar to those of R134a.
Abstract In the present work, a new CO2 refrigeration cycle, with the ejector expansion cycle ser... more Abstract In the present work, a new CO2 refrigeration cycle, with the ejector expansion cycle serving as a harvesting tool of gas cooler wasted heat, is investigated. An attempt has been made to harvest and utilize the low-grade wasted energy, in the gas cooler component of the refrigeration basic cycle, through a transcritical carbon dioxide Rankine cycle. The work produced by the new cycle is used to drive the compressor and the feed pump, hence reducing the consumption work input and, as a result, it will enhance the performance characteristics of the whole system. The system operating and performance characteristics are investigated theoretically by energetic and exergetic methods. The simulation results were obtained by a computer FORTRAN program, where REFPROP 9 database was used to get the refrigerant thermodynamic properties. The simulation results showed that the proposed new refrigeration ejector expansion cycle (NEERC) had higher coefficient of performance and higher system second law efficiency in compare to the basic ejector expansion refrigeration cycle (BEERC). An enhancement of 12% in the COP and exergy efficiency of NEERC was found in comparison with BEERC when the cooling capacity and operating conditions of the two systems were the same. The increase of COP of NEERC and its efficiency along with the reduction of power consumption make it more practical for the use in residential air conditioning and cooling applications. A techno-economic analysis to compare ORC with Rankine cycle is provided. The results indicated that Rankine cycle for transcritical CO2 refrigeration cycle is more appropriate and has an advantage over the use of ORC. In addition, the small scale Rankine cycle combined with BEERC is economically viable for countries where the electricity price is above 15 c€/kW h.
Abstract A hybrid vapor compression refrigeration (HVCR) system, which combines a vapor compressi... more Abstract A hybrid vapor compression refrigeration (HVCR) system, which combines a vapor compression refrigeration (VCR) system and an ejector refrigeration (ER) system, was developed. The waste heat energy from the gas cooler in the VCR system is applied as driven source towards ER system. Thermodynamic investigations on the performance of the HVCR system, using CO2 as a refrigerant, are performed with energetic and exergetic methods, and the comparative analyses with the VCR system are conducted. Comprehensive effects of key operating parameters on the system performance are also studied. The results indicate that for the same cooling capacity, the coefficient of performance (COP) of the HVCR system shows 25% higher COP and the total mechanical power consumption is reduced by 20% than that of conventional VCR system, respectively. The performance characteristics of the proposed cycle show its application potential in cooling and air-conditioning.
This paper presents a theoretical study of a combined thermal system, which combines the Rankine ... more This paper presents a theoretical study of a combined thermal system, which combines the Rankine cycle and the ejector refrigeration cycle. This combined cycle produces power and refrigeration simultaneously. The thermal system could use low temperature heat sources. A simulation was carried out to evaluate the cycle performance using several working fluids as R123, R141b, R245fa, R601a and R600a. A one-dimensional mathematical model of the ejector was developed using the equations governing the flow and thermodynamics based on the constant area ejector flow model. The ejector is studied in optimal operating regime. The influence of thermodynamic parameters on system performance is studied. The results show that the condenser temperature, the evaporation temperature, the extraction ratio, the fluid nature and the generating temperature have significant effects on the system performances (the coefficient of performance of the combined cycle and the entrainment ratio of the ejector).
A comprehensive energy and exergoeconomic analysis of a novel transcritical refrigeration cycle (... more A comprehensive energy and exergoeconomic analysis of a novel transcritical refrigeration cycle (NTRC) is presented. A second ejector is introduced into the conventional refrigeration system for the utilization of the gas-cooler waste heat. The thermodynamic properties of the working fluid are estimated by the database of REFPROP 9, and a FORTRAN program is used to solve the system governing equations. Exergy, energy, and exergoeconomic analyses of the two cycles are carried out to predict the exergetic destruction rate and efficiency of the systems. The optimum gas cooler working pressure will be determined for both cycles. A comprehensive comparison is made between the obtained results of the conventional and the new cycles. An enhancement of approximately 30% in the coefficient of performance (COP) of the new cycle was found in comparison to the value of the conventional cycle. In addition, the results of the analysis indicated a reduction in the overall exergy destruction rate a...
Abstract Natural substances are becoming very promising for long term alternative for refrigerati... more Abstract Natural substances are becoming very promising for long term alternative for refrigeration purposes. In this paper, two natural refrigerants have been proposed and analyzed for a novel ejector expansion transcritical cascade refrigeration (NEETCR) system. Nitrous oxide (N2O) is used in the low temperature circuit (LTC) whereas carbon dioxide (CO2) is used in the high temperature circuit (HTC) of the NEETCR system. The reject of refrigerant vapor heat in the HTC is carried out through the use of transcritical carbon dioxide Rankine cycle. This produces work, which will be used to reduce the consumption work of compressors and feed pump thereby resulting in the improvement of the energy efficiency of the whole system. The simulation results were obtained by a computer FORTRAN program, where REFPROP 9 database was used to get the refrigerant thermodynamic properties. The simulation results showed that the (NEETCR) system had higher coefficient of performance and higher system second law efficiency compared to the EETCR system. An enhancement more than 9% in the COP and exergy efficiency of NEETCR system was found in comparison with EETCR system, when the cooling capacity and operating conditions of the two systems were the same. The increase of COP of NEETCR system and its efficiency along with the reduction of power consumption make it more practical for the use in cooling applications.
Waste heat from the gas cooler is a form of free energy, which can be utilized to drive an ejecto... more Waste heat from the gas cooler is a form of free energy, which can be utilized to drive an ejector cooling cycle. This paper presents a new CO2 ejector-cascade refrigeration cycle. The effects of important parameters on the thermodynamic performance of the new cycle are theoretically investigated based on energetic and exergetic analyses. Furthermore, the performance comparison of the proposed cycle and conventional cycle is carried out. The theoretical study shows that the new cycle exhibits a reasonable value of COP (coefficient of performance) and system second law efficiency. For the same cooling capacity, the improvements of the maximum COP and second law efficiency could reach 37% and 12%, respectively, over those of the conventional cascade cycle under the given operating conditions and at the optimum gas cooler pressure.
The objectives of this paper are to develop a novel combined refrigeration system, and to discuss... more The objectives of this paper are to develop a novel combined refrigeration system, and to discuss the thermodynamic analysis of the cycle and the feasibility of its practical development. The aim of this work was to study the possibility of using geothermal energy to supply vapour ...
Multistage flash (MSF) desalination plants are energy intensive and it is, therefore, important t... more Multistage flash (MSF) desalination plants are energy intensive and it is, therefore, important to use operating parameters that lead to reduction of energy consumption and consequently reduction of fresh water production cost. In this study, an optimization of operating parameters of an actual MSFBR desalination plant was performed using as objective the improvement of the main plant performance indicators. Four decision variables related to the operating conditions were chosen for optimization, i.e., the temperature of the heating steam, the cooling seawater flow rate, the brine recycle flow rate, and the make-up flow rate. These decision variables were subjected to constraints to ensure that maximum and minimum bounds were adhered. A multiobjective function that consists of the main plant performance indicators, i.e., the thermal performance ratio, the specific cooling water flow rate, the specific recirculating brine flow rate, and the specific feed flow rate, were used in the o...
Información del artículo Ciclo de compresión/eyección para refrigeración doméstica: análisis del ... more Información del artículo Ciclo de compresión/eyección para refrigeración doméstica: análisis del rendimiento.
Abstract Three different refrigeration cycles, namely the vapor compression cycle, the combined r... more Abstract Three different refrigeration cycles, namely the vapor compression cycle, the combined refrigeration cycle and the new combined refrigeration cycle for power and cold, are investigated. The principles of mass and energy conservation are applied to every component of the systems, and the resulted linear system of equations was numerically solved. It was found that the new proposed cycle had a lower optimum gas cooler pressure than other refrigeration cycles, and this would enhance the lifetime and safety of the system. Besides, it was found that the coefficient of performance of the new cycle is higher than that of the vapor compression and combined refrigeration cycles 110% and 50%, respectively. The exergy efficiency was approximately 78% and 58% higher than that of the vapor and combined refrigeration cycles, respectively. Furthermore, the exergoeconomic results of the new cycle showed that the total unit cost was lower by 16.6% and 13% than that for the vapor compression and combined refrigeration cycles, respectively.
Abstract This paper presents a theoretical thermodynamic analysis of a novel Ejector Enhanced Vap... more Abstract This paper presents a theoretical thermodynamic analysis of a novel Ejector Enhanced Vapor Compression Refrigeration (EEVCR) cycle using zeotropic mixture of propane and isobutane (R290/R600a) as a refrigerant to replace R134a in domestic refrigerators/freezers. 1 D thermodynamic model for a constant area mixing ejector is used to estimate the cycle performance under the condition of optimal operating regime. The Coefficient of Performance (COP), the Volumetric Cooling Capacity (VCC), Qv and the compressor pressure ratio are studied for the novel EEVCR cycle and the results are compared to the conventional cycle using pure fluid R134a and zeotropic mixture R290/R600a. A comparative study was carried out to determine the propane mass fraction, z in the zeotropic mixture that would be a suitable replacement for R134a. The results indicated that the cycle COP and Qv could be improved by 23% and 62.71%, respectively. In addition, the cycle COP and Qv for the proposed EEVCR cycle were higher by 70% than those for a modified ejector expansion cycle. Finally, the propane mass fraction of 60% in the zeotropic R290/R600a mixture was found to have similar saturation pressure as R134a and the cycle COP and Qv were found similar to those of R134a.
Abstract In the present work, a new CO2 refrigeration cycle, with the ejector expansion cycle ser... more Abstract In the present work, a new CO2 refrigeration cycle, with the ejector expansion cycle serving as a harvesting tool of gas cooler wasted heat, is investigated. An attempt has been made to harvest and utilize the low-grade wasted energy, in the gas cooler component of the refrigeration basic cycle, through a transcritical carbon dioxide Rankine cycle. The work produced by the new cycle is used to drive the compressor and the feed pump, hence reducing the consumption work input and, as a result, it will enhance the performance characteristics of the whole system. The system operating and performance characteristics are investigated theoretically by energetic and exergetic methods. The simulation results were obtained by a computer FORTRAN program, where REFPROP 9 database was used to get the refrigerant thermodynamic properties. The simulation results showed that the proposed new refrigeration ejector expansion cycle (NEERC) had higher coefficient of performance and higher system second law efficiency in compare to the basic ejector expansion refrigeration cycle (BEERC). An enhancement of 12% in the COP and exergy efficiency of NEERC was found in comparison with BEERC when the cooling capacity and operating conditions of the two systems were the same. The increase of COP of NEERC and its efficiency along with the reduction of power consumption make it more practical for the use in residential air conditioning and cooling applications. A techno-economic analysis to compare ORC with Rankine cycle is provided. The results indicated that Rankine cycle for transcritical CO2 refrigeration cycle is more appropriate and has an advantage over the use of ORC. In addition, the small scale Rankine cycle combined with BEERC is economically viable for countries where the electricity price is above 15 c€/kW h.
Abstract A hybrid vapor compression refrigeration (HVCR) system, which combines a vapor compressi... more Abstract A hybrid vapor compression refrigeration (HVCR) system, which combines a vapor compression refrigeration (VCR) system and an ejector refrigeration (ER) system, was developed. The waste heat energy from the gas cooler in the VCR system is applied as driven source towards ER system. Thermodynamic investigations on the performance of the HVCR system, using CO2 as a refrigerant, are performed with energetic and exergetic methods, and the comparative analyses with the VCR system are conducted. Comprehensive effects of key operating parameters on the system performance are also studied. The results indicate that for the same cooling capacity, the coefficient of performance (COP) of the HVCR system shows 25% higher COP and the total mechanical power consumption is reduced by 20% than that of conventional VCR system, respectively. The performance characteristics of the proposed cycle show its application potential in cooling and air-conditioning.
This paper presents a theoretical study of a combined thermal system, which combines the Rankine ... more This paper presents a theoretical study of a combined thermal system, which combines the Rankine cycle and the ejector refrigeration cycle. This combined cycle produces power and refrigeration simultaneously. The thermal system could use low temperature heat sources. A simulation was carried out to evaluate the cycle performance using several working fluids as R123, R141b, R245fa, R601a and R600a. A one-dimensional mathematical model of the ejector was developed using the equations governing the flow and thermodynamics based on the constant area ejector flow model. The ejector is studied in optimal operating regime. The influence of thermodynamic parameters on system performance is studied. The results show that the condenser temperature, the evaporation temperature, the extraction ratio, the fluid nature and the generating temperature have significant effects on the system performances (the coefficient of performance of the combined cycle and the entrainment ratio of the ejector).
A comprehensive energy and exergoeconomic analysis of a novel transcritical refrigeration cycle (... more A comprehensive energy and exergoeconomic analysis of a novel transcritical refrigeration cycle (NTRC) is presented. A second ejector is introduced into the conventional refrigeration system for the utilization of the gas-cooler waste heat. The thermodynamic properties of the working fluid are estimated by the database of REFPROP 9, and a FORTRAN program is used to solve the system governing equations. Exergy, energy, and exergoeconomic analyses of the two cycles are carried out to predict the exergetic destruction rate and efficiency of the systems. The optimum gas cooler working pressure will be determined for both cycles. A comprehensive comparison is made between the obtained results of the conventional and the new cycles. An enhancement of approximately 30% in the coefficient of performance (COP) of the new cycle was found in comparison to the value of the conventional cycle. In addition, the results of the analysis indicated a reduction in the overall exergy destruction rate a...
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