A class of two-heat-reservoir heat engine model with heat leakage,finite heat capacity high-temperature source and infinite heat capacity low-temperature heat sink,is researched with the finite-time thermodynamic theo...A class of two-heat-reservoir heat engine model with heat leakage,finite heat capacity high-temperature source and infinite heat capacity low-temperature heat sink,is researched with the finite-time thermodynamic theory and the entransy theory.The optimal configuration based on the minimum entropy generation and the maximum entransy loss under the given cycle is searched,which are compared with the optimal configuration based on the maximum output work,and all the heat transfer in the model is assumed to obey the Newton’s law.The results show that,for the infinite heat capacity high-temperature source,the optimal configuration does not change whether heat leakage exists or not;however,for the finite hightemperature reservoir,the optimal configuration is different among which based on the minimum entropy generation,the maximum entransy loss,and the maximum output work when the heat leakage exists.展开更多
A model of an energy selective electron (ESE) engine with linear heat leakage and Lorentzian transmission probability is established in this paper.The expressions for the main performance parameters of the ESE engine ...A model of an energy selective electron (ESE) engine with linear heat leakage and Lorentzian transmission probability is established in this paper.The expressions for the main performance parameters of the ESE engine operating as a heat engine or a refrigerator are derived by using the theory of finite time thermodynamics.The optimum performances of the ESE engine are explored and the influences of the heat leakage,the central energy level of the resonance,and the width of the resonance on the performance of the ESE engine are analyzed by using detailed numerical examples.The optimal operation regions of power output and efficiency (or cooling load and coefficient of performance (COP)) are also discussed.Moreover,the performances of the ESE engine with Lorentzian transmission probability are compared with those with rectangular transmission probability.It is shown that the power output versus efficiency (or cooling load versus COP) characteristic curves with and without heat leakage are all closed loop-shaped ones.The efficiency (or COP) of the ESE engine decreases as the heat leakage increases.It is found that as the resonance width increases,the power output and efficiency (or cooling load and COP) increase to a maximum and then decrease due to the finite range of energies which contribute positively to the power generation or refrigeration in the electron system.Especially,when heat leakage is taken into account,the characteristic curves of maximum efficiency (or maximum COP) versus half resonance width are parabolic-like ones,which are quite different from the monotonic decreasing characteristic curves obtained in previous analyses without considering heat leakage.The results obtained in this paper can provide some theoretical guidelines for the design and operation of practical electron energy conversion devices such as solid-state thermionic refrigerators.展开更多
Based on the finite time thermodynamics theory,the entransy theory and the entropy theory,the Stirling cycles under different conditions are analyzed and optimized with the maximum output power as the target in this p...Based on the finite time thermodynamics theory,the entransy theory and the entropy theory,the Stirling cycles under different conditions are analyzed and optimized with the maximum output power as the target in this paper.The applicability of entransy loss(EL),entransy dissipation(ED),entropy generation(EG),entropy generation number(EGN) and modified entropy generation number(MEGN) to the system optimization is investigated.The results show that the maximum EL rate corresponds to the maximum power output of the cycle working under the infinite heat reservoirs whose temperatures are prescribed,while the minimum EG rate and the extremum ED rate do not.For the Stirling cycle working under the finite heat reservoirs provided by the hot and cold streams whose inlet temperatures and the heat capacity flow rates are prescribed,the maximum EL rate,the minimum EG rate,the minimum EGN and the minimum MEGN all correspond to the maximum power output,but the extremum ED rate does not.When the heat capacity flow rate of the hot stream increases,the power output,the EL rate,the EG rate and the ED rate increase monotonously,while the EGN and the MEGN decrease first and then increase.The EL has best consistency in the power output optimizations of the Stirling cycles discussed in this paper.展开更多
The mass entransy and its dissipation extremum principle have opened up a new direction for the mass transfer optimization. Firstly, the emergence and development process of both the mass entransy and its dissipalion ...The mass entransy and its dissipation extremum principle have opened up a new direction for the mass transfer optimization. Firstly, the emergence and development process of both the mass entransy and its dissipalion extremum principle are reviewed. Secondly, the combination of the mass entransy dissipation extremum principle and the finite-time thermodynamics for opti- mizing the mass transfer processes of one-way isothermal mass transfer, two-way isothermal equimolar mass transfer, and iso- thermal throttling and isothermal crystallization are summarized. Thirdly, the combination of the mass entransy dissipation ex- tremum principle and the constructal theory for optimizing the mass transfer processes of disc-to-point and volume-to-point problems are summarized. The scientific features of the mass entransy dissipation extremam principle are emphasized.展开更多
基金supported by the National Natural Science Foundation of China (51176203,51206184)
文摘A class of two-heat-reservoir heat engine model with heat leakage,finite heat capacity high-temperature source and infinite heat capacity low-temperature heat sink,is researched with the finite-time thermodynamic theory and the entransy theory.The optimal configuration based on the minimum entropy generation and the maximum entransy loss under the given cycle is searched,which are compared with the optimal configuration based on the maximum output work,and all the heat transfer in the model is assumed to obey the Newton’s law.The results show that,for the infinite heat capacity high-temperature source,the optimal configuration does not change whether heat leakage exists or not;however,for the finite hightemperature reservoir,the optimal configuration is different among which based on the minimum entropy generation,the maximum entransy loss,and the maximum output work when the heat leakage exists.
基金supported by the National Natural Science Foundation of China (Grant No. 10905093)the Program for New Century Excellent Talents in Universities of China (Grant No. NCET-04-1006)the Foundation for the Author of National Excellent Doctoral Dissertation ofChina (Grant No. 200136)
文摘A model of an energy selective electron (ESE) engine with linear heat leakage and Lorentzian transmission probability is established in this paper.The expressions for the main performance parameters of the ESE engine operating as a heat engine or a refrigerator are derived by using the theory of finite time thermodynamics.The optimum performances of the ESE engine are explored and the influences of the heat leakage,the central energy level of the resonance,and the width of the resonance on the performance of the ESE engine are analyzed by using detailed numerical examples.The optimal operation regions of power output and efficiency (or cooling load and coefficient of performance (COP)) are also discussed.Moreover,the performances of the ESE engine with Lorentzian transmission probability are compared with those with rectangular transmission probability.It is shown that the power output versus efficiency (or cooling load versus COP) characteristic curves with and without heat leakage are all closed loop-shaped ones.The efficiency (or COP) of the ESE engine decreases as the heat leakage increases.It is found that as the resonance width increases,the power output and efficiency (or cooling load and COP) increase to a maximum and then decrease due to the finite range of energies which contribute positively to the power generation or refrigeration in the electron system.Especially,when heat leakage is taken into account,the characteristic curves of maximum efficiency (or maximum COP) versus half resonance width are parabolic-like ones,which are quite different from the monotonic decreasing characteristic curves obtained in previous analyses without considering heat leakage.The results obtained in this paper can provide some theoretical guidelines for the design and operation of practical electron energy conversion devices such as solid-state thermionic refrigerators.
基金supported by the Tsinghua University Initiative Scientific Research Program
文摘Based on the finite time thermodynamics theory,the entransy theory and the entropy theory,the Stirling cycles under different conditions are analyzed and optimized with the maximum output power as the target in this paper.The applicability of entransy loss(EL),entransy dissipation(ED),entropy generation(EG),entropy generation number(EGN) and modified entropy generation number(MEGN) to the system optimization is investigated.The results show that the maximum EL rate corresponds to the maximum power output of the cycle working under the infinite heat reservoirs whose temperatures are prescribed,while the minimum EG rate and the extremum ED rate do not.For the Stirling cycle working under the finite heat reservoirs provided by the hot and cold streams whose inlet temperatures and the heat capacity flow rates are prescribed,the maximum EL rate,the minimum EG rate,the minimum EGN and the minimum MEGN all correspond to the maximum power output,but the extremum ED rate does not.When the heat capacity flow rate of the hot stream increases,the power output,the EL rate,the EG rate and the ED rate increase monotonously,while the EGN and the MEGN decrease first and then increase.The EL has best consistency in the power output optimizations of the Stirling cycles discussed in this paper.
基金supported by the National Natural Science Foundation China(Grant Nos.51176203 and 10905093)
文摘The mass entransy and its dissipation extremum principle have opened up a new direction for the mass transfer optimization. Firstly, the emergence and development process of both the mass entransy and its dissipalion extremum principle are reviewed. Secondly, the combination of the mass entransy dissipation extremum principle and the finite-time thermodynamics for opti- mizing the mass transfer processes of one-way isothermal mass transfer, two-way isothermal equimolar mass transfer, and iso- thermal throttling and isothermal crystallization are summarized. Thirdly, the combination of the mass entransy dissipation ex- tremum principle and the constructal theory for optimizing the mass transfer processes of disc-to-point and volume-to-point problems are summarized. The scientific features of the mass entransy dissipation extremam principle are emphasized.
