The structural,magnetic and magnetocaloric properties of perovskite manganites La_(0.67)Sr_(0.28)Pr_(0.05)Mn_(1-x)Co_(x)O_(3)(x=0.05,0.075 and 0.10)(LSPMCO)are investigated.LSPMCO crystallizes as a rhombohedral struct...The structural,magnetic and magnetocaloric properties of perovskite manganites La_(0.67)Sr_(0.28)Pr_(0.05)Mn_(1-x)Co_(x)O_(3)(x=0.05,0.075 and 0.10)(LSPMCO)are investigated.LSPMCO crystallizes as a rhombohedral structure with R-3c space group.As the Co content increases,the cell volume expands,the Mn-O-Mn bond angle reduces and the length of the MnO bond increases.The samples show irregular submicron particles under a Zeiss scanning electron microscopy.The particle size becomes larger with increasing doping.The chemical composition of the samples is confirmed by x-ray photoelectron spectroscopy(XPS).The ferromagnetic(FM)to paramagnetic(PM)phase transition occurs near the Curie temperature(TC),and all transitions are second-order phase transitions(SMOPT)characterized by minimal thermal and magnetic hystereses.Critical behavior analysis indicates that the critical parameters of LSPMCO closely align with those predicted by the meanfield model.The T_(C)declines with C_(o) doping and reaches near room temperature(302 K)at x=0.075.The maximum magnetic entropy change(-ΔS_(M)^(max))at x=0.05 is 4.27 J/kg·K,and the relative cooling power(RCP)peaks at 310.81 J/K.Therefore,the system holds significant potential for development as a magnetic refrigeration material,meriting further professional and objective evaluation.展开更多
With the entropy generation minimization （EGM） method, the thermodynamical performance optimization in a thermoelectric refrigeration system is studied. The optimization is affected by the irreversibility of heat tr...With the entropy generation minimization （EGM） method, the thermodynamical performance optimization in a thermoelectric refrigeration system is studied. The optimization is affected by the irreversibility of heat transfer caused by finite temperature differences, the heat leak between external heat reservoirs and the internal dissipation of working fluids. EGM is taken as an objective function for the optimization. The objective function and design parameters are obtained. Optimal performance curves are presented by thermal and electronic parameters. Effects of these parameters on general and optimal performances are investigated. Results are helpful in determining optimal design conditions in real thermoelectric refrigeration systems.展开更多
This paper studies the magnetic hysteresis and refrigeration capacity of Ni-Mn-Ga alloys in detail during heating and cooling isothermal magnetisation processes. The Ni-Mn-Ga alloys show larger magnetic hysteresis whe...This paper studies the magnetic hysteresis and refrigeration capacity of Ni-Mn-Ga alloys in detail during heating and cooling isothermal magnetisation processes. The Ni-Mn-Ga alloys show larger magnetic hysteresis when they trans-form from austenite to martensite, but smaller magnetic hysteresis when they transform from martensite to austenite. This behaviour is independent of either the pure Ni-Mn-Ga alloys or the alloys doped with other elements. Because of the existence of the magnetic hysteresis, the relation between the magnetic entropy change and refrigeration capacity is not simply linear. For practical consideration, magnetocaloric effect of Ni-Mn-Ga alloys should be investigated both on cooling and heating processes.展开更多
This paper focuses on the mixed-refrigerant refrigeration process flows which are applied in the cryogenic separation section of ethylene plant. Based on a 120 kt/a ethylene plant which employs a sequence separation p...This paper focuses on the mixed-refrigerant refrigeration process flows which are applied in the cryogenic separation section of ethylene plant. Based on a 120 kt/a ethylene plant which employs a sequence separation process flow and lowpressure demethanization system, the energy consumption of three refrigeration process flows（typical cascade refrigeration, binary refrigeration and tertiary refrigeration） was calculated by means of the ASPEN PLUS simulation software. An optimized mixed-refrigerant composition which achieved the minimum energy consumption of refrigeration systems was found out and the exergy loss was analyzed and compared. Results indicated that the energy consumption of typical cascade refrigeration and binary refrigeration systems was almost equal and that of tertiary refrigeration system was higher than the other two systems. Based on the current situation of production, the suggestions on production optimization and refrigeration process flow selection were put forward.展开更多
An irreversible Ericsson refrigeration cycle model is established, in which multi-irreversibilities such as finite-rate heat transfer, regenerative loss, heat leakage, and the efficiency of the regenerator are taken i...An irreversible Ericsson refrigeration cycle model is established, in which multi-irreversibilities such as finite-rate heat transfer, regenerative loss, heat leakage, and the efficiency of the regenerator are taken into account. Expressions for several important performance parameters, such as the cooling rate, coefficient of performance （COP）, power input, exergy output rate, entropy generation rate, and ecological function are derived. The influences of the heat leakage and the time of the regenerative processes on the ecological performance of the refrigerator are analyzed. The optimal regions of the ecological function, cooling rate, and COP are determined and evaluated. Furthermore, some important parameter relations of the refrigerator are revealed and discussed in detail. The results obtained here have general significance and will be helpful in gaining a deep understanding of the magnetic Ericsson refrigeration cycle.展开更多
A new model of a quantum refrigeration cycle composed of two adiabatic and two isomagnetic field processes is established. The working substance in the cycle consists of many non-interacting spin-1/2 systems. The perf...A new model of a quantum refrigeration cycle composed of two adiabatic and two isomagnetic field processes is established. The working substance in the cycle consists of many non-interacting spin-1/2 systems. The performance of the cycle is investigated, based on the quantum master equation and semi-group approach. The general expressions of several important performance parameters, such as the coefficient of performance, cooling rate, and power input, are given. It is found that the coefficient of performance of this cycle is in the closest analogy to that of the classical Carnot cycle. Furthermore, at high temperatures the optimal relations of the cooling rate and the maximum cooling rate are analysed in detail. Some performance characteristic curves of the cycle are plotted, such as the cooling rate versus the maximum ratio between high and low ＂temperatures＂ of the working substances, the maximum cooling rate versus the ratio between high and low ＂magnetic fields＂ and the ＂temperature＂ ratio between high and low reservoirs. The obtained results are further generalized and discussed, so that they may be directly applied to describing the performance of the quantum refrigerator using spin-J systems as the working substance. Finally, the optimum characteristics of the quantum Carnot and Ericsson refrigeration cycles are derived by analogy.展开更多
The airborne high power electrical equipments have been widely used in modern aircrafts , which consequently causes the dramatic increase of heating load up to dozens of kilowatts.Accordingly , vapor-compression refri...The airborne high power electrical equipments have been widely used in modern aircrafts , which consequently causes the dramatic increase of heating load up to dozens of kilowatts.Accordingly , vapor-compression refrigeration system ( VCRS ) with lower engine bleed air and larger refrigeration capacity has been paid much attention in recent years.Therefore , based on the analysis of the characteristics of VCRS , an experiment system of VCRS using R134ais set up to simulate operation performances.The influences of different parameters including evaporation pressure , condensing pressure , refrigerant mass flow rate and compressor rotation speed are also investigated.The impacts of different parameters on the system performance are various.This work can help to establish the specific control law under different work conditions.展开更多
An open loop cycle carbon dioxide(CO2)refrigeration system is established,and the cooling performances of high-pressure CO2 under different storage conditions(25℃,30℃,and 35℃)are investigated.Moreover,the experimen...An open loop cycle carbon dioxide(CO2)refrigeration system is established,and the cooling performances of high-pressure CO2 under different storage conditions(25℃,30℃,and 35℃)are investigated.Moreover,the experimental mass flow rates of CO2 are compared with the theoretical values at different conditions and refrigeration capacities.The results indicate that the storage condition of CO2 has a significant impact on the refrigeration performance,and the mass flow rate of CO2 increases with the increasing storage temperature in a given refrigeration capacity.展开更多
We have successfully developed cryogen-free dilution refrigerators with medium cooling power that can be applied to quantum experiments. Breakthroughs have been made in some key technologies and components of heat swi...We have successfully developed cryogen-free dilution refrigerators with medium cooling power that can be applied to quantum experiments. Breakthroughs have been made in some key technologies and components of heat switches and dilution units. Our prototype has been running continuously and stably for more than 100 hours below 10 m K, with a minimum temperature of 7.6 m K and a cooling power of 450 μW at 100 m K. At the same time, we have also made progress in the application of dilution refrigerators, such as quantum computing, low-temperature detector, and magnet integration. These indicators and test results indicate good prospects for application in physics, astronomy, and quantum information.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.52162038)。
文摘The structural,magnetic and magnetocaloric properties of perovskite manganites La_(0.67)Sr_(0.28)Pr_(0.05)Mn_(1-x)Co_(x)O_(3)(x=0.05,0.075 and 0.10)(LSPMCO)are investigated.LSPMCO crystallizes as a rhombohedral structure with R-3c space group.As the Co content increases,the cell volume expands,the Mn-O-Mn bond angle reduces and the length of the MnO bond increases.The samples show irregular submicron particles under a Zeiss scanning electron microscopy.The particle size becomes larger with increasing doping.The chemical composition of the samples is confirmed by x-ray photoelectron spectroscopy(XPS).The ferromagnetic(FM)to paramagnetic(PM)phase transition occurs near the Curie temperature(TC),and all transitions are second-order phase transitions(SMOPT)characterized by minimal thermal and magnetic hystereses.Critical behavior analysis indicates that the critical parameters of LSPMCO closely align with those predicted by the meanfield model.The T_(C)declines with C_(o) doping and reaches near room temperature(302 K)at x=0.075.The maximum magnetic entropy change(-ΔS_(M)^(max))at x=0.05 is 4.27 J/kg·K,and the relative cooling power(RCP)peaks at 310.81 J/K.Therefore,the system holds significant potential for development as a magnetic refrigeration material,meriting further professional and objective evaluation.
文摘With the entropy generation minimization （EGM） method, the thermodynamical performance optimization in a thermoelectric refrigeration system is studied. The optimization is affected by the irreversibility of heat transfer caused by finite temperature differences, the heat leak between external heat reservoirs and the internal dissipation of working fluids. EGM is taken as an objective function for the optimization. The objective function and design parameters are obtained. Optimal performance curves are presented by thermal and electronic parameters. Effects of these parameters on general and optimal performances are investigated. Results are helpful in determining optimal design conditions in real thermoelectric refrigeration systems.
基金supported by the National Basic Research Program of China (Grant No.2006CB601101)the National High Technology Research and Development Program of China (Grant No.2007AA03Z440)the National Natural Science Foundation of China(Grant No.50731007)
文摘This paper studies the magnetic hysteresis and refrigeration capacity of Ni-Mn-Ga alloys in detail during heating and cooling isothermal magnetisation processes. The Ni-Mn-Ga alloys show larger magnetic hysteresis when they trans-form from austenite to martensite, but smaller magnetic hysteresis when they transform from martensite to austenite. This behaviour is independent of either the pure Ni-Mn-Ga alloys or the alloys doped with other elements. Because of the existence of the magnetic hysteresis, the relation between the magnetic entropy change and refrigeration capacity is not simply linear. For practical consideration, magnetocaloric effect of Ni-Mn-Ga alloys should be investigated both on cooling and heating processes.
文摘This paper focuses on the mixed-refrigerant refrigeration process flows which are applied in the cryogenic separation section of ethylene plant. Based on a 120 kt/a ethylene plant which employs a sequence separation process flow and lowpressure demethanization system, the energy consumption of three refrigeration process flows（typical cascade refrigeration, binary refrigeration and tertiary refrigeration） was calculated by means of the ASPEN PLUS simulation software. An optimized mixed-refrigerant composition which achieved the minimum energy consumption of refrigeration systems was found out and the exergy loss was analyzed and compared. Results indicated that the energy consumption of typical cascade refrigeration and binary refrigeration systems was almost equal and that of tertiary refrigeration system was higher than the other two systems. Based on the current situation of production, the suggestions on production optimization and refrigeration process flow selection were put forward.
基金supported by the Program for Excellent Young Teachers Foundation of Shanghai in China(Grant No.thc-20100036)
文摘An irreversible Ericsson refrigeration cycle model is established, in which multi-irreversibilities such as finite-rate heat transfer, regenerative loss, heat leakage, and the efficiency of the regenerator are taken into account. Expressions for several important performance parameters, such as the cooling rate, coefficient of performance （COP）, power input, exergy output rate, entropy generation rate, and ecological function are derived. The influences of the heat leakage and the time of the regenerative processes on the ecological performance of the refrigerator are analyzed. The optimal regions of the ecological function, cooling rate, and COP are determined and evaluated. Furthermore, some important parameter relations of the refrigerator are revealed and discussed in detail. The results obtained here have general significance and will be helpful in gaining a deep understanding of the magnetic Ericsson refrigeration cycle.
基金Project supported by the National Natural Science Foundation of China （Grant No 10465003） and the Natural Science Foundation of Jiangxi Province, China （Grant No 0412011）.
文摘A new model of a quantum refrigeration cycle composed of two adiabatic and two isomagnetic field processes is established. The working substance in the cycle consists of many non-interacting spin-1/2 systems. The performance of the cycle is investigated, based on the quantum master equation and semi-group approach. The general expressions of several important performance parameters, such as the coefficient of performance, cooling rate, and power input, are given. It is found that the coefficient of performance of this cycle is in the closest analogy to that of the classical Carnot cycle. Furthermore, at high temperatures the optimal relations of the cooling rate and the maximum cooling rate are analysed in detail. Some performance characteristic curves of the cycle are plotted, such as the cooling rate versus the maximum ratio between high and low ＂temperatures＂ of the working substances, the maximum cooling rate versus the ratio between high and low ＂magnetic fields＂ and the ＂temperature＂ ratio between high and low reservoirs. The obtained results are further generalized and discussed, so that they may be directly applied to describing the performance of the quantum refrigerator using spin-J systems as the working substance. Finally, the optimum characteristics of the quantum Carnot and Ericsson refrigeration cycles are derived by analogy.
文摘The airborne high power electrical equipments have been widely used in modern aircrafts , which consequently causes the dramatic increase of heating load up to dozens of kilowatts.Accordingly , vapor-compression refrigeration system ( VCRS ) with lower engine bleed air and larger refrigeration capacity has been paid much attention in recent years.Therefore , based on the analysis of the characteristics of VCRS , an experiment system of VCRS using R134ais set up to simulate operation performances.The influences of different parameters including evaporation pressure , condensing pressure , refrigerant mass flow rate and compressor rotation speed are also investigated.The impacts of different parameters on the system performance are various.This work can help to establish the specific control law under different work conditions.
基金supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘An open loop cycle carbon dioxide(CO2)refrigeration system is established,and the cooling performances of high-pressure CO2 under different storage conditions(25℃,30℃,and 35℃)are investigated.Moreover,the experimental mass flow rates of CO2 are compared with the theoretical values at different conditions and refrigeration capacities.The results indicate that the storage condition of CO2 has a significant impact on the refrigeration performance,and the mass flow rate of CO2 increases with the increasing storage temperature in a given refrigeration capacity.
基金supported by the Beijing Commission of Science and Technology(Grant No.Z211100004021012)Special Research Assistant Program of the Chinese Academy of Sciences(Grant No.E3VP021RX4)。
文摘We have successfully developed cryogen-free dilution refrigerators with medium cooling power that can be applied to quantum experiments. Breakthroughs have been made in some key technologies and components of heat switches and dilution units. Our prototype has been running continuously and stably for more than 100 hours below 10 m K, with a minimum temperature of 7.6 m K and a cooling power of 450 μW at 100 m K. At the same time, we have also made progress in the application of dilution refrigerators, such as quantum computing, low-temperature detector, and magnet integration. These indicators and test results indicate good prospects for application in physics, astronomy, and quantum information.
