The use of air conditioning and refrigeration systems improved the standard of living. However, the system contributes to global warming by releasing potential global warming refrigerants directly and powering the sys...The use of air conditioning and refrigeration systems improved the standard of living. However, the system contributes to global warming by releasing potential global warming refrigerants directly and powering the system. There is an obligation, like UN Kyoto Protocol, EU MAC Directive and Japan METI Directive to find an alternative low-GWP refrigerant with excellent thermophysical properties. In this paper, the global warming effect of an air-conditioning system is analyzed theoretically using few low-GWP refrigerant mixtures. New refrigerant mixtures are formed based on low GWP, high volumetric capacity, and refrigerating effect. After analyzing, refrigerant blends of R1234yf/R32 (40/60, 50/50, and 60/40 by wt%) and R1234ze/R32 (40/60, 50/50, and 60/40 by wt%) are found promising to replace the widely used R410A. The best performance of the refrigerant blend is found for R1234yf/R32 (40/60). These analyses are crucial for selecting suitable refrigerants for domestic air conditioning systems.展开更多
Aluminum alloys have drawn considerable attention in the area of automotive lightweight.High strength aluminum alloys are usually deformed at elevated temperatures due to their poor formability at room temperature.In ...Aluminum alloys have drawn considerable attention in the area of automotive lightweight.High strength aluminum alloys are usually deformed at elevated temperatures due to their poor formability at room temperature.In this work,the yield behavior of 7075 aluminum alloy in T6 temper(AA7075-T6)within the temperature ranging from 25°C to 230°C was investigated.Uniaxial and biaxial tensile tests with the aid of induction heating system were performed to determine the stress vs.strain curves and the yield loci of AA7075-T6 at elevated temperatures,respectively.Von Mises,Hill48 and Yld2000-2d yield criteria were applied to predicting yield loci which were compared with experimentally measured yield loci of the AA7075-T6.Results show that yield stress corresponding to the same equivalent plastic strain decreases with increasing temperature within the investigated temperature range and the shape of yield loci evolves nearly negligibly.The experimental yield locus expands with an increase of equivalent plastic strain at the same temperature and the work hardening rate of AA7075-T6 exhibits obvious stress-state-dependency.The nonquadratic Yld2000-2d yield criterion describes the yield surfaces of AA7075-T6 more accurately than the quadratic von Mises and Hill48 yield criteria,and an exponent of 14 in the Yld2000-2d yield function gives the optimal predictions for the AA7075-T6 at all investigated temperatures.展开更多
文摘The use of air conditioning and refrigeration systems improved the standard of living. However, the system contributes to global warming by releasing potential global warming refrigerants directly and powering the system. There is an obligation, like UN Kyoto Protocol, EU MAC Directive and Japan METI Directive to find an alternative low-GWP refrigerant with excellent thermophysical properties. In this paper, the global warming effect of an air-conditioning system is analyzed theoretically using few low-GWP refrigerant mixtures. New refrigerant mixtures are formed based on low GWP, high volumetric capacity, and refrigerating effect. After analyzing, refrigerant blends of R1234yf/R32 (40/60, 50/50, and 60/40 by wt%) and R1234ze/R32 (40/60, 50/50, and 60/40 by wt%) are found promising to replace the widely used R410A. The best performance of the refrigerant blend is found for R1234yf/R32 (40/60). These analyses are crucial for selecting suitable refrigerants for domestic air conditioning systems.
基金Supported by National Natural Science Foundation of China(Grant No.51805375).
文摘Aluminum alloys have drawn considerable attention in the area of automotive lightweight.High strength aluminum alloys are usually deformed at elevated temperatures due to their poor formability at room temperature.In this work,the yield behavior of 7075 aluminum alloy in T6 temper(AA7075-T6)within the temperature ranging from 25°C to 230°C was investigated.Uniaxial and biaxial tensile tests with the aid of induction heating system were performed to determine the stress vs.strain curves and the yield loci of AA7075-T6 at elevated temperatures,respectively.Von Mises,Hill48 and Yld2000-2d yield criteria were applied to predicting yield loci which were compared with experimentally measured yield loci of the AA7075-T6.Results show that yield stress corresponding to the same equivalent plastic strain decreases with increasing temperature within the investigated temperature range and the shape of yield loci evolves nearly negligibly.The experimental yield locus expands with an increase of equivalent plastic strain at the same temperature and the work hardening rate of AA7075-T6 exhibits obvious stress-state-dependency.The nonquadratic Yld2000-2d yield criterion describes the yield surfaces of AA7075-T6 more accurately than the quadratic von Mises and Hill48 yield criteria,and an exponent of 14 in the Yld2000-2d yield function gives the optimal predictions for the AA7075-T6 at all investigated temperatures.
