140℃蒸汽热泵循环热力性能优化研究OA

To address the issue of performance limitations of high-temperature heat pumps under wide temperature lift conditions,a heat pump cycle scheme was proposed to efficiently generate 140℃steam using 70℃industrial waste heat.Under typical operating conditions with an evaporation temperature of 60℃and a condensation temperature of 145℃,four high-temperature working fluids,namely R1233zd(E),R1336mzz(Z),R1234ze(Z)and R245fa were selected to analyze their suitability in a quasi-second-stage compression heat pump cycle.The effects of intermediate pressure,subcooling degree,superheat degree and operating condition fluctuation on the coefficient of performance(COP)of the system were investigated.Furthermore,a cascade compression heat pump system model was developed,taking the influence of intermediate temperature on COP as an example,a comparison between the cascade compression heat pump and the quasi-second-stage compression heat pump was conducted.The results indicate that in the quasi-second-stage compression heat pump cycle,the optimal intermediate pressure is approximately 1.2 times the geometric mean pressure,and the minimum superheat degree is significantly affected by the operating conditions.In the cascade compression heat pump system,the optimal performance is achieved when R1233zd(E)is used as the working fluid in both the high-temperature and low-temperature stages.With an intermediate heat exchange temperature difference of 5℃,the COP is improved by approximately 12%compared with the quasi-second-stage compression system.R1233zd(E)demonstrates significant comprehensive performance advantages under the operating conditions in this study.This research can provide a theoretical basis for the system optimization design of quasi-second-stage and cascade high-temperature heat pumps,as well as for the selection of environmentally friendly and highly efficient working fluids.