摘要
Abstract
Selecting appropriate high-temperature working fluids was crucial for the reliable and economic operation of the high-temperature heat pump system.However,the commonly used R245fa was restricted in use because of its relatively high global warming potential(GWP)value.Based on the vapor injection enhanced enthalpy cascade high-temperature heat pump system,the thermophysical properties of four new types of low-GWP working fluids,namely R1234ze(Z),R1233zd(E),R1224yd(Z)and R1336mzz(Z),were analyzed.MATLAB was used to establish models,and their cycle performances were compared and analyzed and then compared with that of R245fa.The results showed that the four working fluids were superior to R245fa in terms of environmental protection and safety.In terms of basic thermophysical properties,R1234ze(Z)had the lowest density of 546 kg/m3 and was better than the other working fluids in terms of specific heat at constant pressure and thermal conductivity,and its viscosity was equivalent to that of R1224yd(Z).In terms of cycle performance,R1336mzz(Z)had the smallest condensation pressure and the highest average coefficient of performance(COP)and exergy efficiency,which were 4.9 and 79.5%respectively,but its unit volumetric heating capacity was also the smallest,with an average of 2330.2 kJ/m3,so it was suitable for small-capacity heat pump systems.R1234ze(Z)had the largest unit volumetric heating capacity,with an average of 4 327.2 kJ/m3,but its average condensation pressure was the highest,at 2 320.3 kPa,so it was suitable for large-capacity systems with relatively low heat demand temperatures.The remaining two working fluids were slightly better than R245fa in terms of COP,exergy efficiency and exhaust temperature under high condensation temperatures.Therefore,all four working fluids had the possibility of becoming substitutes for R245fa.关键词
余热利用/高温热泵/温室效应指数/循环性能/工质替代/循环性能参数Key words
waste heat utilization/high-temperature heat pump/GWP/cycling performance/refrigerants replacement/COP分类
能源科技
