水工质热泵多种循环的理论研究与性能对比

Theoretical study and performance comparison of different heat pump cycles using water as working fluid

水工质安全、稳定、无毒、不易燃,是一种优秀的高温热泵用制冷工质。为了研究水蒸气热泵系统循环性能,设计了3种具有不同循环方式和辅助设备的水蒸气热泵系统,分别是单级压缩喷水系统、单级压缩带喷射器系统和两级压缩带中间换热器系统。并进行了理论建模与分析,理论分析与对比结果表明两级压缩系统在排气过热度、制热量、系统功耗和COP等方面均具有最优的性能。单级喷水系统比常规循环系统具有更好的性能,尤其是能有效降低排气过热度。在80℃蒸发、140℃冷凝时,常规系统的COP为3.01,而单级喷水系统和两级换热系统的COP分别为3.15和4.07,相比较于常规系统分别提升了4.7%和35.2%。而单级带喷射器系统在大温升工况下比常规循环系统有更优的COP。

As the working fluid of heat pump systems,water has the advantages of cheap,safe,stable,no toxicity and no flammability.It is a promising working fluid in the application of heat pumps.To find and study the water vapor heat pump system cycle with the best performance,three water vapor heat pumps with different system cycles and auxiliary equipment(the single-stage system with water-injection,the single-stage system with ejector,the two-stage system with internal heat exchanger)were designed and analyzed with simulation models.In the simulation,the twin-screw compressor was used as the power equipment in these systems.The simulation results indicated that compared with other systems,the two-stage system with internal heat exchanger is the best choice and has the best system performance including the discharge superheat,heating capacity,power consumption and COP.The single-stage system with water-injection has better performance than the conventional cycle,especially it can effectively decrease the discharge superheat.At 80℃evaporation temperature and 140℃condensation temperature,COP of the conventional cycle was 3.01.Meanwhile,COP of the single-stage system with water injection and the two-stage system with internal heat exchanger was 3.15 and 4.07,which are 4.7%and 35.2%higher than that of the conventional cycle,respectively.For the single-stage system with ejector,it has better COP than the conventional cycle at high condensation temperature conditions with higher temperature lift.At 80℃evaporation temperature and 145℃condensation temperature,COP of the single-stage system with ejector was 2.53,which is higher than COP of the conventional cycle,2.42.So it is also a good choice for high temperature lift conditions when used in water vapor heat pumps.