Theoretical And Experimental Study On Variable Composition Capacity Regulation Heat Pump System

The variable composition capacity regulation can be defined as the regulation of cooling capacity or heating capacity of the system by changing composition of the mixture in the system according to characteristics of the nonazeotropic mixtures. Comparing with other capacity regulation methods, it has a good modulation effect and can avoid additional energy consumption as well as many problems such as compressor sympathetic vibration, leakage etc. Therefore, it has a good future. This thesis studies theoretically and experimentally on the performances of a novel air source heat pump system using mixture. The main research contents are as follows:1.The research history and present status of variable composition capacity regulation systems at home and abroad were reviewed. Based on the conventional systems, we proposed a novel system in which a variable composition device is used in the low pressure section of the cycle. It has a simple structure and can easily be controlled.2. Thermodynamic calculations of the cycle are conducted on five refrigerant pairs including hydrocarbon and its derivant such as R32/R134a, R143a/R134a, R143a/R227ea, R290/R227ea and R125/R227ea. The suitable mixture for variable capacity regulation is selected according to the thermodynamic characteristics of the cycle, distillation characteristics and impacts on environment. Finally, R32/R134a is selected as the best mixture for further research.3. A steady state simulation of the performance of the variable composition capacity regulation heat pump system in winter weather is conducted. The relations between the main performance parameters and the temperature at the inlet of the evaporator are obtained. The effects on the performance of the system due to different structure parameters are analyzed. Comparisons are also made between R22 conventional heat pump system as well as R32/R134a constant composition heat pump system and this new heat pump system. These provide a theoretical basis for design and modification of the system.4. An experiment apparatus for this novel variable capacity heat pump system is designed and set up. Experiments are conducted on the operation performance of the systemwhen R32/R134a and R22 are used. The experimental results show that the theoretical model is reliable and the novel variable capacity heat pump system is practical. Several problems in design and operation are also exposed. It gives a direction in further developing of this system.5. The automatic control manners of capacity regulations for variable composition capacity regulation heat pumps are discussed and semi-automatic control is realized. It lays a foundation for the application of this novel heat pump system.