Simulation And Optimization And Experimental Study Of Tube-fin Evaporator Of CO₂Heat Pump

With the attention to the destruction of the ozone layer and the greenhouse effectissues of the worldwide, energy conservation and emission reduction, advocating lowcarbon HVAC increasingly become the today’s social themes, research on the newenvironmentally and friendly refrigerant CO₂has also caused the attention of researchscholars increasingly. At the same time, with the increasing requirements of quality oflife, the increasing demand for sanitary hot water results to the popularization andapplication of heat pump water heater widely. Because of the special thermophysicalproperties of CO₂, the CO₂refrigerant is widely used in the transcritical cycle of heatpump system. With the continuous development and progress of science andtechnology, especially the commercial market of carbon dioxide heat pump waterheater in Japan, the heat transfer performance and the optimization design for tube-finevaporator of CO₂heat pump get close attention to more domestic and foreign researchscholars.At present, the pressure capacity of evaporator which is used in the conventionalair conditioning system is most below4Mpa in the commercial market. In order to beused in high pressure CO₂heat pump system, we shoud reinvent and design thetube-fin evaporator. At the same time, we found that the method of establishingsteady-state lumped parameter model for the tube-fin evaporator was used to analysisthe affect on system performance, while there are less research on these aspects whichused the method of establishing steady-state partition distributed parameter model toanalyze the heat transfer performance on the evaporator and optimize and design the structure size of evaporator. This subject intends to use the steady-state partitiondistributed parameter model and the optimization of structure size as the starting point,combine with the actual situation of the commercial market and expand the simulationand optimization and experimental studies on the tube-fin evaporator of CO₂heatpump system.In order to analysis the heat transfer performance of the CO₂heat pumpevaporator in detail, we go on the optimization design for its structure size parameters.In this paper, we established a simulation mathematical model of the tube-finevaporator for air source CO₂transcritical cycle system and set up a performance testequipment for the evaporator of air source CO₂heat pump system with the design andselection. The main research work are listed in the followings：（1）Establish steady-state partition distributed parameter model for tube-finevaporator of air-source CO₂transcritical cycle, based on thermodynamics-relatedknowledge and EES programming software;（2）Set up a performance test equipment for the evaporator of air source CO₂heatpump system with the design and selection;（3）Verify the accuracy of the simulation mathematical model of tube-finevaporator of CO₂heat pump system through the test data;（4）Analyze the system state parameters, structure size parameters on theperformance of an evaporator through the simulation of mathematical models andintended to optimize the design of a tube-fin evaporator of CO₂heat pump system bysensitivity analysis of the structure size parameters on the performance of anevaporator.The simulation results show that: the established simulation mathematical modelof tube-fin evaporator of CO₂heat pump system can better reflect the heat transferperformance of the test evaporator, which the error of heat transfer of evaporator is lessthan7%; at the same time, we go on sensitivity analysising the evaporator structureand size parameters with the simulation mathematical model of tube-fin evaporator ofCO₂heat pump system and found that the effect of number of tube rows, length ofsingle row of tube and tube spacing on the heat transfer of evaporator is more sensitive,which of corresponding heat transfer are increased average rate of the followed by14.7%,7.49%,9.05%with the increase in structural size parameters. We optimized anddesigned a tube-fin evaporator of CO₂heat pump system, which compared with the testevaporator, the space volume of the evaporator is reduced24.86%, heat transfer coefficient is increased5.17%, heat transfer of Per unit area is increased by15.58%,the cold weight ratio of copper and aluminum are increased21.75%,130.20%correspondly in the same case which the heat transfer is essentially constant.