Optimal Design And Experimental Research Of Heat Exchanger On Heating Side Of R744/R290 Heat Pump Water Heater

The application of heat pump water heater technology is of great significance to energy conservation and environmental protection.Non-azeotropic alternative refrigerants composed of environmentally friendly refrigerants have been attracted much attention because of their environmental friendliness and excellent thermodynamic properties.The research team conducted a lot of research on R744/R290 in the early stage and proved that it is a very potential alternative refrigerant.At present,there are relatively few researches on heat exchanger optimization for the heat pump water heater systems with R744/R290,and heat exchanger optimization is one of the main issues to improve the energy efficiency and economy of the heat pump water heater systems.Therefore,in this paper,the tube in tube heat exchanger on the heating side of the instant heat pump water heater with R744/R290 is chosen as the research object,and the optimization design and experimental research of the heat exchanger on the heating side was taken.The main study contents and conclusions are as follows:（1）In order to improve the heat transfer performance and economic performance of the tube in tube heat exchanger on the heating side,the constructed heat exchanger design model is used to complete the design of different optimization schemes,and the heat transfer coefficient,pressure drop,copper consumption and other factors is considered comprehensively,the combined the tube in tube heat exchanger is optimized.（2）Based on the processing of the combined tube in tube heat exchanger,the transformation of the heat exchanger performance test system on the heating side of the heat pump water heater is completed.With the aid of the experimental system,the heat transfer performance and economic performance of the combined double-pipe heat exchanger and the original tube in tube heat exchanger are compared.The experimental results show that under the nominal conditions of the water source heat pump water heater,the heat transfer,heat transfer coefficient,pressure drop,K/ΔP^1/3,and other parameters of the combined tube in tube heat exchanger are better than the original heat exchanger;in addition,the copper consumption of the heat exchanger has been reduced by 17.35%,achieving the goal of optimizing the design of the original tube in tube heat exchanger on the heating side.（3）The influence of heat sink flow rate,heat sink inlet temperature,and R744/R290 mass ratio on the heat transfer performance of the combined tube in tube heat exchanger is studied.The experimental results show that under a fixed system superheat condition,as the heat sink flow increases,the heat transfer coefficient,heat transfer,and pressure drop of the heat exchanger increase accordingly,and the length of the heat exchanger integrated tube corresponding to the process of refrigerant from superheated gas to saturated liquid is shortened.As the inlet temperature of the heat sink increases,the heat transfer coefficient,heat transfer,and pressure drop decrease accordingly,and the length of the heat exchanger integrated tube corresponding to the process of refrigerant from superheated gas to saturated liquid is shortened.During the change of the heat sink flow,a local heat transfer disadvantageous area will appear on the water side of the heat exchanger,and as the heat sink flow becomes smaller,this area tends to move toward the heat sink outlet of the heat exchanger.As the concentration of R744 in R744/R290 increases,the heat transfer coefficient and heat transfer increase,and the pressure drop decreases,and the length of the heat exchanger integrated tube corresponding to the process of refrigerant from superheated gas to saturated liquid becomes longer.