Research On Flow And Heat Transfer Characteristics Of Microchannel Heat Collector/evaporator

With the increasing consumption of fossil energy and environmental problems,energy saving and emission reduction has become an important issue of sustainable development.The combination of direct expansion solar assisted heat pump technology and microchannel heat exchanger technology integrates the advantages of the two technologies.It greatly enhance the energy saving effect.Combined currently available microchannel evaporator structure data with experimental data are used as the known parameters to carry out one-dimensional and three-dimensional simulation.The flow and heat transfer characteristics of the microchannel evaporator in the heat pump system are studied.The parameters simulation is changed to compare and analyze the structure to optimal the design.The establishment of the experimental platform of direct expansion solar assisted heat pump system is introduced.Including:system structure and circulation process,system components and whole machine establishment,system experiment data collection and control.The test platform realizes the control of the switch of the compressor and the opening of the electronic expansion valve to make it start and keep the stable operation,and monitor,collect and save the measurement parameters in real time.The thermal physical property calculation model of R290 was established by using state equation and polynomial fitting method.A mathematical model of direct expansion solar micro channel evaporator was established by distribution parameter method.The one-dimensional simulation program of the evaporator was compiled with Matlab,and the flow and heat transfer characteristics of the refrigerant in the microchannel evaporator were investigated.Under the stable condition,the calculated heat transfer of the microchannel evaporator is 2288.5W and the pressure drop is 98.23kPa.By comparing with the experimental data,it is found that the error between the calculated value and the experimental value is less than 10%.The influence of environmental parameters(solar radiation,outdoor wind speed,ambient temperature),different flow rate and flat tube number on the performance of evaporator were studied.The distribution characteristics of refrigerant in the microchannel evaporator were simulated,and the effects of different dry degree and inlet position on the refrigerant flow distribution were studied by the visual advantage of commercial software CFD.The results show that the different dryness has little effect on the refrigerant distribution,and when the inlet of the evaporator is perpendicular to the center of the collector tube,the refrigerant distribution is best,and the inhomogeneity of S is 0.002 lower than the original structure.