| Electric vehicles have been rapid developed in recent years for the characteristics of low noise,zero emission and energy saving,while most of the air conditioning systems still use traditional way of single cold combined with PTC heating.Large power consumption,low energy efficiency of PTC heating will greatly shorten the mileage of electric vehicles.Heat pump air conditioning system of electric vehicles have the advantages of higher energy efficiency,more comfortable,it is the direction of future development.In the winter,the outdoor heat exchanger of heat pump air conditioning system is easy to frost.When the frost layer reaches a certain thickness,it will seriously reduce the efficiency of heat transformation of outdoor heat exchanger,thus affecting the heating effect of the whole system.Therefore,further study of defrosting mode of the heat pump air conditioning system in electric vehicles is needed.In this study,the following works have been done:(1)In order to solve the problem of easy frost of the outdoor heat exchanger of the heat pump air conditioning system in winter,the method of directly drawing back a part of the high-temperature and high-pressure refrigerant discharged from the compressor to suction port is adopted.(2)A numerical model of hot gas bypass for defrosting in heat pump air conditioning system for electric vehicle system is established.It mainly includes the mathematical model of the physical properties for R134a;the correlations of motor coefficient and gas transmission coefficient for compressor,which are based on numerical experimental data;the model of heat exchanger,throttling device and hot gas bypass valve.And the dispersed models are linked by sequential module method.Also,the numerical model is validated and optimized based on experimental data,which comes from the newly built experimental platform.(3)Through the comprehensive analysis of the indoor heat transformation,the indoor air outlet temperature,the evaporation pressure and the suction temperature of the compressor,it is concluded that the system has the best operating status when the opening degree of the hot gas bypass valve is 6.Based on this,energy analysis of frost and defrost process is carried out,and find out that the best defrosting period is 25 minutes and the defrosting time is 5 minutes. |
PDF Full Text Request