Simulation Optimization And Experimental Research Of Transcritical CO₂ Heat Pump And Air-conditioning System For Pure Electric Vehicle

The pure electric vehicles have characteristics of no pollution,low noise,light and comfortable,which has been warmly received by consumers.However,compared with the fuel vehicles,there is no engine waste heat available for pure electric vehicles in winter,and the way of using thermistor heater will consume too much electricity,which will greatly reduce the range of driving.Therefore,it is urgent to improve the range of pure electric vehicles and alleviate the damage of CFCS to the environment and the ozone layer.Based on the above problems,a transcritical CO₂ heat pump system is designed for pure electric vehicles,and the simulation optimization and experimental study of the transcritical CO₂ system are performed in this article.The main research contents and conclusions of this article are as follows:（1）A transcritical CO₂ single stage compression cycle simulation model was established.The physical property module,compressor model,gas cooler model,evaporator model,expansion valve model and the transcritical CO₂ single stage compression cycle simulation model were established.The effects of operating conditions on the transcritical CO₂ single stage compression cycle were studied,and the results showed that the heating capacity of the transcritical CO₂ single stage compression cycle was too low at low temperature.（2）A simulation model of transcritical CO₂ quasi two-stage compression cycle was established.The effects of operating conditions on the performance of the transcritical CO₂ quasi two-stage compression cycle were studied,and the results of the transcritical CO₂ quasi two-tage compression cycle were compared with that of the transcritical CO₂single stage compression cycle.The results showed that the heating capacity of the transcritical CO₂ quasi two stage compression cycle increased by 58.6～71.1%,and the discharge temperature decreased by 9.4～10.0℃,when compared with that of the transcritical CO₂ single stage compression cycle.（3）According to the load demand of pure electric vehicle,an experimental platform of the transcritical CO₂ heat pump air conditioning system was designed,and the components of the system were designed and selected.（4）The effect of discharge pressure on the performance of the single stage compression cycle and the effect of the injection pressure on the performance of the quasi two-stage compression cycle was studied.According to the experimental data,the correlations of the optimal discharge pressure and the optimal injection pressure were developed.（5）The effects of operating conditions on the transcritical CO₂ single stage compression cycle and the transcritical CO₂ quasi two-stage compression cycle were studied.The results showed that the compressor work,heating capacity and cooling capacity increased with the increasing of compressor speed,but the increase rate of heating capacity and cooling capacity was less than that of the compressor work.When the evaporation temperature increased 5℃,the cooling capacity increased by535.9～948.4 W.The heating capacity of the system increased 47.2%on average,when the inlet temperature of glycol solution changed from-18℃to 0℃.Under the same conditions,The COP（Coefficient of Performance）of the transcritical CO₂ quasi two-stage compression cycle is 4.4%higher than that of the transcritical CO₂ single stage compression cycle.Therefore,the performance of the quasi two-stage compression cycle is better than that of the single-stage compression cycle under low temperature conditions.