车用热泵系统结霜化霜实验研究

Experiment on Frost and Defrost of Vehicle Heat Pump System

针对车用热泵系统在冬季室外换热器易结霜的问题,本文设计并搭建了实验系统对室外换热器结霜和化霜特性进行了研究,总结出了在实车上判断结霜以及化霜完成的方法,最后比较了∅2.1 mm和∅3.0 mm两种阀口直径的电子膨胀阀对化霜时间的影响。实验结果表明:换热器结霜程度可通过吸气温度或吸气压力相对于无霜状态下的变化率来判断,化霜完成可通过室外换热器出口温度大于0℃来判断。在不同环境温度及不同霜层的化霜工况中,电子膨胀阀阀口直径对化霜时间的影响并非一致,较大阀口直径电子膨胀阀前期化霜效果好,但后期因为阀口直径较大压缩机排气压力升速缓慢,导致室外换热器入口温度增速变缓反而不如较小阀口直径电子膨胀阀。因此在实际整车应用中,可选用较大阀口直径的电子膨胀阀结合智能控制,使总体化霜效果达到最优。

Focusing on the problem where in the outdoor heat exchanger of a vehicle heat pump system is prone to frost in winter,this study designs and builds a corresponding experimental system for testing.The frost and defrost characteristics of the outdoor heat exchanger were studied.Then,the effects on defrosting time of two different electronic expansion valve(EXV)calibers,∅2.1 mm and∅3.0 mm,were compared.The experimental results show that the degree of frosting on the heat exchanger can be judged by the change rate of the suction temperature or pressure relative to the non-frosted state,and the completion of defrosting can be judged by the temperature by which the outdoor heat exchanger outlet exceeds 0℃.For defrosting conditions with different ambient temperatures and different frost layers,the impact of EXV caliber on defrosting time is not consistent.The EXV with a large caliber has a good defrosting effect in the early stage,but in the later stage,it is not as good as the EXV with a small caliber because the compressor exhaust pressure of the large-caliber EXV rises slowly,causing the inlet temperature of the outdoor heat exchanger to increase slowly.Therefore,in real vehicle applications,a larger caliber EXV can be used in combination with intelligent control to achieve the best overall defrosting effect.