节流机构对风冷热泵逆循环除霜性能的影响

为研究不同节流机构对逆循环除霜时间的影响，分别用一根外径为22mm的旁通铜管和热力膨胀阀作为除霜时的节流机构，在一台名义制冷量为55kW的风冷热泵冷热水机组上进行了实验研究，结果表明：旁通铜管系统与热力膨胀阀系统对比，总的除霜时间减少了40s，其中融霜时间减少了34s，排水时间减少了10s；在恢复阶段，由于制冷剂的流量较大和板式换热器的内容积比较小，两种节流机构的排气压力都剧烈上升，旁通铜管系统上和热力膨胀阀系统分别上升了488.7kPa和389.9kPa；排水阶段结束时，旁通铜管系统的排气压力比热力膨胀阀系统高453.8kPa，并且在恢复阶段排气压力上升的幅度更大，导致旁通铜管系统的排气压力接近高压保护值。

Effect of expansion devices on the dynamic charactristics of an air-source heat pump during the reverse-cvcle defrost period

The influence of the expansion device on the reverse cycle defrost performance in an air-to-water heat pump was investigated experimentally. Experiments were conducted on a 55 kW unitary air-to-water heat pump. A copper tube with an outer diameter of 22 mm and the thermal expansion valve (TEV) were used as the expansion devices for the defrost cycle respectively. It is shown that the defrost time for the copper tube test is 40 seconds shorter than that for TEV test. The melting time and the draining time for the copper tube test are 34 seconds and 10 seconds shorter respectively,but defrost initiation time is 4 s longer. Due to the small inner volume of the plate heat exchanger and the larger refrigerant flow rate during the defrost termination and recovery time, the discharge pressure had the sudden increase of 488.7 kPa for copper tube test and 389.9 kPa for TEV test. In addition, the discharge pressure for the copper tube test was 453.8 kPa higher at the end of draining time than that for TXV test. So the peak of discharge pressure for the copper tube test was 2 495.6 kPa at the defrost termination and recovery time, which was close to the discharge protection value (2 550 kPa).