空气源热泵蒸发器表面霜层生长特性实验研究

在室外环境空气温度-15℃~5℃、相对湿度65%~90%范围内,对一台空气源热泵室外换热器表面霜层生长特性及热泵系统动态性能进行了实验研究。实验结果表明,翅片表面霜层厚度呈分段增长模式,在结霜初始段,霜层主要由粒状冰晶组成,并逐渐形成柱状冰晶,其厚度增长较快;在第二阶段为柱状冰晶主要在其半径方向生长,霜层厚度增长速度减慢;而在第三阶段,柱状冰晶主要在其高度方向生长,逐渐形成针状冰晶,霜层厚度增长速度迅速增大至第二阶段的3~5.8倍。对实验结果的分析表明,热泵机组性能恶化主要是由于蒸发器表面温度下降、霜晶形态变化引起霜层厚度快速增长及空气流动阻力增加导致风机流量下降三个因素之间形成的恶性循环所致,其中换热器表面温度下降引起的霜晶形态变化起到了至关重要的作用。

Experimental Study of Frost Growth Characteristics on Outdoor Heat Exchanger of Air Source Heat Pump Unit

The frost growth characteristics on the outdoor heat exchanger and the dynamic performance of an air source heat pump(ASHP)were experimentally investigated.The experimental outdoor air temperature ranged from-15 to 5℃,and relative humidity was from 65% to 90%.The results indicate that the frost grew in three stages.In the initial stage,the granular ices grew on the surface,and then the column-shaped ice crystals were formed gradually and the frost thickness rose quickly.After the first stage,the column-shaped ice crystals grew in its radius rather than in its length,and thus the growth rate of frost thickness decreased with the frosting time.In the third stage,the column-shaped ice crystals grew mainly in its length and the ice crystals had the acerose shape gradually,and the growth rate of frost thickness increased rapidly to 3-5.8 times that in the second stage.It is found that the performance degradation of the ASHP unit was caused by the wall temperature drop of the evaporator,the rapid increase in the frost thickness,and the decrease in the air flow rate.