空气源跨临界CO2热泵系统热气除霜的实验研究
An Experimental Investigation on Hot Gas Defrost of Air？？Source Transcritical CO2 Heat Pump Systems

为了解决跨临界CO2热泵系统在低温环境下运行蒸发器的结霜问题,对一种可应用于CO2跨临界循环的热气除霜方法进行了实验研究。在对热气除霜过程中系统循环特性分析的基础上,搭建了空气源跨临界CO2热泵热水器实验台,根据系统各参数点压力和温度变化曲线的实验结果,分析了除霜过程中系统循环的变化规律和蒸发器的除霜特性,发现除霜时热泵系统的流量增大,气体冷却器内的温降减小,故增大气体冷却器出口的CO2气体温度是提高除霜效率的关键。同时,结合实时采集的蒸发器表面霜层变化图像,分析了蒸发器的动态除霜过程,直观观测了热气除霜的除霜效果,整个除霜过程保持了600 s,热气除霜的除霜效率为35.6％。根据实验结果可以得出,热气除霜方法是用于空气源跨临界CO2热泵系统除霜切实可行的方法。
A hot gas defrosting method is investigated to solve the frost accumulation on the finned tube evaporator for transcritical CO2 heat pump systems. It is based on the analysis of defrost cycle process, and an air？？source transcritical CO2 heat pump water heater test rig is built in an environmental laboratory. Based on the experimental results of the pressure and temperature variations that the defrost cycle process and defrosting characteristic in the evaporator are discussed, and it is found that the mass flow rate increases and the temperature difference between gas cooler inlet and outlet decreases during the defrosting process. It is also found that the key to improve the defrost efficiency is to increase the gas cooler outlet temperature of CO2 gas. Meanwhile, instant defrosting pictures of evaporator surface are captured to record the dynamic defrosting process and to evaluate the defrost effect of hot gas defrosting. The whole defrosting process maintains 600 s and the defrosting efficiency of the hot gas defrosting method is 35？？6％. It can be concluded from the experimental results that the hot gas defrosting method is a reasonable and practicable method for CO2 heat pump systems