负压下水在水平铜管表面沸腾换热的实验研究

以天然制冷剂水(R718)为工质的蒸气压缩式制冷及热泵系统,工作压力通常低于常压。为研究负压条件下水的沸腾换热特性,搭建了水在水平铜管表面换热的实验装置,在1.8~3.3 k Pa的压力范围内对水在水平铜管表面的沸腾换热进行实验研究。结果表明,换热系数随压力的升高和热流密度的增加而增大。将实验数据与相同条件下Cooper公式的计算结果进行对比,并利用最小二乘法回归出适用于本实验条件的换热系数的经验公式,以方便工程实际应用。本实验对水蒸气压缩式制冷及热泵系统中蒸发器的换热及强化研究具有一定的指导作用。

Experimental Study on Water Boiling Heat Transfer on a Horizontal Copper Tube Surface at Sub-atmospheric Pressure

Vapor compression refrigeration and heat pump systems, which use the natural refrigerant R718 as refrigerant, usually work at sub-atmospheric pressure. In order to study the water boiling heat transfer characteristics at sub-atmospheric pressure, one test system was built, and the heat transfer performance was studied under the pressures of 1.8~3.3 kPa. The results show that the coefficient of heat transfer increases with the increase of pressure and heat flux. Experimental data were compared with the calculated results by cooper correlation at the same conditions. Regression equations of the coefficient of heat transfer, which apply to the conditions of this experiment, were fitted using the least square method for the sake of practical application. This experiment can offer a useful reference for the study of evaporator heat transfer and heat transfer enhancement in water vapor compression refrigeration and heat pump systems.