R32在水平管内流动沸腾换热特性的试验研究

Experimental study on boiling heat transfer characteristics of R32 in horizontal tubes

对R32在水平光滑管和微肋管(外径均为7mm)内的沸腾换热特性展开试验研究,测试的制冷剂质量流速为100~250 kg/(m^2·s),饱和蒸发温度为7~11℃,热流密度为3~8 kW/m^2,测试管内制冷工质平均干度值为0~0.7。试验结果表明:热流密度是影响R32沸腾换热系数的主导因素之一,质量流速的增大、饱和蒸发温度的升高、热流密度的增大均有利于提高R32的沸腾换热系数;微肋管有强化传热的效果,其平均沸腾换热系数比光管增大11.8%~33.2%;干度对R32沸腾换热系数的影响比较复杂,R32的沸腾换热系数随干度的增加先增大后减小,这是由于出现了干涸值,本文试验测得的干涸值范围为0.41~0.57,制冷剂质量流速的降低和热流密度的增大均有利于干涸值的增大。

The experimental study is carried out on the boiling heat transfer characteristics of R32 in horizontal smooth tube and micro-fin tube with the diameter of 7 mm.The mass flux range of refrigerant is 100-250 kg/（m^2·s）.The saturated evaporating temperature range is 7-11℃.The heat flux range is 3-8 kW/m^2.The average dryness fraction range of the refrigerant is 0-0.7.The experimental results show that the boiling heat transfer coefficient of R32 increases with the increase of mass flux,saturated evaporating temperature and heat flux,among which heat flux is playing a dominant role.The average boiling heat transfer coefficient of R32 in the micro-fin tube increases by 11.8%-33.2%than that in the smooth tube.The dryness fraction has complicated influence on the boiling heat transfer coefficients of R32.Due to the emerging dry-out point which ranges from0.41 to 0.57 obtained by the test,the boiling heat transfer coefficients of R32 increase with the increase of dryness fraction at first,and then turn to decreasing with dryness fraction.The decrease of mass flux and the increase of heat flux effectively help to delay the arrival of the dry-out point.