R32制冷剂在小管径水平管内的沸腾换热与阻力特性实验研究

Experimental Study on the Flow Boiling Heat Transfer and Pressure Drop of Refrigerant R32 in Horizontally Oriented Small-Diameter Tubes

针对污染小、能效高、可燃性差、低毒性的新型R32可替代制冷剂在水平管内低温工况下的沸腾换热特性开展研究,设计并自主搭建了管内对流沸腾相变换热实验系统,分别开展了3 mm、4 mm小管径水平管内低温R32沸腾换热的实验研究,探究了质量流速、热流密度、饱和温度等参数对R32对流沸腾换热特性的影响,分析了蒸干对沸腾换热系数恶化的影响机制。结果表明:3 mm内径管的沸腾换热相比4 mm通道平均提升约8%~12%,且高质量流速下的临界干度几乎与管径无关;相较传热特性,R32饱和温度对两相流动阻力更为敏感,饱和温度自13℃降低至11℃时阻力损失提高约23%;利用改进的Fang关联式,可实现小管径水平管内R32对流沸腾换热系数预测,88.56%的实验数据误差可控制在±10%范围内。

In this paper,the boiling heat transfer characteristics of the new R32 alternative refrigerant with low pollution,high energy efficiency,poor flammability and low toxicity are investigated under low-temperature conditions in horizontally orientated tubes.The flow boiling system is established and applied to study the R32 flow boiling heat transfer and pressure drop in small-diameter tubes with 3 mm and 4 mm diameters in horizontal orientation.The impact of mass flow rate,heat flux,saturated temperature and vapor quality on the R32 two-phase thermohydraulic performance is experimentally considered.The heat transfer jeopardization by the dry-out mechanism is also observed.The result shows that the heat transfer coefficient of the 3mm tube can be improved by 8%~12%compared to that of the 4mm tube while the critical heat flux is independent of tube diameter at a high flow rate.Meanwhile,compared with heat transfer characteristics,R32 saturation temperature is more sensitive to the two-phase flow resistance,the resistance loss increases by about 23%when the saturation temperature is reduced from 13℃to 11℃.Finally,the corrected Fang’s correlation is applied to precisely predict the two-phase heat transfer coefficient of R32 in which over 88.56%of data can be controlled within the error of±10%.