Abstract:

For the flooded evaporator in refrigeration or air conditioning systems, refrigerant is boiling on the shell side and water is flowing in the tube side. The pool boiling heat transfer coefficient of R134a outside one smooth tube and one reentrant cavity enhanced tube No.1 is investigated with an experimental approach. At the saturate temperature of 6, 10 and 16℃, the heat flux of 10-250 kW·m^-2, the heat transfer coefficient versus heat flux of smooth tube is investigated and compared with Cooper correlation. The external diameter of smooth tube and enhanced tube are 15.93 mm and 25.36 mm, respectively. At the heat flux of 10-250 kW·m^-2, it is found that the deviation of experimental result and Cooper correlation is within ±15%. the average value of m in h∝q^m, is 0.67. For the enhanced tube, the enhanced ratio is the largest at the heat flux less than 40 kW·m^-2. The enhanced ratio is decreasing as the increment of heat flux. At the heat flux larger than 250 kW·m^-2, the heat transfer coefficient of enhanced tube is approaching the smooth tube, and even smaller than smooth tube.

Key words: pool boiling, heat flux, saturate temperature, heat transfer coefficient, enhanced tube

摘要：

在制冷空调的满液式蒸发器中，制冷剂在壳侧沸腾蒸发，管内为水的单相对流传热。实验研究了高热通量下R134a在一根光管和一根强化管（No.1）外的池沸腾传热，并将光管实验结果和Cooper公式进行了比较。在不同的饱和温度下，热通量10～250 kW·m^-2的范围内，研究了R134a在光管和强化管外的沸腾传热系数随热通量的变化关系。光管和强化管外径分别为15.93 mm 和 25.36 mm。通过研究发现，在热通量10～250 kW·m^-2的范围内，光管的池沸腾传热系数和Cooper公式符合较好，偏差小于±15%。在双对数坐标下传热系数和热通量实验结果拟合直线斜率为0.67。在较高热通量，即热通量大于250 kW·m^-2时，光管的传热系数相对Cooper公式偏差开始增大。对于高效管，在小于40 kW·m^-2热通量下的传热效果最好。强化管的强化倍率随热通量增加一直减小，在较高热通量250 kW·m^-2下，强化管的传热系数和光管相同，甚至比光管小。

关键词: 池沸腾, 热通量, 饱和温度, 传热系数, 强化管