Flow Boiling Heat Transfer to a Non-Azeotropic Refrigerant Mixture of HFC32+HFC134a in Horizontal Tubes

在水平管内对HFC32+HFC134a非共沸制冷剂混合物进行了流动沸腾换热实验。该混合物有望成为HCFC22的替代制冷剂之一。实验结果如下：HFC32+HFC134a混合物在水平光滑管内流动沸腾时，强制对流占主导区的换热系数与HCFC22的换热系数基本相等，可以用纯制冷剂的相关性进行预测，且精度较高。然而，在有核沸腾对传热有很大贡献的区域，由于传质阻力，对混合物的传热显著降低，降至HCFC22的三分之二。内螺旋槽管对混合物的换热是有效的，特别是在低质量速度下，但对混合物的强化效果明显小于HCFC22，因为在槽管中混合物本身的换热系数低于HCFC22.3。在光滑管和槽管中，混合物的摩擦压降都比HCFC22大几~ 20%左右。对于混合物来说，沟槽管内的压降比相同长度的光滑管内的压降大20% ~ 60%或更多，而在相同传热率的情况下，沟槽管内的压降比光滑管内的压降小，这是由于沟槽管内的传热增强。

Experiments were carried out on the flow boiling heat transfer to a non-azeotropic refrigerant mixture of HFC32+HFC134a in horizontal tubes. This mixture is expected to be one of alternative refrigerants to HCFC22. Following results were obtained.1. For the flow boiling of the mixture of HFC32+HFC134a in a horizontal smooth tube, heat transfer coefficients in the forced convection dominated region are almost equal to those of HCFC22 and can be predicted by a correlation for a pure refrigerant with good precision. In the region where nucleate boiling contributes substantially to the heat transfer, however, the heat transfer to the mixture is significantly degrade, down to two-thirds the value of HCFC22, due to a mass transfer resistance.2. An internally spirally grooved tube is effective in enhancing the heat transfer to the mixture, especially at a low mass velocity, but the enhancement for the mixture is considerably smaller than for HCFC22, because in the grooved tube the heat transfer coefficient of the mixture itself is lower than that of HCFC22.3. The frictional pressure drop of the mixture is larger than that of HCFC22 by a few to about 20 percent in both the smooth and grooved tubes. For the mixture, the pressure drop in the grooved tube is larger by about 20 to 60 percent or more than in the smooth tube with the same length, while it is not so larger than in the smooth tube in the condition of the same heat transger rate, because of the heat transfer enhancement for the grooved tube.