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

对非共沸混合工质HFC32+HFC134a在水平管内的流动沸腾换热进行了实验研究。这种混合物有望成为HCFC22的替代制冷剂之一。取得了以下研究结果：1.对于水平光滑管内HFC32+HFC134a混合物的流动沸腾，强迫对流占优势区域的换热系数与HCFC22的对流换热系数基本相同，对于纯制冷剂可以用关联式进行预测，具有较好的精度。然而，在核态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。内螺旋槽管对混合工质的强化换热是有效的，特别是在低质量流速下，但由于槽管内混合物本身的换热系数低于HCFC22.3，所以对混合物的强化作用比HCFC22小得多。在光滑管和槽管中，混合气的摩擦压降均比HCFC22大几个百分点到20%左右。对于混合工质，由于槽管的强化换热作用，槽管内的压降比相同长度的光管大20%~60%甚至更多，而在相同的换热速率下，槽管的压降并不比光管大。

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.