Heat Transfer Analysis of Zeotropic Refrigerants with Falling Film Evaporation on Plain Tubes

This study investigated mixtures of the refrigerants R-152a and R-245fa with various blending ratios and saturation temperatures in falling film evaporation heat transfer. It explored the respective heat transfer properties of R-152a/R-245fa at blending ratios of 0.75/0.25 and 0.25/0.75. For the falling film evaporation, a plain tube was placed horizontally in a chamber with saturated temperatures of 10°C and 20°C. The test results showed that the heat transfer performance variation is not linearly proportional to the blending ratio of the refrigerant. The heat transfer distribution band of the R-152/R-245fa ratio = 0.25/0.75 mixed refrigerants was wider than that of the 0.75/0.25 mixed refrigerant. A possible reason for this was that the blending ratios caused differences in temperature glide. The heat transfer performance of the mixture was higher than pure R-245fa. The top tube was effectively increased by 0.39-0.55 and the center tube was effectively increased by 0.57-0.78. The boiling heat transfer performance of both mixtures are less than the ideal heat transfer coefficient calculated from the boiling curve of the pure R-152a and R-245fa. Instead of performance degradation, the falling film evaporative heat transfer of the R-152a/R-245fa mixture is greater than the ideal value at 0.25 mass concentration of R-152a.