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CSME 2020/06
Volume 41 No.3
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297-309
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Heat Transfer Analysis of Zeotropic Refrigerants with Falling Film Evaporation on Plain Tubes
Ching-Hung Changa and Liang-Han Chiena
aDepartment of Energy and Refrigerating Air-Conditioning Engineering, National Taipei University of Technology, Taipei, 10608, ROC.
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Abstract:
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.
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Keywords: zeotropic, falling film evaporation, heat transfer coefficient, refrigerant
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©
2020
CSME , ISSN 0257-9731
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