Abstract The flow boiling heat transfer characteristics of R245fa, R134a and non-azeotropic mixture R134a/R245fa (0.33/0.67 by mass) at high saturation temperatures were investigated in a horizontal tube with 10 mm I.D. Effects of high saturation temperatures on heat transfer coefficients of R134a, R245fa and the mixture were investigated from 55 °C to 95 °C. Heat flux was controlled from 6 to 24 kW/m2 and mass flux ranged from 100 to 300 kg/m2.s. The results show the heat transfer coefficient of the mixture (R134a/R245fa with 33%/67% by mass) is much lower than that of pure R134a and is close to that of pure R245fa. At high saturation temperatures, mass flow rate has less influence on heat transfer coefficient of R245fa and the mixture at a large heat flux. The heat transfer coefficients of three working fluids increase slightly when the saturated temperatures change within 10 °C. The pressure drops of pure R245fa and the binary mixture were studied and the pressure drop of the mixture (R134a/R245fa with 33%/67% by mass) is a little higher than that of R245fa. A modified heat transfer correlation considering the mixing effect of binary mixture is proposed for the mixture of R245fa/R134a, and the mean absolute deviation is within 20%. A modified two phase frictional factor for the mixture is proposed and the deviation of the mixture using modified two phase frictional factor is between −6% and +22%.

中文翻译：

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R134a、R245fa和R134a/R245fa混合物在高饱和温度下流动沸腾传热特性的实验研究

摘要 在内径为 10 mm 的水平管中研究了 R245fa、R134a 和非共沸混合物 R134a/R245fa（质量分数为 0.33/0.67）在高饱和温度下的流动沸腾传热特性。 R134a、R245fa 和混合物在 55 °C 至 95 °C 下进行研究。热通量控制在 6 到 24 kW/m2 之间，质量通量控制在 100 到 300 kg/m2.s 之间。结果表明，混合物的传热系数（R134a/R245fa 为 33%/67%）远低于纯 R134a，接近纯 R245fa。在高饱和温度下，质量流量对 R245fa 和大热通量混合物的传热系数影响较小。当饱和温度在 10 °C 内变化时，三种工质的传热系数略有增加。研究了纯 R245fa 和二元混合物的压降，混合物的压降（R134a/R245fa 的质量百分比为 33%/67%）略高于 R245fa。针对R245fa/R134a混合料提出了考虑二元混合料混合效应的修正传热关系式，平均绝对偏差在20%以内。提出了混合物的改进的两相摩擦系数，使用改进的两相摩擦系数的混合物的偏差在-6%和+22%之间。研究了纯 R245fa 和二元混合物的压降，混合物的压降（R134a/R245fa 的质量百分比为 33%/67%）略高于 R245fa。针对R245fa/R134a混合料提出了考虑二元混合料混合效应的修正传热关系式，平均绝对偏差在20%以内。提出了混合物的改进的两相摩擦系数，使用改进的两相摩擦系数的混合物的偏差在-6%和+22%之间。研究了纯 R245fa 和二元混合物的压降，混合物的压降（R134a/R245fa 的质量百分比为 33%/67%）略高于 R245fa。针对R245fa/R134a混合料提出了考虑二元混合料混合效应的修正传热关系式，平均绝对偏差在20%以内。提出了混合物的改进的两相摩擦系数，使用改进的两相摩擦系数的混合物的偏差在-6%和+22%之间。