Abstract

In this experimental study, heat transfer and pressure drop characteristics of R134a evaporating flow are investigated inside a horizontal internally grooved tube with discrete inclined grooves. The test evaporators are made of smooth and grooved copper tubes of 20 mm inner diameter. The length, width, and depth of grooves are 6, 2, and 0.5 mm, respectively, and the angle of the grooves with the tube centerline is 30°. The test conditions include mass flux in the range of 16.5 to 105 kg/m²s, vapor quality of 0.06 to 0.98, and heat flux of 3.5 to 25 kW/m². The experiment results show that the boiling heat transfer coefficient of R134a in the grooved tube is 1.25 to 1.65 times higher than that of the smooth one. The frictional pressure drop of R134a inside the grooved tube is 10% to 60% higher than the smooth tube. Moreover, by increasing mass flux, the heat transfer coefficient, and frictional pressure drop of R134a refrigerant inside horizontal smooth and grooved tubes increase as well. In conclusion, the energy performance of R134a evaporating flow inside the grooved tube is more efficient than that in the smooth tube regarding energy saving in most experiments.

摘要

在这项实验研究中，R134a 蒸发流的传热和压降特性在具有离散斜槽的水平内槽管内进行了研究。测试蒸发器由内径为 20 毫米的光滑带槽铜管制成。凹槽的长、宽、深分别为6、2、0.5mm，凹槽与管子中心线的夹角为30°。测试条件包括质量通量范围为 16.5 至 105 kg/m ² s，蒸汽质量为 0.06 至 0.98，热通量为 3.5 至 25 kW/m ². 实验结果表明，R134a在槽管中的沸腾传热系数比光滑管高1.25～1.65倍。R134a在槽管内的摩擦压降比光管高10%～60%。此外，随着质量流量的增加，R134a 制冷剂在水平光滑和沟槽管内的传热系数和摩擦压降也增加。综上所述，在大多数实验中，R134a 蒸发流在槽管内的能量性能在节能方面比在光滑管中更有效。