Abstract:

A test rig with a horizontal smooth tube was built to measure flow boiling heat transfer of nanolubricant/refrigerant. The experimental study on heat transfer characteristics of graphite-nanorefrigerant flow boiling inside a horizontal smooth copper tube, with total length of 2.5 m, outside diameter of 9.52 mm, inside diameter of 8 mm and wall thickness of 0.76 mm was performed. Influence of graphite on flow boiling heat transfer characteristics of nanorefrigerant/oil mixture was investigated. There were three kinds of fluid under experiment:R600a, R600a/oil and graphite nanorefrigerant/oil with different graphite mass fractions (0.05%, 0.1% and 0.2%). Flow boiling heat transfer coefficients of these fluid versus vapor quality were measured respectively in a horizontal smooth tube under the mass flow density of 150, 200, 250, 300 kg·m^-2·s^-1. The results indicated that the presence of graphite enhanced the flow boiling heat transfer. A correlation for predicting the flow boiling heat transfer coefficient of nanorefrigerant/oil mixture with graphite was proposed and it agreed with 94.5% of the experimental data within a deviation of ±15%.

Key words: nanoparticles, heat transfer, measurement, heat transfer coefficient, prediction, correlation

摘要：

搭建了纳米冷冻机油/制冷剂水平光管内流动沸腾换热测试实验台,研究了石墨/R600a纳米制冷剂在水平直光管内流动沸腾换热特性,分析了纳米石墨对含油制冷剂流动沸腾换热的影响。实验测试段为总长2.5 m、外径9.52 mm、内径8 mm、壁厚0.76 mm的紫铜管。在质量流速为150、200、250、300 kg·m^-2·s^-1下,分别测量纯R600a、含油R600a、不同质量分数(0.05%、0.1%、0.2%)纳米石墨冷冻机油和R600a混合物在水平光滑圆管内流动沸腾传热系数随干度的变化趋势。实验结果表明:纳米石墨的添加增强了含油制冷剂的流动沸腾换热。实验获得了基于石墨的含油纳米制冷剂流动沸腾换热关联式,关联式的预测值与94.5%的实验数据偏差在±15%以内。

关键词: 纳米粒子, 传热, 测量, 传热系数, 预测, 关联式