Abstract:

As a low GWP refrigerant, R32 is widely used in room air-conditioners in which the working fluid is the mixture of refrigerant and lubricating oil. In order to optimize R32 air conditioner, it is necessary to know the flow boiling heat transfer characteristic of R32-oil mixture. The purpose of this paper is to test the flow boiling heat transfer characteristics of R32-oil mixture inside tubes and develop a new correlation of heat transfer coefficient according to the actual working conditions of air conditioners. A new experiment rig with explosion-proof function was set up to test the heat transfer performance of R32-oil mixture inside tubes. Copper tube with 7 mm outer diameter was chosen as the test section, and the test conditions include the mass flux ranged from 200 to 400 kg/(m²·s), the vapor quality ranged from 0.2 to 0.7 and the oil concentration ranged from 0 to 5%. The test results indicated that, the heat transfer coefficient of R32-oil mixture increases with the increase of mass flux; moreover, the presence of oil enhances the heat transfer at the range of low and intermediate vapor qualities; there is a peak of local heat transfer coefficient at about 3% oil concentration at higher vapor qualities. A new heat transfer coefficient correlation of R32-oil mixture inside 7 mm smooth tube was developed based on the mixture properties and the flow pattern, and it agrees with 85% of experimental data within deviation of ±20%.

Key words: R32, lubricating oil, flow, evaporation, heat transfer, correlation

摘要：

R32作为低温室效应制冷剂得到广泛应用，空调器中循环的介质是制冷剂与润滑油的混合物，掌握R32-润滑油混合物的流动沸腾特性是R32空调器优化设计的关键。本文的目的是参照空调器实际运行工况，测试R32-润滑油混合物的管内流动沸腾换热特性，开发传热系数关联式。新搭建了具有防爆功能的R32-润滑油混合物管内换热性能测试台，采用换热管为7 mm铜管，测试的质流密度200~400 kg/(m²·s)、干度0.2~0.7、油浓度0~5%。实验结果表明，R32-润滑油混合物管内流动沸腾传热系数随质流密度的增大而增大；在中低干度下传热系数随油浓度的增大而增大，在高干度下随油浓度增大先增大后减小并于3%油浓度处取得最大值。基于混合物物性与流型开发了传热系数关联式，预测值与85%的实验数据的误差在±20%内。

关键词: R32, 润滑油, 流动, 蒸发, 传热, 关联式