Abstract:

To test the effect of lubricating oil on the boiling heat transfer characteristics of carbon dioxide flow, the heat transfer of CO₂/lubricating oil mixture in a compact channel with an outer diameter of 6 mm and an inner diameter of 4 mm was experimentally studied at mass flow rate of 2.74—5.61 kg·h^-1, saturation temperature of -4—8℃, heat flux of 3.2—5 kW·m^-2 and oil concentration of 0—6%. The results show that the higher the concentration of lubricating oil, the smaller the local heat transfer coefficient of CO₂ and the delay of dryout. The average heat transfer coefficient with 1.5% oil concentration was reduced by about 42.4% compared with that without oil. With the increase of mass flow rate, the initial dryness of drying increased, and the heat transfer coefficient increased with the increase of mass flow rate. The heat transfer coefficient increases with the increase of heat flux and saturation temperature. Dryout is delayed with decreasing heat flux and increasing saturation temperature. Dryout characteristics have significant influence on heat transfer coefficient, and dryout stage accounts for 35.4% of the whole heat transfer process.

Key words: carbon dioxide, lubricating oil, heat transfer, mixtures, compact channel, dryout characteristics

摘要：

为了测试润滑油对二氧化碳流动沸腾换热特性的影响，对外径6 mm、内径4 mm紧凑通道内的CO₂/润滑油混合物的换热进行实验研究。实验工况为质量流量2.74～5.61 kg·h^-1,饱和温度-4～8℃，热通量3.2～5 kW·m^-2，油浓度0～6%。结果表明：润滑油浓度越大，CO₂的局部传热系数越小；含1.5%油浓度相对于无油工况下平均传热系数下降了约42.4%; 传热系数随热通量、饱和温度的升高而增加，干涸后随着质量流量的增加传热系数增加；干涸随油浓度的增加、热通量的减小、饱和温度的升高、质量流量的增加而延迟；干涸特性对传热系数有显著影响，干涸阶段占整个换热过程的35.4%。

关键词: 二氧化碳, 润滑油, 传热, 混合物, 紧凑通道, 干涸特性