CO_2/润滑油混合物在水平管内流动沸腾换热的试验研究

为了测试润滑油对CO2流动沸腾换热特性的影响,以指导CO2换热器的设计,对CO2/润滑油混合物在水平管内的流动沸腾换热系数进行了试验研究,试验工况质量流量为2.74~5.61kg/h,热流密度为3.2~5k W/m2,测试段入口干度为x=0.2~0.5,蒸发温度在-4~8℃之间,选择PAG作为润滑油,浓度为0~6%。试验结果表明,润滑油浓度越大,CO2的局部换热系数越小;润滑油浓度较低时(<3%),换热系数下降较大,再增大含油量,换热系数下降的趋势减缓。增大蒸发温度可以延迟干涸的发生,相反地,大的热流密度和质量流量可以使管内提前出现干涸。CO2/润滑油混合物的换热系数随蒸发温度的升高而增大,随热流密度和质量流量的增大而减小。

Experimental Study on Heat Transfer Characteristics of CO2/oil Mixtures Flow Boiling Inside Horizontal Tubes

To test the boiling heat transfer characteristics of CO2/ lubricant mixtures,guiding the design of the CO2 heat exchanger,the heat transfer coefficients of CO2/ lubricant mixtures were investigated in a horizontal tube. The experiments were conducted by varying the mass flux of CO2 from 2. 74 to 5. 61 kg / h,heat flux from 3. 2 to 5k W / m2 and saturation temperatures from-4 to 8℃. PAG was selected as the lubricant,whose concentration was altered from 0 to 6%. The results show that larger oil concentration degrades the heat transfer coefficient. The heat transfer coefficient decreased largely at low oil concentration( <3%),then with the increasing of the oil,h decreased slowly. Higher evaporation temperature results in increasing the critical mass quality,while higher heat flux and mass flux make the dry-out occur in advance. Heat transfer coefficient increases versus the rise of the evaporation temperature. Conversely,larger heat flux and mass flux will weaken the heat transfer.