润滑油对超临界二氧化碳对流换热特性的影响

Effect of lubricating oil on convective heat transfer characteristics of supercritical carbon dioxide

为了得到加热条件下润滑油对超临界二氧化碳换热特性的影响,利用Fluent软件建立CO_2/润滑油两相混合物流动传热模型,通过改变润滑油浓度、质量通量、热通量和压力进行换热特性分析。结果表明,润滑油的存在显著削弱超临界二氧化碳的对流换热过程,随着润滑油浓度的增加,对流换热进一步恶化。当油浓度小于1%时,不影响对流传热系数的变化趋势,当油浓度超过3%,温度高于二氧化碳拟临界温度时,传热恶化程度降低。热通量的增加使得对流换热进一步恶化,提高质量通量能有效改善对流换热恶化现象。二氧化碳在润滑油中的溶解度直接影响对流换热过程,提高运行压力可增加二氧化碳在润滑油中的溶解度以降低高润滑油浓度下的传热恶化程度。

To obtain the effect of lubricating oil on the heat transfer characteristics of supercritical carbon dioxide under heating conditions, the flow and heat-transfer model of CO2/lubricating oil two-phase mixture was established by using Fluent software. The model was used to analyze the heat transfer characteristics in detail at different oil concentrations, mass fluxes, heat fluxes and operation pressures. The results show that the presence of lubricating oil significantly weakened the convective heat transfer process of supercritical carbon dioxide. With the increase of lubricating oil concentration, the convective heat transfer was further deteriorated. The concentration of lubricating oil had a marked impact on the heating characteristics of supercritical carbon dioxide. When the oil concentration was less than 1%, the change trend of heat transfer coefficient was not affected. When the oil concentration exceeded 3% and the temperature was higher than the pseudo critical temperature of carbon dioxide, the degree of heat transfer deterioration decreased. The increase of heat flux made the convective heat transfer worse, but increasing the mass flux can effectively improve the phenomenon of heat transfer deterioration. The solubility of carbon dioxide in lubricating oil directly affected the convective heat transfer process. The increase of operating pressure can enhance the solubility of carbon dioxide in lubricating oil which contributed to reducing the degree of heat transfer deterioration under high lubricating oil concentration.