超临界CO2-丙烷混合物管内传热特性数值研究

采用SST k-w湍流模型对超临界CO₂/丙烷混合工质水平管内的传热特性进行数值模拟研究。管径d=4 mm,加热段L₂=800 mm;混合工质浓度配比为100/0、95/5、90/10、85/15、80/20、75/25;质量流速为150～250 kg·m^?2·s^?1;热流密度为30～40 kW·m^?2,入口温度293 K,入口压力7.5～30 MPa。随着丙烷浓度的增加,CO₂/丙烷二元混合工质的临界压力降低,临界温度升高,丙烷浓度从5%增加到25%,换热系数峰值降低6.19%～31.45%,但增加丙烷浓度可提高拟临界温度后的换热效果。P=7.5～8.5 MPa,换热系数有明显峰值;P=20～30 MPa,换热系数变化规律无明显峰值,并随压力的升高而减小。混合工质的换热系数随质量流速的增大而增大。同一流体温度所对应的换热系数,随着热流密度的增加而减小。

Numerical Simulation of Heat Transfer Characteristics for Supercritical CO2-Propane Mixture in Tubes

The heat transfer characteristics of supercritical CO₂/propane mixture in horizontal tube were numerically simulated by SST k?w turbulence model.Tube diameterd=4 mm,Heating section L₂=800 mm;The mixing working medium concentration ratio is 100/0,95/5,90/10,85/15,80/20,75/25;Mass flux rate is 150～250 kg·m^?2·s^?1;Heat flux is 30～40 kW·m^?2,Inlet temperature is 293 K,Inlet pressure is 7.5～30 MPa.With the increase of propane concentration,when the propane concentration increased from 5%to 25%,the peak heat transfer coefficient decreased by 6.19%～31.45%.Increasing the propane concentration could improve the heat transfer effect after the pseudo-critical temperature.P=7.5～8.5 MPa,and the heat transfer coefficient has an obvious peak value;P=20～30 MPa,the heat transfer coefficient has no obvious peak value,and decreases with the increase of pressure.The heat transfer coefficient of the mixed medium increases with the increase of mass velocity.The heat transfer coefficient of the same fluid temperature decreases with the increase of heat flux.