竖直圆管内超临界流体混合对流传热特性理论分析

Theoretical Analysis of Mixed Convective Heat Transfer Characteristic for Supercritical Fluid Flowing in Vertical Bare Tube

理论推导了变密度引起的浮升力效应和流动加速效应对超临界流体混合对流传热特性的影响。结果表明,浮升力效应和流动加速效应通过改变壁面边界层外缘的切应力影响湍流对传热传质的贡献,进而改变超临界流体混合对流传热特性。浮升力效应通常在加热区域入口及上游区域表现明显,而流动加速效应在主流区流体温度达到拟临界温度时更显著。与实验研究结果对比发现,新建立的浮升力因子和流动加速因子可较好地预测竖直圆管内超临界流体混合对流条件下拟临界区域的局部传热特性。

T he theoretical analysis about the influence of buoyancy effect caused by den‐sity variation and flow acceleration effect on forced convective heat transfer to supercriti‐cal fluid was carried out . The analysis results show that buoyancy and acceleration effects may change the turbulent heat and mass transfer through reducing or enhancing the shear stress magnitude at the verge of boundary layer ,and make a big difference to supercritical fluid heat transfer at certain conditions .Often buoyancy effect is obvious near the entrance or upstream ,w hile acceleration at w here the bulk temperature is just beyond the pseudo‐critical temperature .Compared with experimental result ,it’s found that the buoyancy and acceleration factors are able to predict the local heat transfer char‐acteristics in the pseudo‐critical zone suitably .