竖直圆管内超临界二氧化碳强迫对流传热实验研究

Investigation of Correlation for Forced Convective Heat Transfer to Supercritical Carbon Dioxide Flowing in a Vertical Tube

为分析超临界二氧化碳强迫对流传热特性,开展竖直圆管内超临界二氧化碳强迫对流传热特性实验研究。实验结果表明:实验参数范围内存在明显的浮升力效应和流动加速效应;对于向上流动工况,随浮升力效应增强超临界二氧化碳从强迫对流传热过渡至混合对流传热,最后发展为自然对流传热,传热能力有弱化到逐渐恢复直至强化;对于向上流和向下流动工况,流动加速效应皆弱化传热。基于实验数据建立新的超临界流体传热关联式,在实验工况范围内95.03%的预测值与实验值偏差为±30%以内。

An experimental investigation of turbulent heat transfer in vertical upward and downward supercritical carbon dioxide flow was conducted in a heated bare tube with an inner diameter of 10 mm. In the experimental conditions, it shows that the phenomenon of buoyancy and acceleration is obvious. For the upward cases, as the buoyancy effect increasing the forced convective heat transfer of carbon dioxide will transient to mixed convective heat transfer, then free convective heat transfer, in which the heat transfer capacity is weakened firstly, then resumed and strengthened. The acceleration often weakens the heat transfer capacity both for upward flow and downward flow. A new heat transfer correlation for vertical upward flow of supercritical carbon dioxide was developed, by which 95.03% of the predicted Nusselt numbers agree with the experimental data within ±30%.