水平管内超临界二氧化碳非均匀冷却对流传热特性研究

he Study of Heat Transfer Performance of Unevenly Cooled Supercritical CO_(2) in the Horizontal Tube

针对超临界CO_(2)空冷换热器中存在的非均匀传热问题,本文利用数值模拟计算了水平空冷翅片管中管壁热流分布规律及超临界CO_(2)在非均匀冷却时的换热特性,同时分析了非均匀冷却工况下不均匀度、质量流量和浮升力等因素对换热规律的影响。结果表明:翅片管热流密度沿周向管壁位置呈现显著的不均匀分布,且不均匀度随风速增大而增大;超临界CO_(2)非均匀冷却的平均换热系数在远离准临界点时高于均匀冷却,靠近准临界点时低于均匀冷却;非均匀冷却与均匀冷却的差异随不均匀度、质量流量增大而增大。CO_(2)在准临界点处的非线性物性变化与浮升力作用是造成两者差异的主要原因。

To address the problem of uneven heat transfer in supercritical CO_(2) dry-cooled heat exchangers,the heat fow distribution and heat transfer characteristics of supercritical CO_(2) in horizontal air-cooled finned tubes were calculated by numerical simulation.At the same time,the effects of the unevenness,mass flow rate and buoyancy on the heat transfer under uneven cooling conditions are analyzed.The results show that the heat fux distribution along the circumferential wall of the finned tube is uneven,and the unevenness increases with the increase of the wind speed The average heat transfer coefficient of uneven cooling in supercritical CO_(2) is higher than that of even cooling when the average temperature is far from the pseudocritical point,and lower than that of even cooling near the pseudocritical point.The difference between uneven cooling and even cooling increases with the increase of unevenness and mass fow rate.The main reason for the difference is the nonlinear physical property change of CO_(2) at the pseudocritical point and the buoyancy effect.