高雷诺数下降液膜流动换热分析

本文分析了降液膜高雷诺数区域换热系数随液膜长度变化趋势,引出临界长度的概念。在较高雷诺数的湍流区,回流区的存在以及表面波的影响能有效地减少局部薄膜厚度并增加对流换热,流速的增加进一步强化换热,增加降膜整体传热系数。在高雷诺数区域,厚度形成的热阻超过回流的增强作用,而使换热削弱。液膜小于临界长度L换热系数随长度增长而增加,大于L换热系数随液膜增长而减小。

THE ANALYSIS OF FALLING FILM HEAT TRANSFER BY HIGH REYNOLDS NUMBER

A critical length concept is introduced to describe the heat transfer performance of thin film flows with high Reynolds number in this investigation. The theoretical analysis indicates that liquid refluence and surfacial wave existing in the film flows could reduc?the film thickness and increase the heat transfer, and increasing flow velocity would further intensify the heat transfer. At high higher Reynolds number the increased film thickness causes higher heat resistance and its influence would be stronger than the heat transfer enhancement due to liquid refluence. As a result, this would make the heat transfer weaker. Generally, the heat transfer coefficient increases along flow direction for the film length less than the critical length, and heat transfer coefficient would decrease if liquid film is greater than the critical length.