基于流动沸腾气泡脱落行为的重力无关性分析

在流动沸腾现象中,气液两相密度差异导致重力对流动和传热性能产生很大影响,因此重力效应研究对于流动沸腾的航天应用具有重要意义.在对Bower-Klausner-Sathyanarayan重力无关准则(BKS准则)分析的基础上,提出其判据存在理论缺陷,不能正确反映重力效应.采用与BKS准则相同的气泡脱落模型,但忽略气泡沿加热管壁的滑动效应,重新计算常重力条件下不同流动方向起始沸腾阶段单气泡的脱落尺寸,归纳得到一个新的基于Fr (Froude数)的重力无关准则.该准则与实验结果符合更好,且与主导作用力准则基本相符.

Gravity Independence Analysis Based on Bubble Departure in Flow Boiling

The density difference between gas and liquid phases in the flow boiling phenomenon leads to the important influence of gravity on the flow and heat transfer performance. Therefore, the study of gravity effect is of great significance for the space application of flow boiling. The Bower-Klausner-Sathyanarayan gravity independent criterion, i.e. BKS criterion, is revisited. It is pointed out that BKS criterion has congenital defect in theory and cannot reflect the gravity effect correctly. Using the same departure model of growing vapor bubble in flow boiling as adopted in BKS criterion, but neglecting the sliding effect of bubble along the heating wall, the departure diameters of single bubble in the initial segment after the boiling incipience under different flow directions in normal gravity are calculated. A new gravity independent criterion based on Froude number is concluded, which is in better agreement with the experimental results. The new criterion is in principle consistent with the dominant force criterion.