不同重力条件下单气泡池沸腾现象的数值研究

Numerical Simulation on Single Bubble Pool Boiling in Different Gravity Conditions

对不同重力条件下常压饱和水中单气泡池沸腾现象的气泡生长过程及传热特性进行了数值模拟.采用简化的润滑流模型计算生长气泡底部微液膜的贡献,而其他宏观区域的气液两相介质则用连续界面模型统一处理.气液界面形状和加热面上接触线的运动分别采用Level Set方法和固定的表观接触角来近似刻画.计算结果表明,气泡生长过程中,当量直径近似与生长时间的1/3～1/2次方成正比,重力对相关趋势的影响不大,但强烈影响着气泡脱落直径和生长时间,其中脱落直径反比于重力的1/3次方,生长时间反比于重力的4/5次方.在固定的核化点数密度条件下,加热面平均热流密度近似与壁面过热度的3/2次方成正比,该趋势并不随重力的减弱而改变.

In this paper, the growth processes of a single bubble on a fixed single site and the relative heat transfer under different gravity are numerically investigated for saturated water at 0.1 MPa. A simplified lubrication theory is used to predict the contribution from the micro-wedge area underneath the growing bubble, while vapor and liquid phases in other macro-area are treated as one fluid by using the continuum interface model. The Level Set Method and constant superficial contact angle are used to capture the interface between the vapor and liquid phases and the motion of contact line on the heating wall, respectively. The numerical results indicate that the equivalent diameter is proportional to about （1/3-l/2）-power of the growing time in spite of whatever gravity levels. But gravity has great influences on both the departure diameter and the growing time. The bubble departure diameter is proportional inversely to about 1/3-power of gravity, while the growing time is proportional inversely to about 4/5-power of gravity. The areaaveraged heat fluxes are approximately proportional to the 3/2-power of the wall superheat when the number density ofactive nucleation sites fixes. ~rthermore, this trend has no change with the decrease of gravity.