加热面尺寸对饱和池沸腾换热性能的影响

Influence of heater size on saturated pool boiling heat transfer performance

为揭示加热面尺寸对饱和池沸腾换热性能的影响,对8种不同尺寸光滑硅片表面在FC-72中的池沸腾换热性能进行了实验研究,通过高速相机观察了不同热流密度下各尺寸硅片表面的气泡动力学行为,分析了加热面尺寸对汽泡成核、脱离特性和换热系数的影响。结果表明,自然对流区内,相同热流密度条件下加热面尺寸越大,硅片对液体的热对流扰动越小,壁温越高且换热系数越小;随热流密度增大,换热面周边最先产生汽泡,大尺寸换热面与绝热胶的接触周长更大,产生的缺陷和凹坑能捕捉更多气体,因此率先进入核态沸腾。核态沸腾区内,小尺寸加热面汽泡脱离直径小、脱离频率高,换热性能好。高热流密度范围内,大尺寸表面的汽泡脱离直径和脱离频率随热流密度增大而迅速增大,表面换热增强。临界沸腾点时,换热系数随加热面尺寸的增加呈先增大再减小最后缓慢增大的变化趋势。

In order to study the influence of heater size on FC-72 pool boiling heat transfer performance,saturated pool boiling experiments were conducted on eight smooth silicon chips in different sizes.The bubble dynamics were observed with a high-speed camera.The effects of heater size on bubble nucleation,bubble departure characteristics as well as the heat transfer coefficient were discussed.It is found that in natural convection region,the heat transfer coefficient decreases with increasing heater size.This is because at a given heat flux larger surface generates smaller thermal convection disturbance to the bulk liquid,which leads to a higher wall temperature.With increasing heat flux,bubbles are usually generated at the periphery of heating surface.The contact perimeter of heating surface and the insulating adhesive increases with heater size,the formed larger number of defects and pits can capture more non-condensable gas,resulting in an earlier transformation of the nucleate pool boiling pattern.In the nucleate pool boiling region,the small-sized heating surface exhibits good heat transfer performance due to the smaller bubble departure diameter and the faster bubble departure frequency.In the high heat flux region,the bubble departure diameter and departure frequency of the large heating surface increase rapidly with the increase of heat flux,which enhances the boiling heat transfer.Accordingly,the wall temperature doesn’t increase significantly with the increase of heat flux,and the heat transfer coefficient increases rapidly.At the critical heat flux,the heat transfer coefficient first increases,then decreases,and finally increases slowly with the increasing of heater size.