Numerical Analysis of Boiling Bubble Growth under Electric Fields

通过数值分析，揭示了EHD（Electro-Hydro-Dynamic）效应强化传热的机理。模拟代码已经开发了以下三个阶段：（A）的情况下，没有电场和相变，（B）的情况下，有电场和没有相变，和（C）的情况下，有电场和相变。首先，为了验证程序的正确性，模拟了均匀电场作用下R113气泡的伸长过程，并与加顿等人的实验结果进行了比较，验证了程序的正确性。将初始直径为0.2mm、接触角为15 μ m的R113气泡放置在直径为0.4mm的下圆盘电极上。上圆盘电极直径为1 mm，两电极之间的距离为1 mm。施加到电极上的电压为5、10和20 kV。在每个施加电压下，气泡变形并与下电极分离。在5 kV的情况下，通过粗略估计发现，静电力是重力的100倍。这一结果从定性上解释了在非均匀场作用下产生细小沸腾气泡的原因。为了检验程序的最后阶段（C），模拟了加热平板上氦泡的行为。实验的计算条件为：初始气泡直径20 μ m，表面过热度0.1K，大气压。得到的气泡脱离直径为55 μ m，这与实验结果定性一致。在外加非均匀电场作用下，氦泡的行为与R113泡的结果基本一致。

Numerical analysis has been performed to disclose the mechanisim of heat transfer enhancement by EHD (Electro-Hydro-Dynamic) effects. The simulation code has been developed in the following three stages ; (A) the case without electric field and phase change, (B) the case with electric field and without phase change, and (C) the case with electric field and phase change. First, to check the program in stage (B), elongation of R113 bubble under uniform electric fields was simulated and confirmed by comparing the results with the experiment reported by Garton et al.The second, bubble diparture under non-uniform electric fields were simulated. An R113 bubble initially at a diameter of 0.2mm with a contact angle of 15ﾟ are placed on the lower disc electrode of 0.4mm in diameter. Upper disc electrode has 1mm in diameter and the distance between two electrodes is 1mm. The voltage applied to the electrodes are 5,10 and 20kV.The bubble was deformed and separated from the lower electrode in each applied voltage. It was found by the rough estimation in case of 5kV that the electrostatic force is 100 times as much as the gravity force. This results gives us a qualitative explanation why fine boiling bubbles are created under non-uniform fields.To check the program in final stage (C), behavior of helium bubble on a heated plate was simulated. Calculation conditions tested are iniial bubble diameter of 20mum, surface super heat of 0.1K and atmospheric pressure. The bubble departure diameter obtained is 55mum which qualitatively agrees with a reported experimantal result. When we applied non-uniform electric field on the helium bubble, the bubble behavior was almost the same as the results in R113 bubble.