Numerical Analysis of Boiling Bubble Growth under Electric Fields

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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.