The electrically induced bubble behaviors considering different bubble injection directions

The electrohydrodynamic (EHD) is an effective method to enhance boiling heat transfer in the terrestrial and space applications. To simplify the coupling effect of hydrodynamics and heat transfer processes, a varieties of adiabatic researches have been carried out recently, mainly for the upward surfaces. Actually, in industrial application, the boiling heat surface can be in any direction. The EHD effects on bubble dynamics on vertical surfaces and downward surfaces should be paid particular attention. In this work, a systematic experimental research was performed to study the effect of EHD on bubble behaviors considering the different bubble injection directions. A uniform DC electric field was applied to the testing zone with coarse bubbles generated from an orifice of 1.5 mm. Both the positive and negative directions of the electric field were considered in the measurement. The retarding effect of EHD on bubble detachment was demonstrated from the experimental results. This phenomenon was confirmed in all the three bubble injection conditions and was proved to be related to the bubble size by an extra experimental case. To explain the mechanism of the influence of electric field on the bubble dynamics, the main forces acting on the single bubble were analyzed qualitatively based on the evolution characteristics of the bubbles. The force distribution around the coarse bubble was proved to be in imbalance and the net force inhabited the bubble growth, prolonging the bubble detaching time.