G0500103 Measurement and formulation of drag coefficient for single bubbles under inclined plate

Abstract

In high-voltage equipment, partial discharge in the void present in insulation layer is directly connected to product lifetime. In order to optimize the mold structure and molding condition for suppressing the void, it is effective to numerically analyze the void behavior which cannot be directly visualized in the mold. To predict void behavior in molding process, it is necessary to formulate the void terminal velocity under inner parts in various liquid. In this work, to construct the void behavior analysis technology, we measured terminal velocity of the void rising under the inclined plate as an alternative for inside wall of mold construction and inner parts in various liquids, and developed the high precision prediction formula. By the experimental results, drag coefficient (C_D) is expressed as a function of Re and Morton number (Mo) when Reynolds number (Re) is low. By contrast, C_D is expressed as a function of Eotvos number (Eo), inclination angle of wall (θ), and Mo when Re is high. We developed the predictive formula of C_D based on above knowledge, and enable the high precision prediction of terminal velocity of the void rising under the inclined plate compared with existing predictive formula for free-rising void.