Flow behavior around single nucleate boiling bubble quantitatively grasped by particle tracking visualization

Abstract

In this study, a single nucleation site was made on the upper surface of heated substrate, and small tracer particles suspended in water for flow visualization. Single vapor bubble dynamics and particle movements were recorded by high speed camera, then the flow field was quantitatively grasped by particle tracking visualization. Resulting of the visualization, in earlier stage of nucleate boiling, rapid growth motion of bubble pushed liquid surrounding bubble interface outwardly. There was no retracting flow into root of boiling bubble though it needed to feed water into root of boiling bubble due to evaporation in case of lower heat flux condition. Liquid flow pushed by rapid bubble growth was explained by combining thermal diffusion equation with mass conservation law, moreover the pressure increase caused this liquid flow was estimated. In bubble departure process, liquid near substrate was horizontally pulled to nucleation site, but the eddy to enhance a vertical mixing of superheated liquid near substrate was not observed. After bubble departure, it was found that a hot liquid plume under a rising bubble was not mainly caused by entrainment of superheated liquid layer formed on heated substrate, but by a relative descending flow around a rising bubble induced by mass conservation law.