Formation characteristics of microlayer between elongated bubble and heating surface in mini-gap boiling system

Abstract

In this study, experiments were performed to measure the thickness of the liquid film formed between the heating surface and the vapor bubble with the laser extinction method for the gap size of 0.5, 0.3 and 0.15mm.Water, toluene and HFE7200 were used as test fluids. It was found that the gap size and bubble forefront velocity determined the initial thickness of microlayer no matter of the kind of testing liquid. Vapor bubble generated by boiling in the present mini-gap grows exponentially due to the rapid evaporation of the thin liquid layer, which makes the phenomena highly transient as opposed to the steady situations considered before. Based on the experimental data and scaling arguments a non-dimensional correlation in terms of capillary number and Bond number is proposed.