On the Coupled Thermal and Hydrodynamic Interaction of Adjacently Located Vapor Bubbles on Highly Wetting Surfaces.

Abstract

Spatio-temporally resolved IR measurements coupled with high-speed videography have been made to propose the regime map of the interaction between two adjacently located vapor bubbles on high-wettability surfaces. The modes of interaction (thermal and/or hydrodynamic) have been studied as a function of distance between the two nucleation sites under saturated nucleate pool boiling conditions with water as the working fluid, and their effects on the wall heat-transfer rates have been quantified. Based on the comprehensive observations and analyses of the simultaneously mapped vapor bubble dynamics, substrate surface temperature, and the associated wall heat flux distributions, the possible regimes of bubble interactions have been identified. Experiments revealed three dominant mechanisms of bubble interactions: hydrodynamic interaction (HI), thermal interaction (TI), and horizontal coalescence (C). Depending on the relative spacing of the two nucleation sites, a regime map has been prepared wherein various possible bubble interactions (and/or their combinations) have been classified as HI + TI + C, HI + C, and HI. The IR thermography-based measurements revealed a strong dependence of bubble base evaporation-driven heat transfer on the possible bubble interaction mechanism(s) encountered in each regime. The dependence of microlayer formation beneath the growing vapor bubble(s) and its evaporation on HI is further corroborated through thin-film interferometric measurements. Plausible explanation(s) for mechanisms through which bubble interactions influence heat transfer have been discussed. A trend of variation of wall heat-transfer performance with bubble interaction regimes has been deduced and discussed.