Two-dimensional mesoscale simulations of saturated pool boiling from rough surfaces. Part Ⅱ: Bubble interactions above multi-cavities

摘要

Bubble interactions and their effects on saturated pool boiling heat transfer from superheated horizontal surfaces having multi-cavities of rectangular shapes under constant wall temperature conditions are investigated numerically by a liquid-vapor phase-change lattice Boltzmann method. It is shown that mutual suppression of bubble nucleation between cavities exists, and this effect depends not only on pitch distance of cavities but also on the depth/width and location of the cavities as well. For cavities with unequal sizes, bubbles tend to nucleate preferentially in wider or deeper cavities while bubble nucleation in narrow or shallow cavities can be totally suppressed at small pitch distances. Saturated pool boiling curves, from natural convection regime to stable film boiling regime on a hydrophilic rough surface, a hydrophobia rough surface as well as a mixed wettability rough surface (a hydrophilic surface having hydrophobic cavities) are obtained numerically. Simulated results show that presence of roughness on the heating surface promotes boiling incipience and enhances boiling heat flux in the nucleate boiling regime. A more pronounced enhancement of the nucleate boiling heat transfer is observed on a hydrophobic rough surface than that on a hydrophilic rough surface at the same wall superheat. Among three types of rough surfaces, the mixed wettability rough surface (with hydrophobic cavities on a hydrophilic surface) exhibits the best overall boiling heat transfer performance with higher boiling heat flux in the nucleate boiling regime than the hydrophilic rough surface and the highest critical heat flux.