Lattice Boltzmann simulations for surface wettability effects in saturated pool boiling heat transfer

摘要

Effects of wettability on saturated pool boiling heat transfer from a smooth superheated substrate, with a finite thickness at constant wall temperatures at the bottom, are investigated based on a recently developed liquid-vapor phase-change lattice Boltzmann method. For a hydrophilic surface, it is shown that bubble departure diameter and bubble departure frequency increase with the increase of contact angle and superheat, and the whole bubble departs from the surface with a waiting period in the ebullition cycle. A microlayer of liquid exists between the bubble and the heated hydrophilic surface and this region exhibits a high local heat flux during bubble growth period. On the other hand, a residual bubble will be left on the surface when bubble departs from a hydrophobic surface and hence no waiting period exists. No microlayer exists on the heated hydrophobic surface, and the three-phase contact line region has the highest local heat flux and lowest local temperature. Time histories of the wall temperature on the top of a hydrophilic substrate and a hydrophobic substrate as well as the associated heat flux are studied in details during the nucleate boiling process. Effects of wettability, superheat and heater size on number of nucleation sites in saturated pool boiling are investigated. Saturated boiling curves (from onset of nucleate boiling to critical heat flux, to transition boiling to stable film boiling) for hydrophilic and hvdroDhobic heatinz surfaces are obtained bv numerical simulation for the first time.