Dry spot dynamics and wet area fractions in pool boiling on micro-pillar and micro-cavity hydrophilic heaters: A 3D lattice Boltzmann phase-change study

Abstract

A three-dimensional lattice Boltzmann phase-change study is carried out on dry spot characteristics in pool boiling on micro-pillar and micro-cavity hydrophilic heaters under constant bottom wall temperature conditions. The degree of superheat and geometry of these micro-structures (i.e., the pitch distance p, the height h, and the width d) are found to have significant effects on the cycle-average dry spot diameter. Pool boiling curves for these micro-structured heaters are obtained, which are compared with a smooth surface under same conditions. The micro-pillar structured hydrophilic heater is found to have the highest CHF because of capillary wicking, and geometric effects (p/d and h/d) on pool boiling curves from micro-pillar structured hydrophilic heaters are investigated. Although p/d and h/d have small effects on the developing nucleate boiling regime in pool boiling, these parameters have significant effects from fully-developed nucleate boiling to CHF and in transition boiling regime. Critical heat fluxes are shown to be related to wet area fractions: the higher is the wet area fraction, the higher is the CHF.