Effects of nanoparticles’ wettability on vapor bubble coalescence in saturated pool boiling of nanofluids: A lattice Boltzmann simulation

Abstract

Vapor bubble coalescence in saturated pool boiling of nanofluids containing moderately hydrophilic nanoparticles (θ=33∘∼51∘) is investigated numerically by a single component multiphase particle suspension lattice Boltzmann model. It is shown that the vapor bubble coalescence time in a nanofluid is prolonged by the presence of moderately hydrophilic nanoparticles adsorbed at vapor bubble interfaces comparing with those in a base fluid. The prolonged bubble coalescence time is owing to the following three reasons: (i) the adsorbed nanoparticles deform the liquid film interface between two closely adjacent bubbles, resulting in a capillary pressure in the liquid film which resists the liquid drainage pressure (Pgas bubble-Pliquid film). (ii) The nanoparticles, confined in the liquid film between the closely adjacent bubbles, block the passage for liquid drainage between the two vapor bubbles, and (iii) the rigidity of vapor bubble interfaces is strengthened by the adsorbed nanoparticles at bubble interfaces. The prolonged bubble coalescence time is more effective for more hydrophilic nanoparticles with contact angle in the range of θ=33∘∼51∘. Since the prolonged bubble coalescence time would lead to smaller bubble size, the bubble size in pool boiling of a nanofluid with moderately hydrophilic nanoparticles is smaller than those in a base fluid, which is in agreement with results of our previous pool boiling experiments of a nanofluid.