Pore-scale investigation on flow boiling heat transfer mechanisms in gradient open-cell metal foams by LBM

Abstract

Flow boiling heat transfer mechanisms inside gradient open-cell metal foam are investigated based on the newly proposed metal foam model. This new model considers thermal responses of metal skeletons. The structural effects of gradient metal foam, including porosity gradient, thermal conductivity gradient and wettability gradient, on flow boiling heat transfer performance are studied by pseudopotential lattice Boltzmann method. Reynolds number effect on bubble departure characteristics, such as bubble departure diameter, bubble departure frequency and the corresponding probability density distributions, are investigated based on statistical analysis. The results show that bubble confinement weighs heavily over bubble movement inside pore cell during bubble escaping process in porosity-gradient metal foams. Bubble nucleation is depressed by the highly thermal conductive gradient metal foam at high heat fluxes. The interaction between escaping bubble and pore throat shifts from “complete contact” mode to “thin liquid film” mode in the positive wettability-gradient metal foam. Shear force dominates over buoyant force with increasing Reynolds number, resulting in the sliding motion of premature bubbles.