Phase-change lattice Boltzmann simulation of condensate falling and heat transfer on hybrid-wettability surface in the presence of non-condensable gas

Abstract

• Condensate falling off hybrid-wettability surfaces is studied under non-condensable gas effect. • Pseudopotential MRT LB method is coupled with finite difference for phase-change multicomponent flow. • Droplet nucleation, growth and departure time prolong as non-condensable gas fraction increases. • Hydrophilic-superhydrophobic hybrid surface exhibits higher heat transfer performance. A hybrid phase-change lattice Boltzmann model is employed to investigate the condensate falling from subcooled surface in the presence of non-condensable gas. The effects of hydrophilic length ratio, the non-condensable gas fraction ( w NCG ) and the hybrid-wettability of the subcooled surface on condensate droplets dynamics and heat transfer characteristics are investigated systematically. It shows that the average heat flux at the subcooled surface first increases and then decreases with the increase of hydrophilic length ratio. Owing to the increased thermal resistance by the thicker non-condensable gas layer, the nucleation time, growth time as well as departure time of condensate droplets are prolonged as the non-condensable gas fraction increases. The nucleation time of w NCG = 0.4 is 1.5 times higher than that of w NCG = 0.1 , and the growth time and departure time of w NCG = 0.4 are 1.7 times higher than those of w NCG = 0.1 . As the surface wettability changes from hydrophilicity-superhydrophobicity ( θ y = 60 o - θ g = 150 o ) to hydrophilicity-more hydrophilicity ( θ y = 60 o - θ g = 30 o ), the condensation pattern transits from dropwise to filmwise mode. Moreover, the local heat flux at hydrophilic-superhydrophobic ( θ y = 60 o - θ g = 150 o ) and hydrophilic-hydrophobic ( θ y = 60 o - θ g = 105 o ) surface is obviously higher than that at hydrophilic-hydrophilic ( θ y = 60 o - θ g = 75 o ) and hydrophilic-more hydrophilic ( θ y = 60 o - θ g = 30 o ) surface. The present simulations clarify the mechanism of condensate droplets falling off subcooled surface with the existence of non-condensable gas and are conducive to the design of hybrid-wettability surfaces for condensation heat transfer enhancement, which is of great significance to energy resources conservation.