Direct numerical simulations of sessile droplet evaporation on a heated horizontal surface surrounded by moist air

摘要

In this paper, the newly developed multi-component multi-phase (MCMP) lattice Boltzmann method (LBM) is extended for direct simulation on effects of ambient humidity of air and wall temperatures on sessile droplet evaporation. The effect of repulsive strength between gas component and moisture component is taken into consideration by proposing an equivalent gas density based on equilibrium of total pressure between bulk liquid phase and moist air. Relative humidity (RH) is defined under different repulsive strengths, which can be adjusted according to moist air with different humidities. Based on this extended MCMP LBM, characteristics of sessile droplet evaporation into unsaturated humid air on a heated surface near Leidenfrost point under normal gravity conditions are investigated. Effects of surface wettability on interfacial temperature and evaporation flux distribution at liquid-vapor interface are analyzed. The simulated total evaporation time versus ambient RH is found following an exponential curve which is in agreement with an existing analytical model, suggesting the feasibility and reliability of simulating humidity effects based on this novel MCMP LBM. Transitional stage of sessile droplet evaporation on a heated surface near Leidenfrost point is also studied. When the droplet is detached from the wall above the Leidenfrost temperature, no buoyancy flow is observed inside the hovering droplet, and the maximum heat flux on the surface occurs where the vapor layer adjacent to the heating surface has a minimum thickness. It is found that the variation of total evaporation time versus surface temperature near the Leidenfrost point is a U-shape curve, which is in qualitative agreement with existing experimental data. (C) 2019 Elsevier Ltd. All rights reserved.