Evaporation of a small water droplet sessile on inclined surfaces

Abstract

A three-dimensional numerical model is developed to explore the evaporation of a small water droplet sessile on inclined surfaces. Important transport mechanisms, including evaporative cooling, heat transfer, vapor diffusion and natural convections in both liquid and gas domains are taken into account. The accuracy of the present model is first validated by comparing the total evaporation times and volume evolution curves obtained by the present model with those measured from experiments in the literature. The transport details and evaporation characteristics are then investigated. Under the influence of the combining effect of natural convection and evaporative cooling, the overall evaporation rate increases first as the inclination angle gets enlarged till ∼75°, and then decreases with further increase of the inclination angle. The flow field in the gas domain is converted from symmetry to asymmetry with the increase of the inclination angle, and the flow intensity near the droplet is also enhanced, which accelerates the evaporation. At the same time, the local evaporation flux distribution at gas-liquid interface changes from symmetry to asymmetry and the location of the lowest evaporation flux moves from the droplet apex to its waist (on the higher side of the droplet). The total evaporation times of droplets evaporating on vertical surfaces are shorter than those on horizontal surfaces by up to ∼9.38% when the substrate temperature is 40 °C higher than the ambient. The flow behavior inside the droplet is also discussed. With the increase of the inclination angle (0°∼180°), the flow pattern inside the droplet changes from double-vortex flow to single-vortex flow and to double-vortex flow again. The flow velocity magnitude is remarkably increased with the inclination angle increases from 0° to 90°