Evaporation of droplets on inclined biphilic surfaces

The evaporation of droplets on biphilic surfaces inclined at angles of 0°, 45°, 90°, 135°, and 180°, is studied experimentally. The fastest evaporation was observed for droplets on vertical surfaces, and the slowest was observed for sessile droplets on surfaces inclined at an angle of 45°. A pendant droplet evaporating on a surface at an angle of 180° had the highest temperature. Numerical and analytical/numerical models are applied to the analysis of the experimental data. The first is based on ANSYS Fluent, while the second is based on the earlier developed variable density model. Function Φ, used in the second model, is inferred from the numerical solution of the Laplace equation by COMSOL Multiphysics. The numerical model can take into account or ignore the effect of natural convection on droplet evaporation. This effect is ignored in the analytical/numerical model. The predictions of the numerical model are shown to be reasonably close to the experimental data. A very small difference between the results predicted by the numerical and analytical/numerical models in the absence of gravity is considered to be a verification of both models. It is shown that the evaporation rates of the droplets on inclined surfaces are mainly controlled by the re-direction of the flow around them driven by natural convection and not by their deformation and changes in their surface areas.