Dynamic contact angle and liquid displacement of a droplet impinging on heated textured surfaces

Abstract

This study investigates the temporal evolution of the dynamic contact angle (DCA) of a droplet impinging on the flat and textured surfaces with different surface temperatures of 30 degrees C, 50 degrees C, and 80 degrees C. The hole-patterned textured surfaces are manufactured by using a drilling machine with two texture area fractions to examine the variation in DCA according to the Weber number, surface temperature, and texture area fraction. It is found that at low Weber number, the DCAs on the textured surfaces are larger than those on the flat surface in the first spreading and receding phases. The measured DCA shows the increasing tendency with the increase in the texture area fraction. On the contrary, the measured DCA becomes smaller for impinging droplet with higher Weber number on the textured surfaces because the inertia effect becomes dominant and the liquid penetration through the holes occurs. Moreover, we analyze the wetting and non-wetting pressures for better understanding of the liquid displacement on the hole-patterned textured surface. The DCAs on the textured surfaces increase with the surface temperature, affecting a substantial decrease in the viscous energy dissipation and enhancing the recoiling momentum.