A numerical study of geometrical effects on solidification of a compound droplet on a cold flat surface

Abstract

In this study, the solidification process of a compound droplet is numerically simulated by an axisymmetric front-tracking/finite difference technique. The compound droplet placed on a cold flat surface in a gas environment consists of an inner gas core surrounded by a concentric shell phase-change liquid that forms an outer droplet. The initial droplet shape assumed as a spherical cap is therefore determined by two wetting angles known as the inner wetting angle (?0i for the inner core) and the outer wetting angle (?0o for the outer droplet). During the solidification process, there is the presence of two three-junction points where a prescribed growth angle ? is specified. We analyze the solidification process undergoing the influence of the geometrical aspects of the compound droplet including the growth angle and the wetting angles. It is found that the outer wetting angle ?0o and the growth angle have a strong influence on the solidified droplet that the droplet height increases with an increase in ?0o or ? while the height increment decreases with an increase in ?0o or with a decrease in ?. On the contrary, changing the shape of the inner core, in terms of ?0i, does not affect the outer shape after complete solidification. The effects of these parameters on the solidification time are also considered.