Solidification of a hollow sessile droplet under forced convection

Abstract

This study presents a front-tracking-based numerical analysis of the forced convection solidification of a sessile droplet on a cooling surface. The droplet, a hollow (or compound) droplet with an encapsulated gas core, undergoes a liquid-to-solid phase change in its shell. This phase change starts from the surface. Meanwhile, the surrounding gas, which is characterized by its Reynolds number Re and temperature, moves toward the droplet parallel to the axis of symmetry. When the temperature of the forced flow is below the solidification value (i.e., cold-forced convection), increasing the strength of the forced flow shortens the solidification process. In contrast, increasing the Re number of a hot-forced convection system prolongs solidification. In other words, an increase in the forced flow temperature causes the entire liquid shell to solidify more slowly. Thinner shells require more time to solidify completely than thicker ones. The forced flow does not influence the formation of an apex at the top of the outer droplet surface. The aforementioned apex results from volume expansion. The effects of other parameters, for example, the capillary number and the morphologies of the droplet and cooling surface, are also determined.