A numerical study of a suspended compound droplet solidifying under forced convection

Abstract

In this study, we numerically investigate the solidification process of a suspended compound droplet in a cold environment under forced convection by a front-tracking method. The compound droplet consisting of an inner gas core (i.e., inner bubble) surrounded by a phase-change liquid shell (i.e., outer droplet) starts solidifying from a nucleus at its bottom. The phase-change interface evolves upward to form the solid shell with an upper conical outer surface due to volume expansion. We monitor main parameters such as the Reynolds number (Re) in the range of 25–200, the Stefan number (St) in the range of 0.05–1.6, the inner-to-outer radius ratio (Rio) in the range of 0.2–0.7, the solid-to-liquid density ratio (ρs1) in the range of 0.8–1.2, the nucleus size (r0/R) in the range of 0.05–0.3, the initial eccentricity (ε0) in the range of -0.15–0.3 and the growth angle (ϕgr) in the range of 0°–15°. It is found that an increase in St, ρsl or a decrease in ϕgr leads to a decrease in the height of the solidified droplet. In contrast, an increase in Re, r0/R, ε0 or Rio has a minor effect on the drop height after complete solidification. In contrast to ρsl, which has less influence on the solidification time, the change in the value of these parameters considerably modifies the solidification time. The inner and outer aspect ratios of the solidified droplet are also revealed.