Solidification of subcooled gallium poured into a vertical cylindrical mold

Abstract

The present investigation is aimed at the solidification of subcooled liquid gallium. The gallium, in its liquid state, is contained in a cylindrical shell of copper or polypropylene, and poured into the shell, which is immersed in a cold bath. The experimental degree of subcooling varied between 5°C and 45°C. The phenomena empirically observed have been simulated in four stages: subcooling of the liquid gallium down to its nucleation temperature, a rapid transfer from nucleation to the stable solidification temperature, stable solidification up to its completion and finally cooling down of the solid gallium. The conductivity of the sample shell affects the length of each stage. In the copper shell the sample loses up to 5% of its released heat along the second stage. In the polypropylene shell, the sample does not lose any heat in that stage. The entire process for initially contained liquid gallium is analyzed by formulation of heat transfer rates at each stage. The only empirical figure used in the analysis is the nucleation temperature. Matlab software is used to solve the formulations. The model presents time-dependent temperatures and melt fraction. The model agrees well with the experiments. For the flowing liquid gallium, the rate was 0.12 - 0.3 ml/s. The numerical study explored solidification of the flow of liquid gallium by a two-dimensional (axially symmetric) model, using Fluent 6.2 software. Previous investigations in our laboratory, using other flowing phase-change materials, have demonstrated that the solidified phase at the cooled boundaries adheres to the walls with irregular cavities. In the present study the flowing and solidifying gallium has formed an irregular boundary at the walls, too. However, the numerical model has closely predicted the entire process of solidification and cooling of the solid. At higher flow rates the solidification approached the behavior of a static liquid gallium.

Keywords

• Solidification,Subcooling; Gallium; Transient; Experimental; Simulation.