Dynamics of phase change of gallium under magnetic field and thermocapillary effects under variable gravity conditions

Abstract

We have numerically investigated the melting and solidification process of a low melting temperature metallic phase change material, gallium, in a semi-circular enclosure with a hot circumferential wall under the influence of thermocapillarity and externally applied uniform magnetic field for different gravity conditions. The governing equations coupled with the enthalpy porosity method are solved to predict the effects of applied magnetic field direction (0 ≤ θ ≤ 90°), and strength (0 ≤ Ha ≤ 125), Rayleigh number (Ra = 4.656 × 102, 4.656 × 104, 1 × 105, 1 × 10⁶), Marangoni number (Ma = -1.44 × 103, −5 × 103 and −1 × 104) and gravity conditions (0.05g, 0.25g, 0.5g and 1g) on the velocity, temperature and liquid fraction profiles. The predictions of the developed numerical models are compared with the experimental and numerical data reported in the literature and found to be in good agreement. The results reveal that the surface tension gradient driven convection significantly enhances the melting process under the microgravity condition without the magnetic field. Fluctuating behaviour of transient average Nusselt number under normal gravity conditions observed during melting of gallium in the presence of thermocapillary and natural convection is reduced by applying the magnetic field. The complete gallium melting time is increased by 5.48% for the change in Hartmann number from 0 to 25 applied at θ = 45°. The direction of the applied magnetic field marginally increases the complete melting time for θ ≥ 75° and insignificantly affects the complete solidification time. The increase in Rayleigh and Marangoni numbers considerably alters fluid flow patterns and the temperature field.