Numerical Study of Effect of Thermocapillary Convection on Melting Process of Phase Change Material subjected to Local Heating

We numerically investigate the effect of thermocapillary convection on melting and deforming processes of Phase Change Material (PCM) subjected to local heating. Mass, momentum and energy conservation equations are solved in a 2-D system based on a fixed grid by means of a finite volume method. The Volume of Fluid (VOF) method and the Enthalpy-Porosity method are applied to model the deformable liquid-gas interface and the melting processes, respectively. Thermocapillary effect is accounted in the momentum equation as one of additional external force (related to surface tension force and it is controlled by temperature dependency of surface tension coefficient). In this study, temperature dependency of surface tension coefficient is given by linear function of temperature, which is considered as numerical parameter to examine the thermocapillary effect. Results successfully show that the thermocapillary convection under normal gravity environment appears clearly only at the early stage of melting at which the substantial deformation of PCM is not observed. Once the gravity drag starts to deform the molten PCM, thermocapillary convection seems to be masked, revealing that the gravity-induced deformation is dominant factor of internal motion of molten PCM. In zero-gravity, on the other hand, thermocapillary convection is continuously observed, ensuring that it dominates the internal motion so as to enhance the heat flux toward the un-melted solid. Importantly, even in zero-gravity case, the total effect of thermocapillary convection on melting is not so significant, at most 5% in the present system.