Thermocapillary effects during the melting in microgravity of phase change materials with a liquid bridge geometry

Abstract

A detailed numerical investigation of the melting of phase change materials (PCMs) in microgravity is presented. We consider the high Prandtl number alkane n-octadecane and quantify the effect of thermocapillary convection on the heat transfer observed during axisymmetric melting with a liquid bridge geometry. The phase change is studied by varying key dimensionless parameters including Marangoni (Ma) and Stefan (Ste) numbers, which are selected by the applied temperature difference between the circular supports, and geometry, which is characterised by the aspect ratio Γ=L/R and the dimensionless volume V. The case of cylindrical geometry with V=1 is considered first, and detailed analyses of the effect of both Ma (Ste) and Γ on heat transport and the type of oscillatory flow that appears in the liquid phase are provided. The results are compared with those available in the literature for rectangular geometry, demonstrating an improvement of approximately 50% for the cylindrical case. We further extend the analysis to noncylindrical configurations with V≠1 that correspond to stable liquid bridges when fully melted.