Experimental and numerical studies on molten salt migration in porous system with phase change

Abstract

Molten salt is promising high temperature heat transfer fluid, and its transport in porous media is an important problem for molten salt application. In this paper, molten salt migration and phase change in cold porous system packed with sand particles is experimentally and numerically studied. Experimental results show that high temperature molten salt continuously migrates and a transparent liquid molten salt layer appears during discharge stage with molten salt pouring into porous bed, and then it solidifies as white opaque solid block during post-discharge stage. A transient axial-symmetrical flow and heat transfer model is developed using volume of fluid model and linear approximation in mushy zone, and the simulated results very well fit with experiment. After molten salt discharges and contacts with the cold surface, a thin solid layer quickly forms for solidification, and then it gradually expands and finally becomes a solid block. Since the earlier solid layer hinders molten salt vertical flow, liquid molten salt will flow across the outer boundary of solid layer, and then molten salt layer below the surface becomes thicker. After molten salt totally solidifies, an inner region with little molten salt will probably exist inside molten salt solid block. The maximum migration region for molten salt in cold porous system is affected by structural and operating parameters. For larger porosity and particle diameter or higher molten salt temperature, molten salt flow in porous system has less flow resistance, and then the maximum migration height can be increased, while the migration diameter is reduced.