A comprehensive parametric investigation on the fluid flow and heat transfer in a Latent-heat based energy storage/release system is explored for the axisymmetric melting and solidification process inside an encapsulated spherical container of 10, 20, 30 and 40mm in diameter. A numerical solution is developed using the finite-volume method and the enthalpy-porosity technique to solve Navier–Stokes and energy equations for natural convection coupled to a solid-liquid phase change. The study focused on Phase Change Materials (PCMs) with a melting temperature lying in the practical range of operation of concentrated solar thermal power generation (573.15K to 673.15K). Numerical calculations are performed in order to compute the evolution of the melting front and the velocity and temperature fields for different Grashof, Stefan and Fourier numbers. Also the effect of different metal coating materials subjected to a uniform wall temperature from 5K to 11K above the mean melting temperature of the PCM is presented. Simulation results show that a recirculating vortex is formed between the top region of the solid phase and the inner wall of the capsule that causes a more intense melting process in the upper part of the solid phase compared to the bottom region. The location of the eye of the recirculation pattern is observed to be dependent on the Grashof number and moves toward the unmelted portion of the PCM as natural convection is intensified.

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