This study examined the heat characteristics of a vertical shell-tube thermal storage system with phase change materials. A three-dimensional finite volume method involving an interface mesh was employed to reduce the computational time. The regime of the heat transfer flow was laminar based on the heat transfer fluid flow regime. The numerical method was first validated against data obtained from the literature, and a Mushy coefficient of 105 was found to yield accurate results. Furthermore, the effects of a continuous porous medium with varying porosity and locally porous media in three different zones of the phase change system on related parameters of the phase changing process were investigated. These parameters include temperature changes, the solid-liquid interface, the distribution of the liquid fraction, and the total melting time of the phase change materials. It was found that as the porosity decreased, it was possible to reduce the melting time by up to 82%. Furthermore, using the middle part of the phase change material as a porous zone led to an increase in temperature gradient and a reduction in the resistance of the PCM to melting, which eventually increased the rate of phase change.

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