Abstract

Thermal energy storage plays a crucial role in meeting human energy demands and is particularly essential for many solar energy applications. Among the various storage methods, phase change materials (PCMs) have attracted significant attention because their thermal performance can be greatly influenced by the material properties, physical characteristics, and the geometry of the encapsulating container. In this paper, the melting process of phase change materials (PCMs) within an elliptical enclosure using the finite volume method is analyzed. Gallium is selected as a PCM with a low Prandtl number. A physical model employing the enthalpy porosity formulation is elaborated to describe the coupling between natural convection and the melting process of PCMs. Numerical simulations are performed to examine the influence of the aspect ratio (n = b/a), ranging from 1 to 4, and inclination angles from 0° to 90° of the elliptical enclosure on the melting process. It has been found that the use of the elliptical capsule can reduce the melting process time. For a Rayleigh number of 106, the melting time decreases as the aspect ratio increases from 1 (circle) to 4. The horizontal orientation (θ = 0°) is found to be the most efficient, with a melting rate higher than that observed for inclined positions (30°, 45°, 60°, and 90°). For a low Rayleigh number of 104, the inclination angle has an imperceptible effect on the phase change. Empirical correlations are proposed to relate the Nusselt number to the Rayleigh number, with coefficients adapted to different Fourier numbers and geometric parameters.

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