Melting of PCM-graphite foam composites with contact thermal resistance: Pore-scale simulation

Abstract

Latent heat energy storage systems have emerged as a solution to intermittency and instability in renewable energy sources, the phase transition of phase change materials (PCMs) within these systems is hindered by their poor thermal conductivity. Graphite foam, renowned for its superior thermal properties, stands as an ideal choice to improve the melting efficiency of PCMs. In the current study, the melting behavior of PCM-graphite foam composites is simulated by the pore-scale numerical simulation (PNS) by employing cubic idealized cells with spherical pores and cylindrical channels. The computed results demonstrate that the porosity and contact thermal resistance of graphite foam are key factors affecting the melting efficiency of PCMs. The full melting time (FMT) of PCMs increases with porosity, achieving a 53.1 % improvement as porosity decreases from 0.90 to 0.75. In addition, the absence of natural convection markedly diminishes the maximum melting rate of PCM, reducing it by 33.5 % to 50.3 % for porosity from 0.75 to 0.90. Notably, it needs to be emphasized that the melting rate of PCM is significantly reduced when the contact thermal resistance surpasses 1.0 × 10–4 m2·K·W−1. Compared to the idealized condition without contact thermal resistance, the dimensionless FMTs for porosities of 0.75, 0.80, 0.85, and 0.90 extend by 27.3 %, 27.1 %, 22.2 % and 23.9 % for a contact thermal resistance of 5.0 × 10–4 m2·K·W−1, respectively.