Fabrication and thermal performance of high conductive ceramic PCM capsule for solar thermal energy storage applications

Latent heat storage system consists of salt based PCMs (phase change materials) is one of the promising alternatives to sensible heat storage systems in concentrating solar power (CSP) plants, because of their cost effectiveness and high storage capacity. However, the low heat transfer rate and high corrosivity have limited their applications. In this study, a novel high conductive ceramic capsule has been developed by macro-encapsulation of PCM for packed bed thermal energy storage (TES) systems. Major challenges associated with this system are encapsulation technique to build a stable and long-lasting capsule and the evaluation of heat transfer characteristics during phase change process. To conduct a comprehensive heat transfer analysis, a numerical model has been developed. The phase change characteristics, including melting-front, of the capsule during phase change process have been analyzed experimentally and numerically. The model has been validated by comparing with the experimental data, including visualization. The influences of Reynolds, Stefan and Grashof number on the concurrent conduction and convection, melting dynamics and latent heat storage performance of the capsule have been examined, to obtain how far the thermal performance of the capsule is influenced by operating and geometrical parameters. It has been noticed that increasing the Stefan number (0.089–0.282) enhances the heat transfer, accordingly decreases the full melting time around 64 %. Ultimately, a dimensionless analysis has been conducted and generalized correlations for melt faction and Nusselt number have been derived from the combination of Stefan, Fourier, Reynolds and Grashof numbers.