Investigation of the effect of thermal resistance on the performance of phase change materials

The thermal performance of a latent heat energy storage system utilising tightly fitted, thermally bonded and non-bonded metal inserts as a heat transfer enhancement material has been investigated. Two methods were used for this purpose. Firstly, a numerical study using volume averaging method was performed and secondly, an analytical study using scale analysis to obtain the theoretical prediction of the performance of the phase change material. Both models agreed with the experimental data in the literature. A further numeric-parametric study was performed to determine the effect of increasing the thermal resistance gap on the total melting/solidification time. It was observed that the storage performance (complete charge/discharge) asymptotically decreased as the gap grows in size and that convection was negligible when periodic structures are used. Generally, it can be concluded that having tightly inserted metal inserts in the storage improves the performance by about three times compared to a case with a 1 mm thermal resistance gap. Numerical results show that when a thermally adhesive glue is used to make ligaments touch the inner wall (thus eliminating the gap), an improvement of about 10% of heat transfer enhancement in charge/discharge is realised as compared to the case of a 1 mm thermal resistance gap.