A comparative analysis on charging performance of triplex-tube heat exchanger under various configurations of composite phase change material

In present work, the melting performance of triplex-tube latent heat thermal energy storage (LHTES) unit was numerically studied using equal volumes of PCM and metal foam composite PCM (CPCM) in various arrangements. For the n-eicosane (as PCM), the study was conducted at the fixed Rayleigh number (Ra) = 4.08x107, Prandtl number (Pr) = 62.9, and Stefan number (Ste) = 0.14. The results showed that positioning the metal foam on the bottom side and distributing segmented CPCM with alternating PCM zones effectively improved the system performance. Moreover, this also prevents the overheating of thermal layers in the LHTES unit. While the model labelled M2 exhibited the highest economic efficiency among all isotropic models, its low dimensionless thermal energy storage (TES) density (i.e., q' - 0.6) led this study to focus on models falling under the category having a TES density of - 0.8. Compared to a pure PCM model, the configurations under equal volume ratio category demonstrated up to - four times higher TES rate (p') and the significant reduction of - 75 % in melting time. The optimized isotropic model achieved the highest TES rate per unit cost with peak value of - 3 at a price ratio (N) of 1. Lastly, the testing of metal foam anisotropy on the chosen design showed a substantial increase in melting/heat storage rates. The largest drop of - 33 % in the total melting time was noticed for model M2 as compared to isotropic case.