Experimental and numerical investigation on composite fins with different volumetric ratios in a shell-and-tube solar latent heat thermal energy storage device

Enhancing the thermal storage performance of shell-and-tube solar latent heat thermal energy storage (LHTES) devices is crucial for achieving efficient utilization of thermal energy in solar heating systems. However, their performance is limited by the inherently low thermal conductivity of phase change materials (PCM). To address this issue, the present study focuses on composite fins integrated into a shell-and-tube LHTES device. By combining experimental and numerical methods, a comparative investigation is first carried out among annular fins, longitudinal fins, and composite fins with the same fin volume. Subsequently, two approaches, referred to as number variation and dimension variation, are employed to systematically examine how different volumetric ratios of annular and longitudinal fins within the composite configuration affect the melting performance of the device. The results demonstrate that, compared with configurations using only annular fins or longitudinal fins, composite fins provide a more uniform axial temperature distribution, accelerate the melting process of the PCM, and improve both the heat storage rate and the thermal response rate. For number variation of composite fins, the LHTES device exhibits better performance when the volumetric ratios of annular and longitudinal fins are both 50%. For dimension variation, favorable performance is observed when the volumetric ratios are 37.5% and 62.5%. Furthermore, comparison of the two approaches shows that when the volumetric ratio of annular fins is below 50%, dimension variation performs better, whereas when it exceeds 50%, number variation becomes more advantageous. Within the scope of conditions considered in this study, under dimension variation with a volumetric ratio of annular fins of 37.5%, the LHTES device achieves optimal performance. Compared with the better-performing volumetric ratio obtained under number variation, the complete melting time is shortened by 6.75%, while the heat storage rate and thermal response rate are increased by 7.60% and 7.14%, respectively.