Investigation and optimization of Shell-and-tube thermal energy storage unit with biomimetic leaf-vein fins and carbon nanotubes for superior PCM efficiency

This study investigates the performance of a PCM (Phase Change Material) shell-and-tube heat exchanger enhanced with leaf vein-inspired fins and multi-walled carbon nanotubes (MWCNTs). Given the increasing demand for efficient thermal energy storage (TES) systems, which are often limited by slow thermal response and low thermal conductivity, we explore the integration of these design innovations to enhance heat transfer rates. The analysis compares four configurations without MWCNTs and four with MWCNTs, varying in fin thickness and angles. Key performance metrics, including temperature distribution, liquid fraction, and natural convection phenomena, velocity contours, sensible and total heat storage, and mean heat storage rates, were evaluated. The geometrical parameters (Length, width and Angle) of the storage unit are optimized utilizing the Box-Behnken designs (BBD) with response surface method (RSM). The significance of geometric parameters namely fins length, fin width and fin angle on the heat release time of Latent Heat Thermal Energy Storage (LHTES) are scrutinized, and corresponding quadratic equation is fitted. The function of the optimized target variable melting time on each factor is fitted and it is noted that with increasing the fins length and width of angle has a significant impact on the optimized target (melting time). Findings reveal that Case 03 with MWCNTs, featuring the thickest fins, achieves the shortest melting time of 1040 s, reflecting a time-saving of 58.06 %. This case also exhibits the highest mean heat storage rate of 437.903 W, representing a 123 % increase compared to the base case without fins or MWCNTs. Additionally, Case 01 with MWCNTs shows the highest sensible heat storage of 61.46 KJ and total heat storage of 490.9 KJ, whereas Case 01 without MWCNTs has total heat storage of 490.11 KJ. The inclusion of MWCNTs consistently enhances heat storage rates across all configurations, demonstrating the potential of optimized fin design and MWCNT integration to improve the thermal performance of PCM-based heat exchangers.