Evaluation and comparison of heat transfer enhancement in a new design of a multi-tube finned heat exchanger containing phase change material with different tube and fin arrangements

The incorporation of fins and the application of multi-tube configurations in phase change materials (PCMs) are recognized as effective strategies for augmenting heat exchange with heat transfer fluids (HTF). The optimal arrangement of fins is essential for achieving high efficiency in latent heat thermal energy storage (LHTES) system design. The objective of this research is to identify the most effective fin arrangement and quantity, as well as the optimal number of middle tubes, to improve the charging performance of a multi-tube heat exchanger (MTHE). As the working fluid, water circulates inside the middle and outer tubes, whereas the space between them is filled with RT35 acting as the PCM. To assess the influence of middle tube quantity on the melting dynamics, the middle tube is split into two, three, and four sub-tubes, at fixed PCM quantity and HTF mass flow rate. The melting process of the PCM was modeled using the enthalpy-porosity formulation, incorporating natural convection within a bidimensional framework. Numerical simulations were carried out in ANSYS Fluent using the finite volume technique. The results were validated against previously published studies. The effects of adding varying quantities of inward, outward, and combined inward-outward fins to MTHE designs on the heat exchange process, melting dynamics, and melting time were systematically examined. The findings reveal that adding fins substantially improves the heat transfer rate, leads to a more even temperature distribution between the middle tubes, and results in faster melting than when fins are absent. Significantly, the combined fin arrangement produced the highest efficiency, resulting in melting time reductions of 35.44%, 30.98%, 40.32%, and 29.81% for the single-tube (A), double-tube (B), three-tube (C), and four-tube (D) designs, respectively.