A novel integrated computational framework for optimizing fin-enhanced triplex-tube latent thermal energy storage

Slow heat transfer in latent thermal energy storage can limit thermal performance, encouraging designs that increase heat transfer with minimal loss in storage capacity. This study identifies a fin configuration for a horizontal triplex-tube latent thermal energy storage operating under simultaneous charge and discharge, while balancing heat transfer rate, liquid fraction, and stored energy. A hybrid framework combining computational modelling with multi-criteria decision-making evaluates direct and indirect rectangular fins in an outer-tube charge and inner-tube discharge arrangement, varying fin number, placement, and length. Three ranking methods (TOPSIS, PROBID, and PROMETHEE II) and three weighting schemes (entropy, analytic hierarchy process, and equal weighting) are used on steady-state criteria. Vertical direct fins increase heat transfer rate from 0.148 to 0.802 kW, with only small reductions in liquid fraction (1.91%) and stored energy (3.12%). Indirect fins provide additional gains, but performance depends on tube location and angle i.e. for the charge tube, benefits occur up to 45° from vertical, whereas for the discharge tube, fins can be applied up to 75° from vertical without noticeably impeding buoyancy-driven motion of the phase change material. A mixed-length approach is preferred, with longer indirect fins near the vertical axis on the charge tube and shorter fins on the discharge tube. The optimal design achieves a heat transfer rate of 0.844 kW, a liquid fraction of 0.916, and stored energy of 0.402 kWh, under steady state simultaneous charge and discharge operation, offering practical guidance for manufacturable finned triplex-tube latent thermal energy systems.