This study aims to investigate how inner-tube cross-sectional geometry and radial-fin number interact to influence phase change material (PCM) charging in a shell-and-tube latent heat thermal energy storage system. The objective is to distinguish the individual and combined effects of these two design variables under controlled geometric and operating conditions. The comparison is performed at equal heat-transfer-fluid (HTF) flow area and fixed shell dimensions; the resulting wetted-perimeter and active-PCM-volume differences are reported explicitly.
A three-dimensional transient CFD model based on the enthalpy–porosity method was developed using temperature-dependent PCM properties. Circular, square and triangular inner tubes were combined with zero, four, six and eight radial fins. All configurations were compared under identical operating conditions and equivalent HTF flow area. The numerical model was supported by grid-independence analysis and validation against experimental charging data for the reference configuration. Additional time-step, mushy-zone-constant and liquid-fraction-threshold checks were implemented to assess numerical robustness.
The interaction between tube shape and fin number was not monotonic. At 6,000 s, the liquid-fraction difference between triangular and circular tubes increased from 0.116 without fins to 0.145 with four fins, then decreased to 0.085 with eight fins, indicating reduced geometry sensitivity at high fin density. The triangular eight-fin case achieved the shortest effective melting time of 5,875 s, 62.1% below the unfinned circular reference.
Unlike many previous comparisons where tube geometry and fin characteristics are altered simultaneously, this work establishes a controlled geometry–fin matrix to separate and quantify their individual and coupled effects. The results reveal how increasing fin density changes the relative importance of tube geometry and allow charging enhancement to be interpreted alongside PCM displacement and added fin material. The analysis distinguishes response speed, stored energy, energy density, mean storage power and copper-mass effectiveness, so the preferred design depends on the stated objective.
