Heat transfer enhancement in shell and tube Latent Heat Thermal Energy Storage units for waste heat recovery applications: A 3D numerical study on melting–solidification kinetics

This study presents a novel three-dimensional (3D) numerical investigation of a finned diamond-shaped multi-tube latent heat thermal energy storage (LHTES) unit for low-temperature industrial waste heat recovery applications. Unlike existing studies that rely on simplified two-dimensional (2D) simulations and square shaped tubes geometry, this work introduces an innovative diamond-shaped tube configuration with longitudinal fins, enhancing both melting and solidification dynamics. The proposed heat storage unit is compared at iso-volume of PCM to a finless multi-tube unit, considered a reference case. Using erythritol as phase change material (PCM) and Hytherm 600 as heat transfer fluid (HTF), the study demonstrates that the proposed design achieves reductions of 24.5 % and 45.5 % in the melting and solidification times, respectively, compared to a finless reference case. Additionally, the influence of axial temperature gradients and Reynolds number variations on phase change dynamics is thoroughly examined, revealing non-negligible three-dimensional effects and significant improvements in heat transfer performance. The axial temperature gradient in the tubes and the tridimensionality effect involved influence phase change dynamics with a difference exceeding 17 % and 16.36 % in melting and solidification, respectively. Moreover, the Reynolds number effect is more significant during the melting process and for the enhanced configuration. Up to 14 % and 8 % reductions in melting and solidification times is achieved for the improved configuration, compared with 12.1 % and only 3 % for the reference case when the Reynolds number was increased from 1000 to 2000.