Coupled parameters evaluation of three different finned structures for concentrated solar thermal energy storage

The main objective of this study is to improve the heat transfer of three cylindrical shell and tube exchangers including a novel honeycomb based finned structure, which is then compared to other finned structures (circular and longitudinal) for different thicknesses. This comparison is important in order to evaluate the honeycomb finned structure, however, to provide a reasonable comparison the PCM volume was kept constant for the three finned geometries compared at each thickness. For this reason, a 3D numerical model is performed using the COMSOL Multiphysics software, which is based on the FEM. Sodium Nitrite/Nitrate (NaNO2-NaNO3) is used as PCM and DelcoTerm is used as heat transfer fluid (HTF). The effect of thickness and number of fins for the three geometries was studied. However, most studies neglect the impact of the PCM volume, thus the methodology adopted in this work includes a coupled parametric combination of the number and thickness of the fins for three different fin structures. The results of this study have shown that the longitudinal finned geometry provided the shortest melting time for the configuration with a fin thickness of 1 mm. On the other hand, the evaluation of the fin thickness shows that even when keeping the same fins volume, the thickness still has a significant effect on the thermal performance of the units studied, where it can decrease the melting time around 3.6% for the circular geometry, 4.3% for the longitudinal geometry and 9.6% for hexagonal geometry.