Solar-driven melting dynamics in a shell and tube thermal energy store: A numerical analysis

© 2022 Elsevier LtdThe numerical modeling of solar-driven melting in a shell-and-tube accumulator using paraffin RT70HC as PCM is presented. The coupling between an array of evacuated-tube solar collectors and the TES system is implemented in ANSYS Fluent, allowing for the proper evaluation of the time-dependent heat transfer fluid inlet temperature. A simplification of the TES geometry to a 2D section is accomplished, and an algorithm for the continuous evaluation of the heat transfer fluid temperature across the tubes in a serpentine-type configuration is developed. Validation with experimental results obtained in an outdoor test rig is carried out in terms of PCM temperature evolution. The model provides simulation results in a realistic configuration to be used in low-temperature applications of thermal energy storage for the residential sector. Energy performance is discussed, and the influence of the physics of melting and buoyancy forces leading to stratification are also analyzed, using temperature and liquid fraction contours during the solar irradiance cycle. The numerical results confirmed that natural convection plays an important role during melting of PCM: the motion of the melting front from the bottom to the top of the accumulator is described. Moreover, the results show that an increase of 50% of the solar surface improves the thermal storage by 28.8%, while doubling the solar surface increases the stored energy by 46.2%.