CFD Investigation of Fin Design Influence on Phase Change Material Melting for Solar Thermal Energy Storage

Abstract

In this study, an investigation was conducted on four distinct configurations, designated as Case-1, Case-2, Case-3, and Case-4, focusing on parametric analysis. Each configuration features a cylindrical enclosure containing pure Gallium, a phase change material (PCM). The solid-to-liquid phase transition of the encapsulated material was examined using a 2D CFD methodology. Additionally, the effect of applying three temperatures, T1=32∘C, T2=39∘C, and T3=42∘C, along the generator of the enclosure, with or without fins, was also studied. To accurately model the melting process of the PCM, the Enthalpy- Porosity Method was employed, and meticulous detailing of underlying assumptions was under- taken to ensure precise representation. The validation process involved comparing outcomes of the physical solidification/melting model with reference data from a state-of-the-art study. The specific cases comprised Case-1 - a slender finless cylinder; Case-2 - a thin finned cylinder (l=10mm, t=0.6mm); Case-3 - featuring larger fins (l=20mm, t=0.6mm); and Case-4 - incorporating the largest fins (l=30mm, t=0.6mm). Strategically incorporating thin fins accelerates Gallium melting significantly, reducing times by up to 89%. This enhancement is driven by a 96% increase in the heat transfer coefficient (h), leading to faster melting rates. In addition, fins boost the Nusselt number (Nu) by 91%, indicating improved convective heat transfer and enhanced melting. Melting rates increase by around 30%, notably in Case-3. Temperature T1 shifts dominant heat transfer from convection to conduction, as seen in 2D CFD contours with stratified patterns in Case-3 at t=240s and Case-4 at t=240s and t=300s. A localized cold spot at t = 300s in Case-4 signals localized heat transfer effects.