No fins attached? Numerical analysis of internal–external fins coupled PCM melting for solar applications

Abstract

Thermal energy storage/sink is imperative for any type of solar energy harnessing system/technology. However, the inevitable challenge remains in developing and optimizing a thermal energy storage (TES) system suitable for long cyclic operation. This work numerically analyses the melting characteristics of phase change material (PCM; RT42)-based latent thermal energy storage (LTES) as a two-dimensional rectangular enclosure. The consequence of utilizing internal–external extended surfaces (fins) with realistic convective boundary condition is studied for photovoltaic thermal (PVT) applications. The application of internal–external fins is intended for enhancing the charging (melting) duration according to the long cyclic solar operation and better dissipation of heat after complete melting. Three kind of fins-rectangular, triangular, and Y-type- are investigated for two orientations of storage/sink enclosures-upright ( θ = 90°) and inclined ( θ = 35°). Moreover, three fin configurations are analyzed-equal, decreasing and increasing-stepped-based on the arrangement of fins along the enclosure height. Two-dimensional, transient numerical simulations are conducted for governing PCM melting, contemplating the consequences of natural convection. The performance assessment of each storage unit (orientation/fin-type/fin-arrangement) is made based on parameters such as time enhancement ratio, suppression ratio, liquid fraction, temperature distribution, melt velocity magnitude, storage capacity/rate, and enhancement in Nusselt number. The melting is delayed for triangular and Y-fins enclosures as compared to that for rectangular fins. Equal and increasing-stepped Y-fin arrangements yielded the largest time enhancement ratios of 42.38% and 29.86% for inclined and upright enclosures, respectively. Moreover, Y-fins-based enclosure produced a larger average suppression ratio as compared to other types of fins. A 2.56, 2.67, and 2.64 times enhancement in Nusselt number is observed for increasing-stepped fin arrangement of rectangular, triangular, and Y-finned upright enclosures, respectively. However, for the inclined enclosure, a 2.32 times enhancement in Nusselt number is reported for increasing-stepped Y-fin. • Internal–external fin-coupled thermal storage for cyclic solar PVT applications. • Utilization of rectangular, triangular, and Y-fins in augmenting PCM melting. • Assessment of 3 configurations/fin-immersions for intensifying convection currents. • Effect of cavity inclination on melting characteristics for long duty operation. • Maximum 2.67 times Nusselt number enhancement for increasing triangular fin.