Harnessing off-peak renewable electricity via resistive heating in solar salt based latent heat storage: Performance enhancement through fins and shell configurations

Abstract

Phase change material based thermal energy storage is a better choice due to its high energy density and charging and discharging occur at nearly constant temperature. In the present study, solar salt (60 % NaNO₃ + 40 % KNO₃) is considered as the storage media. Various passive performance enhancement techniques are analyzed by attaching fins (rectangular, triangular, and T-shaped fins) and grooves (circular, triangular, and square grooves) on the shell side for charging of the storage media. To quantitatively assess the impact of fins and shell configurations on the performance of latent heat storage system, complete melting time, maximum rise in phase change material temperature, and the portion of total energy utilized for the phase change are used as performance evaluation indexes. In particular, focus is given to justify the contribution of the average circulation velocity of phase change material to melting rate. The results indicate that fins significantly reduce both the melting time and the maximum temperature rise in the PCM domain as compared to various shell configurations. In comparison with all studied configurations, rectangular fin with 3.81 cm radial length have maximum reduction in melting time of 7.4 % and triangular fin with 3.81 cm radial length have a maximum reduction in temperature rise of 33 K. The study shows that increasing fin radial length enhances charging performance. Although melting starts earlier in the base configuration, fins complete melting faster by distributing heat inward. Raising the heat flux from 0.5 kW/m² to 14 kW/m² shortened the charging time by 21.8 times but also caused significant superheating, increasing the local maximum temperature of the phase change material from 512 K to 723 K, with the proportion of superheated energy rising from 2.8 % to 22.9 % of the total heat input.