Enhancement of the charging and discharging performance of a vertical latent heat thermal energy storage unit via conical shell design

Abstract

Adopting phase change materials (PCMs), the latent heat thermal energy storage (LHTES) technology provides a potential solution to solve the fluctuation and instability of solar energy utilization. However, its applicability is strictly limited by the poor thermal conductivity of PCM. In this study, a novel shell structure of the LHTES unit was designed and optimized to enhance the charging and discharging performance. Verified by experimental data, a three-dimensional computational model considering the effect of natural convection based on the enthalpy-porosity method is established to simulate the melting and solidification processes of PCM. The results reveal that the melting time decreases with the increase of R/r (the ratio of the upper radius to the lower one of LHTES unit) until a nearly constant value is reached, while the solidification time first decreases and then increases. An optimum conical shell design was obtained based on the summation of melting and solidification time, which is independent on the inlet velocity and temperature of the heat transfer fluid (HTF). Although the deviation of heat stored or released varies little among different designs, significant reduction in the charging and discharging time is observed for the LHTES unit with the optimum conical shell if compared with the cylindrical shell under the same heat transfer area and PCM usage.