Numerical optimization of a finned cavity latent thermal energy storage enclosure for solar power production

Abstract

The utilization of thermal solar energy has significantly increased in recent times. However, due to the daily temporal nature of solar irradiation, which is affected by, for instance, cloud coverage, efficient thermal energy storage (TES) techniques are needed. Latent heat energy storage using phase change materials (PCMs) is a promising technology for concentrated solar power (CSP), but due to the low thermal conductivity of many PCMs, careful geometric design is required to sustain acceptable energy charging and discharging rates. In this numerical investigation the heat transfer rate in a latent heat thermal energy storage enclosure containing sodium nitrate PCM and horizontal high-conductive aluminium plate fins was considered. An enthalpy-porosity technique was used to model the phase change process in a two-dimensional domain while also considering buoyancy driven flow. The influence of the fin pitch on the heat rate during energy discharge, when the PCM solidifies, was studied. The width of the enclosure and the thickness of the fins relative to the enclosure volume was kept constant. Two thermal boundary condition cases were investigated, being, when the outer wall was 10 K and 5 K colder than the phase change temperature. The results revealed a definite optimum fin pitch exist when the wall temperature is 10 K colder than the phase change temperature.