Estimation of thermal performance and design optimization of finned multitube latent heat thermal energy storage

This paper presents the effectiveness of finned multi-tube latent heat thermal energy storage system (LHTES) for medium temperature (∼200 °C) solar thermal power plant in reducing the fluctuations in heat transfer fluid (HTF) temperature caused due to the intermittent solar radiation. Commercially available phase change material (PCM) of melting temperature 168.7 °C is used as the storage material in the shell of LHTES, whereas a thermic oil based HTF passes through the tubes. Majority of the available PCMs have very low thermal conductivity (∼0.2-0.5 W/m.K), which drastically affects the thermal performance of the thermal storage system. Hence, in this study, thermal conductivity enhancer (TCE) in the form of fin is used to enhance heat transfer in the PCM. The fluid flow and heat transfer behaviour latent heat thermal energy storage system in the LHTES is studied by using a numerical model coupled with the enthalpy technique to account for the phase change process in the PCM. The developed numerical model, which is validated with the lab-scale experimental setup, is used to investigate the effect of number of fin, fin thickness and fin height on the HTF temperature at the outlet of the storage system. It is found that the number of fins and fin thickness significantly affect the thermal performance of the storage system, whereas the enhancement in heat transfer for high thermal conductivity material fin is marginal. Further, optimization of LHTES is performed for a defined objective function to identify the best configuration.