Melting and solidification characteristics of a semi-rotational eccentric tube horizontal latent heat thermal energy storage

Abstract

• Effect of eccentricity was investigated for the latent heat thermal energy storage. • Bottom eccentricity significantly improved the melting process. • Top eccentricity showed the potential to enhance the solidification process. • A novel semi-rotation of the storage system was proposed. • An optimum eccentricity was justified, and key parameters were investigated. Research showed that bottom eccentricity improved the melting performance in the horizontal shell-and-tube latent heat thermal energy storage (LHTES) system. However, it largely reduced the solidification performance. To solve this problem, this study investigated the effects of different eccentric positions of the inner heat transfer fluid (HTF) tube on the thermal performance of a horizontal shell-and-tube LHTES system during the melting and solidification processes. A novel technique with the intermittent rotation of the LHTES device was proposed to take the advantage of eccentric tube configurations for enhancing both the melting process during charging and the solidification process during discharging. Numerical simulations were conducted and validated in the FLUENT application of ANSYS software by utilizing the enthalpy-porosity method. Liquid fraction, average temperature, energy storage rate, and velocity distribution were used to evaluate the LHTES system thermal performance. Results showed that the bottom eccentricity significantly improved the melting process, however, it slowed down the solidification process. But the further study found that the top eccentricity could enhance the solidification process. Based on the average energy storage rate, the optimum bottom eccentricity laid between 0.60 and 0.75 for the charging process, which improved the melting rate by 64–74%. However, the optimal top eccentricity was between −0.15 and −0.30 for the discharging process. The proposed novel rotational technique well adapted the bottom eccentricity to improve the melting process during charging and the top eccentricity to enhance the solidification process during discharging. It was found that an optimal eccentricity of 0.30 could well tradeoff between the bottom eccentricity for charging and top eccentricity for discharging process in the proposed approach. Both the HTF cooling temperature and shell-to-tube radius ratio did not show a significant impact on the optimal eccentricity of the LHTES system.