The growth in renewable energy generation highlights a demand for an effective energy storage system for future power grid. Energy storage systems have a crucial role in balancing the power grid and compensating for intermittency of renewable energy sources. The state-of-the-art of grid-scale energy storage technologies (e.g., pumped-hydro and conventional compressed air energy storage) require special topological considerations; however, thermal energy storage remains as a scalable technology for storing the energy from solar thermal plans and the power grid. In this paper elemental sulfur is further investigated as a storage medium for its driving low cost and high energy storage density capabilities. Presented work numerically investigates the heat transfer behavior between elemental sulfur and an internal heat source that is placed within the thermal energy storage element. The heat transfer from the internal heat source to the thermal storage medium (elemental sulfur) is investigated computationally to understand the heat transfer behavior during charge cycle. The computations were performed with a commercial CFD package (ANSYS FLUENT) using variable properties for the storage medium. A comprehensive grid refinement study was performed to ensure the accuracy of the computational results. The results of this study show that buoyancy-driven flow induced by the internal heat source forms a rising jet toward the top of the thermal energy storage element and enhances the mixing of the boundary layer leading to enhanced heat transfer from the internal heat source.

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