Inorganic salts (e.g., chloride salts) have gained attention in the energy field as a new thermal energy storage medium. Low cost, high melting temperature and high heat capacity of inorganic salts make them attractive in utility-scale thermal storage applications as higher energy storage temperatures lead to higher efficiency in power generation. There is a potential to use the dry byproduct of water desalination, i.e., Reverse Osmosis Concentrate (ROC) as a thermal storage medium. Using ROC as a thermal energy storage medium would prevent a harmful waste to be released to the environment while introducing a novel and low-cost alternative for thermal energy storage medium. In this study, heat transfer behavior of an ROC-based thermal energy storage system is studied using CFD. A computational model is developed, verified, and validated to simulate the phase change process and buoyancy-driven flow in a square ROC-based thermal energy storage element. The computational results provide a predictive model for charge and discharge cycles of an ROC-based thermal energy storage system.