Investigation of molten salts incorporated with anodic aluminum oxide as thermal energy storage fluid on heat transfer efficiency

The aim of this research is to investigate mass and heat transfer of anodic aluminum oxide in packed-bed thermocline vessel with molten salt system (5% Lithium, 20% sodium, 50% potassium and 25% calcium). According to the computational fluid dynamic simulation, the ceramic ball that is packed inside the vessel does not have a significant impact on the mass transfer of anodic aluminum oxide in the molten salt system. Heat storage performance testing was conducted in a thermocline vessel (packed-bed zone 0.7 m in length and 0.3 m diameter) and molten salt flow rate between the ranges of 0.5–0.7 m3/h. Two different molten salt systems were studied including a normal molten salt system and a molten salt system with 0.5 wt% anodic aluminum oxide. An increase in molten salt flow rate have a positive impact on heat transfer inside the vessel due to the increase in turbulence of the flow. A decrease in charging time from 3.75 h to 3.5 h was observed for molten salt with 0.5 wt% anodic aluminum oxide. A seven-cycle charge/discharge test revealed that addition of 0.5 wt% anodic aluminum oxide resulted in a smaller reduction in heat transfer efficiency and actual energy storage. Heat storage decreased from 20.42 to 19.54 MJ corresponding heat transfer efficiency of only 87 to 85% for molten salt system consisting of anodic aluminum oxide.