Mixing enhancement in thermal energy storage molten salt tanks

An appropriate degree of mixing in molten salt tanks for Thermal Energy Storage (TES) in Concentrated Solar Power Plants (CSPPs) is required in order to ensure the safe operation of the tank. Otherwise, cooling due to thermal heat losses is prone to result in a high thermal stratification of the salts and eventually local solidification. In this work, the mixing performance of different configurations of ejectors is investigated by means of Computational Fluid Dynamics (CFD). A set of different ejector configurations has been resolved, modifying the number of ejectors, flow direction, and ejector angle. The best configurations are identified, where the highest fluid circulation capacity is achieved by 10 ejectors directing the jet flow in the tangential direction with an inclination angle of 0° with respect to the tank bottom surface. This is increasing the fluid circulation capacity of the tank by more than 100% with respect to the usual configuration implemented in such tanks (ejectors directed to the tank central vertical axis, at 30° angle). In addition, such configuration ensures an enhanced flow circulation in the bottom part of the tank (with an increase of more than 6 times in the flow velocity in the lower section of the tank), reducing the risk of local salt solidification due to heat loss through the bottom surface. However, the shortest mixing times (95% and 99%) are achieved by the configuration with 10 ejectors pumping flow towards the central tank axis with an inclination angle of 0°.