CFD analysis of a thermal storage tank driven by natural convection
Abstract
This work addresses a numerical research on a concept of thermal energy storage tank by natural convection. The design of the tank comprises a single reservoir with molten salt and two indirect heat exchangers (thermal oil to molten salt) inside. For discharging, cold thermal oil circulates in the heat exchanger located at the top of the tank, and due to natural convection, the cooled molten salt moves to the bottom of the tank through an adiabatic channel. For charging, the hot thermal oil circulates through the bottom heat exchanger, heating the molten salt and causing it to move up through a second channel. To analyze this concept, a two-dimensional computational fluid dynamics (CFD) model is developed and used to investigate the storage system for different discharge and charge conditions of the heat exchangers. The mass flow rate of the molten salt in the channels, inlet and outlet temperatures of the heat exchangers, and temperature and velocity distribution in the tank are analyzed for different imposed resistance of the flow and discharge/charge rate of the heat exchangers. As main results, the pattern of the mass flow rate of the molten salt in the channels are identified, and its magnitude depends on the design of the heat exchanger, temperature, and heat sink/source. The evolution of the inlet and outlet temperature in the heat exchangers are key indicators to identify the discharge and charge duration of the thermal storage tank and assessing its potential to work as a thermocline system.