The effect of turbulent natural convection in vertical storage tubes containing a supercritical fluid is investigated computationally. In a supercritical thermal storage system, thermal energy is transferred to the storage fluid and is stored as the internal energy of the fluid in supercritical state. The heat is conducted from the heat transfer fluid to the storage fluid through the storage tube wall. Unlike phase-change systems, the heat transfer mechanism within the storage tubes of supercritical thermal storage system is dominantly affected by rigorous turbulent natural convection. The natural convection enhances the heat transfer and compensates for the low thermal conductivity of the storage fluid. The turbulent buoyancy-driven flow field in vertical storage tubes with different aspect ratios is investigated in this paper and the effect of vertical orientation of storage tubes on the characteristics of the flow field is explored. A standard k-epsilon method is utilized to model the Reynolds stresses in turbulent natural convection flow. The results of this study show that the turbulent buoyancy-driven flow and natural convection play an important role in charge and discharge of the supercritical thermal storage system. The charge time of the system is a function of Rayleigh number and aspect ratio of the storage tube.

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