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Sodium receiver designs for integration with high temperature power cycles

Conroy, Tim, Collins, Maurice N., Grimes, Ronan
Energy 2019
geometry, heat exchangers, heat transfer, power plants, sodium, superalloys, temperature
A variety of tube materials and geometries are considered in an analysis that identifies suitable sodium receiver designs for integration with next-generation thermodynamic power cycles. Sodium is capable of delivering outlet temperatures of >750∘C, however the net power output diminishes with rising temperatures due to tube material limitations on allowable flux density and increasing heat losses. Small tube diameters facilitate large thermal efficiencies and heat fluxes for all materials, however a large pressure drop penalty can somewhat mitigate these advantages. Traditional heat exchanger alloys perform quite poorly in comparison to Inconel 617 and Haynes 230, with allowable heat flux decreasing significantly as temperatures are increased beyond 600∘C. Multi-pass concepts offer greater control of flow-path exposure to the heat flux boundary condition than straightforward single-pass designs. A triple-panel design with small diameter Inconel 617 tubes balances thermal, hydraulic, and mechanical performance most effectively across all temperatures. For all candidate materials, sodium can augment power plant efficiency when integrated with a high temperature cycle (>600∘C). A combined receiver and power cycle efficiency percentage point improvement of 1.5% is possible using Ni-based superalloys at ∼650−700∘C compared to a baseline outlet temperature of 550∘C, resulting in a solar-to-electric power output increase of over 4%.