Study of Coherent Structures of Turbulence in Flows with Wall Heat Flux in Supercritical Fluids

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Proposed advanced designs for power-generation plants with improved thermal efficiency and reduced size include configurations with supercritical working fluids, such as nuclear reactors utilizing supercritical water as the coolant for the nuclear core and Brayton cycles utilizing supercritical working fluids in a closed-cycle configuration. The success of such advanced power plants is dependent on our ability to accurately predict the rate of heat transfer in certain components of the power plant. There is experimental evidence that for certain combinations of heat and mass fluxes in supercritical fluid flows in heated channels, the measured rate of forced-convection heat transfer notably deviates from those predicted by existing correlations that are based on single-phase subcritical fluids. The proposed study aims to improve our fundamental understanding of the role of flow turbulence in these observed variations in the heat-transfer rate. The study makes use of direct numerical simulations - solution of the governing equations of fluid dynamics without any assumptions on turbulence motion - on clusters of computers supplemented by experimental measurements in a supercritical refrigerant (R134a) and supercritical water. The study includes systematic variations in parameters known to affect shear-layer turbulence, such as streamwise pressure gradient and flow Reynolds number.