Assessment on heat transfer deterioration to supercritical carbon dioxide in upward flows via large eddy simulation

The direct numerical simulation (DNS) of supercritical carbon dioxide flowing in heated circular tubes by Bae et al. [Phys. Fluids, 2005, 17: 105104] is reproduced by the present large eddy simulation (LES). Cases of forced convection and mixed convection of upward flows in different-diameter tubes are considered, which were also re-run by Nemati et al. [Int. J. Heat Mass Transfer, 2015, 83: 741-752] and Chu et al. [J. Nucl. Eng. Raidat. Sci., 2016, 2: 031019] using DNS technology. Heat transfer deterioration and recovery are well captured in the simulation. The wall temperature predicted by current work shows excellent consistency with those DNS data, even lower than deviations among them. Buoyancy effect, mean flow characteristics and turbulence statistics are comparatively analyzed for the mixed-convection cases. For upward flow in the 1-mm tube, the turbulence kinetic energy and Reynolds stresses are continuously reduced along the tube, where heat transfer is inhibited by buoyancy. For upward flow in the 2-mm tube, the mean velocity profile distorts to an M-shaped distribution in the downstream of the tube, corresponding to the regeneration of turbulence kinetic energy and Reynolds stresses. The instantaneous turbulent streaks and vortex structures are displayed to intuitively understand the development of turbulence along the tube. Considering the huge cost of DNS on computing resources and time consumption, LES technology is a reliable and feasible means to explore supercritical heat transfer.