Large eddy simulation of the heat transfer and unsteady pulsation of supercritical carbon dioxide in a square subchannel

Abstract In the present study, a large eddy simulation was conducted to study the heat transfer and turbulent flow pulsation of supercritical carbon dioxide (SCO2) in a square subchannel. Three Reynolds numbers of 5385, 13,028 and 18,934 were selected corresponding to the friction Reynolds number ( R e τ ) of 180, 395 and 550, respectively. Both of the upward flow, downward flow and pure forced convection (g = 0) were covered. Attention was paid to clarifying the effects of flow direction and Reynolds number on the circumferentially nonuniform heat transfer, the cross-sectional velocity redistribution and the macroscopical flow pulsation. It was found that the wall-temperature distribution along the rod circumference is closely related to buoyancy. The heat transfer of the downward flow is superior to upward flow under identical conditions. Besides, the heat transfer of the upward flow is better than that of the forced convection, indicating buoyancy could enhance the heat transfer. In addition, for the upward flow, the cross-sectional velocity is high near the rod gap, but is low at the subchannel center. A quasi-periodic large-scale velocity pulsation was identified near the rod gap. The magnitude of the velocity pulsation is affected by the flow direction, but is independent of the Reynolds number. On the other hand, the dominant frequency of the velocity pulsation increases with increasing Reynolds number, but is unaffected by the flow direction.