Numerical Study of Turbulent Convective Cooling of Vertical Heat-Generating Rods Using Supercritical Water

The heat-generating rod with an inner diameter of 10.2 mm and the pitch-to-diameter ratio (P/D) of 1.098 is studied for mass flux ranging between 550 and 1270 kg/ms and heat flux of 560 kW/m at pressures of 25MPa. V2F eddy viscosity turbulence model is used and, to isolate the effect of buoyancy, constant values are used for thermo-physical properties with Boussinesq approximation for the density variation with temperature in the momentum equations. The computed Nusselt number normalized by that of the same Reynolds number with no buoyancy against the buoyancy parameter proposed by Jackson and Hall's criterion. A significant decrease in Nusselt number was observed in the range of 10 < Gr/Re Pr < 10 before entering a serious heat transfer deterioration regime. Based on an analysis of the shear-stress distribution in the turbulent boundary layer, it is found that the same mechanism that leads to impairment of turbulence production and thus heat transfer, in a vertical tube is present in square lattice heat-generating rod bundles at supercritical pressure.Convection heat transfer in upward flows of supercritical water in rectangular tight rod bundles is numerically investigated using the commercially-available CFD software ANSYS Fluent