CFD analyses of mixed and forced convection in a heated vertical rod bundle

The effects of spacer grid blockage ratio and spacer grid spacing on heat transfer in a vertical rod bundle are presented in this study. A 3-D model of a 1/8th cross-section of a subchannel with and without spacer grids has been considered for CFD simulation. The inlet flow Reynolds number (Re) was varied from 1640 to 12,000 to investigate the flow effect on heat transfer. A suitable turbulence model was selected for this study by comparing the local Nusselt number (Nu) in the subchannel with previously published experimental data. The simulation results predicted the experimental data satisfactorily with maximum 10% deviation when compared with published experimental data for a pitch-to-diameter (P/D) ratio of 1.25 and maximum 7% deviation for a P/D ratio of 1.5. Different spacer grid blockage ratios (0.1, 0.2, 0.3, and 0.4) were studied and the dependence of the pressure drop on the Re at the grid was analyzed. Furthermore, the effect of the spacer grid spacing was investigated. The simulation results were found to compare very well with some notable correlations found in the literature.