Numerical computation of heat transfer enhancement of a PWR rod bundle with mixing vane spacers

A series of computational fluid dynamics (CFD) simulations has been conducted to analyze the heat transfer enhancement in a fully heated rod bundle with mixing-vane spacers. The predicted Nusselt numbers downstream of the split-vane spacer are compared with the available experimental measurements and with correlation. The CFD calculations at Re = 28 000 and 42 000 showed a lower heat transfer enhancement close to the space grid but a good agreement of the decay rate with the fully heated experimental data at similar to 6D(h) downstream of the grid. The CFD simulations also showed a maximum enhancement of the heat transfer at 6 to 7D(h) downstream of the split-vane spacer due to the multiple vortices predicted near the spacer. In addition, the present paper compares the thermal-hydraulic performance of two different mixing vane spacers, i.e., a split-vane spacer and a hybrid-vane spacer, based on CFD simulations at a pressurized water reactor's operating conditions. The split vane is predicted to have a higher overall heat transfer enhancement but a lower local heat transfer far downstream of the spacer where the minimum departure from nucleate boiling ratio is anticipated.