Fluid dynamics and heat transfer of turbulent flow in rod bundle subchannels

The fluid dynamics and convective heat transfer for turbulent flow through rod bundles representative of those used in pressurized water reactors are examined. The rod bundles consist of a square array of parallel rods that are held on a constant pitch by support grids spaced axially along the rod bundle. In pressurized water reactors, pressurized water is used in an indirect cycle to convert the heat generated within the fuel rods into electricity. Since an increase in the single-phase convective heat transfer in the rod bundle accommodates higher power generation within the reactor core, modifications to the support grid design are implemented to improve the heat transfer.;Split-vane pair support grids, which create swirling flow in the rod bundle, as well as disc and standard support grids are investigated in the present study. An experimental facility is designed and constructed to measure single-phase heat transfer coefficients. In addition, the lateral velocity fields downstream of split-vane pair support grids are examined using particle image velocimetry (PIV). Computational fluid dynamics (CFD) is implemented to further understand the fluid dynamics and heat transfer for swirling flow in rod bundles.;Single-phase convective heat transfer coefficients are measured for flow downstream of support grids in a rod bundle. The rods are heated using direct resistance heating, and a bulk axial flow of air is used to cool the rods in the rod bundle. Results indicate that the heat transfer is enhanced for up to 10 hydraulic diameters downstream of the support grids. A general correlation is developed to predict the heat transfer development downstream of support grids. Circumferential heat transfer variations identify hot streaks that develop on the rods downstream of split-vane pair support grids.;PIV and CFD results document the different swirling flow structures that develop downstream of split-vane pair support grids. Strong lateral flows along the rods and impingement of the swirling flow structures on the rods correspond with regions of increased heat transfer. In addition, lateral flow separation from the rods leads to decreased regions of heat transfer and the development of hot streaks.