Numerical Investigation of Single-Phase Heat Transfer in a 2 × 2 Rod Bundle with Spacer Grids for a High Pressure Heat Transfer Facility

Numerical simulation has been widely used in nuclear reactor safety analyses to gain insight into key phenomena. This paper compares simulations of a single-phase steady flow in a 2 × 2 rod bundle with spacer grids among different codes based on the high pressure heat transfer facility at University of Wisconsin. The detailed computational fluid dynamics modeling methodology was developed using FLUENT to help in the facility design and pretest analyses. After comparison between different turbulence models, the Standard k-ω was chosen to simulate the effect of unheated solid walls and grid spacers. It was found that solid walls had a small influence on the flow and heat transfer behavior. We note the effect of rod-to-wall gap needs be taken into account if it is larger than half of the gap between the rods. We compared the simulations of FLUENT, COBRA-TF, and TRACE to determine the position of thermocouples to be used in the planned experiments. An investigation was performed on the effect of bending angles of the grid spacer mixing vanes. Results showed that a larger bending angle results in higher turbulence mixing and locally higher Nusselt numbers downstream of the mixing vanes. Also, a small change of the bending angles results in a notable difference in the temperature distributions of the main flow.