CFD investigation on conjugate heat and mass transfer in wire-wrapped fuel assembly

The Computational Fluid Dynamics (CFD) modeling of wire-wrapped fuel assembly is challenging due to the geometric complexity and many contacts between the wire and fuel rod. To obtain the reliable and accurate predictions in pressure drop, velocity and temperature fields of wire-wrapped geometry, the uncertainty of CFD model should be identified and minimized. The present study conducted the sensitivity tests of pressure drop, velocity and temperature profile to the mesh density, boundary layer mesh and turbulence model by employing a commercially available CFD software, STAR-CCM+ version 12.06.010. The fluid-only and conjugate heat transfer models with 7-pin fuel assembly were adopted to find the baseline model parameters for the full geometry modeling with 217 pins. The CFD results show that the size of mesh and presence of boundary layer mesh play an important role in predictions of the pressure drop. The effects of mesh size, boundary layer mesh and turbulence model on the peak temperature of fluid and cladding wall were not significant. The fluid-only model with closed-gap approach could overestimate the peak temperature around the contacts.