Prediction of natural mixing in tightly packed seven-rod bundles ( [formula omitted

Abstract

In this study the predicted fine structure of flow within a seven-rod bundle at a fixed rod-to-rod gap distance ( P/D = 1.1) and at different rod-bundle-to-wall distances are presented ( N Re = 10 5 ; N Pr ≈ 1.0 ). The numerical code VANTACY-II has been used to calculate the single-phase, fully developed turbulent flow conditions in arbitrary two-dimensional solution domains. The code includes a validated model of the anisotropic turbulent exchange of momentum and heat appropriate for tight lattices. The different rod-bundle boundary structures affect the fluid flow conditions, although the influence of the hydraulics on the temperature field is partly compensated by the turbulent microconvective heat transport between the central and the wall subchannels. In other words, the turbulent mixing depends to a great extent on the size and on the wetted perimeter of the edge region. It may be concluded that a distributed parameter approach using two-dimensional turbulence models is • bb modelling the flow in detail, providing the local distributions of the fluid velocities and temperatures, the wall shear stresses and the wall heat fluxes, and integral quantities like the axial pressure gradient • bb helping to interpret experiments and to expand their results • bb and providing well defined input data for lumped-parameter analysis codes.