Numerical Simulation of Cross-Flow in Tube-Bundles to Model Flow Circulation of the Moderator in CANDU-6

Abstract

The knowledge of external wall temperature distributions around calandria tubes is a major concern during normal and off-normal operating conditions of CANDU power reactors. To this aim, the use of Computational Fluid Dynamics (CFD) techniques to model moderator local flow velocities and temperatures can largely help in performing nuclear safety analyses. However, present numerical codes applied for this purpose makes use of the well known porous media approach. This method necessitates a previous knowledge of distributed hydraulic resistances that must be obtained from appropriate scaled experiments. Within this framework, this paper presents a set of 2D CFD simulations of incompressible cross-flows along in-line and staggered tube bundles. The numerical results are validated against experimental data obtained from the open literature. Calculations are performed using FLUENT-6 code. The Reynolds-Average Navier Stokes (RANS) equations are used in conjunction with several turbulence models and both the SIMPLE (Semi-Implicit Pressure Linked Equation) as well as the coupled pressure-based algorithm. In general, it is observed that two-equation turbulence models are able to reproduce mean velocities. Even though reasonably good predictions of flow distributions along staggered tube set-ups are obtained, the predictions of the pressure drop along in-line tubes are in general not satisfactory. In most cases, the coupled pressure-based algorithm seems to perform better but requires longer computation time. In general, the standard κ-ԑ is superior to others κ-ԑ models. The κ-ω model behaves better for fairly well developed flows.