Analysis of the flow of secondary steam through a reheater using 3D CFD

Sammanfattning: In this study 3D CFD was used to study the mass flow distribution in a reheater in a nuclear power plant. The aim was to see if 3D-modeling provide different results than traditionally used 1D-analysis. Models with detailed geometry were created for a section of the tube package in the reheater to obtain pressure drop coefficients. The set up of the model for pure cross-flow over the tubes was first validated against an experiment by Ward [33]. The model showed good agreement with the experimental data for pressure drop and heat transfer, with both unsteady simulations using LES and steady simulations using the SST k - w model. It also showed that using the empirical correlations by Ward and Young [32] and Rabas et al. [22], without any experimental data for the tube bank, gave an overestimation of the pressure drop. The pressure drop coefficients obtained from the tube package simulations were used to model the tube package in the reheater as a porous medium. A set of perforated plates in the reheater needed to be modeled as a porous medium as well. These plates were originally meant to be mounted on the inlet side of the tube package to even out the mass flow distribution. However, due to a manufacturing error they were now mounted on the outlet side. A set of simulations using the SST k - w for a part of the plate geometry gave the required pressure drop coefficients. With all coefficients for the porous medium obtained a full scale model of the reheater was created. In the 3D-model the IAPWS-IF97 formulation was used to model the pressure and temperature dependent properties of the steam. Both the SST k - w model and DES were used for turbulence closure. A 1D-simulation of the reheater was also performed using RELAP5. The 3D-simulations showed a larger difference in the mass flow distribution between the upper and lower part of the tube package than the 1D-model. The 1D-model showed a clear connection between the pressure drop over the perforated plates and the mass flow distribution. However, in the 3D-model the mass flow distribution appeared to also be affected by other properties.