Calculation of Inter-Subchannel Turbulent Mixing Rate and Heat Transfer in a Triangular-Arrayed Rod Bundle Using Direct Numerical Simulation

The direct numerical simulation, extended to boundary-fitted coordinate, has been carried out for a fully-developed turbulent flow thermal hydraulics in a triangular rod bundle. The rod bundle is premised to be an infinite array. The spacer grid effects are ignored. The purpose of this work is to verify DNS methodology to be applied for deriving coefficients for inter-subchannel turbulent mixing and heat transfer on a rod. These coefficients are incorporated in subchannel analysis codes. To demonstrate the validity of this methodology, numerical calculation was performed for the bundle with the pitch to diameter ratio 1.2, at friction Reynolds number of 600 and Prandtl number of 1. The results for the hydraulic parameters are compared with published DNS data, and the results for the heat exchange coefficients — with those obtained using semi-empirical correlations.