Turbulent diffusion of heat between connected flow passages Part 2: Predictions using the “κ-ϵ” turbulence model

Abstract

Axial velocity contours, temperature contours and the amount of inter-subchannel mixing by turbulent diffusion and secondary flow for turbulent flow in ducts simulating smooth bare rod bundles have been investigated both experimentally and analytically. This paper, part 2, deals with the computer prediction of the turbulent flow in three duct configurations simulating pitch to diameter ratios of 1.833, 1.375 and 1.1; in part 1 the problem was outlined and detailed measurements were reported for the three ducts. The analytical work has been performed by solving the basic differential equations of the turbulent flow and heat flux using the “κ-ϵ” turbulence model and the “Gosman” numerical integration procedure. This is believed to be the first application of these procedures to the prediction of inter-subchannel mixing. A detailed comparison between the computer predictions and the results of the experimental work revealed that secondary flows were not an important determinant in the mixing rate and did not allow agreement to be obtained with the measured axial velocity and temperature contours. Predictions assuming that the effective diffusivity was isotropic, produced gap Stanton numbers an order less than those measured. To obtain gap stanton numbers of the correct order it was found necessary to use anisotropic effective diffusivities in which the anisotropy distribution rose sharply near the walls to very high values (≈50).