Effects of graphite surface roughness on bypass flow computations for an HTGR

Tung, Y.-H.*; Johnson, R. W.*; Sato, Hiroyuki  

The present study examines the effects of graphite surface roughness on the bypass flow for different relative roughness factors on three gap widths. Wall shear stress and heat transfer results for several turbulence models and their associated wall treatments are first compared for flow in a single tube in the prismatic HTGR core. The results are compared to published correlations for wall shear stress and Nusselt number in turbulent pipe flow. Calculations are also compared to ones made previously using a different CFD code. Results indicate that increasing surface roughness increases the maximum fuel and helium temperatures as do increases in gap width. However, maximum coolant temperature variation due to increased gap width is not changed by surface roughness.