Development of heat transfer correlation of turbulent forced convection in subchannels with rough surfaces based on CFD

Changes in roughness caused by crud deposits on the surface of nuclear fuel rods can impact the convective heat transfer characteristics of the fuel assembly. Therefore, it is necessary to establish Nusselt number correlations to estimate the heat transfer in subchannels with different surface roughness. In this paper, an analytical Nusselt number of rough round tubes was first driven by integrating the product of the wall temperature and velocity distribution functions. Then, the realizable k-epsilon turbulence model with the standard wall function is verified using the Dittus-Boelter correlation for smooth tubes, the analytical Nusselt number correlation for the rough tubes, and Markcozy bundle heat transfer correlation for smooth subchannels, respectively. Finally, the convective heat transfer in different rough subchannels is calculated using the verified realizable k-epsilon turbulence model. And a new single-phase heat transfer correlation for the rough subchannels is proposed based on the CFD results.