Development of Nusselt number and friction factor models for rough rod bundles based on wall functions

Abstract

The fuel assembly in the reactor undergo surface roughening due to fouling deposits and material corrosion, which significantly impact the pressure drop and convective heat transfer performance of the fuel assembly. In this study, new models were developed based on the wall velocity and temperature distribution functions. The Nusselt number and friction factor are obtained by integrating these functions over the flow cross-section. The findings demonstrate the accuracy of the method in predicting the friction factor and Nusselt number for both rough tube and smooth rod bundles. The models developed in this study can be utilized to predict the friction factor and Nusselt number in rod bundles with different relative roughness under turbulent flow states, considering square and hexagonal arrangements with P/D<1.5. The present study reveals that the roughness promotes convective heat transfer to a slightly less extent as the pressure drop.