The applicability of artificial roughness in light-water reactors is investigated for the purpose of heat transfer improvement in fuel rod bundles. Since the roughening technique has a significant impact on friction losses, the investigation is divided in two distinct steps: flow resistance and convective heat transfer. The present paper deals with roughness effects on flow resistance. The technique consists of a multiplicity of small elements distributed on the surface of the simulated fuel rod. A parallel rib-type roughness is selected for this work for simplicity and since it has been extensively investigated in the past. Locally flow resistance is simulated using Computational Fluid Dynamics, CFD, in smooth and in rough rod bundles downstream of support grids with and without flow-enhancing features (vanes). This investigation is performed with basis on experimental testing. With model parameters established, various candidate roughness designs can evaluated for minimum flow resistance.

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