Simulations of external flow around twisted elliptical tubes for above unity Prandtl numbers and low to moderate Reynolds numbers

Twisted elliptical tubes are a proposed heat transfer enhancement (HTE) for use in Molten Salt Reactors (MSRs) due to their enhanced thermal performance compared to plain tubes. The twisting ellipsoid geometry causes the fluid to swirl as it passes over the tubes, enhancing mixing and inducing turbulence at lower Reynolds numbers. This effect increases overall convective heat transfer; however, this is at the cost of increased frictional pressure losses. Previous work by the authors has investigated the dependency of cross-sectional aspect ratio ( A R = 1.1 − 2.1 ) and below-unity Prandtl numbers ( P r = 0.001 − 1 ) for this geometry, and this study aims to extend this work by investigating above-unity Prandtl numbers and varying Reynolds numbers. In this study, the Nek5000 computational fluid dynamics (CFD) code is used to perform Large Eddy Simulations (LES) of external flow around twisted elliptical tube bundles. This study aims to further characterize the heat transfer phenomena seen around twisted elliptical tubes when varying the tube aspect ratio, which is a dependency that has not been historically accounted for. Simulations were performed for three different tube cross-sectional aspect ratios (maximum versus minimum diameter), Reynolds numbers of 2000 and 7000, and Prandtl numbers of 10, 20, and 30.