Numerical investigation on heat transfer characteristics of liquid metal cross flow over tube bundles

Abstract

Helical tube Once Through Steam Generator (OTSG) could further improve the compactness of liquid metal cooled reactors. The heat transfer characteristics of liquid metal cross flow over inline tube bundles is important for the design of helical tube OTSG. In order to consider the low molecular Prandtl number (Pr) effects on turbulent heat flux, different turbulent Prandtl number (Prt) models are validated by a Direct Numerical Simulation (DNS) database for convective Poiseuille flow. Applicability of the Prt and turbulence models for convection with flow separation or adverse pressure gradients is further assessed by DNS results of backward-facing step convection with a fluid Prandtl number of 0.025. Heat transfer of liquid metal cross flow over tube bundle is simulated with k-ω SST turbulence model and the selected Prt model. Heat transfer performances of cross flow over tube bundles with different Pr, Reynolds number (Re) and geometry parameters are simulated. The very large molecular thermal diffusivity (a) of liquid metal results in different temperature distributions and heat transfer characteristics in tube bundles compared with conventional fluids (Pr around and higher than 1). The normalized heat transfer coefficients of liquid metal are enhanced on the upwind side of the tubes and are weaken on the rear side of the tubes compared with conventional fluids. The increments of Pr and Re both weaken the low Pr effect of liquid metal and lead to circumferential heat transfer characteristic more similar to that of conventional fluids. Geometry parameters have little impact on the time and area averaged Nu of liquid metal cross flow over tube bundles. A new Nusselt (Nu) number correlation with wide applicable ranges is proposed based on the numerical results.