Speaker
Description
Liquid metals, such as Sodium, Gallium and Gallium alloys have applications as heat transfer fluids in a broad temperature range. They possess low Prandtl numbers, which makes them ideal as a heat transfer medium for applications such as concentrated solar power plants (CSPs). Due to their low Prandtl numbers the heat transfer mechanism for liquid metals is different than for medium or high Prandtl number fluids, such as air or water. Therefore, a deeper understanding of the heat transfer mechanisms in low Prandtl number fluids is necessary for a safe and optimal design of concentrated solar power plants.
Most of the existing literature in this topic regards only canonical flows without considering the thermal entrance. This study now includes the thermal entrance region in numerical large-eddy simulations at a bulk Reynolds number of Re_b = 5300. Two different Prandtl numbers are considered. A low Prandtl number of Pr=0.025, corresponding to a typical class of liquid metals, and a medium Prandtl number of Pr=0.71, corresponding to air. The results are validated with a reference simulation for the fully developed state (S. Straub (2019) Azimuthally inhomogeneous thermal boundary conditions in turbulent forced convection pipe flow for low to medium Prandtl numbers). The numerical simulation provides additional information about the thermal entrance region, that was not considered in the reference. An azimuthally non-homogeneous boundary condition was hereby set to investigate the effect of the inhomogeneity on the thermal statistics. In this study, the non-homogeneous wall heat flux consists of an adiabatic wall at the lower half of the pipe and a constant wall heat flux at the upper wall of the pipe. The whole setup is commonly denoted as the turbulent Graetz problem with homogeneous and azimuthally non-homogeneous wall heat flux.
Furthermore, the numerically determined turbulent solution is compared with the analytically determined laminar solution. For the laminar case, a series solution for the thermal entrance was obtained for both the homogeneous and non-homogeneous boundary condition.
