Abstract
Gas-cooled space nuclear reactor system usually utilizes the helium-xenon gas mixture as the working fluid. Since the typical helium-xenon mixture has the Prandtl number of about 0.2, which is lower than that of water and air, the turbulent flow and heat transfer features need to be further investigated among the helium-xenon mixture and other fluids. In the current paper, numerical investigations by ANSYS Fluent are performed on helium-xenon mixture flow (HeXe40, M = 40.0 g/mol, Pr = 0.21), airflow (Pr = 0.71), and water flow (Pr = 6.99) in the circular tube. Direct numerical simulation results of liquid metal flow (Pr = 0.01) are also adopted for comparison. Results show that the dimensionless velocity profile and shear stress in the boundary layer of HeXe40 are close to those of other fluids. The empirical correlations from other fluids can also predict well the friction factor of helium-xenon mixtures. Due to the discrepancy in turbulent heat diffusivity ratio, the dimensionless radial temperature profile and turbulent heat conduction of HeXe40 significantly differ from those of other fluids. The molecular conduction region of HeXe40 develops up to y+ ≈ 30 and extends to the logarithmic region of the flow boundary layer. Moreover, the available experimental Nusselt numbers of helium-xenon mixtures are compared with several convective heat transfer correlations, in which Kays correlation is better.
Highlights
Deep-space exploration and planetary outposts will become certain things in the near future [1]. ese ambitious missions substantially require advanced and reliable space power
Comparing the variation of momentum transport is helpful to reveal the characteristics of the turbulent flow for heliumxenon mixture and the fluids with other Prandtl numbers
The applicability of existing correlations on the wall friction factor and Nusselt number are evaluated for low-Pr heliumxenon mixtures. e following conclusions can be drawn: (1) e velocity profiles and the shear stress variation of different fluids are similar, and the empirical correlations of friction factor used for conventional fluids are found to have good predictions on heliumxenon mixtures, indicating that the turbulent flow characteristics for helium-xenon mixtures are consistent with those of other fluids
Summary
Deep-space exploration and planetary outposts will become certain things in the near future [1]. ese ambitious missions substantially require advanced and reliable space power. To further investigate the effect of the Prandtl number on the turbulent convective heat transfer, many related experimental and numerical studies have been carried out. Duponcheel et al [15] conducted LES to investigate the convective heat transfer for liquid metals with different Prandtl numbers and evaluated the rationality of the current RANS model. To better reveal the underlying mechanism of high-Re turbulent flow and heat transfer for low-Pr helium-xenon gas mixtures, it is necessary to carry out in-depth research. To better reflect the particularity of low-Pr helium-xenon mixture on the turbulent flow and heat transfer in the near-wall region, a numerical comparison between HeXe40 and air (Pr 0.71) and liquid water (Pr 6.99) is conducted. The applicability of the existing correlations for wall friction factor and Nusselt number to helium-xenon gas mixtures is evaluated. is study can provide a certain reference for the subsequent thermal-hydraulic design of helium-xenon-cooled space nuclear reactors
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