Direct Numerical Simulation Study on Turbulent Flow and Heat Transfer Behavior of Helium-Xenon Gas Mixture in a Round Pipe

Abstract Helium-Xenon (He-Xe) gas mixture is widely adopted as the working fluid for space gas cooled nuclear reactors with CBC engines. The Prandtl number of He-Xe gas mixture in the preferred mixing-ratio range is approximately at 0.2–0.3, which is significantly lower than air or water. To better reveal the flow and heat transfer mechanism of He-Xe gas mixture, 2 direct numerical simulation (DNS) cases of He-Xe gas mixture flowing through a heated pipe were performed. One is based on the experiment case (RUN696) of Taylor (1988), and another one is set with a higher temperature range. The DNS results are in good agreement with the experiment data. The Taylor Nu heat transfer correlation was evaluated by DNS results. Further analyses of other turbulent statistics distribution, such as Reynolds stress, and turbulent heat flux were conducted. Reynolds-Averaged Navier-Stokes (RANS) simulations with 6 different turbulent models of the same case were also performed. The DNS data was used to evaluate the calculation results of different RANS turbulent models. The result shows that the three k-ε and the linear pressure-strain RSM models perform barely the same, and the SST k-ω model relatively behaves the best. It is also found that the current default turbulent Prandtl number model (Prt = 0.85) deviates largely from the calculated DNS data, especially in the near wall region.