Numerical investigation of the effect of mixing vanes on subcooled boiling in a 3 x 3 rod bundle channel with spacer grid

Mixing vane grids (MVGs) are an integral part of nuclear reactor fuel assembly, and significantly impact the flow and heat transfer characteristics of the coolant in a rod bundle channel. To investigate the effect of mixing vanes on subcooled flow boiling in the rod bundle channel, a multiphase flow model based on Eulerian was proposed, and was verified by comparing with the experimental data. In addition, the effects of different components in the MVG, deflection angles, and arrangements (of mixing vanes) on the axial distribution of thermal-hydraulic parameters of subcooled boiling in a 3 x 3 rod bundle channel were studied. Compared to other components, mixing vanes exhibited a stronger and more lasting influence on the generation of lateral disturbance, which resulted in a substantial decrease in the values of wall superheat and near-wall void fraction. It was found that with an increase in deflection angle of mixing vanes, the corresponding convective heat transfer increased; however, on exceeding 30 degrees, this tendency decreased significantly. Furthermore, compared to circle-type and series-type arrangement, cross-type arrangement indicated more persistent ability to produce lateral disturbance. (C) 2021 Elsevier Ltd. All rights reserved.