| The spacer grid is a device that supports and fixes the fuel rods in the fuel assembly.At the same time,its mixing vanes and other components have a profound impact on the flow field distribution,evolution and flow heat transfer characteristics in the heating section of the fuel rods.The inner critical heat flux density plays a crucial role.In this paper,the method of combining PIV flow field measurement and CFD numerical simulation is adopted.A systematic study was carried out on the influence of the mixing vane in the rod bundle channel on the flow field characteristics.The experimental research first established a high-flow water circulation experimental system,and then built a rod bundle channel transverse flow field PIV measurement system and an axial pressure drop measurement system.Secondly,using3 D printing technology to prepare the mixing vanes lattice,and taking the enlarged 2 × 2lattice and sub-channels as the research object,the cross flow field and axial pressure drop in the rod bundle channel by the mixing vanes structure and Reynolds conditions were carried out.The experimental study of the influence has finally obtained the influence law of the type of the stirring blade,the bending angle and the Reynolds on the evolution characteristics of the lateral flow field distribution and the axial pressure drop characteristics.The experimental results shows,the grid of each type of mixing vanes will produce obvious lateral flow and vortex flow in the sub-channels of the rod bundle,but the distribution forms of the lateral flow field and the axial vortex downstream of the different types of mixing vanes are quite different,and the increase is under the condition of large bending angle and Reynolds of the agitator,the lateral velocity and axial vorticity in the downstream of the grid increase accordingly.The numerical simulation research first establishes the CFD model,The model is completely consistent with the experimental research object,and uses the STAR-CCM+software to carry out numerical simulation calculations for a typical single working condition of the experiment,and the simulation results are compared with the experimental results to verify the accuracy of the mesh model and turbulence model used in the simulation.After that,thermal boundary conditions will be added to the numerical simulation calculation,and all experimental conditions will be simulated and calculated,and the simulation results will be systematically compared with the experimental results.The comparison results show that the numerical simulation results are in good agreement with the experimental results.Then,the complex flow field characteristics in the rod bundle channel are further described by the eddy current turbulence factor and turbulence intensity factor.Combined with the pressure drop along the path and the Nusselt number,the different types of turbulent blades,different bending angles and different Reynolds are comprehensively analyzed.Influence of flow field characteristics and pressure drop characteristics on heat transfer characteristics.The results show that the increase of the eddy current stirring factor is beneficial to the enhanced heat transfer inside the subchannel,and the split-type mixing vane have excellent performance of high heat transfer intensity and low pressure loss.And the greater the Reynolds and the bending angle of the mixing vane,the greater the convective heat transfer intensity in the sub-channels of the rod bundle,but at the same time,it will cause more pressure loss.The work of the thesis fully combines the PIV flow field measurement method and the CFD numerical simulation method,and studies the flow field characteristics,pressure drop characteristics and heat transfer characteristics in the rod bundle channel with the stirring blade lattice,and obtains the type of mixing vane,folding characteristics.The influence law of the bending angle and Reynolds on these characteristics has accumulated experience for the application of PIV in the measurement of the flow field of the rod bundle channel,and provided the experimental basis for the accuracy of the CFD calculation.The foundation is laid for the improvement of the thermal-hydraulic performance of the components. |
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