从质量流向漏斗流转变过程中的动力学分析

Dynamics of the transition of mass flow to funnel flow in a silo

球床模块式高温气冷堆的堆芯是全陶瓷型包覆铀燃料制成的球形颗粒,与石墨颗粒混合堆积而成,堆芯颗粒流的流态取决于颗粒尺度的平移、旋转等动力学量,以及力链、涡旋等介尺度物理量。为了分析颗粒的平移、旋转等动力学量对颗粒流流态的影响。基于筒仓颗粒流的物理模型,首先开展了筒仓颗粒流流变过程的实验测量,并使用基于Hertz-Mindlin和RVD(relative velocity dependent)滚动摩擦接触模型的离散单元法(distinct element method,DEM),研究了锥形筒仓颗粒流流变过程中球形颗粒的动力学量。进一步,基于DEM计算结果进行分析,发现筒仓自上而下呈现出质量流向漏斗流过渡的混合流状态。在筒仓混合流的不同流型区域中,平移速度和旋转速度之间的相关性是相反的;颗粒间的相对切向运动较大的区域集中在漏斗流区域与边壁区域。了解筒仓流变过程中颗粒的动力学特征,有助于优化筒仓颗粒流动,并减少颗粒表面的磨损。

The flow of fuel element spheres in the pebble-bed high temperature reactor(HTR)is a typical granular flow.A mixed flow including mass flow and funnel flow can be found during HTR operation.Particle scale dynamics and mesoscale dynamics control the flow states and their transitions.In this work,we focus on analyzing the effects of particle translation,rotation and other dynamic quantities in physical model of the silo flow.We firstly carried out the experimental measurement of the rheological process of the silo particle,and used the discrete element method based on the Hertz-Mindlin and RVD(relative velocity dependent)rolling friction contact model.The kinetic quantities of spherical particles in the rheological process of particles in a conical silo were studied.Further,based on the analysis of DEM calculation results,it is found that the silo presents a mixed flow state of transition from mass flow to funnel flow from top to bottom.In the different flow pattern regions of the silo mixed flow,the correlation between the translational speed and the rotational speed is opposite;the regions with larger relative tangential motion between particles are concentrated in the funnel flow region and the side wall region. Understanding the dynamics of particles during silo rheology can help optimize silo particle flow and reduce particle surface wear.