Numerical Studies Of Dense Granular Flow In A Chute

A new type of spallation target concept,the gravity-driven dense granular flow target(DGT),has been proposed for the China-ADS project.Based on this new concept,the ADS target team propose a target design,the gravity-driven dense chute granular flow target,for a neutron irradiation facility capable of providing high-energy & highflux neutrons suitable to advance fusion reactor material research.The new concept adopts a gravity-driven berylium granular flow to act as target body as well as the heat carrier.The essential idea of the concept is to exchange the heat deposition offline easily,just as what liquid heavy mental(HLM)target dose,and avoid many critical problems that occur in HLM target at the same time,such as the flow instability,the material corrosion and the leak of chemical toxicity.As an initiative target concept,the granular flow target is so different with regular HLM targets in many ways,one of the most significant differences lies in the flow stability.The overall of objective of this work is to perform the stability analysis of granular flow based on discrete element method(DEM)to simulate the flow behaviors of the granular flow and to study the fluctuation of the velocity and volume fraction in a chute flow.And the linear stability analysis and the calculation of Lyapunov exponent of energy difference after perturbation are used to further study the flow stability.In additon,we also study the effect of the geometrical and material parameters of the model on the flow.At last,we conduct an assessment of the feasibility of the new conceptual design.The emphases of this dissertation focus on three aspects.(1)The granular flow down an inclined hexagonal-ordered base is simulated under periodic boundary condition.The effect of the inclination angle on the flow is mainly investigated.(2)We numerically simulate the granular flow in feeding reservoir and chute.And we analyse the spatial field of velocity,volume fraction and their fluctations.(3)We propose a new target design,the gravity-driven dense chute granular flow target.The effect of the geometrical and material parameters of the model on the flow is investigated.At last we study the flow stability by using the linear stability analysis and the calculation of Lyapunov exponent of energy difference after perturbation.Specific details are as follows:We first study the grunular flow down an inclined base under periodic boundary condition.How the periodic boundary condition work in DEM is introduced at first.And then the model and the process of simulation are described.At last,we mainly investigate the effect of the inclination angle on the flow.Then we numerically study the granular flow in feeding reservoir and chute.We investigate the effect of the inclination angles of the reservoir and the plane on granuar flow.Since the reservior is similar to the eccentric hopper,we also study granular flow in eccentric hopper,including the effect of the width of the eccentric hopper and outlet width on the flow rate,the spatial field of volume fraction,velocity and their fluctuations.At last,the influence of the height of gate of the feeding reservior on flow is studyed,including the flow rate,the spatial field of volume fraction,vellcity and their fluctuations.Subsequently,we study the garnular flow in chute granular flow target.We first propose a new target design,the gravity-driven dense chute granular flow target,and simplify the target model for DEM simulation.Then we investigate the effect of the geometrical and material parameters of the model on the flow.At last,by using the linear stability analysis and the calculation of Lyapunov exponent of energy difference after perturbation,we study the flow stability in chute.At the end of the dissertation,the main conclusions are summarized and the further work is suggested.