Discrete Particle Flow Separation And Shear Stress Fluctuations In Experimental Research

There are a great deal of natural phenomenon and engineering applications dealing with the granular flows. It is of important theory meaning to the research of ecology and environment protection, such as coast, debris flow, the evolvement of sand dune, the migration of particles in atmosphere and river, and of practical meaning to the environmental engineering, such as cement, metallurgy, foodstuff, pipeline transportation and energy sources.Experiment method was adopted to do some research on the shear flow from the point of physic and mechanics to investigate the inner mechanism of granular flow. The research contents include three following important content: the vertical segregation, shear stress and force chain in granular flow.Above three problems are the hot spot in the research of granular flow and closely related. The segregation is the sub-product of granular flow as long as there is difference in the size of particle. The shear stress is an important parameter to reflect the flow state, affecting the process and result of segregation. Force chain is an important way to transfer inner stress in density granular flow affecting the magnitude of shear stress.Different particles divided into groups were sheared to flow in shear cell shear cell system which was designed by us in order to reach our aims. The experimental system is composed of parts such as three-phase electric motor, frequency conversion governor, torsion meter, shear ring and shear cylinders. One can easily make adjusting to the system specifically for the characteristic of the three experiments. Compared with the experiment system in the past, the experiment system can easily adjust flow rate and time, which makes no restrict to the flow length. The broad accommodation and strong operatability makes it best system to do the research.Based on analysis to the experimental results, we get some inclusions. The vertical segregation in s-system is dominated by the "random fluctuating sieve" mechanism, the time and degree of segregation is closely related to the concentration and flow velocity. When the neutrally buoyant non-homogeneous spherical particles are shorn, the shear stress is aggrandizing with the enhancing of the concentration and shear rate. Under the identical shearing rate condition, the magnitude of mixed particles' shear stress among the small and big particle's, and the different in shear manner is the main reason which makes the discrepancy in experiments of Savage and Bagnold. As to the dry particles system in slow shear velocity, the big fluctuation in shear stress is closely connected with the force chain, which with the characteristics of structure instability and peculiar strain transfers way. The flow rate, particle diameter, the degree of desiccation and irregular will affect the magnitude force and the occurrence frequency in different extent.