Study On The Dynamic Properties Of Chute Flow And Compartmentalized Vibration Of Granular Material

Granular material is the collection of many solid particles whose sizes are greater than micron. It is a major category of substance different from the continuous media, such as solid, fluid and gas. Granular material exhibit many special behaviors, including the non-linear dynamics, structural heterogeneity, disorder to order and free flow to jam transition. It is a new growing point in the condensed matter physics research. The major role of interaction between particles are friction and inelastic collisions. The granular system is far from equilibrium because of the dissipative properties. There are more extra energy needed to maintain the movement of particles. The forms of input energy often contain the gravity, vibration, shear or impact force, etc. Granular material show similar characteristics of soil, liquid and gas under some conditions. Although granular material and continuous media have a lot in common, there are fundamental differences between them because of the discrete property. Some researchers have suggested that the granular material can be classified as "the forth substance form".The scale of granular system cross six orders of magnitude started from micron. Therefore granular material exist universally in engineering, agricultural, industrial, construction, pharmaceutical processes, and so on. It is also involved in many natural phenomena (such as avalanche, landslide, debris flow etc.) and production process (such as the transport and processing of bulk material). So the research of granular material is beneficial for both economy and society.This paper presents experimental, theoretical, computational studies on the liquid-like and gas-like dynamic behaviors of granular material. Discrete element simulations are carried out in some respects of study. We hope this paper will reveal various nonlinear properties of granular system and provide some theoretical guidance for the engineering problems about the transport of pipeline, multi-channel merging flow and optimization, and so on. The contents of the paper are as follows.Considering the actual process of granular chute flow is often restricted by multi-bottleneck, we studies the granular flow down a chute with two successive turnings, which play the role of bottlenecks for the granular flow system and determine the granular flow state in main section between them. With the increase of main section width D, phase transition from dilute to dense granular flow is observed: when the main section width D is small (large), the granular flow at upper (lower) bottleneck is dense and the granular flow is dilute (dense) in the main section. More interestingly, a bistable region is exhibited, in which either dilute flow or dense flow may occur and continue for the entire run. In this region, the packing in the reservoir will affect initial flow rate and then affect the flow pattern. We adopt the method of complex network theory to analyze the problem. We also carry out discrete element simulation for the upper (lower) bottleneck. The results show qualitative agreements with the experimental results. Finally, a suggestion of the optimization of flow rate has been proposed.The merging granular flow of two channels is similar to the on-ramp system in traffic flow problem, we studied the dilute-dense transition behavior of two granular flow channels (A and B) merging into one channel at a joint point. Varying the inflow rate from the two channels, the system shows four flowing states:LL, LH, HL, and HH, where L is dilute flow (Low density flow) and H is dense flow (High density flow). In the case of channel size combination DA=40mm and DB=30mm, the outflow rate shows a remarkable two-sudden-drops behavior. That is different from a typical on-ramp system of vehicular traffic. When channel sizes are DA=20mm and DB=50mm, the outflow rate keeps constant for the LH, HL and HH states, so that only one sudden drop can be observed in the outflow rate. We find that the dilute to dense transition will occur when the area fraction of particles at the joint point exceeds a critical value near Φc=0.63±0.03. The study can give some clues for the merging flow of n (n>3) channels.In granular gas, the loss of kinetic energy in collisions due to microscopic degree of freedom of the system balances the energy gained from the shaking mechanism. We design a experiment on a vertically vibrated bidisperse granular mixture in a wide compartmentalized container. Within a certain range of vibration acceleration, a granular clock could stop and restart because of the forming of the horizontal segregation in the container. The experiments show that with proper vibration acceleration, the granular clock stops when horizontal segregation of the large spheres residing in the far end from the barrier wall occurs. When the segregation is broken, the granular clock restarts. We present the phase diagrams of vibration acceleration versus container width, ratio of the radius and small particle number to find out the Granualr Clock-Clustering state. A generalized flux model is proposed to reproduce the phenomenon of stop and restart of the granular clock by introducing a probability P. The results may shed some light on the understanding of the stochastic granular system.The studies of this paper are useful for both practical applications and physical mechanism of granular material. We hope that this work is helpful for understanding the complex nature of granular materials and is useful for the efficient transport of granular materials in industrial, mining and agricultural processes.