Study On The Mechanism Of Granular Motion Under The Vibro-fluidization

With the rapid development of our national economy, the requirement of energy source becomes more and more crucial. China is an important country of coal’s production and consumption, but there are some scientific problems to be solved in the process of the exploitation, the storage and transport, the clean separation of coal source. The coal mined, which is accumulated on the ground with the form of discrete material’s shape, is a typical granular system. As a matter of fact, the granular matter are ubiquitous and familiar in our daily lives. However, the granular media composing of a lot discrete grains exhibit the specific dynamic properties, and how to understand and interpret the unique behaviors of granular materials remains a major challenge in the physical and engineering field. The detailed investigation of granular media not only can help us to understand and master the rules of granular flows, but also is very pivotal to the fluidized separation of the coal grains in the chemical engineering science. In this thesis, We mainly perform the following four works on the vibrofluidized granular matter :1. Based on the continuous media theory and discrete mechanics, the model of a 1D fluidized granular system is established. The dynamic properties of the granular chain droved by two distinct pulse signals are investigated. It is found that the wave and the energy can propagate perfectly through the granular chain due to the energy conservation law without the damp. The simulative signal can complete the incident transport and the reflected one in the granular chain with the weak damp, and the wave energy shows the decreasing trend after the energy reaches the value. In the presence of the strong damp, the wave can not propagate in the granular chain, and the damping effect becomes remarkable with the increase of the grain number. It is found that the distinct shapes of two vibratory sources affect markedly the propagation feature of wave and energy in 1D granular system, the reason of which is also presented.2. The discharge flow of granular media before the vibro-fluidization is investigated by means of the discrete element method(DEM) simulations. It is found that the flow rate is greatly influenced by the interorifice distance and the oblique angle of the hopper. The reduction of the outlet distance leads to the cooperative discharge effect, this results from the fact that the rupture and recombination of the force chain networks in the granular pileup, the transmission of the local fluctuation cause theemerge of cooperative discharge phenomenon. The increase of the silo wall obliquity can enhance the occurrence of the cooperative discharge. The maximum discharge can not be obtained when the limiting value of the interorifice distance is taken, and the appropriate interorifice distance can promote the maximum discharge rate.3. We analyze the grain motion in the vibro-fluidized granular system and give the physical model of vibrated granular media. The function of the state transition of vibrated granular media is analytically derived, the formula between the frequency of taps and the filling fraction of vibro-fluidized granular systems is achieved in terms of the relation between the filling fraction and the state transition rate.The reliability of the above formula is validated via the experiment, and the properties of the filling fraction versus the frequency of vibration is also analyzed.4. The hydrodynamics of a fluidized granular system(gas-solid fluidized bed) is studied by means of the Discrete Element Method(DEM) and the Computational Fluid Dynamics(CFD) method. At a low gas velocity, the bubble is small and the force chain networks is not easily broken. The increase of the gas velocity induces the big voidage and the fracture of force chains in the granular bed. Multilayers of granular materials exhibit particular pattern formation and the granular system shows the breath motion. The particle motion exhibits the stochastic and chaotic behaviors in the fluidized bed under the action of the contact force, the gravity and the gas flow. At a high gas velocity, the flown line is curved and wrested in the fluid field. Due to the bubble coalescence and split, the local pressure fluctuation and the local voidage one shows the sharp variation and the quasi-periodic oscillation. With the increase of the velocity of flow, the magnitude of frictional energy of granular system is also enhanced, and transition from to the linear behavior to the nonlinear one also appears. The kinetic energy magnitude of the granular bed also increases and shows the quasi-periodic oscillation, which stems from the slugging motion of grain assemble in the fluidized bed.