Study On Flow Behaviours Of Granular Matter In A Two-Dimensional Channel

Granular flows exist widely in the handling of granular materials for coal gasification.Exploring the machanisms behind the granular flows is scientifically and industrially relevant to the process optimization,production stabilization and efficiency inprovement.The present thesis is devoted to the flow behaviours of granular matter in a two dimentional channel with a visualization method.A viscosity model and a percolation resistance model are proposed to describe the particle motions in the granular flow.Furthermore,a new method is proposed for the segregation of granular mixtures.The main contents and results are summarized as follows:1.The flow behaviours of spherical particles are investigated in a two-dimensional channel.By setting the boundary of the granular flow as the locus of points where the particle velocity decreases down to 1%of the surface velocity,the particle motions in the flowing layer can be uniformly described with a velocity profile expressed as u=Us?1-y/??².According to the flow properties,a shear-thinning viscosity model is proposed and is further validated by conducting a rotational-shear test with a FT4 Powder Rheometer.The viscosity model indicates that the apparent viscosity depents not only on the physical property of the material but also on the flow parameters:2.The flow behaviours of irregular particles are investigated in a two-dimensional channel,and the flowability of the particles is characterized by employing the flow parameters.The inclination and surface velocity of the granular flow increase with the volumetric flow rate,and is inversely related to the flowability.The ratio of the height to the thickness of the granular flow h/? is essentially constant for each material,independent of the flow rate.The parameter sin?/? is essetially a constant of the granular flow,independent of the material and the shape,and is about 2.59×10^-3s.The ratio ?/cos? is a parameter characterizing the frictional property of the granular flow,and is inversely related to the flowability.According to the flow parameters,the flowability of the granular materials can be ranked in the folowing order:Glass beads>Coal>SiC>Sillicon sand.3.The flow behaviours of binary mixtures of spherical particles are investigated in a two-dimensional channel,and the effect of the content of small particles on the streamwise velocity profile is revealed.The streamwise velocity profile near the free surface tends to be linear for granular flow with single component.When mixing particles with two different sizes,small particles fill into the void spaces and weaken the interaction between large particles.The initial linear portion of streamwise velocity profile is then curved and the overall velocity profile becomes S-shaped.Moreover,a percolation resistance model is proposed as f=kDv,and a linear percolation velocity profile is derived as v=-kpy+v0,which is consistent with the experimental results.4.The segregation of binary mixtures is investigated in a two-dimensional channel.The segregation efficiency decreases with the content of small particles,and increases with the flow distance.Compared to the flow of granular mixtures moving directly on an inclined plane,the granular heap flow will be trapped by the erodible granular beneath it and the overall velocity of the granular flow is then reduced.Therefore,the interaction between large particles is less vigorous in the granular heap flow,which favors the percolation motion of small particles and further increases the segregation efficiency.5.The flow behaviours of spherical particles is investigated in a two-dimensional hopper.The particles in the flowing layer accelerate along the flow,but the velocity profile remains invarient in shape and can always be expressed as u=us?1-y/??².Both the surface velocity and the flowing-layer thickness are proportional to the square of the descending height,and can be expressed as:us ????,?????.Thereby,the velocity profile in the granular flow can be predicted according to the descending height:...