| dc.description.abstract | This thesis examines the dynamic behavior of a granular material sheared in a shear cell. This type of flow is known as a Couette flow in fluid mechanics. In this thesis, we study two different kinds of granular Couette flows. One is the cohesionless granular material flow and the other is the cohesive granular material flow with adding little amount of water or silicone oils.
Experiments are performed in a shear cell device. The glass spheres are used as granular materials. The motions of the granular materials are recorded by a high-speed camera. The image processing technology and particle tracking method are employed to measure the average and fluctuation velocities in the streamwise and the transverse directions. By tracking the movements of particles continually, the variation in the mean-square diffusive displacements with time is plotted and the self-diffusion coefficient is determined. Three bi-directional stress gages are installed to measure the normal and shear stresses along the upper wall.
In granular material flows, the interactive collisions between particles are the dominant mechanism affecting the flow behavior and cause the random motions of particles. In the first part of this thesis, the influence of solid fraction of granular material on the transport properties is discussed. For the denser granular flows, the shear rate, the granular temperature, the wall stresses, the effective viscosity and the energy dissipation are greater. However, the denser granular flow has the smaller self-diffusion coefficient.
In granular flow, the cohesive forces between particles include Van Der Waals force, sintering force, liquid bridge force and electrical force. The liquid bridge force is more important than the other forces in a high moisture system. A series of experiments were performed by adding different amount of water to the granular material system. The influence of the dimensionless liquid volumes of water added is studied in the second part of this thesis. The energy dissipations in the shear cell device are generated from the friction and inelasticity between particles and viscous resistance due to surrounding moisture. The energy dissipation increases monotonously with the increase of the dimensionless liquid volume.
Because the energy dissipations in the shear cell are also contributed from the viscous resistance, thus the viscosity of the adding liquids have strongly influence on the behavior of wet granular system. The third part of this thesis discusses the influence of adding different silicone oils with different viscosities. The Granular Bond Number and the Collision Number are used to discuss the behaviors of the wet granular flow system.
The works in this thesis are relatively fundamental. However, these issues are important for developing the insides of sheared granular flows, especially wet systems. We wish that the results will bring some new information to the research field and also be contributed to the related industries. | en_US |