| Granular materials are used in many engineering applications. The flow of granular materials plays a critical role in industrial processes such as mixing, crunching, separation and suspension. The flow of granular material also plays a role in many modern products such as appliances, printers, and copiers. Therefore a good understanding of this granular flow is important for on-going product design and development. For most of these applications, the flow of granular material is not influenced by cohesive forces. In some applications, however, cohesive forces have a major influence on understanding the material's flow characteristics.;Toner is the material that forms the printed image in the electrophotographic (EP) process. Toner is distinguished from other granular materials by its fine particle size and tribocharging properties. The flow of toner is highly influenced by cohesive forces. The major contributors of cohesive forces in toner are due to Van der Waals forces, because of the fine particle size, and electrostatic forces, due to the tribocharging properties of toner.;In order to better understand the flow of this fine granular material, toner flow is simulated using the Discrete Element Method (DEM). The DEM uses a time-stepping algorithm. It consists of repeated applications of the law of motion to each particle, the force-displacement law to each contact, and the contact updating of surface and particle positions. Most of current DEM efforts involve simulating the flow of cohesionless granular materials. However, the DEM is not limited to cohesionless granular materials. The main objective of this dissertation is to develop a DEM model to describe cohesive granular flow, especially toner flow. To validate the model, the overall DEM model is decomposed into three parts: cohesionless DEM model, cohesionless DEM model incorporated with Van der Waals forces, and cohesionless DEM Model incorporated with electrostatic forces. These decomposed sub-models are validated by comparing with experimental results.;The overall model is used to study toner mass transfer, one of the most important processes of EP process. Factors (particle size, charge, and distance between particles when they are on the first roller surface) impacting toner mass transfer are investigated using statistically designed simulation runs. The results show that in order for toner particles to be transferred to the desired positions, a smaller charge is desired. On the other hand, in order for toner to be transferred quicker, a higher charge is desired. That is to say, a trade off has to be made if we want to transfer toner to the desired position as quickly as possible. |
