Mixing Kinematics in Granular Materials using X-ray Rheography

Abstract

This dissertation introduces a novel method for understanding granular mixing kinematics through high-speed X-ray observations. It contains three interlinked main chapters, each addressing key challenges and building upon the previous ones to enhance our understanding of mixing kinematics in cylindrical mixers.

The first chapter uses the X-ray rheography image analysis method to determine internal velocity fields in antisymmetrical granular flows, such as those in a two-bladed impeller mixer. This chapter highlights the significant role of X-ray sources and detector alignment in capturing antisymmetric flow characteristics, setting a methodological basis for subsequent chapters.

The second chapter is focused on creating an experimental setup and framework for examining granular mixing dynamics via X-ray rheography. A granular mixer was designed for X-ray imaging from three orthogonal views. The experimental results obtained using the rheography method were compared with those from the discrete element method (DEM) simulations, which replicated the experimental mixing scenarios studied to evaluate the effectiveness of X-ray rheography in the analysis of mixing kinematics. This chapter establishes the foundation for an extensive investigation of mixing kinematics for different particle shapes in the third chapter.

The third chapter examines the influence of the particle shape and impeller blade angle on mixing kinematics. We examine 3D velocity fields and fabric orientation by mixing spherical glass beads, slightly elongated barley, and long jasmine rice. Our findings indicate that elongated particles align along their main principal axis, which impacts their mixing kinematics, while spherical particles, being axisymmetric, exhibit no notable alignment. DEM simulations confirm these findings, emphasising the effectiveness of the X-ray method in studying the internal mixing kinematics of diverse particle shapes.