Granular mixing has received less attention than fluid mixing due to the unique properties of granular materials and the complexity of their flow behaviors. Unlike fluid flows, where a continuum perspective accurately captures flow behavior, neither a continuum nor a discrete perspective by itself can describe the global behaviors of granular flows. The tendency of particle mixtures to segregate based on varying physical properties further complicates the mixing problem. In this work, a 3D granular tumbler flow system is considered as a prototype to study the behaviors of granular mixing that can be understood using dynamical systems approaches based on the "cutting-and-shuffling'' mixing paradigm. The proposed mixing mechanism is a synergy of "cutting-and-shuffling'' and "stretching in the flowing layer,'' a combination of discrete and continuum perspectives. This dissertation addresses two main points, mixing and non-mixing behaviors induced by the underlying flow dynamics (no segregation), and the interaction between segregation and the flow dynamics. The role of mixing with "cutting-and-shuffling'' is first studied by taking into consideration uncertainty in operations in a simplified one-dimensional case. In the 3D granular flow system, x-ray based particle tracking techniques are used to identify mixing and non-mixing behaviors corresponding to dynamical systems features predicted by the continuum model. A continuum model, based purely on the flow kinematics, demonstrates that complex non-mixing and mixing regions exist in the system. When segregation is induced by using two physically distinct particle species, a pattern formation process occurs as a result of the interaction of segregation and flow dynamics including a weak axial perturbation. Statistical analysis enabled by discrete element method simulations (DEM), combined with continuum descriptions are used to uncover the mechanism of pattern formation for segregating granular materials in 3D tumbler flows.

Creator

• Yu, Mengqi

DOI

• https://doi.org/10.21985/n2-xan1-my24

Subject

• Chemical engineering

Language

• en

Alternate Identifier

• etdadmin_upload_780245
• http://dissertations.umi.com/northwestern:15389

Keyword

• Granular materials
• Mixing and segregation
• tumbler flow

Date created

• 2020-01-01

Resource type

• Dissertation

Rights statement

• In Copyright