Skip to Main Content
 

Global Search Box

 
 
 

ETD Abstract Container

Abstract Header

Shear Induced Migration of Particles in a Yield Stress Fluid

Gholami, Mohammad
http://orcid.org/0000-0002-5865-7414
http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1502793185991791

Abstract Details

2017, Master of Science (MS), Ohio University, Mechanical Engineering (Engineering and Technology).
Concentrated suspensions have been an area of research for years, with wide range of applications in industry and nature. One of the main issues encountered when handling such materials is the development of particle concentration inhomogeneities under shear, as a result of sedimentation and Shear Induced Migration (SIM). Experimental techniques to study the dynamics of suspension flows thus require high spatial and temporal resolutions to capture profiles of solid volume fraction in both transient and steady-state conditions. When optical access is possible, methods like particle tracking are employed due to their high temporal and spatial resolutions; however, optical access is limited in real systems and even in the majority of model suspensions. In these last cases, methods involving Nuclear Magnetic Resonance (NMR) are employed. These methods require the use of homemade devices, which makes them rare and expensive. Moreover, the time required for data acquisition is large, making them incapable of studying fast changes and monitoring volume fraction evolutions continuously. Available methods may thus not fully meet all the requirements to study most suspension flows. The objective of this thesis is to study SIM of particles in yield stress fluids. The contribution of this thesis comes into two parts. First, we introduce a new technique based on X-ray radiography with high temporal (O(0.1 sec)) and spatial (O(10 μm)) resolutions to overcome the above-mentioned limitations. This technique allows us to study the evolution of the solid volume fraction in fast suspension flows regardless of optical access. We benefit from the axial symmetry in our flow configuration, a wide gap Couette setup, to extract a 3D solid volume fraction field from a single X-ray projection image. We propose a mathematical algorithm based on the inversion of Abel transform in conjunction with H1 regularization and data denoising to measure the solid volume fraction field in suspensions in a fraction of a second. We show that the results are in excellent agreement with those obtained from micro Computed Tomography (CT scan) in one hour. This significant reduction in the data acquisition time opens a new avenue in the field of suspensions. As a proof of concept, we study the kinetics of shear-induced migration for suspensions of particles in a yield stress fluid in two different conditions: with and without an unyielded region. In both cases, we are able to capture in detail the kinetics of migration. In the presence of a plug region, we manage to accurately describe the particle accumulation at the interface between the sheared and the static regions. Remarkably, even in the absence of sedimentation, the concentration profiles show a complex 2D structure, with no z-invariant region, which illustrates the strong impact of top and bottom boundary effects on migration. This further shows the necessity of developing techniques that give access to the full spatial concentration field, as the one we present here. Second, we propose a model framework based on diffusive flux models to study one dimensional SIM in a yield stress fluid. The model framework is validated via performing rheometry coupled with X-ray radiography using the technique developed in the first part of this thesis. All of the experiments are performed in a narrow gap Couette cell. The rheometry results give us insight into understanding the bulk rheology in the presence of shear rate and solid volume fraction inhomogeneities. In addition to that, X-ray radiography provides detailed information about the evolution of the solid volume fraction in the domain. These measurements allow us to refine the model framework for SIM of particles in a non-Newtonian suspending fluid, particularly a yield stress fluid. We show that complex rheology of the yield stress suspending fluid (i.e., islands of unyielded regions) strongly affects the SIM of particles. This feature is absent when we deal with a Newtonian suspending fluid.
Sarah Hormozi, Dr. (Advisor)
David Bayless, Dr. (Committee Member)
Alexander Neiman, Dr. (Committee Member)
Monica Burdick, Dr. (Committee Member)
154 p.
Engineering; Mechanical Engineering; Mechanics
Migration; Shear Induced Migration; SIM; X-ray; Abel transformation; Suspension; yield stress; visco-plastic; concentration map; radiography; non-Newtonian fluid; rheology; rheometry; viscometry; NYSS; diffusion; image analysis; Couette flow;

Recommended Citations

Citations

  • Gholami, M. (2017). Shear Induced Migration of Particles in a Yield Stress Fluid [Master's thesis, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1502793185991791

    APA Style (7th edition)

  • Gholami, Mohammad. Shear Induced Migration of Particles in a Yield Stress Fluid. 2017. Ohio University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1502793185991791.

    MLA Style (8th edition)

  • Gholami, Mohammad. "Shear Induced Migration of Particles in a Yield Stress Fluid." Master's thesis, Ohio University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1502793185991791

    Chicago Manual of Style (17th edition)

ohiou1502793185991791
144
© 2017, all rights reserved.
This open access ETD is published by Ohio University and OhioLINK.