Citation
Koos, Erin (2009) Rheological measurements in liquidsolid flows. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd03032009092653
Abstract
This thesis presents experimental measurements of the shear stresses of a fluidparticulate flow at high Reynolds numbers as a function of the volume fraction of solids. From the shear stress measurements an effective viscosity, where the fluidparticulate flow is treated as a single fluid, is determined. This viscosity varies from the fluid viscosity when no solids are present to several orders of magnitude greater than fluid viscosity when the particles near their maximum packing state. It is the primary goal of this thesis to determine how the effective viscosity varies with the volume fraction of solids.
A variety of particle sizes, shapes, and densities were obtained through the use of polystyrene, nylon, polyester, styrene acrylonitrile, and glass particles, used in configurations where the fluid density was matched and where the particles were nonneutrally buoyant. The particle sizes and shapes ranged from 3 mm round glass beads to 6.4 mm nylon to polystyrene elliptical cylinders. To properly characterize the effect of volume fraction on the effective viscosity, the random loose and random closepacked volume fractions were experimentally determined using a countertop container that mimicked the in situ (concentric cylinder Couette flow rheometer) conditions. These volume fractions depend on the shape of the particles and their size relative to the container.
The effective viscosity for neutrally buoyant particles increases exponentially with volume fraction at fractions less than the random loosepacking. Between the random loose and random closepacked states, the effective viscosity increases more rapidly with volume fraction and asymptotes to very large values at the closepacked volume fraction. The effective viscosity does not depend on the size or shape of particles beyond the influence these parameters have on the random packing volume fractions.
For nonneutrally buoyant particles, the difference in particle buoyancy requires an additional correction. The volume fraction at the time of the force measurement was recorded for several different ratios of particletofluid density. This volume fraction increases with the shear rate of the Couette flow and decreases with the Archimedes number in a way that when plotted against the Reynolds number over the Archimedes number, these curves collapse onto one master curve. When the local volume fraction is used, the effective viscosity for nonneutrally buoyant particles shows the same dependence on volume fraction as the neutrally buoyant cases.
Particle velocities were also measured for both neutrally buoyant and nonneutrally buoyant particles. These particle velocities near the stationary inner wall show evidence for a small region near the walls with few particles. This particle depletion layer was measured directly using the velocity data and indirectly using the difference between the measured effective viscosities for the smooth and roughwall configurations. The slip in the smooth wall experiments can significantly affect the measured viscosity, but this deficiency can be corrected using the thickness of the depletion layer to find the actual value for the effective viscosity.
Item Type:  Thesis (Dissertation (Ph.D.)) 

Subject Keywords:  LiquidSolid Flows; Rheology; Suspensions 
Degree Grantor:  California Institute of Technology 
Division:  Engineering and Applied Science 
Major Option:  Mechanical Engineering 
Thesis Availability:  Public (worldwide access) 
Research Advisor(s): 

Thesis Committee: 

Defense Date:  19 March 2009 
NonCaltech Author Email:  erinkoos (AT) gmail.com 
Record Number:  CaltechETD:etd03032009092653 
Persistent URL:  http://resolver.caltech.edu/CaltechETD:etd03032009092653 
Default Usage Policy:  No commercial reproduction, distribution, display or performance rights in this work are provided. 
ID Code:  858 
Collection:  CaltechTHESIS 
Deposited By:  Imported from ETDdb 
Deposited On:  06 Jul 2009 
Last Modified:  26 Dec 2012 02:33 
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