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Rheological measurements in liquid-solid flows

Citation

Koos, Erin (2009) Rheological measurements in liquid-solid flows. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-03032009-092653

Abstract

This thesis presents experimental measurements of the shear stresses of a fluid-particulate flow at high Reynolds numbers as a function of the volume fraction of solids. From the shear stress measurements an effective viscosity, where the fluid-particulate 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 non-neutrally 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 close-packed volume fractions were experimentally determined using a counter-top 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 loose-packing. Between the random loose- and random close-packed states, the effective viscosity increases more rapidly with volume fraction and asymptotes to very large values at the close-packed 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 non-neutrally 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 particle-to-fluid 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 non-neutrally buoyant particles shows the same dependence on volume fraction as the neutrally buoyant cases.

Particle velocities were also measured for both neutrally buoyant and non-neutrally 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 rough-wall 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:Liquid-Solid 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):
  • Hunt, Melany L.
Thesis Committee:
  • Hunt, Melany L. (chair)
  • Brennen, Christopher E.
  • Brady, John F.
  • Shepherd, Joseph E.
  • Zenit Camacho, Jose Roberto
Defense Date:19 March 2009
Author Email:erinkoos (AT) gmail.com
Record Number:CaltechETD:etd-03032009-092653
Persistent URL:http://resolver.caltech.edu/CaltechETD:etd-03032009-092653
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 ETD-db
Deposited On:06 Jul 2009
Last Modified:26 Dec 2012 02:33

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