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Flow of non-newtonian fluids in open channels

Dissertation (DTech (Civil Engineering))--Cape Technikon, Cape Town, 2003 / Flume design for homogeneous non-Newtonian fluids is problematic and not much research has
been conducted in this field. This application is industrially important in mining where slurries
have to be transported to processing or disposal sites at higher concentrations because water is
becoming a scarce and expensive commodity. This thesis addresses the problem of flume design
and develops predictive models for the laminar, transitional and turbulent flow behaviour of
non-Newtonian fluids in rectangular open channels.
The relevant literature pertaining to Newtonian and non-Newtonian pipe and open channel flow
is reviewed and research aspects are identified.
A unique test facility was designed, constructed and commissioned for this project. The facility
includes a 5 m-long by 75 mm-wide rectangular tilting flume, as well as a 10 m by 300 mmwide
rectangular tilting flume that can be partitioned to form a 150 mm wide flume. The flumes
are in series with an in-line tube viscometer which has tubes of diameter 13, 28 and 80 mm. The
experimental investigation covers a wide range of widths (75 mm-300 mm), slopes (1º-5º), flow
rates (0.05 l/s-45 l/s), relative densities (1.0067-1.165), volumetric concentrations (0%-10%),
and yield stresses (0-21.3 Pa). The fluids tested are kaolin and bentonite slurries and CMC and
Carbopol polymer solutions. The resulting database of empirical flow behaviour enabled the
identification of the important flow behaviour characteristics.
Existing models are compared and evaluated using the experimental database compiled for this
thesis and it is concluded that no model exists to predict the database compiled for the various
materials from laminar flow through the transition region into turbulence.
For the correlation of laminar flow data, a Reynolds number was developed from the Reynolds
number proposed for pipe flow by Slatter (1994). Using this Reynolds number, all the laminar
flow data available was collapsed onto the 16/Re line on a standard Moody diagram.
Criteria were developed to predict the onset of transition and the onset of ‘full turbulence’.
These criteria are functions of the Froude and Reynolds number as well as the viscous
characteristics of the fluids. These models performed better than the methods proposed by Naik
(1983) and Coussot (1994), which were based on the Hanks criterion.
A turbulent flow model was developed based on the turbulent model presented by Slatter (1994)
for pipe flow. Flow predictions using this model were more accurate than those presented by
Torrance (1963), Naik (1983), Wilson and Thomas (1985), and Slatter (1994).
The new models were tested with the database compiled for this thesis as well as with two
published data sets, one by Naik (1983) and the other by Coussot (1994). The new flow models
predicted all the available data within acceptable limits, providing a basis for design.
A new and experimentally validated design protocol is presented for the design of rectangular
non-Newtonian open channel flow in laminar, transitional and turbulent flow.
Date January 2003
CreatorsHaldenwang, Rainer
PublisherCape Technikon
Source SetsSouth African National ETD Portal
Detected LanguageEnglish

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