the effect of the particle size distribution on non-newtonian turbulent ...

ABSTRACT
THE EFFECT OF THE PARTICLE SIZE
DISTRIBUTION ON NON-NEWTONIAN
TURBULENT SLURRY FLOW IN PIPES
The handling <strong>of</strong> solid-liquid suspensions is an important concern within <strong>the</strong> chemical and
processing industries and many <strong>the</strong>oretical models have been proposed to try and explain and
predict turbulent flow behaviour. However, <strong>the</strong> prediction <strong>of</strong> turbulent flow from only <strong>the</strong>
viscous properties <strong>of</strong> non-Newtonian suspensions has over <strong>the</strong> years been questioned by
researchers. This <strong>the</strong>sis considers <strong>the</strong>oretical models well established in <strong>the</strong> literature and
<strong>the</strong> Slatter model, which uses both <strong>the</strong> rheology <strong>of</strong> <strong>the</strong> suspension and <strong>the</strong> <strong>particle</strong> <strong>size</strong>
<strong>distribution</strong> <strong>of</strong> <strong>the</strong> solids. These models are used to analyze <strong>the</strong> experimental data and <strong>the</strong>
<strong>effect</strong> that <strong>particle</strong> <strong>size</strong> and <strong>the</strong> <strong>particle</strong> <strong>size</strong> <strong>distribution</strong> has on turbulent flow behaviour.
The literature concerning <strong>the</strong> rheological fundamentals relevant to fluid flow in pipes has
been examined. The Newtonian turbulent flow model as well as <strong>the</strong> non-Newtonian models
<strong>of</strong>Dodge & Metzner, Torrance, Kemblowski & Kolodziejski, Wilson & Thomas and Slatter
have been reviewed.
Test work was conducted at <strong>the</strong> University <strong>of</strong> Cape Town's Hydrotransport Research
Laboratory using a pumped recirculating pipe test rig. The test apparatus has been fully
described and calibration and test procedures to enable collecting <strong>of</strong> accurate pipeline data
have been presented. Three slurries were used in test work namely kaolin clay, mixture I
(kaolin clay and rock flour) and mixture 2 (kaolin clay, rock flour and sand) with ad,s
<strong>particle</strong> <strong>size</strong> ranging from 24/Lm to 170/Lm.
The yield pseudoplastic model has been used to model and predict <strong>the</strong> laminar flow <strong>of</strong> <strong>the</strong>
suspensions that were tested and <strong>the</strong> meth9J adopted by Neill (1988) has been used to
determine <strong>the</strong> rheological constants. The pipeline test results have been presented as pseudoshear
diagrams toge<strong>the</strong>r with <strong>the</strong> <strong>the</strong>oretical model lines providing a visual appraisal <strong>of</strong> <strong>the</strong>
performance <strong>of</strong> each model. The Slatter model predicts <strong>the</strong> test data best with <strong>the</strong> o<strong>the</strong>r
<strong>the</strong>oretical models that were considered tending to under predict <strong>the</strong> head loss. The reason
<strong>the</strong> Slatter model performs better than <strong>the</strong> o<strong>the</strong>r <strong>the</strong>oretical models is because this model can
account for <strong>the</strong> wall roughness and <strong>particle</strong> roughness <strong>effect</strong>. Evidence to support this
statement has been presented.
This <strong>the</strong>sis highlights <strong>the</strong> fact that <strong>the</strong> <strong>particle</strong> <strong>size</strong> <strong>distribution</strong> is a vitally important property
<strong>of</strong> <strong>the</strong> suspension and that it does influence turbulent flow behaviour. It shows that
turbulence modelling using <strong>the</strong> <strong>particle</strong> roughness <strong>effect</strong> (eg Slatter, 1994) is valid and can
be adopted for non-Newtonian slurries. It is concluded that <strong>the</strong> <strong>particle</strong> <strong>size</strong> <strong>distribution</strong> must
be used to determine <strong>the</strong> <strong>particle</strong> roughness <strong>effect</strong> and this <strong>effect</strong> must be incorporated in <strong>the</strong>
turbulent flow analysis <strong>of</strong> non-Newtonian slurries.