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

Appendix B Conference Paper B.3
preventing suspensions settling and enabling higher throughputs (Mun, 1988). Many
<strong>the</strong>oretical models have <strong>the</strong>refore been proposed to try and explain and predict turbulent
flow behaviour. However, two major problem areas are that <strong>the</strong> turbulent behaviour <strong>of</strong>
non-Newtonian slurries appears unrelated to <strong>the</strong>ir laminar behaviour and yet has been
found strikingly similar to Newtonian turbulent flow behaviour, in spite <strong>of</strong> <strong>the</strong> obvious
difference in rheology.
This paper explores <strong>the</strong>se and o<strong>the</strong>r problem areas in <strong>the</strong> literature and shows how
previous models have failed to address <strong>the</strong>m adequately. Slatter's (1994) approach to
turbulence modelling, based on his findings on <strong>the</strong> <strong>particle</strong> roughness <strong>effect</strong>, is reviewed.
This model addresses <strong>the</strong>se problem areas - however <strong>the</strong> model was initially evaluated
on a limited number <strong>of</strong> slurries and <strong>particle</strong> <strong>size</strong>s.
Experimental work was conducted at <strong>the</strong> University <strong>of</strong> Cape Town's (UCT)
Hydrotransport Department, South Africa, using a pumped recirculating pipe test rig <strong>of</strong>
pipe diameters 25mm, 80mm, 150mm and 200mm. Non-Newtonian slurries with varying
<strong>particle</strong> <strong>size</strong> <strong>distribution</strong>s (PSD's) were tested and analysed, and <strong>the</strong> results are presented
and discussed.
2. LITERATURE REVIEW
2.1 The Yield Pseudoplastic Model
Non-Newtonian slurries can <strong>of</strong>ten be modelled as yield pseudoplastics (Govier & Aziz,
1972 and Hanks, 1979) and <strong>the</strong> larninar flow <strong>of</strong> all <strong>the</strong> slurries tested have been
successfully characterized using this model. The constitutive rheo10gical equation is
where Ty is <strong>the</strong> yield stress, K is fluid consistency index and n is <strong>the</strong> flow behaviour
index.
2.2 Laminar Pipe Flow
For laminar pipe flow, volumetric discharge, Q, and average velocity, V, can be
determined using <strong>the</strong> equation
(1)
(2)