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

Appendix B Conference Paper
ABSTRACT
PARTICLE ROUGHNESS
TURBULENCE
PT SLATTER, G S THORVALDSEN & F W PETERSEN
Cape Technikon, Cape Town, South Africa
The turbulent flow <strong>of</strong>non-Newtonian slurries has remained a problem, despite much
research in this area. The successful resolution <strong>of</strong>this problem is vitally imponanr not
only for hydrotranspon applications involving fine slurries, but also for mixed regime
slurries, where <strong>the</strong> vehicle component is usually a non-Newtonian slurry. Two major
problem areas are that <strong>the</strong> turbulent behaviour <strong>of</strong><strong>the</strong>se slurries appears unrelated to
<strong>the</strong>ir laminar behaviour and yet has been found to be strikingly similar to Newtonian
turbulent 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 <strong>the</strong>oretical models havefailed to address <strong>the</strong>m adequately. A new approach to
turbulence modelling is reviewed which does address <strong>the</strong>se problem areas. This approach
is based on <strong>the</strong> panicle roughness <strong>effect</strong>, but is as yet relatively untested outside <strong>the</strong>
range ojslurries and panicle <strong>size</strong>s on which it was originally evaluated.
An experimentalprogramme has been initiated to investigate and accumulate a data base
<strong>of</strong><strong>the</strong> behaviour <strong>of</strong>a wider range <strong>of</strong>non-Newtonian slurries. including slurries with a
bimodal panicle <strong>size</strong> <strong>distribution</strong>. These new data are analysed and <strong>the</strong> results are
presented and discussed. It is concluded that <strong>the</strong> new approach to turbulence modelling
using <strong>the</strong> panicle roughness <strong>effect</strong> is valid for <strong>the</strong> slurries tested.
1. INTRODUCTION
The prediction <strong>of</strong>turbulent flow or pipe flow energy requirements from only <strong>the</strong> viscous
properties <strong>of</strong> non-Newtonian suspensions has over <strong>the</strong> years been questioned by
researchers. It has been found that <strong>the</strong> flow behaviour and rheology <strong>of</strong><strong>the</strong>se suspensions
is influenced by such factors as <strong>particle</strong> <strong>size</strong>, shape, weight and <strong>distribution</strong> (philipp<strong>of</strong>f
1944, Hedstrom 1952, Orr & Blocker 1955, Zettlemoyer & Lower 1955, Maude &
Whitmore 1956, Thomas 1963, Thomas 1983, Mun 1988, Slatter 1994).
The turbulent flow <strong>of</strong> non-Newtonian suspensions is complex and is <strong>of</strong>ten considered
problematic to design. However, in many situations it has beneficial characteristics,
B.2