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

Appendix B Conference Paper B.18
This investigation highlights <strong>the</strong> fact that <strong>the</strong> PSD is a vitally important property <strong>of</strong> <strong>the</strong>
slurry and should be used for <strong>the</strong> turbulent flow analysis <strong>of</strong> non-Newtonian slurries, as
has been used in <strong>the</strong> <strong>the</strong>ory for <strong>the</strong> new analysis, to account for rough wall turbulent
flow and to predict <strong>the</strong> change from smooth wall to rough wall turbulent flow.
Park et al (1989) and Pokryvalio & Grozberg (1995) used very different slurries and
experimental techniques, yet both reported significantly higher relative turbulence
intensities in <strong>the</strong> wall region for <strong>the</strong>ir slurries, when compared with air. This empirical
evidence strongly supports <strong>the</strong> concept <strong>of</strong> <strong>particle</strong> roughness turbulence.
Where Slarter's model fails to -accurately predict Sive's data it is felt <strong>the</strong> reason is that
<strong>the</strong> slurries tested by Sive were settling slurries and not homogenous slurries on which
<strong>the</strong> <strong>the</strong>oretical model was originally based. Fur<strong>the</strong>r investigation is required to determine
<strong>the</strong> limit <strong>of</strong> validity <strong>of</strong> <strong>the</strong> <strong>particle</strong> roughness <strong>effect</strong>. In fact, <strong>the</strong> limit <strong>of</strong> validity <strong>of</strong> <strong>the</strong>
<strong>particle</strong> roughness <strong>effect</strong> could provide a more logical basis for vehicle/load cut-<strong>of</strong>f in
mixed regime slurries than is used at present.
Future <strong>the</strong>oretical modelling <strong>of</strong>non-Newtonian slurries should take into account both <strong>the</strong>
PSD and <strong>the</strong> rheology <strong>of</strong> <strong>the</strong> slurry.
6. CONCLUSION
Particle roughness turbulence does not apply to settling slurries (as tested by Sive,
1988). Fur<strong>the</strong>r investigation is required to determine <strong>the</strong> limit <strong>of</strong>validity <strong>of</strong> <strong>the</strong> <strong>particle</strong>
roughness <strong>effect</strong>, and this limit could well serve as <strong>the</strong> criterion for vehic1elload cut-<strong>of</strong>f
in mixed regime slurries.
The <strong>particle</strong> roughness turbulence model is <strong>the</strong> first model to incorporate <strong>the</strong> continuum
compromise which must arise as <strong>the</strong> laminar sub-layer thickness is limited, and it is <strong>the</strong>
only model to explain <strong>the</strong> empirical evidence <strong>of</strong> increased turbulence intensities in <strong>the</strong>
wall region.
It can be concluded from <strong>the</strong> test data results that <strong>the</strong> new approach to turbulence
modelling using <strong>the</strong> <strong>particle</strong> roughness <strong>effect</strong> is valid and can be successfully adopted for
non-Newtonian slurries.
Acknowledgement
The co-operation <strong>of</strong> Pr<strong>of</strong>. Mike de Kock for <strong>the</strong> use <strong>of</strong> <strong>the</strong> Hydrotransport test facilities
at <strong>the</strong> University <strong>of</strong> Cape Town is gratefully acknowledged.