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

Chapter 5 Discussion Page 5.13
5.7 CONCLUSIONS
Experimental work has been conducted using homogeneous non-Newtonian slurries and <strong>the</strong>
analysis and discussion <strong>of</strong> <strong>the</strong> results has been presented. As can be seen from <strong>the</strong> results
Slatter's model best predicts <strong>the</strong> turbulent flow <strong>of</strong> <strong>the</strong> <strong>the</strong>oretical models which were
considered. From <strong>the</strong> evidence it can be concluded that <strong>the</strong>oretical models based on <strong>the</strong>
<strong>particle</strong> roughness <strong>effect</strong> are justified in adopting <strong>the</strong> approach and in fact <strong>the</strong> <strong>particle</strong>
roughness <strong>effect</strong> which does exist should be considered in turbulent flow analysis. There is
room for improving on <strong>the</strong> Slatter model and fur<strong>the</strong>r test work should be conducted to fur<strong>the</strong>r
vindicate or disprove <strong>the</strong> assumption on which <strong>the</strong> model is based but <strong>the</strong> <strong>particle</strong> roughness
<strong>effect</strong> is defmitely a viable starting point to consider in <strong>the</strong> turbulent flow <strong>of</strong> homogeneous
non-Newtonian suspensions. The following conclusions can be drawn from <strong>the</strong> discussion
<strong>of</strong> <strong>the</strong> results and analysis <strong>of</strong> <strong>the</strong> test data:
• A <strong>particle</strong> roughness <strong>effect</strong> does exist.
• Fur<strong>the</strong>r investigation is required and a large data base should be established to
accurately determine <strong>the</strong> limit <strong>of</strong> validity <strong>of</strong> <strong>the</strong> <strong>particle</strong> roughness <strong>effect</strong>
• The d 85 <strong>size</strong> does not necessarily give <strong>the</strong> best representative <strong>particle</strong> <strong>size</strong> for <strong>the</strong>
<strong>particle</strong> roughness <strong>effect</strong> but will depend on <strong>the</strong> shape <strong>of</strong> <strong>the</strong> PSD.
• The viscous sub-layer cannot exist if it is smaller than <strong>the</strong> <strong>particle</strong>s which comprise
<strong>the</strong> slurry and <strong>the</strong> continuum approximation must be compromised in turbulent flow
analysis.
• The viscous sub-layer breaks down for Re, > 3,32 which is at a viscous sub-layer
thickness <strong>of</strong> approximately" = 3*d 85 for <strong>the</strong> Slatter model. For <strong>the</strong> Maude &
Whitmore (1956, 1958) correlation <strong>the</strong> viscous sub-layer breaks down when <strong>the</strong>
<strong>particle</strong> diameter is greater than half <strong>the</strong> thickness <strong>of</strong> <strong>the</strong> viscous sub-layer. Fur<strong>the</strong>r
investigation is required to accurately predict <strong>the</strong> exact point at which <strong>the</strong> viscous sub-