concentrations of up to 10% will behave in a Newtonian way with a
viscosity value only moderately above that of water alone.
Therefore it was here considered reasonable to use A' = 1 in
the model (Eq. (6)) for the iron ores.
In light of the fact that the model has not been verified for
high density solids, the results with the two industrially corn-
minuted iron ores showed that friction losses were estimated
well with the model for the hematite ore, while the model
tended to underestimate losses for the slightly heavier and
coarser magnetite ore.
The experimental results showed that a mixture of coarse
granite particles and tar sand railings were transported under
pseudohomogeneous-like conditions when the total volu-
metric solids concentration was 31%. Similar flow conditions
were also seen with the copper ore when transported at a
concentration of 39%. The copper ore results show that trans-
port of products with even and broad particle size distribu-
tions can be very energy effective.
The copper ore had about 24% of the particles liner than
75/xm. This portion may influence the rheology, thus giving
A' ~ 0 in the model. Wilson et al. [ 20] pointed out the impor-
tance of the non-Newtonian behaviour in their analysis of
phosphate slurries containing clay. However, following the
earlier discussion of the iron ores, it is expected here that the
comparatively low friction losses are more related to the size
distribution and its influence on pipe wall friction than to the
effect of true rheological mechanisms. This is in accordance
with Maciejewski et al. [ 2 ] who found that a fine sand slurry
(dso=0.15 ram) was very effective as a transport medium.
Following results by Shook et al. [7] they related the result
to the role of buoyancy in reducing mechanical friction along
the pipe wall, that is, to a local reduction of the settling of
large particles. Following the discussion by Sundqvist et al.
[ 14] it can be concluded that the use of a constant value of
P+s may be an over-simplification of very complex phenomena
occurring in the near-wall region in the lower part of the pipe.
It was seen in Fig. 8 that the partially-stratified model
(Appendix) compared well with measured data for the
crushed rock (6% < C< 13%). The crushed rock had a rel-
ative solids density of 2.65 and it can also be described by a
rather broad particle size distribution for particle sizes less
than dso(