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the rheometer’s measurement cell. The bitumen concentrates also
were diluted in the rheometer’s cell by adding an equal volume of
industrial dilutant so that a studied emulsions contained 25 vol.%
of bitumen and 20 vol.% of water. Each emulsion was formed by
mixing for 1 hour at conditions close to a maximum rheometer’s
torque (shear stresses ≈0.7–0.8 N/m
2
), at a fixed formation tem-
perature TF in the range from 20 to 60°C. After formation was
completed, each sample under constant mixing was cooled at the
rate of 1–1,5°C per minute to the lowest measurement (flow) tem-
perature of 8–10°C.
At each operating temperature, the system was initially main-
tained at a constant shear rate for 20 min. The measurements con-
tinued with a step-like decrease of the shear rate down to
0.1–0.2 s
-1
. At each shear rate the torque and shear stress data
were collected for 90–120 s and averaged. Before changing to the
next measurement (flow) temperature (in 2°C steps, up to 30°C),
the shear rate was increased to its initial value. With the above
procedure, the typical duration of one experiment was about 6
hours.
In all studied samples non-Newtonian flow behaviour was ob-
served at shear stresses below 0.2–0.5 Pa. Hence, to characterise
the temperature-induced effects, we have used the viscosity values
at shear stress of 0.7 Pa, i.e. at flow conditions close to Newtonian.
Experimental results
1. The effect of the formation temperature on the vis-
cosity of emulsions
It was observed, that viscosities of emulsions, measured at in-
dustrially-important flow temperatures 10–28°C is strongly af-
fected by their formation temperature TF. Figure 1 shows the ef-
fect of TF on the dynamic viscosity for (1) the bitumen emulsions,
at 16°C; (2) the water/crude oil emulsions, at 12°C; (3) the water-
free oil phase of the W/O emulsions, at 12°C. Note, that the viscos-
ity values are plotted on a log-scale. As can be seen in Figure 1, in
all samples even relatively small variations of the formation tem-
18
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