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3.4. Activation energies of the viscous flow
Activation energies were determined from the dependencies of
the logarithm of viscosity on the reciprocal flow temperature, by
fitting straight line approximations (the Arrhenius plots) between
the consecutive experimental points. To reduce a random scatter,
the obtained sets of activation energies were smoothed with a
three-point sliding data window. The results of these calculations
are presented in Fig.3 A, B, C, where the thick solid lines are the
data for W/O emulsions, thin solid lines – the data for the matrix
crude oil and the dashed lines – the data for bitumen emulsions
(note the log scale for activation energies).
Fig.3A shows the dependencies of activation energies on the
flow (measurement) temperature for samples, subjected to room
temperature formation (20°C for W/O emulsion and the matrix
crude oil, 26°C for bitumen emulsions). The notable feature of
Fig.3A is a virtual coincidence of activation energies for all studied
samples.
For flow temperatures decreasing from 30°C down to about
20°C all activation energies remain fairly constant, slowly increas-
ing within the limits of 8.5-10.5 kcal/mol (≈36-44 kJ/mol).
At temperatures close to 20°C there is a step-like increase of
the activation energies to a new level of 220–29 kcal/mol
(≈92–121 kJ/mol). Below 10–12°C the activation energies show the
tendency of decreasing, so the shape of the curves in the range of
8–20°C may be described as a “flat maximum”.
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