Chemistry Reference
In-Depth Information
16
14
12
10
8
6
4
2
Theoretical profile
Measured profile
0
12
10
8
6
4
2
0
Radius (mm)
Fig. 3.7
The measured velocity profile and the profile calculated with the rheometer
measurement.
3.8.2
Suspension of polyamide in rapeseed oil
The presented data were acquired during a measurement campaign at
SIK Gothenburg conducted together with J. Wiklund. The fluid was a
suspension of 25% polyamide particles with an average size of 10 µmin
rapeseed oil. A flow loop consisting of a vessel, a pump and pipes with an
inner diameter of 22.5 mm was used to circulate the fluid. The transducer
was mounted 'wetted' but pulled back (the second option from the left in
Fig. 3.3). The flow curve (Fig. 3.8) measured with the rheometer shows
a shear-thinning behaviour, which can be approximated with the Sisko
fluid model (
+
η
∞
). For this model, there is no analytical
solution of the flow profile analogue to Equation 3.14. Therefore, the
gradient or point-wise method (Section 3.6.1) is applied.
The measured profile is shown in Fig. 3.9. Although a time-
compensated gain was used for this measurement, the intensities clearly
decrease with depth which is due to the attenuation in the highly concen-
trated suspension. It is obvious that for this example the envelope profile
would be distorted due to this depth-dependent attenuation; therefore,
the central frequency was used for the profile estimation. Towards the
pipe walls, the profile shows a sigmoidal shape, and the maximum shear
rate is shifted a few gates towards the pipe centre. This is an artefact as
the highest shear rate is expected at the pipe wall. In addition to the con-
volution mentioned in Section 3.7.1, the disturbance of the streamlines
η
=
γ
n
−
1
K
˙
