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Abstract
The air content and bubble size distribution in pure
foams and in fibre foams were determined in axial mixing
for varied rotation speed, liquid surface tension and
wood fibre consistency. Onset of flow macro-instabilities
were observed at high rotation speeds both with and
without fibres. Before the instability, the bubble size
decreased and air content increased with increasing
rotation speed. After the instability, the air content
was not only strongly affected by rotation speed but,
interestingly, both the air content and bubble size
increased with reduced surface tension. In both regions,
the average bubble size could be explained based on the
capillary number after the air content was explicitly
included in the model. With kraft fibres included in the
foam, the behaviour of the air content is very similar to
that without fibres but the macro-instability behaviour
begins a bit earlier, roughly at N=5000 RPM for the
surfactant concentration of 0.2 g/l. At this rotation
speed, the air content finds its maximum for both 0.33
and 0.66% consistency.
The main effect of the fibres is to reduce the bubble
size in the stable region. The higher the consistency of
fibres, the greater the reduction in the mean radius
turns out to be. This is probably due to the added local
shear forces due to fibre inertia enhancing the breaking
tendency of the larger bubbles. However, it seems that in
the unstable regime the fibres do not have a similar
effect. For very high rotation speeds, the bubble size is
practically equivalent with and without fibres. This
might be caused by the change in the turbulence spectrum
at the beginning of instabilities - the shear forces due
to the fluid phase may become strong enough to dominate
those caused by the fibre inertia.
Original language | English |
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Publication status | Published - 2014 |
Event | 10th European Conference on Foams and Applications, EUFOAM 2014 - Thessaloniki, Greece Duration: 7 Jul 2014 → 10 Jul 2014 |
Conference
Conference | 10th European Conference on Foams and Applications, EUFOAM 2014 |
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Country/Territory | Greece |
City | Thessaloniki |
Period | 7/07/14 → 10/07/14 |
Keywords
- foam
- fibre
- mixing
- air content
- bubble size
- flow
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Dive into the research topics of 'Wet fibre-laden foams in axial mixing with macro-instabilities'. Together they form a unique fingerprint.Projects
- 1 Finished
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FiFo: Fibre foams
Koponen, A. (Participant) & Timonen, J. (Manager)
1/01/13 → 15/12/14
Project: Academy of Finland project