Wet fibre-laden foams in axial mixing with macro-instabilities

Research output: Contribution to conferenceConference AbstractScientific

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 languageEnglish
Publication statusPublished - 2014
Event10th European Conference on Foams and Applications, EUFOAM 2014 - Thessaloniki, Greece
Duration: 7 Jul 201410 Jul 2014

Conference

Conference10th European Conference on Foams and Applications, EUFOAM 2014
CountryGreece
CityThessaloniki
Period7/07/1410/07/14

Fingerprint

foam
bubble
air
surface tension
inertia
fibre
surfactant
speed
turbulence
liquid
fluid

Keywords

  • foam
  • fibre
  • mixing
  • air content
  • bubble size
  • flow

Cite this

Al-Qararah, A., Hjelt, T., Koponen, A., Harlin, A., & Ketoja, J. (2014). Wet fibre-laden foams in axial mixing with macro-instabilities. Abstract from 10th European Conference on Foams and Applications, EUFOAM 2014, Thessaloniki, Greece.
Al-Qararah, Ahmad ; Hjelt, Tuomo ; Koponen, Antti ; Harlin, Ali ; Ketoja, Jukka. / Wet fibre-laden foams in axial mixing with macro-instabilities. Abstract from 10th European Conference on Foams and Applications, EUFOAM 2014, Thessaloniki, Greece.
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title = "Wet fibre-laden foams in axial mixing with macro-instabilities",
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.",
keywords = "foam, fibre, mixing, air content, bubble size, flow",
author = "Ahmad Al-Qararah and Tuomo Hjelt and Antti Koponen and Ali Harlin and Jukka Ketoja",
note = "Project code: 79706; 10th European Conference on Foams and Applications, EUFOAM 2014 ; Conference date: 07-07-2014 Through 10-07-2014",
year = "2014",
language = "English",

}

Al-Qararah, A, Hjelt, T, Koponen, A, Harlin, A & Ketoja, J 2014, 'Wet fibre-laden foams in axial mixing with macro-instabilities' 10th European Conference on Foams and Applications, EUFOAM 2014, Thessaloniki, Greece, 7/07/14 - 10/07/14, .

Wet fibre-laden foams in axial mixing with macro-instabilities. / Al-Qararah, Ahmad; Hjelt, Tuomo; Koponen, Antti; Harlin, Ali; Ketoja, Jukka.

2014. Abstract from 10th European Conference on Foams and Applications, EUFOAM 2014, Thessaloniki, Greece.

Research output: Contribution to conferenceConference AbstractScientific

TY - CONF

T1 - Wet fibre-laden foams in axial mixing with macro-instabilities

AU - Al-Qararah, Ahmad

AU - Hjelt, Tuomo

AU - Koponen, Antti

AU - Harlin, Ali

AU - Ketoja, Jukka

N1 - Project code: 79706

PY - 2014

Y1 - 2014

N2 - 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.

AB - 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.

KW - foam

KW - fibre

KW - mixing

KW - air content

KW - bubble size

KW - flow

M3 - Conference Abstract

ER -

Al-Qararah A, Hjelt T, Koponen A, Harlin A, Ketoja J. Wet fibre-laden foams in axial mixing with macro-instabilities. 2014. Abstract from 10th European Conference on Foams and Applications, EUFOAM 2014, Thessaloniki, Greece.