Experimental results on the flow rheology of fiber-laden aqueous foams

Ari Jäsberg, Pasi Selenius, Antti Koponen

Research output: Contribution to journalArticleScientificpeer-review

11 Citations (Scopus)

Abstract

We report here the first experimental results on the rheology of fiber-laden aqueous foams. The measurements were carried out in a laboratory-scale environment with a glass pipe of diameter 15 mm. The slip velocity at the pipe wall was measured with high-speed video imaging. Plain aqueous foam was generated from 8.5 mM aqueous solution of sodium dodecyl sulphate (SDS). Foam generation was realized as a combination of tank mixing and injection of compressed air in a special inline generation block (turbulence generator) installed into the flow loop. Fiber-laden foam was prepared by dispersing hardwood fibers into the SDS solution at consistency of 20 g/kg. In the measurements, an absolute slip velocity was observed that increased with the wall shear stress. On the other hand, the relative slip velocity decreased with the wall shear stress. At highest shear stresses relative slip values of ca. 10% were observed, i.e. considerable shearing took place inside the foam. At low wall shear stress relative slip velocities up to 40% were measured. The addition of wood fibers decreased the absolute slip by ca. 25% while the relative slip increased by a factor close to four. The real wall shear rate in foam was calculated with the Weissenberg-Rabinowitsch correction. All the studied foams could be modeled with Herschel-Bulkley law with flow behavior index n = 0.5. The viscosity of the fiber-laden foam was ca. 100% larger than that of the plain aqueous foam at same density and temperature. This increase in viscosity is much less than in the case of plain aqueous fiber suspension, where the viscosity increases by a factor five or more due to fibers being in continuous contact in shearing. Thus the current results imply that in aqueous foams fibers do not interact or flocculate to the same extent as in plain aqueous suspensions. By applying the methodology described here on the data measured with one pipe diameter, one can calculate real material properties that are independent of boundary effects like slip velocity.
Original languageEnglish
Pages (from-to)147-155
JournalColloids and Surfaces A: Physicochemical and Engineering Aspects
Volume473
DOIs
Publication statusPublished - 2015
MoE publication typeA1 Journal article-refereed

Fingerprint

Rheology
rheology
foams
Foams
slip
fibers
Fibers
plains
shear stress
Shear stress
Pipe
Sodium dodecyl sulfate
Viscosity
viscosity
sodium sulfates
shearing
Shearing
Sodium Dodecyl Sulfate
Suspensions
compressed air

Keywords

  • aqueous foam
  • wet foam
  • fiber-laden foam
  • slip velocity
  • rheology

Cite this

@article{2a776e0e7f984c5f999e70fa7f30ad3e,
title = "Experimental results on the flow rheology of fiber-laden aqueous foams",
abstract = "We report here the first experimental results on the rheology of fiber-laden aqueous foams. The measurements were carried out in a laboratory-scale environment with a glass pipe of diameter 15 mm. The slip velocity at the pipe wall was measured with high-speed video imaging. Plain aqueous foam was generated from 8.5 mM aqueous solution of sodium dodecyl sulphate (SDS). Foam generation was realized as a combination of tank mixing and injection of compressed air in a special inline generation block (turbulence generator) installed into the flow loop. Fiber-laden foam was prepared by dispersing hardwood fibers into the SDS solution at consistency of 20 g/kg. In the measurements, an absolute slip velocity was observed that increased with the wall shear stress. On the other hand, the relative slip velocity decreased with the wall shear stress. At highest shear stresses relative slip values of ca. 10{\%} were observed, i.e. considerable shearing took place inside the foam. At low wall shear stress relative slip velocities up to 40{\%} were measured. The addition of wood fibers decreased the absolute slip by ca. 25{\%} while the relative slip increased by a factor close to four. The real wall shear rate in foam was calculated with the Weissenberg-Rabinowitsch correction. All the studied foams could be modeled with Herschel-Bulkley law with flow behavior index n = 0.5. The viscosity of the fiber-laden foam was ca. 100{\%} larger than that of the plain aqueous foam at same density and temperature. This increase in viscosity is much less than in the case of plain aqueous fiber suspension, where the viscosity increases by a factor five or more due to fibers being in continuous contact in shearing. Thus the current results imply that in aqueous foams fibers do not interact or flocculate to the same extent as in plain aqueous suspensions. By applying the methodology described here on the data measured with one pipe diameter, one can calculate real material properties that are independent of boundary effects like slip velocity.",
keywords = "aqueous foam, wet foam, fiber-laden foam, slip velocity, rheology",
author = "Ari J{\"a}sberg and Pasi Selenius and Antti Koponen",
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language = "English",
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pages = "147--155",
journal = "Colloids and Surfaces A: Physicochemical and Engineering Aspects",
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}

Experimental results on the flow rheology of fiber-laden aqueous foams. / Jäsberg, Ari; Selenius, Pasi; Koponen, Antti.

In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, Vol. 473, 2015, p. 147-155.

Research output: Contribution to journalArticleScientificpeer-review

TY - JOUR

T1 - Experimental results on the flow rheology of fiber-laden aqueous foams

AU - Jäsberg, Ari

AU - Selenius, Pasi

AU - Koponen, Antti

PY - 2015

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N2 - We report here the first experimental results on the rheology of fiber-laden aqueous foams. The measurements were carried out in a laboratory-scale environment with a glass pipe of diameter 15 mm. The slip velocity at the pipe wall was measured with high-speed video imaging. Plain aqueous foam was generated from 8.5 mM aqueous solution of sodium dodecyl sulphate (SDS). Foam generation was realized as a combination of tank mixing and injection of compressed air in a special inline generation block (turbulence generator) installed into the flow loop. Fiber-laden foam was prepared by dispersing hardwood fibers into the SDS solution at consistency of 20 g/kg. In the measurements, an absolute slip velocity was observed that increased with the wall shear stress. On the other hand, the relative slip velocity decreased with the wall shear stress. At highest shear stresses relative slip values of ca. 10% were observed, i.e. considerable shearing took place inside the foam. At low wall shear stress relative slip velocities up to 40% were measured. The addition of wood fibers decreased the absolute slip by ca. 25% while the relative slip increased by a factor close to four. The real wall shear rate in foam was calculated with the Weissenberg-Rabinowitsch correction. All the studied foams could be modeled with Herschel-Bulkley law with flow behavior index n = 0.5. The viscosity of the fiber-laden foam was ca. 100% larger than that of the plain aqueous foam at same density and temperature. This increase in viscosity is much less than in the case of plain aqueous fiber suspension, where the viscosity increases by a factor five or more due to fibers being in continuous contact in shearing. Thus the current results imply that in aqueous foams fibers do not interact or flocculate to the same extent as in plain aqueous suspensions. By applying the methodology described here on the data measured with one pipe diameter, one can calculate real material properties that are independent of boundary effects like slip velocity.

AB - We report here the first experimental results on the rheology of fiber-laden aqueous foams. The measurements were carried out in a laboratory-scale environment with a glass pipe of diameter 15 mm. The slip velocity at the pipe wall was measured with high-speed video imaging. Plain aqueous foam was generated from 8.5 mM aqueous solution of sodium dodecyl sulphate (SDS). Foam generation was realized as a combination of tank mixing and injection of compressed air in a special inline generation block (turbulence generator) installed into the flow loop. Fiber-laden foam was prepared by dispersing hardwood fibers into the SDS solution at consistency of 20 g/kg. In the measurements, an absolute slip velocity was observed that increased with the wall shear stress. On the other hand, the relative slip velocity decreased with the wall shear stress. At highest shear stresses relative slip values of ca. 10% were observed, i.e. considerable shearing took place inside the foam. At low wall shear stress relative slip velocities up to 40% were measured. The addition of wood fibers decreased the absolute slip by ca. 25% while the relative slip increased by a factor close to four. The real wall shear rate in foam was calculated with the Weissenberg-Rabinowitsch correction. All the studied foams could be modeled with Herschel-Bulkley law with flow behavior index n = 0.5. The viscosity of the fiber-laden foam was ca. 100% larger than that of the plain aqueous foam at same density and temperature. This increase in viscosity is much less than in the case of plain aqueous fiber suspension, where the viscosity increases by a factor five or more due to fibers being in continuous contact in shearing. Thus the current results imply that in aqueous foams fibers do not interact or flocculate to the same extent as in plain aqueous suspensions. By applying the methodology described here on the data measured with one pipe diameter, one can calculate real material properties that are independent of boundary effects like slip velocity.

KW - aqueous foam

KW - wet foam

KW - fiber-laden foam

KW - slip velocity

KW - rheology

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SN - 0927-7757

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