Abstract
| Original language | English |
|---|---|
| Pages (from-to) | 147-155 |
| Journal | Colloids and Surfaces A: Physicochemical and Engineering Aspects |
| Volume | 473 |
| DOIs | |
| Publication status | Published - 2015 |
| MoE publication type | A1 Journal article-refereed |
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Keywords
- aqueous foam
- wet foam
- fiber-laden foam
- slip velocity
- rheology
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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 journal › Article › Scientific › peer-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
Y1 - 2015
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
UR - https://www.sciencedirect.com/journal/colloids-and-surfaces-a-physicochemical-and-engineering-aspects/vol/473/suppl/C
U2 - 10.1016/j.colsurfa.2014.11.041
DO - 10.1016/j.colsurfa.2014.11.041
M3 - Article
VL - 473
SP - 147
EP - 155
JO - Colloids and Surfaces A: Physicochemical and Engineering Aspects
JF - Colloids and Surfaces A: Physicochemical and Engineering Aspects
SN - 0927-7757
ER -