PTV and PIV study of the motion of viscous drops in yield stress material

► Sedimentation of Newtonian drops in a viscoplastic domain. ► The use of PTV for determination of yielded region boundary around drops. ► Flow field within the yielded region measured by PIV. ► The effect of slip at an adjacent vertical flat wall on the drop motion. We report a study of the slow vi...

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Bibliographic Details
Published in:Journal of non-Newtonian fluid mechanics 2013-03, Vol.193, p.129-143
Main Authors: Holenberg, Yu, Lavrenteva, O.M., Liberzon, A., Shavit, U., Nir, A.
Format: Article
Language:English
Subjects:
Boundaries
Drop motion
Glass
PIV visualization
Sedimentation
Settling
Tracking
Trains
Wall slip
Walls
Yield stress
Yield stress materials
Yielded region
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Summary:► Sedimentation of Newtonian drops in a viscoplastic domain. ► The use of PTV for determination of yielded region boundary around drops. ► Flow field within the yielded region measured by PIV. ► The effect of slip at an adjacent vertical flat wall on the drop motion. We report a study of the slow viscous sedimentation of viscous Newtonian drops in a viscoplastic domain comprised of low concentration Carbopol aqueous solution. The study applies visualization methods. Direct photography is used to track the drop settling speed. In steady sedimentation PTV (Particle Tracking Velocimetry) is applied to determine the boundary of the yield stress region around the drop, while PIV (Particle Image Velocimetry) techniques are employed for the quantitative description of the flow field within this region. In infinite domains, the study addresses undisturbed sedimentation of slow and fast moving single drops and a tracking of the coalescence process of a train of two drops. Maps of the flow structure and intensity within the yielded regions around the drops in these cases are provided. When the sedimentation occurs in the vicinity of an adjacent vertical glass wall the drop settling speed may be either enhanced or retarded depending on the proximity to the wall. It is shown that the motion is retarded when the yielded region boundary remain intact but is deformed toward the drop on the wall side. Whenever the yielded region achieves complete contact with the wall the drop speed is augmented and an apparent slip is evident at the wall.
ISSN:0377-0257
1873-2631
DOI:10.1016/j.jnnfm.2012.09.013