| Summary: | Using a shear cell device, we have studied four associated
problems in foam by experiments: Bubble-bubble coalescence in
sheared two-dimensional foam; lateral migration of a single large
bubble in an otherwise monodisperse foam; size segregation of
bubbles in sheared bidisperse foam; and the effect of
non-Newtonian rheology of foam on lateral migration of bubble. For
bubble-bubble coalescence in sheared two-dimensional foam, we
observed a threshold of shear rate beyond which coalescence of
bubbles happens. The most promising explanation was the model
based on the centripetal force with qualitative agreement with
experimental results.
Next we studied the dynamics of monodisperse foam in the presence
of a single bubble whose size is different from the neighboring
bubbles. We reported the lateral migration of a larger single
bubble away from the wall. We also reported thresholds of shear
rate and bubble size ratio beyond which migration occurs. In this
study we modified the Chan-Leal model and predicted the
experimental trajectories of migrating bubbles.
For bidisperse foams, we reported evolution in foam structure to a
size segregated structure, in which large bubbles accumulate at
the middle of the gap whereas smaller ones close to walls. Then,
we adopted a model based on convection-diffusion equation to
account for both lateral migration and shear induced diffusion.
Finally, we extended the second work by widening the gap of
Couette coaxial cylinder geometry. Similar to the second work, we
found that large bubble migrates laterally to an equilibrium
position close to the inner wall. We believe this new mechanism is
the non-Newtonian feature of foam. We characterized our foam by
measuring its degree of shear thinning and also estimated its
elasticity based on the literature data on foam. Then, we found
out for a shear thinning fluid bubble migrated to position even
closer to the inner wall than in the foam while a bubble in Boger
fluid migrated to a position closer to the outer cylinder.
Therefore, for a viscoselastic fluid which has the same feature
one would expect to see bubble migration to a position between
these two for two fluids. === Applied Science, Faculty of === Chemical and Biological Engineering, Department of === Graduate
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