Handbook of Solvents - George Wypych - ChemTech - Ventech!

370 Semyon Levitsky, Zinoviy Shulman
Figure 7.2.6. Expansion of bubbles in water and POE
aqueous solution at a pressure drop. (a) - water, (b) -
solution of POE with c = 420 ppm. [By permission of
the American Institute of Physics from R.Y. Ting, and
A.T. Ellis, Phys. Fluids., 17, 1461, 1974, the reference
36]
tively different from the concentration dependence
of μ for a bubble in a pure viscous
fluid with the same Newtonian viscosity as
the solution (curve 7 in Figure 7.2.5).
The rheological properties of polymeric
solution highly depend on temperature.
Therefore, its variation affects the
bubble pulsations. Thermorheological features
in bubble dynamics have been studied 35
on the basis of temperature superposition
principle, using relations [7.2.30], [7.2.31].
It was shown that the temperature rise leads
to decrease of the decrement Λ 3, and this effect
is enhanced with the increase of n 1. Note
that the higher is the equilibrium temperature
of the liquid, the less sensitive are the Λ 3
values to variations in n 1. It is explained by
narrowing of the relaxation spectrum of the
solution. 25
Experimental results on bubble dynamics
in solution of polymers are not numerous.
Existing data characterize mainly the integral
effects of polymeric additives on bulk
phenomena associated with bubbles while
only few works are devoted to studying the
dynamics of an individual bubble. The observations
of the bubble growth in water at a
sudden pressure drop were compared with
those for aqueous solution of POE. 36 The results are represented in Figure 7.2.6. It is seen
that the effect of polymeric additives is small. This result is explained by rather large value
of Reynolds number Re p =t 0/t p corresponding to experimental conditions. 36 Therefore, the
inertial effects rather than the rheological ones play a dominant role in bubble dynamics.
The conclusions 36 were confirmed later 37 when studying the bubbles behavior in aqueous
solution of POE (trade mark Polyox WS 301) with the concentration of 250 ppm (for water
1 ppm = 1 g/m 3 ). A similar result was received also in studies 38 of nucleate cavitation in the
PAA aqueous solution with c = 0.1 kg/m 3 . The solution viscosity 38 only slightly (by 10%)
exceeded that of water.
When the polymer concentration (or molecular mass) is sufficiently high and viscosity
of solution exceeds essentially that of solvent, the rheological effects in bubble dynamics
become much more pronounced. In Figure 7.2.7, data 39 are presented for the relative damping
decrement of free oscillations of air bubble with R 0 = 2.8 mm in aqueous solution of
POE via concentration. The dashed line represents theoretical values of the decrement, corresponding
to Newtonian liquid with η = η p. The actual energy losses, characterized by experimental
points, remained almost unchanged, despite the sharp rise in the “Newtonian”
decrement, Λ p, with c. This result correlates well with the above theoretical predictions and
it is explained by viscoelastic properties of the solution. The same explanation has the phe-