Mean and maximal drop size during emulsification in turbulent flow - effect of emulsification conditions

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Mean and maximal drop size during emulsification
in turbulent flow - effect of emulsification
conditions

• Nina Vankova, Slavka Tcholakova,
• Vasko Vulchev, Nikolai D. Denkov, Ivan B. Ivanov
• Laboratory of Chemical Physics Engineering,
• Faculty of Chemistry, Sofia University,Sofia,
  Bulgaria

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Aim To clarify the effect of several factorson
the mean and maximal drop size in emulsions,
prepared with narrow-gap homogenizer

• Studied factors
• Geometry of the processing element
  One vs two slits
• Planar vs cylindrical
• Flow rate
• Re 8450, Re 13270
• Viscosity of the dispersed phase
• From 3 to 500 mPa.s
• Interfacial tension
• From 5.5 to 14 mN/m

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Materials

• Aqueous phase
• 1 wt Brij 58 150 mM NaCl
• 1 wt SDS 10 mM NaCl
• 0.5 wt Na Caseinate 150 mM NaCl 0.01 wt
  NaN3
• Oil phase
• Hexadecane ?D 3 mPa.s ?OW 7. 0
  mN/m
• Soybean oil (SBO) ?D 50 mPa.s ?OW 5.5 to
  14.0 mN/m
• Silicone oil ?D 50 to 500
  mPa.s ?OW 10.3 mN/m

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Emulsification method
Experimental set-up
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Results Flow rate vs applied pressure
At same Q ? p(2 slits) ? 2p(1slit) At
same p ? Q(planar) 1.4 Q(Cyl-1slit)
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Effect of homogenizer construction on mean drop
size
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Effect of the same factorson drop polydispersity

The polydispersity depends mainly on oil
viscosity Higher viscosity ? more polydisperse
emulsions
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Maximal drop size during emulsificationin the
inertial regime of turbulent flowDavies, 1985
Pressure fluctuations
Capillary pressure
Viscous stress inside breaking drop
Batchelor, 1956
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Mean drop size during emulsificationin the
inertial regime of turbulent flow Calabrese et
al., 1986
Mean turbulent energy
Surface energy
Energy dissipated inside breaking drop
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Literature data for the constants A1 and A2
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Analisys of our data with ?-mean(cylindrical
gap)
Data for dV95
Data for d32
A1 1.13 A2 0.195 r2 0.80
A1 0.601 A2 0.198 r2 0.87
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Dynamic interfacial tension of Na caseinate
Na caseinate adsorbs much slower than
low-molecular mass surfactants
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Fit of our data with ?-mean and corrected ?
Data for dV95
Data for d32
A1 0.944 A2 0.280 r2 0.935
A1 0.510 A2 0.285 r2 0.957
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Check of the values of A1 and A2with additional
experimental data
Data for dV95
Data for d32
A1 0.510 A2 0.285
A1 0.944 A2 0.280
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Correlation plotpredicted and measured dmax
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Comparison of our constants A1 and A2with
literature values
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Planar homogenizereffect of ? on the values of
A1 and A2
Mean ?
Maximal ?

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• Conclusions
• Experiment
• The effects of oil viscosity, interfacial tension
  and construction of the processing element on
  drop size are clarified.
• The polydispersity of the obtained emulsions
  increases with oil viscosity.
• Interpretation
• The data for dV95 are reasonably well described
  by Davies equation, which accounts for the
  viscous dissipation inside the drops.
• The values of A1 and A2 are determined from the
  experimental data (but depend significantly on
  the presumed value of ?).
• It is worth to specify better A1 and A2 -
  relative contributions of capillary pressure and
  viscous dissipation in drop breakup
  (collaboration with Graz and Warsaw).

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• To finalize these studies
• Cylindrical homogenizer
• Deeper analysis of the effect of ? - graph ?(V),
  if available.
• More convincing data for the kinetics of
  adsorption (Na caseinate)
• Comparison of the constants with those available
  in the literature.
• Preparation of a paper (SofiaGraz).
• Planar homogenizer
• More emulsification experiments at various
  conditions.
• Graph ?(V), if available, for detailed analysis.
• Paper ?
• Comparison of planar and cylindrical homogenizers
  (hydrodynamic flow, ?)?

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On behalf of the Bulgarian team Thank you for
the kind attitude and fruitful co-operation!