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Nina Vankova, Slavka Tcholakova, Vasko Vulchev, Nikolai D. Denkov, Ivan B. Ivanov

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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Nina Vankova, Slavka Tcholakova, Vasko Vulchev, Nikolai D. Denkov, Ivan B. Ivanov

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  1. 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

  2. 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

  3. 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

  4. Used processing elements Cylindrical Two slits with 1 mm length Cylindrical One slit with 1 mm length Planar One slit with 1 mm length Emulsification method Experimental set-up

  5. Results:Flow rate vs applied pressure • At same Q p(2 slits)  2p(1slit) • At same p Q(planar) ~ 1.4 Q(Cyl-1slit)

  6. Mean: + 8 % - 12 % • d32 for 2-slits is ~ 12 % smaller than that for 1-slit • d32 for planar is ~ 8 % larger than that for cylindrical Effect of homogenizer construction on mean drop size

  7. Effect of the same factorson drop polydispersity • The polydispersity depends mainly on oil viscosity • Higher viscosity  more polydisperse emulsions

  8. Maximal drop size during emulsificationin the inertial regime of turbulent flowDavies, 1985 Pressure fluctuations Capillary pressure Viscous stress inside breaking drop Batchelor, 1956

  9. 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

  10. Literature data for the constants A1 and A2

  11. 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

  12. Dynamic interfacial tension of Na caseinate Na caseinate adsorbs much slower than low-molecular mass surfactants

  13. Fit of our data with -mean and corrected  Data for dV95 Data for d32 A1 = 0.510; A2 = 0.285; r2 = 0.957 A1 = 0.944; A2 = 0.280; r2 = 0.935

  14. 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

  15. Correlation plotpredicted and measured dmax

  16. Comparison of our constants A1 and A2with literature values C’ is a function of the position in the vessel (0.9 to 70) For impellers:

  17. Planar homogenizereffect of  on the values of A1 and A2 Mean  Maximal 

  18. 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).

  19. 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 (Sofia+Graz). Planar homogenizer: • More emulsification experiments at various conditions. • Graph (V), if available, for detailed analysis. • Paper ? Comparison of planar and cylindrical homogenizers (hydrodynamic flow, )?

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

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