nina vankova, slavka tcholakova, vasko vulchev, nikolai d. denkov, ivan b. ivanov
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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
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
Aim: To clarify the effect of several factorson the mean and maximal drop size in emulsions,
prepared with narrow-gap homogenizer
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
Emulsification method
Cylindrical
Two slits with 1 mm length
Used processing elementsExperimental set-up
Cylindrical
One slit with1 mm length
Planar
One slit with1 mm length
Results: Flow rate vs applied pressure
At same Q p(2 slits) 2p(1slit) At same p Q(planar) ~ 1.4 Q(Cyl-1slit)
Pressure, p x 105, Pa
0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0 4.4
Flo
w r
ate
Q,
L/s
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Cyl - 1 slit Cyl - 2 slitsPlanar
0 5271 .Q k p
k1
Planar 4.498
Cylindrical – 1 slit 3.293
Cylindrical – 2 slits 2.307
Effect of homogenizer construction on mean drop size
d32, m Re
D,
mPa.s
OW,
mN/m Planar Cyl - 1 Cyl - 2
5.5 5.8 5.5 5.0
7.4 7.2 6.6 6.0 13270
14.0 10.3 9.7 8.0
8450
50
7.4 12.8 12.0 10.0
3 7.0 3.6 3.3 3.0 13270
95 10.3 11.3 9.7 8.9
d32 for 2-slits is ~ 12 % smaller than that for 1-slit
d32 for planar is ~ 8 % larger than that for cylindrical
Mean: + 8 % - 12 %
% vs Cyl-1
Planar Cyl – 2
+ 5 - 9
+ 9 - 10
+ 6 - 18
+ 7 - 17
+ 9 - 9
+ 16* - 8
The polydispersity depends mainly on oil viscosity
Higher viscosity more polydisperse emulsions
Effect of the same factorson drop polydispersity
dV95, m dv95/d32 Re
D,
mPa.s
OW,
mN/m Cyl - 1 Planar Cyl - 1 Cyl - 2 Mean
5.5 11.2 2.12 2.03 2.02
7.4 13.9 2.08 2.10 1.93 13270
14.0 21.5 2.01 2.22 2.00
8450
50
7.4 23.9 2.03 1.99 2.12
2.1 0.08
3 7.0 5.4 1.67 1.63 1.53 1.6 0.08 13270
95 10.3 20.7 2.13 2.13 1.96 2.1 0.08
Maximal drop size during emulsificationin the inertial regime of turbulent flow
Davies, 1985
3 5 3 51 3 1 31 2 3 5 2 5
2
1 2
4
4
D
OW C
dd C
CC
Pressure fluctuations
Capillary pressure
Viscous stress inside breaking drop
2 321 1 2TP ( d ) C u C C d
4CP d
1 31 22DDC du
d d
3 51 3 1 3 3 5 2 5
1 2OW D Cd A A d
3 5 1 2
1 1 2 2 24 4 1.9; 0.35A CC A C1 20 7 2;C . C Batchelor, 1956
Mean drop size during emulsificationin the inertial regime of turbulent flow
Calabrese et al., 1986
1 22 3 5 3 1 3 1 3
5 3
1 21C C D
OW D OW
d dA A
3 3 2 3 2 3~ ( ) ~6 6TE d P d d d
2~ OWE d
2 323~ ~
6 6CD
DISS Dd
ddE d
Mean turbulent energy
Surface energy
Energy dissipated inside breaking drop
Literature data for the constants A1 and A2
Athors Homogenizer Viscosity range Interfacial tension
A1 A2
Hinze, 1955
Coaxial cylinders low 0.725
for dMAX
0.138 for dMAX Sprow,
1967 Impellers 0.51 mPa.s 41.8 mN/m
0.0524 for d32
Narsimhan et al., 1979
Impellers low 0.053 for d32
Davies, 1985
Clearance valve Colloidal mills Liquid whistles
Turbine impellers
3.5 to 200 mPa.s 30 mN/m 1 ( 0.354)
0.054 for d32
4.08 – 4.42 for d32
Calabrese et al., 1986
Impellers 5 to 500 mPa.s 1 to 45 mN/m 0.09
for dmax
3 51 3 1 3 3 5 2 5
1 2OW D Cd A A d
2 3 5 3 1 3 1 35 3
1 21C D
OW OW
d dA A
Analisys of our data with -mean(cylindrical gap)
A1 = 1.13; A2 = 0.195; r2 = 0.80 A1 = 0.601; A2 = 0.198; r2 = 0.87
D(dV95OW
0 2 4 6 8 10 12 14 16 18
(2/
5 C
d
V95
O
W
0
1
2
3
4
5
6
HexadecaneSBOSilicone oil
SDSBrij 58
NaCaseinate
Data for dV95
D(d32OW
0 2 4 6 8 10 12 14
(2/
5 C
d
32
OW
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
HexadecaneSBOSilicone oil
SDSBrij 58
NaCaseinate
Data for d32
Time, sec
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
- 0,
mN
/m
-10
-8
-6
-4
-2
0
0.02 wt % NaCas
0.0015 wt % SDS
Dynamic interfacial tension of Na caseinate
Na caseinate adsorbs much slower than low-molecular mass surfactants
2 3 5 3 1 3 1 35 3
1 21C D
OW OW
d dA A
D(dV95OW
0 2 4 6 8 10 12 14 16 18
(2/
5 C
d
V95
O
W
0
1
2
3
4
5
6
HexadecaneSBOSilicone oil
SDSBrij 58
NaCaseinate
Data for dV95
D(d32OW
0 2 4 6 8 10 12 14(
2/5
C
d
32
OW
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
HexadecaneSBOSilicone oil
SDSBrij 58
NaCaseinate
Data for d32
A1 = 0.944; A2 = 0.280; r2 = 0.935 A1 = 0.510; A2 = 0.285; r2 = 0.957
Fit of our data with -mean and corrected
Check of the values of A1 and A2
with additional experimental data 2 3 5 3 1 3 1 3
5 3
1 21C D
OW OW
d dA A
A1 = 0.944; A2 = 0.280 A1 = 0.510; A2 = 0.285
D(dv95OW
0 20 40 60 80 100 120 140
(2/
5 C
d
V95
OW
0
10
20
30
40
HexadecaneSBOSilicone oil
SDSBrij 58
NaCaseinate
D(d32OW
0 20 40 60 80 100
(2/
5 C
d
32
OW
0
2
4
6
8
HexadecaneSBOSilicone oilx vs Col 39
SDSBrij 58
NaCaseinate
Data for dV95 Data for d32
dmax, exp (m)
0 10 20 30 40 50
dm
ax,
theo
r (
m)
0
10
20
30
40
50 A1 = 0.944
A2 = 0.280
rel error = 8 %
Correlation plotpredicted and measured dmax
Comparison of our constants A1 and A2
with literature values
Viscosity range Interfacial tension
A1 A2
Hinze, 1955
Coaxial cylinders low 0.725
Sprow, 1967
Impellers 0.51 mPa.s 41.8 mN/m 0.138
Davies, 1985
Clearance valve Colloidal mills Liquid whistles
Turbine impellers
3.5 to 200 mPa.s 30 mN/m 1 ( 0.354)
Calabrese et al., 1986
Impellers 5 to 500 mPa.s 1 to 45 mN/m 0.09 4.08 – 4.42
Current study
Narrow-gap homogenizer
3 to 500 mPa.s 5 to 30 mN/m 0.944 0.28
3 51 3 1 3 3 5 2 5
1 2OW D Cd A A d
For impellers: 3 2'C N L C’ is a function of the position in the vessel (0.9 to 70)
Planar homogenizereffect of on the values of A1 and A2
D(dV95OW
0 5 10 15 20
(2/
5 C
d
V95
OW
0
2
4
6
8
10
12
HexadecaneSilicone oilSBO
SDSBrij 58
NaCaseinate
Mean
D(dV95OW
0 5 10 15 20 25 30
(2/
5 C
d
V95
OW
0
2
4
6
8
10
12
14
16
18
20
22
HexadecaneSilicone oilSBO
SDSBrij 58
NaCaseinate
Maximal
10-5, J/kg.s A1 A2
3.45 1.08 0.36
10.44 1.69 0.25
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).
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, )?
On behalf of the Bulgarian team:
Thank you for the kind attitude
and fruitful co-operation!