J. Zawała , M. Krzan, K. Małysa
description
Transcript of J. Zawała , M. Krzan, K. Małysa
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J. Zawała, M. Krzan, K. Małysa
Institute of Catalysis and Surface Chemistry Polish Academy of Sciences
ul. Niezapominajek 8, 30-239 Cracow, Poland
Influence of Surfactant on Initial Influence of Surfactant on Initial Accelerations, Shape and Velocity Variations Accelerations, Shape and Velocity Variations
of the Detaching Bubblesof the Detaching Bubbles
Cluster A Meeting, 22 September 2005, Poznań
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Bubble MotionBubble Motion
INDUSTRY
flotation
foam fractionation techniques
biotechnology
waste water treatment
EVERYDAY LIFE
washing (detergents)
champagne
beer
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QuestionsQuestions
What determine the bubble velocities?
How important is the type and concentration of the surfactant for:
accelerations of the bubble?
local velocities of the bubble?
terminal velocities of the bubble?
minimum adsorption coverages needed to full immobilization of
bubble interface?
Is there any relation between velocity variations and deformation of
the bubble?
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What affects bubble motion?
viscosity of the continous phase
density
surface tension
properties of gas\liquid interface
Velocity of the rising bubble is very sensitive for presence of surface active substance
>10 % adsorption coverage can diminish bubble velocity 2 x
Bubble motion in surfactant solutionsBubble motion in surfactant solutions
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Uniform coverage
eq
eq
35 cm
eqtop
u
Motion leads to disequilibrationof adsorption coverage
Motion leads to disequilibrationof adsorption coverage
terminal velocity
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in = 0.075 mm
lamp = 100 Hz i 200 Hz
hsolution 35 cm
Experimental SET-UPExperimental SET-UP
PC
CCD camerasvideo
TV square glass column
stroboscopic lamp
syringe pump
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Captured moviesCaptured movies
Detachment of the bubble in :
distilled water
stroboscop illumination frequency – 100 Hz
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Captured moviesCaptured movies
Detachment of the bubble in :
1.5 M pentanol solution
stroboscop illumination frequency – 100 Hz
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Measurements
L – distance from the capillary
x – distance between two subsequent positions of the bubble
Velocity = t
x
t = 0.01 s or 0.005 s
L
x
dv dh dh,dv – horizontal and vertical diameter
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Shape deformationsShape deformations
dh
dv
quantitative parameter characterizing the deformation degree of the bubble
Deformation ratio =
v
h
d
d
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AccelerationsAccelerations
Stroboscop illumination frequency - 200 Hz
Initial acceleration
time [s]
0.00 0.01 0.02 0.03 0.04 0.05ve
loci
ty [
cm/s
]0
5
10
15
20
25
30
water pentanol 2*10-3 M
pentanol 5*10-3 M
c [M] a [cm/s2] sd
0 (water) 925 64
2*10-3 640 48
5*10-3 500 110
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n-pentanol
distance from the capillary [ mm]0 50 100 150 200 250 300 350
velo
city
[cm
/s]
0
10
20
30
40
water1*10-4
5*10-4
1*10-3
1.5*10-3
3*10-3
5*10-3
VelocitiesVelocities
Low pentanol concentrations: 3 stages of the bubble motion
acceleration, deceleration and terminal velocity
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n-pentanol
distance from the capillary [mm]
0 50 100 150 200 250 300 350
dh
/dv
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7n-pentanol
distance from the capillary [mm]
0 50 100 150 200 250 300 350
velo
city
[cm
/s]
0
10
20
30
40
distilled water
1*10-3 M
1.5*10-3 M
2*10-3 M
3*10-3 M
Shape pulsations vs. local velocitiesShape pulsations vs. local velocities
for low concentrations: CORRELATION
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VelocitiesVelocities
n-octyltrimethylammonium bromide
distance from the capillary [mm]
0 50 100 150 200 250 300
velo
city
[cm
/s]
0
10
20
30
40
water5*10-4
1*10-3
5*10-3
1*10-2
2*10-2
4*10-2
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n-pentanol
concentration [mol/dm3]
0.000 0.002 0.004 0.006 0.008 0.010 0.012
term
inal
vel
oci
ty [
cm/s
]
0
10
20
30
40
full immobilization of bubble surface
Adsorption coverageAdsorption coverage
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VelocitiesVelocities
adsorption degree
0.0 0.2 0.4 0.6 0.8
term
inal
vel
oci
ty [
cm/s
]
0
10
20
30
40
n-pentanoln-octanoln-octyltrimethylammonium bromide
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Effect of concentration on shape pulsationsEffect of concentration on shape pulsations
acceleration U max deceleration U terminal
1.10 - 1.22 1.29 1.25 - 1.14 1.06:vh dd
:vh dd 1.06
61 mm16 mmcapillary 2.5 mm 34 mm 84 mm 100 mm 157 mm 216 mm 322 mm7 mm
1). n-pentanol 1.5*10-3
1).
capillary 3.5 mm 7.5 mm 15 mm 33 mm 61 mm 84 mm 102 mm 162 mm 216 mm 325 mm
2). n-pentanol 5*10-3
2).
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CONCLUSIONS
Initial acceleration and terminal velocity of the bubble decreases with increasing concentation of surface active substances
Presence of maximum at the bubble velocity profiles is an indication that dynamic structure of adsorption layer was not yet established there
Shape variations - „Indicators” of establishment of dynamic structure of the adsorption layer (steady state non-equilibrium distribution of the surfactant adsorbed)
Lower adsorption coverages needed in the case of nonionic surface active substances for immobilization of the bubble interface
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ACKNOWLEDGEMENTS
Partial financial support: (grant 3 T09A 164 27) from Ministry of Scientific Research and
Information Technology is gratefully acknowledged
Participation in Cluster C Meeting was made possible by EC grant INCO-CT-2003-003355