Transcript Prezentacja programu PowerPoint

Cluster A Meeting, 22 September 2005, Poznań
Influence of Surfactant on Initial
Accelerations, Shape and Velocity Variations
of the Detaching Bubbles
J. Zawała, M. Krzan, K. Małysa
Institute of Catalysis and Surface Chemistry
Polish Academy of Sciences
ul. Niezapominajek 8, 30-239 Cracow, Poland
Bubble Motion
INDUSTRY
EVERYDAY LIFE
 flotation
 washing (detergents)
 foam fractionation techniques
 champagne
 biotechnology
 beer
 waste water treatment
Questions
 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?
Bubble motion in surfactant solutions
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
Geq
Motion leads to disequilibration
of adsorption coverage
Gtop < Geq
35 cm
h
s
u
Uniform
coverage
Geq
terminal velocity
Experimental SET-UP
TV
hsolution  35 cm
square glass
column
Fin = 0.075 mm
nlamp = 100 Hz i 200 Hz
video
CCD cameras
stroboscopic lamp
PC
syringe pump
Captured movies
Detachment of the bubble in :
distilled water
stroboscop illumination frequency – 100 Hz
Captured movies
Detachment of the bubble in :
1.5 M pentanol solution
stroboscop illumination frequency – 100 Hz
Measurements
dv
dh
dh,dv – horizontal and vertical diameter
L – distance from the capillary
Dx
Dx – distance between two subsequent
positions of the bubble
L
Velocity =
Dx
Dt
Dt = 0.01 s or 0.005 s
Shape deformations
dv
dh
Deformation ratio =
dh
dv
quantitative parameter characterizing the deformation degree of the bubble
Accelerations
Initial acceleration
30
pentanol
2*10-3 M
water
velocity [cm/s]
25
20
pentanol
5*10-3 M
15
10
5
0
0.00
0.01
0.02
0.03
0.04
time [s]
Stroboscop illumination frequency - 200 Hz
c [M]
a [cm/s2]
sd
0 (water)
925
64
2*10-3
640
48
5*10-3
500
110
0.05
Velocities
velocity [cm/s]
40
n-pentanol
30
20
water
1*10-4
5*10-4
1*10-3
1.5*10-3
3*10-3
5*10-3
10
0
0
50
100
150
200
250
300
350
distance from the capillary [ mm]
Low pentanol concentrations: 3 stages of the bubble motion
acceleration, deceleration and terminal velocity
Shape pulsations vs. local velocities
40
1.7
n-pentanol
n-pentanol
30
1.5
dh/dv
velocity [cm/s]
1.6
20
1.4
1.3
1.2
distilled water
1*10-3 M
1.5*10-3 M
2*10-3 M
3*10-3 M
10
0
0
50
100
150
200
250
300
distance from the capillary [mm]
1.1
1.0
350
0.9
0
50
100
150
200
250
300
distance from the capillary [mm]
for low concentrations: CORRELATION
350
Velocities
velocity [cm/s]
40
n-octyltrimethylammonium bromide
30
20
water
5*10-4
1*10-3
5*10-3
1*10-2
2*10-2
4*10-2
10
0
0
50
100
150
200
250
distance from the capillary [mm]
300
Adsorption coverage
terminal velocity [cm/s]
40
n-pentanol
full immobilization of
bubble surface
30
20
10
0
0.000
0.002
0.004
0.006
0.008
0.010
concentration [mol/dm3]
0.012
Velocities
terminal velocity [cm/s]
40
30
20
10
0
0.0
n-pentanol
n-octanol
n-octyltrimethylammonium bromide
0.2
0.4
0.6
adsorption degree
0.8
Effect of concentration on shape pulsations
d h d v : 1.10 - 1.22
1.25 - 1.14
1.29
1.06
1).
capillary
2.5 mm
7 mm
acceleration
16 mm
34 mm
61 mm
84 mm
100 mm
157 mm 216 mm 322 mm
deceleration
U max
U terminal
1.06
dh dv :
2).
capillary
3.5 mm
7.5 mm
15 mm
33 mm
1). n-pentanol 1.5*10-3
61 mm
84 mm
102 mm 162 mm 216 mm
2). n-pentanol 5*10-3
325 mm
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
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