applications of swirling-type micro-bubble generator to...
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2012/12/12 Special Seminar on Micro/Nano-bubble
Technology in Thailand 1
Applications of Swirling-type Micro-bubble Generator
to Engineering Problems
Design:
Pt. 1 Review of the Swirling-type Bubble Generator
Applications:
Pt. 2 Absorption of Pressure by Micro-bubbles
Pt. 3 Forth Flotation of Suspended Soil Particles by Micro-bubbles
Pt. 4 Dissolved Oxygen (DO) by Micro-bubble Aeration
Harumichi Kyotoh
University of Tsukuba,
Tsukuba, Ibaraki 305-8573, Japan
Pt.1 Review of the Swirling-type
Bubble Generator
2 2012/12/12 Special Seminar on Micro/Nano-bubble
Technology in Thailand
3
Review of
Devises using a swirling flow
1. Vortex tube(1933)
2. Burner (Swirling jet flame)
(for instance, Tangirala (1987))
3. Swirling type micro-bubbler
Ohnari(1995)
2012/12/12 Special Seminar on Micro/Nano-bubble
Technology in Thailand
4
Ranque-Hilsch vortex tube(1)
http://www.phys.tue.nl/lt/projects/vortex.html
断熱膨張・圧縮過程を利用して暖気と冷気に分離する。
1933, 1947
Adiabatic expansion and compression
1.
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Technology in Thailand
5
http://www.mech.kuleuven.be/combust/research/burners/
burner
To Enhance the mixing of air and fuel to reduce the NOx
2.
2012/12/12 Special Seminar on Micro/Nano-bubble Technology in Thailand
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Micro-bubble generator(Ohnari(1995), pioneer)
http://www.nanoplanet.co.jp/NP_coinfo.html
3.
gas
liquid
2012/12/12 Special Seminar on Micro/Nano-bubble
Technology in Thailand
There is enough clearance for contaminated water to go through this devise.
7
Micro-bubble generator
Vortex breakdown nozzle for micro-bubble generator
Vane swirler for micro-bubble generator
Vane swirler Vortex breakdown nozzle
hD eD
f
The characteristics of the micro-bubble generator 1. A series arrangement → compact
2. The number of vanes, vane angle, vane channel depth→ control of the swirling flow
3. Vortex breakdown nozzle→ Enhancement of the micro-bubble generation
liquid
2012/12/12 Special Seminar on Micro/Nano-bubble
Technology in Thailand
Gas
MB-nozzle
⇒Design
8
Vane swirler
Air supply tube
Vortex breakdown nozzle
Ou
ter face of th
e VB
-no
zzle
Liquid
h
θf
Gas
D De
δe
Rim
2012/12/12 Special Seminar on Micro/Nano-bubble
Technology in Thailand
MB-nozzle
2012/12/12 Special Seminar on Micro/Nano-bubble
Technology in Thailand 9
Motor
Gas
Suction cover
Rotor vane
Stator vane
MB pump
Pump
Flow
meter
Inverter
wQ
Pressure gage
Gas
Gas is injected at the inlet of the pump
and is pressurized in the outlet pipe.
Experimental facilities
MB nozzle
50cm
50cm
10
50cm
Pump discharge=16L/min, Head 55m, Air discharge=400cc/min,
Pump power 1000W (Air is injected at the inlet of the pump.), ζ=1200. 2012/12/12
Special Seminar on Micro/Nano-bubble Technology in Thailand
11
t=2min 4min later from the start
t=0
t=4min t=6min 2012/12/12 Special Seminar on Micro/Nano-bubble
Technology in Thailand
12
Pump discharge=21L/min, Head= 33m, Air discharge=400cc/min,
Pump power 580W (Air is injected at the inlet of the pump.), ζ=400. 2012/12/12
Special Seminar on Micro/Nano-bubble Technology in Thailand
13 2012/12/12 Special Seminar on Micro/Nano-bubble Technology in Thailand
t=2min
t=4min
3min later from the start
t=0
14
Side view
Cylindrical bubble
(swirling flow)
Flow attachment
(Coanda effect)
Fragmentation
of the cylindrical
bubble
Spiral type
vortex breakdown
2012/12/12 Special Seminar on Micro/Nano-bubble
Technology in Thailand
Gas column is formed
because of the lower
pressure at the center
of the swirling flow.
15
Front view Discharge 700cc/sec
1 frame/1ms
cm4
2012/12/12 Special Seminar on Micro/Nano-bubble Technology in Thailand
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Ligaments
&
Bubble
breakup
2012/12/12 Special Seminar on Micro/Nano-bubble
Technology in Thailand
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A) Mechanism of the vortex-breakdown induced by
the Coanda effect
B) Mechanisms for the bubble breakup
C) Design of the swirling-type micro-bubble generator
D) Spiral-type vortex breakdown and sound
E) Pressure and sound control at the exit of the vortex
breakdown nozzle
F) Micro-bubble generation in a circular pipe
Topics
2012/12/12 Special Seminar on Micro/Nano-bubble
Technology in Thailand
Spiral type
Bubble type
An Album of Fluid Motion, The Parabolic Press, 1982
Vortex-breakdown
Delta wing
Circular pipe
The abrupt change of the vortex core
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Technology in Thailand
Flow separation at the leading edge
generates concentrated vortices.
The breakdown of these vortices
causes the trouble of the airplane
manipulation.
Coanda effect
Wall jet
日本機械学会論文集(B編)54巻500号、p.784
1) Put a spoon near tap water jet. 2) The tap water jet is attracted to the spoon.
Tap
water jet
Wall jet deflection along the curved surface
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Tap
water jet
Spoon
Cylinder
Coanda effect
A. Mechanism of the vortex-breakdown
induced by the Coanda effect
Low
er pressu
re
Hig
her p
ressure
Criteria: 1.Subcritical swirling flow
( Se≡ Azimuthal velocity / Axial velocity ≥ 2)
2.Coanda effect
Hig
h p
ressure
20 2012/12/12
Special Seminar on Micro/Nano-bubble Technology in Thailand
v
1. Flow is Subcritical
602, , fcre
e
e
e Su
vS
ev
ee
e
e
e
e DQ
DvSv
r
Rv
r
Qu
4,,
2
D
Swirl number
R2 er2
eu
2eSSubcritical flow →
eD
Mean velocity
Mass
conservation
Angular momentum
conservation
Suction flow at the center of the channel
Subcritical flow is necessary for the Coanda effect.
21
Circumferential velocity
2012/12/12 Special Seminar on Micro/Nano-bubble
Technology in Thailand
Subcritical flow
Jet
Coanda effect
2. Coanda effect occurs
Strong subcritical flow → wall jet
Curvature of the nozzle edge Low curvature
→ flow attachment but small pressure gradient
High curvature
→ large pressure gradient but flow detachment
Suction flow
Wall jet
High pressure
Low pressure
2 eee Sr
e
er
Condition for flow attachment
22 2012/12/12 Special Seminar on Micro/Nano-bubble Technology in Thailand
1. Generation of secondary bubble (ligaments)
from cylindrical bubble
2. Bubble breakup
by pressure gradient and shear flow
3. Sorting of bubbles
by swirling flow
B. Mechanisms for the bubble breakup
23 2012/12/12 Special Seminar on Micro/Nano-bubble
Technology in Thailand
1. Generation of secondary bubble (ligaments)
from the cylindrical bubble
Low pressure High pressure
Breakup
Collapsing of low pressure bubble
under high pressure environment (Fragmentation of cavitations bubble)
10~20kPa 100kPa
24 2012/12/12 Special Seminar on Micro/Nano-bubble Technology in Thailand
2. Bubble breakup
by pressure gradient and shear flow
ee
e
e
H
rLvu
r
v
L
u
d
,
,3.1
33
5/1
32
3
γ:surface tension coefficient
450
udRe
(J. Fluid Mech., vol. 401, pp. 157-182(1999))
Ligament
breakup
(Fan & Tsuchiya(1990))
・Hinze scale(Inertia dominated) ?
25 2012/12/12 Special Seminar on Micro/Nano-bubble
Technology in Thailand
3. Sorting of bubbles by swirling flow
2/2
1 2
wawaDolwaolw qqqqafds
dPVqqV
dt
d
D
ol
w
wa
f
V
s
:relative velocity
:liquid density
:bubble volume
:drag coefficient
3aVol
:stream direction
Dynamic equation for translational motion of a bubble
Higher pressure
a
sLower pressure
e
ew
r
v
ds
dP2
χ>1
χ<1
26 2012/12/12 Special Seminar on Micro/Nano-bubble
Technology in Thailand
Sound from primary bubble
oscillations
Secondary bubble
(ligament)
Sound from secondary bubble
oscillations
Primary bubble
(a) Generation of secondary bubble
from the cylindrical bubble
Hinze scale
(Inertia dominated)
Secondary bubble
time
(b) Bubble breakup
by pressure gradient
(c) Sorting of bubbles
by swirling flow
Viscosity dominated
small bubbles
Summary of the mechanisms of the bubble breakup
27 2012/12/12 Special Seminar on Micro/Nano-bubble Technology in Thailand
28
1) The radius of curvature at the nozzle edge should satisfy
2) The diameter of the vortex breakdown nozzle is determined so
that the Coanda effect occurs, i.e., Se>2. (Determine the vane angle θf which should be greater than 64 degrees.)
C. Design
of the swirling-type micro-bubble generator
Conservation of the angular momentum
Conservation of the angular momentum flux
)2/(6,2/
ˆ D
hh
Geometric parameters
h/D, De/D, θf, τ
1. Flow attachment
2012/12/12 Special Seminar on Micro/Nano-bubble Technology in Thailand
.2
eee Sr
29
2. Resistance
2012/12/12 Special Seminar on Micro/Nano-bubble
Technology in Thailand
θf=78°,h=3mm,D=19mm
De/D
θf=78°,h=4mm,D=19mm
De/D
fDhDDeFUp
,/,/,2
2
To generate many fine bubbles,
vane angle θf should be larger.
As a result, the resistance of MB-
nozzle becomes larger.
6072,2/1,10/7
1056,2/1,10/7
F
F
30
Miscellaneous
D. Spiral-type vortex breakdown and sound
E. Pressure control
at the exit of the vortex breakdown nozzle
F. Micro-bubble generation in a circular pipe
2012/12/12 Special Seminar on Micro/Nano-bubble
Technology in Thailand
(a) Flow attachment
(b) Flow detachment
D. Spiral-type vortex breakdown and sound
Aco
ust
ic p
ress
ure
A
coust
ic p
ress
ure
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(Vortex whistle)
1. Spectrum of the sound
(a) Flow attachment (b) Flow detachment
fw: Angular frequency of the swirl
fa: Natural frequency of the cylindrical bubble 32 2012/12/12
Special Seminar on Micro/Nano-bubble Technology in Thailand
wcylindercylinder
sphere
cafaa
Pf
aa
Pf
/2ln/2
2
1
23
2
1
32
32
2. Natural frequency of the spherical and cylindrical bubbles
(Dispersion relation)
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Technology in Thailand
a: bubble radius
ρ:liquid density
σ:surface tension
γ:ratio of specific heat
P:gas pressure
E. Pressure control
at the exit of the vortex breakdown nozzle
Purpose:
1. Efficiency of micro-bubble generation
2. Suppression of the sound
Front pressure becomes lower.
Pressure inside the cylindrical bubble decreases.
Pressure gradient increases.
Discharge increases.
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Technology in Thailand
Front nozzle
Distance between the Vortex breakdown nozzle and the plate
・Pressure inside
of the cylindrical bubble
・Resistance of the nozzle
・Acoustic pressure
t0
4/eD
S2
S1
S3
S4
S1 S2 S3 S4
eD t
Effect of the front nozzle
on the efficiency of the swirling-type micro-bubble generator
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Technology in Thailand
36
F. Micro-bubble generation in a circular pipe
1. Swirling flow propagates to
the downstream direction.
2. Bubble merging occurs at the
center of the swirling flow.
3. Flow shear above the front
side of the vortex breakdown
nozzle is weakened,
because the relative velocity
between the swirling flow and
the flow down-stream becomes
smaller.
Problems
2012/12/12 Special Seminar on Micro/Nano-bubble
Technology in Thailand
22
Bubbler
10 mm
1. Front nozzle is installed to suppress the swirling flow downstream.
2. Multi-nozzle whose total circulation is zero
Solutions to the problem
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Technology in Thailand
2012/12/12 Special Seminar on Micro/Nano-bubble
Technology in Thailand 38
Summary
A swirling-type micro-bubble generator is reviewed.
The Coanda effect and the vortex-breakdown are
the key words for the design of the micro-bubble
nozzle.
High-head pump is better for the generation of
small and high density bubbles.
Special care is necessary when the micro-bubble
nozzle is used in the channel.
Sound generation can be suppressed if the front
nozzle is installed.
Pt. 2 Absorption of pressure
A. Japan Proton Accelerator Research Complex
Materials and Life Science Experimental Facility (MLF) is aimed at promoting materials science and life science(protein) using the world highest
intensity pulsed neutron and muon beams which are produced using 3-GeV protons with a
current of 333micro-amps and a repetition rate of 25 Hz. Proton hits the mercury target.
Micro-bubble is used to reduce the heat shock waves.
http://j-parc.jp/MatLife/en/index.html
B. Air-Entrained Concrete The primary purpose of air entrainment is to increase the durability of the hardened
concrete, especially in climates subject to freeze-thaw. During the freeze-thaw, the air
bubble can be compressed a little, and so the bubbles act to reduce or absorb stresses
from freezing.
C. Soil liquefaction describes the behavior of soils that, when loaded, suddenly suffer
a transition from a solid state to a liquefied state. During earthquake loading, loose sands
tend to decrease in volume, which produces an increase in their pore-water pressures and
consequently a decrease in shear strength. It has been known that liquefaction is
refrained if there were cavities in the ground.
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40
http://j-parc.jp/MatLife/ja/index.html
To generate high energy neutron beam,
proton beam is applied to liquid mercury,
where heat shock waves are scattered in
the liquid mercury. That shock waves
cause cavitations at the boundary of the
vessel, which will erode the vessel surface.
The bubbles which can react that strong
pressure rise need to be micron-size
because they have high resonant frequency.
A. Entrainment of micro-bubbles into mercury
1m
2012/12/12 Special Seminar on Micro/Nano-bubble
Technology in Thailand
Joint research
with Japan Proton Accelerator Research Complex
Mercury
Heat shock
waves
Vessel for mercury
Pressure waves Cavitations
Proton pulse beam
(1MW、25Hz)
2012/12/12 Special Seminar on Micro/Nano-bubble Technology in Thailand 41
Reduction of the pressure by gas bubbles
Requirement: Micro-bubbles need to be generated by low pressure loss, since
the power of the mercury pump is limited.
Helium-gas does not dissolve into mercury.
Surface tension of mercury is around 10 times that of water.
The volumetric ratio of He-gas to Mercury is about 0.1%.
Solution: Swirling type micro-bubble generator with low resistance,
i.e., resistance coefficient ζ~10 (θf~60°).
Multi-nozzle whose total circulation is zero.
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Special Seminar on Micro/Nano-bubble Technology in Thailand
Minimum size of bubble generated in water and mercury
ee
e
e
H
rLvu
r
v
L
u
d
,
,3.1
33
5/1
32
3
γ:surface tension coefficient
450
udRe
(J. Fluid Mech., vol. 401, pp. 157-182(1999))
Ligament breakup
(Fan & Tsuchiya(1990))
water mercury
・Hinze scale(Inertia dominated) ?
43 2012/12/12
B. Generation of micro-bubbles in cement paste
Grout pump
Micro-bubble nozzle
Bucket
Cement paste
Joint Research
with Sato Kogyo co. Ltd, Wakachiku Construction co. Ltd
Kawada Construction co. Ltd
2012/12/12 44 Special Seminar on Micro/Nano-bubble
Technology in Thailand
Spacing Factor
Micro-bubble
Plain
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2012/12/12
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46
MB cement
Plain cement
Incremental pore volume
Pore diameter(μm)
Incr
eme
nta
l po
re v
olu
me
(mL/
g)
2012/12/12 47 Special Seminar on Micro/Nano-bubble
Technology in Thailand
Void fraction increases.
Pore distance becomes shorter.
Compressive strength becomes larger.
Durable to freeze-thaw
No decrease of the strength due to pores
Plain
Spacing factor Pore volume Density Strength
Summary
2012/12/12 48 Special Seminar on Micro/Nano-bubble
Technology in Thailand
歌川紀之、金子典由、小俣文良、楠岡弘康、木俣陽一、関東継樹、京藤敏達:
マイクロバブルの建設・環境分野への適用に関する研究、佐藤工業㈱技術研究所報、No.31,pp.29-36,2005-2006.(Sato Kogyo Research Report)
C. Soil liquefaction
To suppress soil liquefaction in the saturated zone, air
may be injected into the soil so that the pore water
pressure will not rise during earthquakes.
Because micro-bubbles can easily permeate into voids
between sand particles, air is supplied as a form of
micro-bubble water.
2012/12/12 49 Special Seminar on Micro/Nano-bubble
Technology in Thailand
Joint research
with Sato Kogyo co. Ltd.
Nagao K., Azegami Y., Yamada S., Suemasa N. and Katada T. : A micro-bubble injection method for a countermeasure against liquefaction, 4th international conference on earthquake geotechnical engineering, paper ID 1764, pp.392, 2007.
Soil(sand particles)
Micro-bubble water
2012/12/12 50 Special Seminar on Micro/Nano-bubble
Technology in Thailand
VideoNo.1
No1Liquefaction.wmv
VideoNo.2
No2(50,100,150gal).wmv
2012/12/12 Special Seminar on Micro/Nano-bubble
Technology in Thailand 51
A. Japan Proton Accelerator Research Complex
Materials and Life Science Experimental Facility (MLF) Micro-bubble can respond high frequency oscillations of pressure and reduce
the heat shock waves.
B. Air-Entrained Concrete The compressive strength of Micro-bubble-entrained cement increases even if
the pore volume increases.
C. Soil liquefaction Micro-bubble water can go through the spacing of sand particles.
Summary
歌川紀之、楠岡弘康、木俣陽一、京藤敏達: マイクロバブルを用いた高度濁水処理装置の開発ー低SS処理水の浮上分離実験 土木学会第64回年次学術講演会、Ⅵ-183,2009.
Pt. 3 Forth flotation of suspended soil particles
by micro-bubbles
Purpose: The muddy water discharged from construction
works need to be disposed of to preserve
environments.
To remove soils, Poly-Aluminum Chlorohydrate
(PAC) and Polymer are used as a flocculating agents
for water purification.
After the water purification, however, suspended
flocs still remains in the water.
Micro-bubbles are used to remove these flocs.
Joint research
with Sato Kogyo co. Ltd. & Wakachiku Construction co. Ltd.
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Experimental facility
Floc suspended water
PAC
Polymer
Micro-bubbles
Experimental procedure
Sampling
Sampling
15min
MB-nozzle
Soil mixed
water
honeycomb
Floated
flocs
pump
PAC(ml/l)
Before MB
After MB
Before MB
After MB
Turb
idit
y
Floated flocs
Susp
en
de
d S
olid
PAC(ml/l) Microscope image of floc
50μm
Turbidity and Suspended Solid 2012/12/12 54 Special Seminar on Micro/Nano-bubble Technology in Thailand
1mm
Floated flocs
MB nozzle
Floated flocs
Before
treatment
After
treatment
Stream-type turbidity treatment
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Summary
To remove soil particles, floc formation is necessary, i.e.,
PAC and Polymer need to be added to the muddy water.
The floc containing micro-bubble is the key point of the
present turbidity treatment, because the flocs containing
micro-bubbles float even if they are fragmented into small
parts by turbulent flows.
The value of Suspended Solid becomes less than 20 mg/L,
which is the present drainage standard of construction
works, after the present treatment.
Pt. 4 Dissolved oxygen (DO)
by Micro-bubble Aeration
Questions Smaller bubbles are better ?
Increase of DO due to air
←Nitrogen hinders the dissolution of oxygen?
Water quality influences DO ?
Purpose:To supply oxygen to aquatic environment,
A. Dissolution of gas into water B. Efficiency of DO-increase C. Water quality and DO
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A. Dissolution of gas into water
Henry’s law
jp jP
jS
/2RURe
jcj DS /
Sherwood number
Reynolds number
Schmid number
Henry’s constant jH
R
jMMole of gas
・Residence time dt
・Diffusion of gas RSj
・Pressure inside bubble pj - Pj
jj
j
jjjpP
H
SRD
dt
dM
2
2012/12/12 58 Special Seminar on Micro/Nano-bubble Technology in Thailand
Dissolution rate of gas into liquid is
proportional to
Micro-bubbles
(Qa is small.)
Aeration tube
(Qa is large.)
1. The total surface-area of the bubbles ○ ○
2. The diffusion of the dissolved gas × ○(significant)
3. Pressure inside the bubble ○(insignificant) ×
Summary of the results according to Henry’s law
10 12 14 16 18 20 22 240
5. 10 10
1. 10 9
1.5 10 9
2. 10 9
temperature deg.
Dif
fusi
on
coef
fici
entm
2s
10 12 14 16 18 20 22 240
50 000
100 000
150 000
temperature deg .
Hen
ryco
nst
ant
mo
l1
m3
Pa
Oxygen
Nitrogen
Oxygen
Nitrogen
Oxygen is around two times more
dissolvable than nitrogen.
Turbulent diffusion is scaled by
uL,
hence, it is proportional to
(the Reynoluds number
×Molecular diffusion) .
Therefore, dissolution of gas is
strongly influenced by the flow
fields, i.e., turbulent or laminar.
Molecular diffusion
2012/12/12 59 Special Seminar on Micro/Nano-bubble
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(1) Rise velocity of a single bubble
182
2 gRU
61/39
61/3961/8961/5038.0
RgU
Solid sphere
Fluid sphere
Residence time h/U
bRR
bRR
Small bubble is advantageous jj
j
jjjpP
H
SRD
dt
dM
2
2012/12/12 60 Special Seminar on Micro/Nano-bubble
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(2) Diffusion of gas in water
41.0
3/1
11 e
e
cjj RR
SS
4001 eR
3/111 cjej SRS
1eR
Large bubble is advantageous. jj
j
jjjpP
H
SRD
dt
dM
2
2012/12/12 61 Special Seminar on Micro/Nano-bubble
Technology in Thailand
(3) Pressure inside a single bubble
RPp
2
Small bubble is advantageous. jj
j
jjjpP
H
SRD
dt
dM
2
mh 5
mh 1
cmh 10S
urf
ace
tensi
on/w
ater
pre
ssure
2012/12/12 62 Special Seminar on Micro/Nano-bubble
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<Numerical simulation> Boundary condition: DO=50%,DN=100%
A micro-bubble with 50μm in radius is released at the depth of 1m underwater.
Dissolution of air micro-bubble
(Numerical simulation)
55秒で12cm浮上後に消滅
Oxygen
dissolution Oxygen and Nitrogen
dissolution
•Oxygen rapidly dissolves at the initial stage.
•Nitrogen also dissolves completely.
O2/N
2
Rad
ius(
μm
)
2012/12/12 63 Special Seminar on Micro/Nano-bubble
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Dissolution of air bubble in a tank
(Numerical simulation)
Nitrogen saturates before DO becomes 100%.
• For micro-bubble,
The super-saturation of nitrogen occurs.
The component of dissolved gas tends to be similar to that of air.
• For milli-bubble, oxygen dissolves dominantly.
Micro-bubble Milli-bubble
Separation of Nitrogen
The micro-bubble aeration might be inefficient for DO-increase. 2012/12/12 64 Special Seminar on Micro/Nano-bubble Technology in Thailand
B. Efficiency of DO-increase
200cm
98cm
94cm
Experimental facility
MB pump Porous stone (pore diameter 100μm)
Purpose: To compare the efficiency of DO-increase between
• Aeration tube (porous stone with diameter 100μm) 74W
• Micro-bubble pump 1000W
MB pump
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MB pump
Oxygen discharge is 1L/min.
Aeration tube
Oxygen discharge is 10L/min.
Oxygen dissolution experiment
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2012/12/12 Special Seminar on Micro/Nano-bubble
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Oxygen aeration by Micro-bubble and Aeration tube
0 20 40 60 80 100 120 140100
200
300
400
500
Time min
Ox
yg
en
Aeration tube:10L min , MB pump :1L min
Dissolved Oxygen
MB-pump
1L/min
Aeration tube
10L/min
0 20 40 60 80 100 120
0.0
0.2
0.4
0.6
0.8
1.0
Time min
Dis
solv
edO
xy
gen
Su
pp
lied
Ox
yg
en
Aeration tube:10L min , MB pump :1L min
The ratio of Dissolved Oxygen
to Supplied Oxygen
Aeration tube
10L/min
MB-pump
1L/min
2012/12/12 Special Seminar on Micro/Nano-bubble
Technology in Thailand 68
0 20 40 60 80 100
100
200
300
400
500
Time(min)
Oxy
gen
(%)
Aeration tube
10L/min
MB-pump
1L/min
MB-Nozzle
1L/min
Oxygen aeration by Micro-bubble and Aeration tube
20 30 40 50 60 70 80
0.0
0.2
0.4
0.6
0.8
1.0
Time min
Ox
yg
en
MB pump ,1L min Oxygen ,770W
0%
20%
40%
60%
80%
100%
120%
0 20 40 60 80 100 120
Dis
solv
ed
Oxy
gen
Time(min)
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MB pump(Air 2L/min)
Aeration tube(Air 31L/min)
DO=78%
Aeration tube:
5% of oxygen in air is dissolved
MB pump
33% of oxygen in air is dissolved
Air aeration by Micro-bubble and Aeration tube
Super-saturation
The efficiency defined by DO-increase per Watt
(electricity consumption)
The efficiency of the micro-bubble pump is roughly 1/20-
times that of the aeration tube.
The efficiencies become comparable at around DO=95%
for air aeration.
Micro-bubble will be useful to dissolve special gases, such
as ozone, since it is dangerous and expensive.
Note that the efficiency depends on the depth of water.
DO is influenced not only by the total surface area of the
injected gas, but also by the diffusion of the dissolved gas
due to turbulent flows. Therefore, the oxygen inside the
large air bubbles also effectively dissolves into water.
Summary
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1.3cm
Water discharge=6ℓ/min
Purpose:
The influence of water quality on DO-increase is studied experimentally.
tap water, refined water, distilled water, salt water, pond water
Micro-bubble nozzle
Experiment:
Oxygen micro-bubbles are generated in a tank, and DO is measured.
C. Water quality and DO due to oxygen micro-bubbles
(Experiment)
Gas discharge=10cc/min
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Photograph
Tap water Refined water Distilled water
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Salt water Pond water
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DO
0
5
10
15
20
25
0 500 1000 1500 2000
t[s]
DO
[mg/L] 水道水
純水
蒸留水
3%食塩水
池水
Pond
Tap
Refined
Distilled
Salt
Pond
Salt
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Technology in Thailand
Summary
DO-increase of pond water in summer is slow.
The rate of DO-increase of salt water abruptly diminishes at some critical point.
Bubble density of pond water and salt water is high, but DO is low.
1. To supply oxygen to pond water, large air bubbles are
more efficient than air micro-bubbles.
2. Aeration due to air micro-bubbles makes the component
of the dissolved gas into the same component of air, so
that the DO in water will not saturate.
3. The gas inside the micro-bubble in contaminant water is
difficult to dissolve since the surface of the bubble is
covered by contaminants.
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Conclusion
for swirling-type bubbler,
1. DO-increase by micro-bubble aeration is inefficient.
2. Micro-bubble may be useful for the dissolution of
expensive gas.
3. Pressure absorption by micro-bubbles is essential
to the reduction of shock waves.
4. Micro-bubble air entrained concrete needs more
study, for instance, the tracking of micro-bubbles
in cement milk and the more efficient method to
mix micro-bubbles into concrete.
5. Micro-bubbles are useful for the flotation of
contaminants.
6. To generate micro-bubbles is easy, but to find their
effectiveness is not easy.