Post on 04-Feb-2018
Hydrodynamic Cavitation: for Water Treatment
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Prof. Aniruddha B. PanditInstitute of Chemical TechnologyUniversity of MumbaiINDIAEmail: abp@udct.org
• Use of Snapping Shrimp for actually visualizinghydrodynamic cavitation technique
• Study carried out at University of Twente, TheNetherlands, indicated that the Snapping shrimp throwsa cavity which travels a certain distance and collapses
Nature also utilizes cavitation!
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a cavity, which travels a certain distance and collapses.
Top ViewFrontal View
Measurements using hydrophone indicated that the pressure pulsegenerated at the collapse is capable of carrying out physical or chemicaltransformations (Versluis et al., Science, Vo. 289, 2114-2117 (2000))
Confirmation by Experiments
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• Aim of hydrodynamic cavitation reactors will be to replicatethis natural phenomena but at multiple locationssimultaneously
• Earlier investigations dealing with hydrodynamic cavitation
Replicate Nature !!!
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g g y yhave been mainly directed towards avoiding it e.g.cavitation erosion of propeller blades of ships
• Concentrated efforts by few research groups worldwidehave led to harnessing the positive effects ofhydrodynamic cavitation
Principle of generation
b l fl f ldOrifice plate
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Turbulent fluctuating pressure fieldHydrodynamic cavitation
• Throttling valve• Single hole orifice• Multiple orifice plate
• Venturi• High speed homogenizer
High intensity turbulence, Increased
Key Effects in the Cavitating zone
Concentrated energy at the location of transformation
Localized intense Pressure & Temperature
conditions
highly reactive free
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,transport coefficient
Order of magnitude reduction in energy requirement for physical/ chemical
transformation
radicals
Engineers Job
Control the Phenomena
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and
Use the Effects in Positive Way
Reservoir
Centrifugal Pump
Orifice plate (differentconfigurations in terms ofnumber and diameter of
Hydrodynamic Cavitation Reactors contd…
Orifice Plate
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the holes)
Bypass line (for controllingthe inlet pressure and theflow rate into thecavitation chamber)
Cooling water jacketP1, P2 = Pressure Gauges; V1, V2, V3 = Control Valves
Schematic representation for experimental setup for the orifice plate hydrodynamic cavitation reactor
Configurations of Orifice Plate
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An orifice plate is characterized byFree area (flow area)Perimeter of the holes (shear layer)
Hydrodynamic cavitation
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ApplicationsEnzyme recovery, Microbial cell disruptionWater & wastewater disinfectionOxidation of pollutants
Enzyme recovery
Experiments with Invertase, Penicillin acylase and yeastSaccharomyces cerevisiae indicate
orifice plate setup gives order of magnitude higheryieldsfollowed by High pressure homogenization &least is obtained for Sonication
Cell Disruption
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least is obtained for Sonication
For equivalent protein concentrations in liquid,Magnitudes of energy inputs:
Mixer-blender system = 900 J/mlUltrasonic Horn = 1500 J/mlPump setup (Hydrodynamic cavitation) = 15 - 20 J/ml
The extent of cell disruption in cavitating flow loop increases with:
an increase in the number of passesan increased pressure drop across the constrictionan increased suspension temperature and
Cell Disruption
Enzyme recovery
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an increased suspension temperature anda decreased biomass concentration
Location factor is another important concept whichdecides the location of the desired enzyme in thecell and the type of cell breakage mechanism tobe applied to get maximum results from the system
Enzyme recovery
Extent of enzyme release for various cavitation numbers
15
20
25
30
35
Rel
ease
Proteina-GlucosidaseInvertaseG6PDH
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0
5
10
15
0 0.2 0.4 0.6 0.8 1
Cavitation Number
% R
Balasundaram & Harrison, Biotechnology and Bioengineering, 94(2) (2006), 303-311
Microbial disinfection
Bore well water disinfectionPump with Power consumption of 5.5kW; Speed of 2900 rpm. The cavitating valve is ball type made of SS.75 L of bore well water
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Discharge pressure used - 1.72, 3.44 and 5.17 barMultiple hole orifice plate placed along the flow of liquid. The orifice plate had 33 holes of 1 mm diameter and the effective flow area was 25.92 mm2
Bore well water disinfection
Microbial disinfection contd..
40
60
80
100
olifo
rms
kille
d
5.17 bar
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Effect of orifice plate on Total coliformsInitial count=50-65 Total coliforms/100ml,
Vol. treated=75L
0
20
0
0 10 20 30 40 50 60 70Time (mins)
% T
otal
co
3.44 bar1.72 bar
Time (Min)
40
50
60
70
80
infe
ctio
n
Microbial disinfection contd..
Bore well water disinfection
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0
10
20
30
Total coliforms Fecal coliforms Fecal streptococci
% D
is
Hydrodynamic cavitation coupled with H2O2 disinfectionHydrodynamic cavitation (5.17 bar)5 mg/l H2O2 Hydrodynamic cavitation (5.17 bar)+ 5 mg/l H2O2
Microbial disinfection contd..
Bore well water disinfection
50
60
70
80
90
100
sinf
ectio
n
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Hydrodynamic cavitation coupled with Ozone disinfectionHydrodynamic cavitation (5.17 bar)2 mg/l O3 Hydrodynamic cavitation (5.17 bar)+ 2 mg/l O3
0
10
20
30
40
Total coliforms Fecal coliforms Fecalstreptococci
HPC Bacteria
% D
is
Sea water disinfection
Extent of killing of various microorganisms in multiple holes sharp edge orifice plate
100Orifice plate
Microbial disinfection contd..
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0
20
40
60
80
Des
truc
tion
(%)
Zooplankton(> 50µ)
Phytoplankton (> 10m)
Bacteria (Associated with
zooplankton)
Fraction of open area= 0.75Flow rate = 1.3 lit/sPressure = 3.2 kg/cm2
Hole dia. = 2 mmPipe dia. = 21.5 mm
Orifice plate
40
60
80
100
Des
truct
ion
(%)
Sea water disinfection Effect of operating parameters
Fraction of open area= 0.25Hole Dia = 2 mmPipe Dia = 21 5 mm
Orifice plate
Microbial disinfection contd..
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0
20
1 2 3D
Case Orifice velocity (m/s)
Pressure (kg/cm2)
Number of Recirculation (cumulative)
Energy (kw.hr)
Energy per unit volume (kJ/lit)
1 15.8 2 147 0.072 26.14
2 18.9 3 323 0.260 93.81
5 21.6 4 525 0.595 214.42
Pipe Dia = 21.5 mm
Oxidation of pollutants
Hydrodynamic cavitation for oxidation of Nitro-phenols
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Kalumuck & Chahine, Journal of Fluids Engineering, 122 (2000), 465-470
Oxidation of pollutants contd…
Hydrodynamic cavitation coupled with Fenton’s process
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Chakinala, Gogate, Burgess & Bremner, Ultrasonics Sonochemistry 15 (2008) 49–54
Oxidation of pollutants contd…
Hydrodynamic cavitation for degradation of Chlorocarbons
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Wu, Ondruschka & Bräutigam, Chem. Eng. Technol., 30(5) (2007), 642–648
Modeling of Cavitation
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Solution to Bubble Dynamics equations
Orifice
Flow
Vena contracta
2
1VPPCv −
=
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PV
P2
P1
Distance downstream to orifice
Pre
ssur
e
Pressure recovery with turbulence
2
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OVCv
ρ
Pressure fluctuations
With turbulenceP = Pv +½ D (Vo
2 - Vtd2 ) - ∆P
Vtd is the actual turbulent velocity at any point estimated as:Vtd = Vt + V’ sin (2π fT t)
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Vt is the average velocity at the point, V΄ is the RMS velocity, fT is the frequency of turbulence.
l
V = fT' dd = l PO
+
208.0
Pressure Profiles using CFD
Simulation of Flow field in the
cavitation device gives pressure
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gives pressure sensed by the cavity
while moving through the flow
domain
Pressure Profiles using CFD contd..
-18
-12
-6
0
6
12
18
-20 0 20 40 60 80
Rad
ial d
ista
nce
alon
g or
ifice
(mm
)
Paths taken by cavities
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Axial distance along orifice (mm)
Pressure sensed by the cavities
Single Bubble dynamics simulations
Single Cavity Approach
Use of Rayleigh Plesset Equation (Basic approach)
R d Rdt
dRdt
pR
dRdt R
pl
i( ) ( ) ( )2
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21 4 2
+ = − − −
∞ρµ σ
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dt dt l ρ
)(42)()2( 3
dtdR
RRRR
RpP o
oocollapse
µσσ γ −−×+=
Estimation of collapse Pressure
Bubble dynamics model gives
Instantaneous value of
RadiusBubble wall velocity Bubble wall accelerationPressure inside the bubble
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as the function of Liquid physicochemical properties
Use above parameters for the Quantification of the collapse Pressure Pulse
Steady cavitation
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Pinlet = 11 atm; Gas fraction = 1.0; Orifice dia. = 0.6 mm;
Pipe dia. = 38; Number of orifice = 1;
Orifice velocity = 36 m/s; Ro = 10 µm;
Transient cavitation
200
300
400
500
600
700
800
Rad
ius
(icro
met
er)
Xg=1.00Xg=0.75Xg=0.50Xg=0.25
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Pinlet = 3 atm; Orifice dia. = 1 mm;
Pipe dia. = 38; Number of orifice = 33;
Orifice velocity = 12 m/s; Ro = 10 µm;
0
100
0 500 1000 1500
Time (microsec)
Cavity collapses in multiple cycle
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Intensity of final cavity collapse is lower than the transient cavitation but higher than stable oscillatory cavitation.
Hydrodynamic Cavitation: Transient cavitation
P R P fil C it D i P fil
-40000-30000-20000-10000
0
10000200003000040000
0 200 400 600
Time (microsec)
Bul
k Pr
essu
re (P
a)
0
100
200
300
400
0 200 400 600Time (microsec)
Rad
ius
(mic
rom
eter
)
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Pressure Recovery Profile
Temperature profile Collapse Pressure Profile
Cavity Dynamics Profile
0
500
1000
1500
2000
2500
3000
0 200 400 600Time (microsec)
Tem
pera
ture
(K)
0
200
400
600
800
1000
1200
0 200 400 600Time (microsec)
Pres
sure
(atm
)
Typical Radicals formation profile at cavity collapse
1.0E+04
1.0E+06
1.0E+08
1.0E+10
1.0E+12
1.0E+14
Mol
ecul
es
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1.0E+00
1.0E+02
412 413 414 415 416 417 418Time (microsec)
H2 H O O2 OH H2O N2 N2O
Ro=10 µm, Xg=1.0
Pin=4 atm, do=1 mm, dp=38 mm,
Cv = 1.0
Conclusion
Strongly oxidizing OH radicals can degrade the chemical pollutants
The high intensity shock waves are capable of disrupting a variety ofaquatic microbes including pathogens
Hydrodynamic cavitation for potable water disinfection coupled withconventional disinfection processes like chlorination, ozonation hasallowed more than 2/3rd reduction in disinfecting chemicals usage
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Hydrodynamic cavitation reactors offer immediate and realisticpotential for industrial scale applications
Scale up is comparatively easier as vast amount of informationabout the fluid dynamics downstream of the constriction is readilyavailable and the operating efficiency of the circulating pumpswhich is the only energy dissipating device in the system is alwayshigher at large scales of operation.
Prof A. B. Pandit Shirgaonkar I.Sivakumar M. Mrs. Jyoti K.K.Moholkar V.Gogate P.Kanthale P.Ajay KumarMahamuni N
Cavitation Research Group, UICT
Senthil KumarVichare N.Tatke P.Alve V.Patil M.Gaikwad S.Mahulkar A.Balasubramanhyam A
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Mahamuni N. Balasubramanhyam A.