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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

13

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

16

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..

18

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 −

=

24

PV

P2

P1

Distance downstream to orifice

Pre

ssur

e

Pressure recovery with turbulence

2

21

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.