1. No category

Hydrodynamic Cavitation: for Water
Treatment
Prof. Aniruddha B. Pandit
Institute of Chemical Technology
University of Mumbai
INDIA
Email: [email protected]
1
Nature also utilizes cavitation!
• Use of Snapping Shrimp for actually visualizing
hydrodynamic cavitation technique
• Study carried out at University of Twente, The
Netherlands, indicated that the Snapping shrimp throws
a cavity,
cavity which travels a certain distance and collapses.
collapses
Frontal View
Top View
2
Confirmation by Experiments
Measurements using hydrophone indicated that the pressure pulse
generated at the collapse is capable of carrying out physical or chemical
transformations (Versluis et al., Science, Vo. 289, 2114-2117 (2000))
3
Replicate Nature !!!
• Aim of hydrodynamic cavitation reactors will be to replicate
this natural phenomena but at multiple locations
simultaneously
• Earlier investigations
g
dealing
g with hydrodynamic
y
y
cavitation
have been mainly directed towards avoiding it e.g.
cavitation erosion of propeller blades of ships
• Concentrated efforts by few research groups worldwide
have led to harnessing the positive effects of
hydrodynamic cavitation
4
Principle of generation
Orifice plate
Turbulent
b l
fl
fluctuating pressure ffield
ld
Hydrodynamic cavitation
•
•
•
Throttling valve
Single hole orifice
Multiple orifice plate
• Venturi
• High speed homogenizer
5
Key Effects in the Cavitating zone
Localized intense
Pressure & Temperature
conditions
highly reactive free
radicals
Concentrated energy at
the location of
transformation
High intensity
turbulence,, Increased
transport coefficient
Order of magnitude reduction in energy
requirement for physical/ chemical
transformation
6
Engineers Job
Control the Phenomena
and
Use the Effects in Positive Way
7
Hydrodynamic Cavitation Reactors
contd…
Orifice Plate
¾ Reservoir
¾ Centrifugal Pump
¾ Orifice
plate
(different
configurations in terms of
number and diameter of
the holes)
¾ Bypass line (for controlling
the inlet pressure and the
flow
rate
into
the
cavitation chamber)
P1, P2 = Pressure Gauges; V1, V2, V3 = Control Valves
¾ Cooling water jacket
Schematic representation for experimental setup for the
orifice plate hydrodynamic cavitation reactor
8
Configurations of Orifice Plate
An orifice plate is characterized by
¾ Free area (flow area)
¾ Perimeter of the holes (shear layer)
9
Hydrodynamic cavitation
Applications
¾Enzyme recovery, Microbial cell disruption
¾Water & wastewater disinfection
¾Oxidation of pollutants
10
Enzyme recovery
Cell Disruption
¾
Experiments with Invertase, Penicillin acylase and yeast
Saccharomyces cerevisiae indicate
¾ orifice plate setup gives order of magnitude higher
yields
¾ followed by High pressure homogenization &
¾ least is obtained for Sonication
¾
For equivalent protein concentrations in liquid,
Magnitudes of energy inputs:
¾ Mixer-blender system = 900 J/ml
¾ Ultrasonic Horn = 1500 J/ml
¾ Pump setup (Hydrodynamic cavitation) = 15 - 20 J/ml
11
Enzyme recovery
Cell Disruption
The extent of cell disruption in cavitating flow loop
increases with:
¾ an increase in the number of passes
¾ an increased pressure drop across the constriction
¾ an increased suspension temperature and
¾ a decreased biomass concentration
Location factor is another important concept which
decides the location of the desired enzyme in the
cell and the type of cell breakage mechanism to
be applied to get maximum results from the system
12
Enzyme recovery
¾
Extent of enzyme release for various cavitation numbers
35
Protein
a-Glucosidase
Invertase
G6PDH
%R
Release
30
25
20
15
10
5
0
0
0.2
0.4
0.6
0.8
1
Cavitation Number
Balasundaram & Harrison, Biotechnology and Bioengineering, 94(2) (2006), 303-311
13
Microbial disinfection
Bore well water disinfection
¾ Pump with Power consumption of 5.5kW; Speed of
2900 rpm.
¾ The cavitating valve is ball type made of SS.
¾ 75 L of bore well water
¾ Discharge pressure used - 1.72, 3.44 and 5.17 bar
¾ Multiple hole orifice plate placed along the flow of
liquid.
¾ The orifice plate had 33 holes of 1 mm diameter and
the effective flow area was 25.92 mm2
14
Microbial disinfection contd..
Bore well water disinfection
% Total co
oliforms killed
100
80
60
5.17 bar
40
0
3.44 bar
1.72 bar
20
0
0
10
20
30
40
50
60
70
Time
(mins)
Time
(Min)
Effect of orifice plate on Total coliforms
Initial count=50-65 Total coliforms/100ml,
Vol. treated=75L
15
Microbial disinfection contd..
Bore well water disinfection
80
70
% Disinfection
60
50
40
30
20
10
0
Total coliforms
5 mg/l H2O2
Fecal coliforms
Hydrodynamic cavitation (5.17 bar)
Fecal streptococci
Hydrodynamic cavitation (5.17 bar)+ 5 mg/l H2O2
Hydrodynamic cavitation coupled with H2O2 disinfection
16
Microbial disinfection contd..
Bore well water disinfection
100
90
80
% Dis
sinfection
70
60
50
40
30
20
10
0
Total coliforms
2 mg/l O3
Fecal coliforms
Hydrodynamic cavitation (5.17 bar)
Fecal
streptococci
HPC Bacteria
Hydrodynamic cavitation (5.17 bar)+ 2 mg/l O3
Hydrodynamic cavitation coupled with Ozone disinfection
17
Microbial disinfection contd..
Sea water disinfection
Extent of killing of various microorganisms in multiple
holes sharp edge orifice plate
100
Orifice plate
80
Destruction (%)
Fraction of open area= 0.75
Flow rate
= 1.3 lit/s
Pressure
= 3.2 kg/cm2
Hole dia.
= 2 mm
Pipe dia.
= 21.5 mm
60
40
20
0
Zooplankton
(> 50µ)
Phytoplankton
(> 10m)
Bacteria
(Associated with
zooplankton)
18
Microbial disinfection contd..
Sea water disinfection Effect
of operating parameters
100
Fraction of open area= 0.25
Hole Dia
= 2 mm
Pipe Dia
= 21.5
21 5 mm
Destruction (%)
D
80
Orifice plate
60
40
20
0
1
2
3
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
19
Oxidation of pollutants
¾
Hydrodynamic cavitation for oxidation of Nitro-phenols
Kalumuck & Chahine, Journal of Fluids Engineering, 122 (2000), 465-470
20
Oxidation of pollutants contd…
¾ Hydrodynamic cavitation coupled with Fenton’s
process
Chakinala, Gogate, Burgess & Bremner, Ultrasonics Sonochemistry 15 (2008) 49–54
21
Oxidation of pollutants contd…
¾
Hydrodynamic cavitation for degradation of Chlorocarbons
Wu, Ondruschka & Bräutigam, Chem. Eng. Technol., 30(5) (2007), 642–648
22
Modeling of Cavitation
23
Flow
Solution to Bubble Dynamics equations
Orifice
Vena contracta
Pressure
P1
P2
P2 − PV
Cv =
1 ρVO2
2
PV
Distance downstream to orifice
Pressure recovery with
turbulence
24
Pressure fluctuations
¾ With turbulence
P = Pv +½ D (Vo2 - Vtd2 ) - ∆P
Vtd is the actual turbulent velocity at any point estimated as:
Vtd = Vt + V’ sin (2π fT t)
Vt is the average velocity at the point, V΄ is the RMS
velocity, fT is the frequency of turbulence.
V'
fT =
l
 dO + d P 
l = 0.08

 2 
25
Pressure Profiles using CFD
Simulation of Flow
field in the
cavitation device
gives pressure
sensed by the cavity
while moving
through the flow
domain
26
Pressure Profiles using CFD contd..
Radial distance along
orifice (mm)
18
12
6
0
Paths taken by cavities
-6
-12
-18
-20
0
20
40
60
Axial distance along orifice (mm)
80
Pressure sensed by the
cavities
27
Single Bubble dynamics simulations
Single Cavity Approach
¾ Use of Rayleigh Plesset Equation (Basic approach)
d2R
3 dR 2
1
R( 2 ) + (
) =
ρl
2 dt
dt
4 µ dR 2σ


 pi − R ( dt ) − R − p∞ 
¾ Estimation of collapse Pressure
Pcollapse
Ro 3γ 2σ 4µ dR
2σ
= ( po +
)×( ) −
−
( )
Ro
R
R
R dt
28
Bubble dynamics model gives
Instantaneous value of
¾
¾
¾
¾
Radius
Bubble wall velocity
Bubble wall acceleration
Pressure inside the bubble
as the function of Liquid physicochemical properties
Use above parameters for the Quantification of the collapse
Pressure Pulse
29
Steady cavitation
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;
30
Transient cavitation
800
Xg=1.00
Radius (icrometer)
700
Xg=0.75
600
Xg=0.50
500
Xg=0.25
400
300
200
100
0
0
500
1000
1500
Time (microsec)
Pinlet = 3 atm; Orifice dia. = 1
mm;
Pipe dia. = 38; Number of orifice = 33;
Orifice velocity = 12 m/s; Ro = 10 µm;
31
Cavity collapses in multiple cycle
Intensity of final cavity collapse is lower than the transient
cavitation but higher than stable oscillatory cavitation.
32
Bulk Pressure (Pa)
40000
30000
20000
10000
0
-10000 0
200
400
600
-20000
Radius (micrometer)
Hydrodynamic Cavitation:
Transient cavitation
-30000
400
300
200
100
0
-40000
0
Time (microsec)
P
Pressure
Recovery
R
P
Profile
fil
600
C it Dynamics
Cavity
D
i Profile
P fil
3000
1200
2500
Pressure (atm)
Temperature (K)
200
400
Time (microsec)
2000
1500
1000
500
0
1000
800
600
400
200
0
0
200
400
Time (microsec)
Temperature profile
600
0
200
400
Time (microsec)
600
Collapse Pressure Profile
33
Typical Radicals formation profile at
cavity collapse
1.0E+14
1.0E+12
Molecules
1.0E+10
1.0E+08
1.0E+06
1.0E+04
1.0E+02
1.0E+00
412
413
414
415
416
417
418
Time (microsec)
H2
H
O
O2
OH
H2 O
N2
N2O
Ro=10 µm, Xg=1.0
Pin=4 atm, do=1 mm, dp=38 mm,
Cv = 1.0
34
Conclusion
¾
Strongly oxidizing OH radicals can degrade the chemical pollutants
¾
The high intensity shock waves are capable of disrupting a variety of
aquatic microbes including pathogens
¾
Hydrodynamic cavitation for potable water disinfection coupled with
conventional disinfection processes like chlorination, ozonation has
allowed more than 2/3rd reduction in disinfecting chemicals usage
¾
Hydrodynamic cavitation reactors offer immediate and realistic
potential for industrial scale applications
¾
Scale up is comparatively easier as vast amount of information
about the fluid dynamics downstream of the constriction is readily
available and the operating efficiency of the circulating pumps
which is the only energy dissipating device in the system is always
higher at large scales of operation.
35
Cavitation Research Group,
UICT
Prof A. B. Pandit
Shirgaonkar I.
Sivakumar M.
Mrs. Jyoti K.K.
Moholkar V.
Gogate P.
Kanthale P.
Ajay Kumar
Mahamuni N
N.
Senthil Kumar
Vichare N.
Tatke P.
Alve V.
Patil M.
Gaikwad S.
Mahulkar A.
Balasubramanhyam A
A.
36