Transcript Application of Gliding Arc Discharge for Control of VOC

Unipolar Injection of Charge into
Quiescent Gaseous Dielectrics
Alexei V. Saveliev
Department of Mechanical and Aerospace Engineering
North Carolina State University
Presented at workshop on
“ Electrostatic Atomization of Electrically Insulating Fluids:
Principles and Applications”
University of Southampton, March 2, 2009
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Outline
1. Introduction
•
Plasma and ionized gases
2. Breakdown of Gaseous Dielectrics
•
•
•
•
•
Uniform field – Paschen’s law
Non-uniform field breakdown
Positive and negative coronas
Corona charge injection devices
Pulsed streamer corona discharges
3. Discharge initiation in Supercritical Fluids
•
•
•
SCFs as a cluster fluid
Generation of SCF plasma in carbon dioxide
Potential applications of SCF plasmas
4. Breakdown and charging on liquid-gas interfaces
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Plasmas and Ionized Gases
• Plasma is an ionized gas
consisting of charged and
neutral particles and
exhibiting collective behavior
(Langmuir, 1929)
• Plasma may carry a current
• Plasma is often considered to
be electrically neutral
• Plasma is an ionised gas
• Ionized gas is not always
plasma
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E-field Breakdown
Thermal Plasma
Te = Ti = Tg
Non-Thermal Electrical Discharges:
1.
Electrons are accelerated in the electric
field gaining energy sufficient for
ionization of neutral molecules
2.
Secondary electrons are produced in
collisions forming electron avalanche
propagating in the interelectrode gap
Non-Thermal Plasma
Te >> Ti>Tg
Development
of electron avalanche
1 eV  10 000 K
Ionization energy  10 eV
E/N parameter
me << mi,mn e >> i
E-field
Ar
Ar
Ar
Ar + e  e + e + Ar+
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Kinetics of Ions and Electrons
Elementary processes:
1. Ionization
e + Ar  2e + Ar+
 
  Pf E P
2. Electron attachment
e + O2  O2
3. Electrode processes
- ion impact
- thermionic emission
- field emission


Fowler – Nordheim, 1928
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E-field Breakdown – Uniform Field
Townsend criterion
 expd  1  1
d
Multiplication of charges during
avalanche propagation
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Paschen’s Law
Breakdown voltage and
breakdown reduced e-field
between two parallel electrodes
B pd 
V
;
C  ln pd 
E
B

P C  ln pd 
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Breakdown in Non-uniform Field
Modified Townsend
criterion
 d
 
 exp  dx   1  1
  0
 
Peek’s formula
Ecr –critical e-field in kV/cm;
r – radius of inner sphere in cm;
 - relative air density
Ecr
9.63
 31.5 

r
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Corona Discharge
Corona configurations
E)
A – wire-in-cylinder;
B – sphere-in-sphere;
C – point-and-plane;
D – parabola-to-plane;
E – wire-to-plane
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Applications of Corona Discharge
•
Charging and discharging of solids and fluids
•
Manufacture of ozone
•
Electrostatic precipitators
•
Pollution control (VOCs, SOx, NOx)
•
Processing of material surfaces
•
Photocopy
•
Ionic wind devices
•
Gas ionizers for mass spectrometers and DMA
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DC Corona Current
Typical voltage-current
characteristics for negative
point-to-plane corona
Solution for wire in cylinder
corona
Vcr – ignition voltage
4 0 V V  Vcr 
i
R 2 lnR r 
I  CV V  Vcr 
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Streamer Propagation and Branching
Positive
corona:
Streamer Model:
Streamer propagation modes:
Veldhuizen and Rutgers, J. Phys. D. Appl. Phys. 35, 2002
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Streamer Propagation and Branching
• Morphology, length , and velocity of streamers are extremely
important for discharge structure and ion generation efficiency
(a)
(b)
Fast intensified CCD imaging of the fast transient plasma generation with 5 ns gating: (a) pulsed corona
discharge in air, (b) pulsed corona discharge in CO2.
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Positive Corona
Existence regions for
positive sphere-to-plane
corona forms in
atmospheric air, r =10 mm
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Negative Corona
Existence regions for
negative sphere-to-plane
corona forms in
atmospheric air
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DC Corona Chargers
Cathode
+
+
+ +
+
Anode
+
+
+
+
+
+
E
+
The need for more efficient
methods to charge gas and
aerosol streams has resulted
in a renewed interest in
corona discharge ionizers.
+ +
+
Space charge buildup in the
positive wire-to-cylinder corona.
Ionization
region
r
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DC Corona Diffusion Chargers
Several types of such
chargers have been proposed
in recent years, most of them
based on the original design
of Hewitt (1957)
Biskos et al., Journal of Electrostatics 63(2005)
Distribution of ion
concentration at
various pressures
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DC Corona Diffusion Chargers
Sharp-point electrode
ionizer
Alguacil and Alonso, Aerosol Science 37 (2006)
Total ion number
concentration at ionizer
outlet
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Pulsed Streamer Corona Discharge
• Pulsed corona discharge can be
readily generated at atmospheric
pressure
• Voltage is applied to the sharp
electrode as a series of fast rising
pulses:
 100 ns duration
 10 ns rise time
 20 kV peak voltage
• Electron energies up to 20 eV
(~230,000 K )
• Generates and efficiently separates
the charges
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Pulsed Electrostatic Precipitators
The first use of corona to remove
particles from an aerosol was by
Hohlfeld in 1824
Electrostatic precipitators were
first used in industry to remove of
sulfuric acid mist from exhaust
fumes in the beginning of the 20th
century
Modern controls minimize
sparking and prevent arcing by
applying pulsed voltage and thus
avoiding damage to the
components.
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Pulsed Corona Discharge for VOC Removal
Electrons
10-10
10-8
Radicals
10-6
10-4
Time, s
By-Products
10-2
Reactions
Reactions
N
High
O
N2 + N4 +
energy
electrons Excitation OH H CH3
Ionization
Dissociation
1
Radical-molecule
Ion-molecule
Clustering
Heterogeneous
102
H2O CO2
CO NO2
O3
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24
10
22
10
20
10
10
10
The area of nonthermal plasmas is
expanding to elevated
pressure gases, liquids
and microplasmas
Liquid
Plasmas
SCF
plasma
1 atm
Elevated
Pressure
Plasmas
18
16
Traditional
area
Nanoplasma
10
Microplasma
Neutral density, cm
-3
Breakdown in Supercritical Fluids
For a given voltage V
Te = f(E/n)=F(V/nd)
1 m
14
10
3
10
2
10
1
10
0
10
-1
10
-2
10
-3
10
-4
10
-5
n - neutral density
d - characteristic
system size
Size, mm
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SCF Plasma - Problem Statement and Motivation
• The generation of non-thermal plasma in supercritical
fluid (SCF) media is interesting both from fundamental and
applied viewpoints. Sustaining plasmas in SCF media
bridges the gap between gaseous and liquid processing since
SCFs have properties that are intermediate between the gas
and liquid states
• Applications of supercritical plasmas:
- pollutant removal
- bacterial deactivation
- plasma polymerization
- material synthesis
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Supercritical Carbon Dioxide
350
o
T =31.4 C
C
300
Melting Line
Pressure, bar
250
Supercritical CO
Solid
200
2
150
Boiling Line
100
P =73.8 bar
CP
C
Liquid
50
Gas
TP
0
-100
-50
0
50
100
Temperature, °C
150
200
250
• Critical point : 304 K, 73 bar
• Environmentally friendly “green”
solvent
• The properties of supercritical
fluids are intermediate to
corresponding gas and liquid
states
• SCF combines heterogeneous
chemistry with efficient mass
transfer realized by the low
viscosity, high diffusivity and
zero surface tension
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Clusters in Supercritical CO2
• SCF is often referred as a cluster
fluid
• Clusters are effectively formed
near the critical point
• Clusters affect reaction and
transport properties of SCF
• Clusters are crucially important for
plasma breakdown mechanism
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SCF Plasma Reactor
Technical Approach
• Non-thermal plasma is initiated
in supercritical carbon dioxide at
pressures above 75 bar using
high-voltage pulses of
nanosecond duration
• The pulses are applied to the
system of microelectrodes
arranged in point-to-plane and
wire-to-plane geometries
• The discharge and plasma
parameters are studied using
optical and electrical diagnostics
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Microbreakdown in Supercritical CO2
d = 80 m
Ito and Terashima, Appl. Phys. Lett.,
80: 2854-56, 2002.
IEEE Trans. Plasma Sci., 33: 850, 2005
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Electron Kinetics in Supercritical CO2
CO 2
Ionization
+
(CO 2)n+
High
energy
electrons
Recombination
CO O
O-(CO 2)n-1
+e
(CO2)n
CO2
Dissociation
Attachment
Ionization
e  CO2 n  CO2 n  2e

Attachment
e  CO2 n  CO2 n

CO 2-
O-(CO 2)n-1
(CO 2)n-
CO
Recombination
e  CO2 n  CO  OCO2 n1

Dissociation
CO2 n  O CO2 n1  CO
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Wire-in-cylinder Corona Discharge
Paschen law : V  V b  C ( pd)
4
2 10
Number of molecules
in cluster
1
2
4
12
y = 466.08 + 45.029x R= 0.99531
4
Voltage, V
1.5 10
4
Ionization
Potential, eV
13.77
13.32
13.18
12.5
1 10
Lock, Saveliev, Kennedy
5000
I = 12.5 eVISCF=0.9ICO2
Te=1 eV

Ito,Teraschima
IG
0
0
100
200
300
400
Pd, MPa*m
Discharge inception voltages in gaseous and
supercritical CO2. The original Paschen’s data
are shown for reference.
500
I SCF

Ae

Ae
I CO2
Te
0.9 I CO2
Te
e

0.1*12.5
1

1
3.5
IEEE Trans. Plasma Sci., 33: 850-3, 2005
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Wire-in-cylinder Corona Discharge
E/p (kV/MPa*m)
1
Lock, Saveliev,Kennedy [1]
Ito, Terashima [2]
Ito, Terashima [2]
Schumann [11]
Kuffel [8]
Hackam [9]
Finkelmann [10]
Bhalla and Craggs [12]
Paschen [4]
FD 
N 2
N
Vb
  FD
Vg
0.1
1
Vb
  3 ,   T  Tc  Tc
Vg
 E

0.01
1
10
100
1000
10
Vc
 
p  b 2 pd lnd d 
0
4
pd (MPa*m)
Dependence of critical E/p on pd in gaseous air
and CO2 for uniform and non-uniform fields.
IEEE Trans. Plasma Sci. , 34: 2467, 2006
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Point-to-plane Corona Discharge
Electrode
assembly
Atomic Force Microscopy
Z= 5 m
(a)
Electrode gap
Z= 4 m
(b)
Z= 4 m
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Periodic Pulsed Corona Discharge
Distance 200 m
Needle tip 5 m
T= 60 C
P= 83 bar
Voltage 13 kV
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Sliding Liquid-Jet Discharge
• The high voltage nanosecond
pulses are applied to the micro-jet
• Overcharged micro-jet generates
corona discharge with sharp liquid
electrode
• Application for material processing
and sensors
• Plasma as an ignition source for
engines and combustors using
liquid fuels
100 m
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Experimental Setup
Surface discharge operation
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Experimental Setup
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Discharge Propagation - Electrolyte Jet
a)
b)
c)
d)
e)
Discharge propagation modes. The lower electrode is anode, R = 840 kΩ, L = 18 mm, δ = 2
mm; (a) – low current degenerated glow discharge at U0 =10 kV, (b) – conversion of the
glow discharge to the single sliding surface discharge, (c, d) – developed surface discharge
at U0 =23 kV; (e) - degenerated arc discharge at U0 =30 kV
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Discharge Modes – Distilled Water
Voltage-current characteristics of the
discharge for distilled water: L = 18 mm,
Q = 0.3 ml/s, d = 0.4 mm, С = 0.47 nF, δ
= 1 (1) , 2 (2), 3 (3), 4 mm (4).
I – the area of a continued degenerated
glow discharge;
II – pulsed surface discharge.
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Discharge Regimes - Electrolyte Jet
Voltage-current characteristics at С = 0.73
nF, L = 20 mm, d = 0.5 mm, Q = 0.5 mL/s.
Ring electrode of 4 mm diameter; σ = 6·10-2
(1), 7·10-2 (2), 2·10-1 (3), 1.2 S/m (4);
I – the area of a continued degenerated glow
discharge;
II
–the
pulse
surface
discharge,
III – continued degenerated arc discharge.
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Jet Atomization
Water jet atomization at Q = 0.5 mL/s, U = 2 (a), 10 kV (b). Appearing the surface
discharge at U = 13 kV (c), I = 8 mA and its development at U = 16 kV, I = 16 mA (d).
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Summary
•
Unipolar injection of charge into quiescent gaseous dielectrics is well
established scientific area.
•
Understanding of ionization and charge separation processes is developed
•
Corona discharges are widely applied for charging of fluids and solid
surfaces
•
Pulsed discharges represent modern trend in plasma generation for various
charge injection devices
•
Discharges in supercritical fluids, liquids, at material interfaces and
discharges in micro and nanoscale are current areas of research interest
THANK YOU!
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Acknowledgements
Collaborators:
Dr. Lawrence A. Kennedy
Dr. Vladimir Shmelev
Dr. Ozlem Yardimci
Dr. Wilson Merchan-Merchan
Emiliano Giacchetti
Mario Sobacchi
Dr. Alexander A. Fridman
Dr. Evgenyia Lock
Research support:
NSF grants #9812905, #0522578
DOE grant FWP 49885
CRDF grant # RUC2-2824
Argonne National Laboratory
Texaco, Inc.
Air Liquide, Inc.
Innovative Energy Solutions, Inc.
Energy Systems Laboratory
2003
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