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Thermodynamics of Microplasma Initiation in Liquids. Robert Geiger Sagar Ghimire, Rei Kawashima Advisor: Dr. David Staack Texas A&M University- Mechanical Engineering Plasma Engineering & Diagnostics Laboratory (PEDL). Outline. Motivation Applications - PowerPoint PPT Presentation
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Thermodynamics of Microplasma Initiation in Liquids
Robert Geiger
Sagar Ghimire, Rei Kawashima
Advisor: Dr. David Staack
Texas A&M University- Mechanical Engineering
Plasma Engineering & Diagnostics Laboratory (PEDL)
Outline
• Motivation– Applications
– Control plasma parameters (ne, Te, d)
• Discharges in liquid– Near liquids– “In” liquids
• Experimental Setup• Transient discharges (OES)• Summary
plasma
wire
cells
Why Generate Plasma in Liquids?Chemical Applications:
Fuel Reforming
Bio/Medical
Physical Applications:
Shock Wave Generation MicrofluidicsSpecies Identification
Water Sterilization
Shock Wave
Discharges in Gases Near Liquids
Inside bubblesAbove liquid surface
Ref: Alyssa Wilson et al 2008 Plasma Sources Sci. Technol. 17 045001
In droplet containing gas
http://www.panoramio.com/photo/2843260
Discharges in Liquids – Steady State
Phase Instability
Steady state supercritical plasma
Ref:27.12 MHz Plasma Generation in Supercritical Carbon Dioxide
Ayato Kawashima et al, J. Appl. Phys.
Discharge in Liquids - Process
1) Initiation Low Density Region1) Electrolysis
2) Boiling (Joule Heating)
3) Electrostatic Cavitations
2) Breakdown1) Primary Streamer
2) Secondary Streamer
3) Spark
3) Thermalization
4) Relaxation
1950s-1980s thoroughly studied breakdown process in dielectrics
r
Discharges in Liquids - Initiation
Boiling Analysis (Energy Balance)
Electrolysis Analysis ( Faradays law of electrolysis)
Electrostatic Cavitation Analysis (Force Balance)
Assumptions: All initiation mechanism achieve a low density reduction n
Const (I) and (V)
Local Low Density Region (n)
Y = (Yeild of Fluid)
Electrode
Fluid
Cavitation
should be larger
Experimental Setup
V
Spark Gap 1R
CSpark Gap 2
Output
Circuit:
Electrode Configurations:
Point to Plane Point to Point Plane to Plane
Diagnostics
Discharges in Liquids – Transient & Plasma SizeSpark Streamer Corona
Water - Corona
Mineral Oil - Corona
Anode (+) Cathode (-)< 50 um
Discharges in Liquids – Transient & Thermalization
200 300 400 500 600 700 800-0.2
0
0.2
0.4
0.6
0.8
1
1.2Broadband spectra of Corona in Water\NaCl\KCl mixtures
Wavelength (nm)
Re
lativ
e In
tesi
ty
130uS310uS540uS780uS
Hα
Hβ ONaOH
Te,Tvib>Tgas Te,Tvib ≈ Tgas
𝛕 = f(ne, υen, Te, E/n, medium, …)
Discharges in Liquids - Transient
630 635 640 645 650 655 660 665 670 675 6800
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1Hydrogen Alpha Peak for different conductivities
Wavelength (nm)
Re
lativ
e In
tesi
ty
130uS310uS540uS780uS
100 200 300 400 500 600 700 8001
2
3
4
5
6
7
8Hydrogen Alpha FWHM for different conductivities at the Anode
Conductivity (nm)
FW
HM
14W18W28W
100 200 300 400 500 600 700 8001
2
3
4
5
6
7
8Hydrogen Alpha FWHM for different conductivities at the cathode
Conductivity (nm)
FW
HM
14W18W28W
Discharges in Liquids - Transient
100 200 300 400 500 600 700 800
0.35
0.4
0.45
0.5
0.55
Conductivity (uS)
OH
/H)
Max Peak (OH/H) Cathode
14W18W28W
100 200 300 400 500 600 700 8000.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Conductivity (uS)
OH
/H)
Max Peak (OH/H) Anode
14W18W28W
100 200 300 400 500 600 700 8000.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
Conductivity (uS)
O/H
)
Max Peak (O/H) Cathode
14W18W28W
100 200 300 400 500 600 700 8000
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
Conductivity (uS)
Na/
H)
Max Peak (Na/H) Cathode
14W18W28W
100 200 300 400 500 600 700 8000
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
Conductivity (uS)
Na/
H)
Max Peak (Na/H) Anode
14W18W28W
(OH/H)
(Na/H)
(O/H)
100 200 300 400 500 600 700 8000.05
0.1
0.15
0.2
0.25
0.3
Conductivity (uS)
O/H
)
Max Peak (O/H) Anode
14W18W28W
Anode Cathode
Summary• Control of plasma properties in liquids
• Characteristic times and initiation mechanisms
• Transient discharge breakdown development
• Experimental results– Discharge size
– Electron density
– Chemical Components
Future Work• Improve transient initiation model
• (dV/dt = const) instead of (V=const)
• ne = f(t) instead of (I = const)
• Dielectric Fluids
• Mechanical/Chemical Energy (Shockwaves vs. Radical Generation)
References
References:
• Alyssa Wilson et al 2008 Plasma Sources Sci. Technol. 17 045001
• Ayato Kawashima et al, J. Appl. Phys.
• D. Staack, A. Fridman, A. Gutsol et al., Angewandte Chemie-International Edition, vol. 47, no. 42, pp. 8020-8024, 2008.
Question?
Acknowledgements:
This material is based upon work suppoerted by the National Science Foundation Grant #1057175