Microsparks Generated By Charged Particles in Dielectric Liquids
Robert Geiger
Advisor: Dr. David Staack
Texas A&M University- Mechanical Engineering
Plasma Engineering & Diagnostics Laboratory (PEDL)
Dielectric Medium – Extra Heavy CrudeExtra Heavy Oil Light OilPlasma in Oil
Can plasma efficiently lower viscosity?
Hydrocracking Steam cracking
Current Methods
Low Energy Plasma in Liquids
Nano-second pulsed discharge from ~ 1μm tips.
20J/pulse
5mJ/pulse
Charcteristics1) Energy Per Pulse ~ C2) Stray Capacitance ~ 5 pF3) Lowest Energy ~ 1 mJLower Energy 1)Smaller size2)More non-equilibrium
V
Spark Gap 1R
CSpark Gap 2
Output
D. Staack, A. Fridman, A. Gutsol et al., Angewandte Chemie-International Edition, vol. 47, no. 42, pp. 8020-8024, 2008.
Low Energy Input – Charge Carrier Method
HV GNDball
Discharge
Electrode
2R
Spherical Capacitor- C = 4πε0R- R ~ 0.5 – 5 mm- C ~ 0.05 - 0.5 pF- E ~ 0.5 – 200 μJ
(V ~ 5 – 30 kV)
Experimental Setups
Multiple Charge Carrier
Discharge Modes for Multiple charge carriers:
1) Gas Bubble Chain Formation– High temperature gas phase– DC Mode Glow Discharge– Duration ~ 5 s– Ballasted– Energy Determined by discharge current
2) Spark Chain Formation– High temperature liquid phase– Transient Spark – Energy determine by External
Capacitance– Duration ~ 10-100 ns
3) Microplasma Mode– Low temperature liquid phase– Power Density ~100 W/l
0 s 4 s 6 s 12 s 14 s 20 s
Multiple Charge Carrier - Batch Reactor
Ground (-)
High Voltage (-13.3 kV)
Electrodes
Metal ball/Charge Carrier
Micro-plasma Discharge
Oil
Acrylic Top
~50W/L
Chemistry – Gas Chromatography of Hexadecane
Difficulty Working with Heavy Crude
50 100 150 200 250 3000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Temperature (F)
Con
duct
ivity
(S
/m)
Composition Conductivity
• Mix Heavy and Light• Wasteful• Easy
• Increase Temperature• Lose Light HC• Increase Conductivity• Difficult
Viscosity Results
Treated samples and controls measured using AR-2000 Rheometer.
Heavy Oil
Mass Fraction Boil Off Analysis
Heavy Oil
Increase in Light HCsDecrease in Heavy HCs
• Input Electrical Discharge Energy (20 kJ, 24g)
• 2.7% by mass converted to lights ( ~ 3.8x10-3 moles)
• 1.43 kJ need to break C-C bonds
• Efficiency 1.43 / 20 = 7% • About 7% of
electrical energy goes into breaking C-C bonds
• System has not been optimized
Summary• Interesting way to initiate nanosecond microsparks• Great control over discharge energy
– Spark Gaps (mJ J)
– Charge Carriers (uJ mJ )
• Control of plasma properties in liquids
• Scaling is possible• Viscosity decreases were observed
• Cracking to lighter hydrocarbons
Future Work• High Temperature and Pressure
• Effect of energy per pulse on chemistry
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
Microsparks – Emission Spectra
Hα
Particle Dynamics – Contact ChargingField Enhancement Factor
Lift off Voltagemg = qEg = qαV/dq = α CVα = (mgd/CV2)1/2
α ~ 1/β
Experimentalα ≈ 0.3
Liu, T. M.-C. (2010). The Design of a Micro/Nano-Particle Electrostatic Propulsion System. Charge relaxation τ = ε/σFor Mineral Oil ~ 0.5 s
Mixing Heavy and Light Oils
0 10 20 30 40 50 60 70 80 90 10010
-2
10-1
100
101
102
103
% Light Oil Addition
Vis
cosi
ty (
Pa*
s)
Viscosity of Heavy/Light Oil MixturesPure Heavy Crude ~ 188.4 Pa . s
Pure Light Oil ~ 0.0196 Pa . s
70/30 mixture ~ 38.2 Pa . s
Change of Mass
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- present thoroughly studied breakdown process in transformer oils and DI water.Plasma’s properties less studied.
Anode (+)
Cathode (-)
Gap ~ 6 cm
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
δ – initial pertubation size
Bubble Formation Time Estimates
V = 10 kVRtip = 5 μm
ne = 1016 cm-3
I= 350 mA
V = 10 kVRtip = 1 μm
ne = 1012 cm-3
I= 10 nA
Microbubble can be generated most quickly by cavitation and even by other methods as conditions similar to experiments.
Experimental Setups
Dielectric LiquidPower Supply
Resistor
Single Charge Carrier
Multiple Charge Carrier
20 30 40 50 60 70 8010
-3
10-2
10-1
100
101
102
103
Viscosity Measurements for mixtures of Heavy/Light Oil
Temperature (C)
Vis
cosi
ty (
Pa*
s)
100%90%75%67%50%33%0%
