Microsparks Generated By Charged Particles in Dielectric Liquids

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%