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Thermodynamics of Microplasma Initiation in Liquids

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

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Thermodynamics of Microplasma Initiation in Liquids

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  1. 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)

  2. Outline • Motivation • Applications • Control plasma parameters (ne, Te, d) • Discharges in liquid • Near liquids • “In” liquids • Experimental Setup • Transient discharges (OES) • Summary

  3. cells plasma wire Why Generate Plasma in Liquids? Chemical Applications: Water Sterilization Bio/Medical Fuel Reforming Physical Applications: Species Identification Microfluidics Shock Wave Generation Shock Wave

  4. Discharges in Gases Near Liquids In droplet containing gas Above liquid surface Inside bubbles Ref: Alyssa Wilson et al 2008 Plasma Sources Sci. Technol. 17 045001 http://www.panoramio.com/photo/2843260

  5. Discharges in Liquids – Steady State Small Perturbation ↑ E/n  Te ↓n ↑ Δεe-T Phase Instability  U Steady state supercritical plasma Ref: 27.12 MHz Plasma Generation in Supercritical Carbon Dioxide Ayato Kawashima et al, J. Appl. Phys.

  6. Discharge in Liquids - Process • Initiation  Low Density Region • Electrolysis • Boiling (Joule Heating) • Electrostatic Cavitations • Breakdown • Primary Streamer • Secondary Streamer • Spark • Thermalization • Relaxation 1950s-1980s thoroughly studied breakdown process in dielectrics

  7. Discharges in Liquids - Initiation Assumptions: All initiation mechanism achieve a low density reduction  n Const (I) and (V) r Local Low Density Region (n) Boiling Analysis (Energy Balance) Electrolysis Analysis ( Faradays law of electrolysis) Y = (Yeild of Fluid) Electrostatic CavitationAnalysis (Force Balance) Cavitation Electrode should be larger Fluid

  8. Experimental Setup Circuit: R Spark Gap 1 Spark Gap 2 Output V C Electrode Configurations: Diagnostics Point to Plane Point to Point Plane to Plane

  9. Discharges in Liquids – Transient & Plasma Size Spark Streamer Corona Anode (+) Cathode (-) < 50 um Water - Corona Mineral Oil - Corona

  10. Discharges in Liquids – Transient & Thermalization Te,Tvib>Tgas Te,Tvib≈ Tgas 𝛕 = f(ne, υen, Te, E/n, medium, …) Hα OH Hβ Na O

  11. Discharges in Liquids - Transient

  12. Discharges in Liquids - Transient Anode Cathode (OH/H) (Na/H) (O/H)

  13. 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)

  14. References Question? 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. Acknowledgements: This material is based upon work suppoerted by the National Science Foundation Grant #1057175

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