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(Bio)Plasma Chemistry

Wouter Van Gaens , Annemie Bogaerts . (Bio)Plasma Chemistry . Plasma to Plasma! Workshop, Jan 2013. PLASMANT University of Antwerp, Belgium. 1. Introduction. Plasma medicine applications Microdischarge Non-LTE plasma at atmospheric pressure Large interest in plasma jets

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(Bio)Plasma Chemistry

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  1. Wouter Van Gaens, Annemie Bogaerts (Bio)Plasma Chemistry Plasma to Plasma! Workshop, Jan 2013 PLASMANT University of Antwerp, Belgium

  2. 1. Introduction • Plasma medicine applications • Microdischarge • Non-LTE plasma at atmospheric pressure • Large interest in plasma jets • Usually noble gas mixing with ambient air • Both physically and chemically complicated processes NOBLE GAS PLASMA MIXING ZONE

  3. 1. Introduction • Aim of this work • Insight in chemical phenomena (generally valid ?!?) • Simple model = low computational load • Mainly qualitative study • Implement humid air chemistry set with argon coupling • Reduced chemistry set (can be used in higher level models ?!?) NOBLE GAS PLASMA MIXING ZONE

  4. 1. Introduction • Other important/relevant humid air reaction chemistry modelling, i.a.: • Kogelschatz et al (1988) & Kossyiet al (1992) : Dry air • NIST Standard reference data (‘90-’00): Humid air • Combustion and atmospheric chemistry community (Herron, Atkinson, Tsang et al) • Gentille and Kushner (1995): Humid air • Plasma remediation of NxOy • Liu, Bruggeman, Iza and Kong (2010): He/H2O • General biomedical applications, hydrogen peroxide generation • Iza et al (‘10): He/O2/H2O • Plasma medicine, RF discharges • Sakiyamaet al (2012): Humid air • Plasma medicine, surface micro discharge • Babaeva and Kushner (2013): Humid air • Plasma medicine, DBD filaments and fluxes towards wounded skin

  5. Recentreview: X Lu et al, Plasma Sources Sci. Technol. 21 (2012) 03400) 2. Typical plasmajet configurations

  6. Recentreview: X Lu et al, Plasma Sources Sci. Technol. 21 (2012) 03400) 2. Typical plasmajet configurations

  7. Device of our choice: Prof. P. Bruggeman, Eindhoven Univ. of Technology Needle electrode (Ø ± 0.5 mm) Coaxially inserted in dielectric tube (inner Ø ±1.8 mm) Needle tip 1.9 mm from nozzle exit 2. Typical plasma jet configurations 3 mm 10 mm

  8. Operating conditions: 6.5 Watt dissipated power RF discharge Ar gas feed 2 slm Possibility of oxygen admixture 2. Typical plasma jet configurations 3 mm 9mm

  9. 0D model ‘GlobalKin' Prof. M. J. Kushner, University of Michigan, US 3. Model Boltzmann solver(*) Species kinetics Electron energy equation (*) can be called very frequently with changing background gas composition!!!!!!!

  10. 0D fluid model ‘GlobalKin' Prof. M. J. Kushner, University of Michigan, US 3. Model Boltzmann solver(*) Species kinetics Power input! Electron energy equation (*) can be called frequently, for example with changing background gas composition

  11. 3. Model • Assumptions to obtain ‘semi-empirical’ model • 1) Pseudo-1D simulation (to give idea of “distance to nozzle”) • Volume averaged element moving along the plasmajet stream > imaginary cylinder • Moving speed ̴ flow velocity & Ø cylinder (1cm ≈ 1msec) • No radial transport (high flow speed) / no axial drift & diffusion flux

  12. 3. Model • Assumptions to obtain ‘semi-empirical’ model • 2) Humid air diffusion • Ar replaced by N2/O2/H2O • Mixing speed fitted to literature values and 2D fluid simulation calculation Ellerweg et al (2012) Reuter et al (2012) 2D Fluid flow model

  13. 3. Model • Assumptions to obtain ‘semi-empirical’ model • 3) Tgas evolution • Fitted to measurements TU/e (Tg, radially averaged) • Self consistent Tgas calculations by model only accurate in first few mm!

  14. Why ‘device specific’ plasma chemistry study (≠ more general approach)? Pdeposition as function of plasma jet position unknown > plasma properties matched to experiment Tgas evolution device specific: crucial for chemistry (eg. NOx and O3) Broad parameter study: more general chemical info 3. Model

  15. Extended Ar/N2/O2/H2O chemistry set 85 implemented species! Someadvantages & differencescomparedtoothermodels: complex waterclusters Argon implementation (lessexpensive) Rot/Vibexcitedstates (partially) included 4. Reaction chemistry set

  16. Extended Ar/N2/O2/H2O chemistry set 1885 reactions! (can be reduced to ± 400 reactions) 278 electron impact & 1596 heavy particle reactions (692 dry air) 4. Reaction chemistry set

  17. Calc. [O3] vs. experim. [O3] by TU/e (2% O2 admixture) Relatively good qualitative agreement Detailed discussion in upcoming paper! Agreement for [O], [NO] and [OH] (literature) for similar devices. 5. Validation

  18. Similar conditions as for TU/e plasmajet device, except no O2 admixture Very rapid chem/phys quenching of energetic Ar states by air Fast charge exchange by Ar ions Strong [e-] drop due to efficient dissociative electron attachment of air 6. Output reaction chemistry model

  19. Biomedically active species O2(a), O3, NO, N2O, H2O2, HNO3 predicted to be very long living species 1-1000 ppm N < H < O in lifetime and density, but ‘distance of treatment’ is crucial! O into O3 if Tgas low/ into NOx if Tgas high Plasma becomes electronegative due to electron attachment in the far effluent 6. Output reaction chemistry model

  20. Water cluster formation Complex mechanism by implementing reaction rates (≠ Arrhenius form) by Sieck et al (2000) Dominant positive charge carrier Water cluster size gradually increasing in time NO+ clusters less abundant 6. Output reaction chemistry model

  21. Example of parameter variation: 300K Large changes in densities (up to order of magnitude) Changes in chemical pathways less drastic! Less NO, much more O3 in far effluent Faster recombination of radicals like O, H into OH, HO2 Favors HNO3 formation! (though net less NOx) Chemical pathway changes taken into account in reduced chemistry set! 6. Output reaction chemistry model Rel. ∆[X] vs. [X] with fitted Tg profile cfr. experiment

  22. 8. Conclusions & Outlook Large amount of chemical data studied Argon implementation Semi-empirical model (validation) More detailed chemical pathway analysis will be given in upcoming paper Idem ditto for effect of power, air humidity & flow speed on chemistry Reduced chemistry set Acknowledgments: Prof. Dr. M. J. Kushner Flemish Agency for Innovation by Science and Technology Computer facility CalcUA Prof. P. Bruggeman of Eindhoven University of Technology for providing experimental data

  23. Thank you for your attention!Questions?

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