Bulletin of the American Physical Society
67th Annual Gaseous Electronics Conference
Volume 59, Number 16
Sunday–Friday, November 2–7, 2014; Raleigh, North Carolina
Session KW2: Reactive Microdischarges |
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Chair: David Go, University of Notre Dame Room: State C |
Wednesday, November 5, 2014 1:30PM - 1:45PM |
KW2.00001: Influence of the amount of N$_2$ admixture on the dynamics of atmospheric pressure helium discharges in capillary tubes Anne Bourdon, Francois Pechereau, Pedro Viegas Since a few years, atmospheric pressure helium microplasma jets ignited in thin dielectric tubes have received considerable interest due to their potential for biomedical applications. In particular, the propagation of discharges in long capillary tubes is studied for the development of medical devices for endoscopic applications. In [1], experiments have been carried out to study the influence of various amounts of N$_2$ admixture on the characteristics of a helium discharge in long capillary tubes. In this work, we study with a 2D fluid model the discharge characteristics in conditions close to those used in experiments. Simulation results show that the discharge dynamics and structure depend on the amount of N$_2$ admixture and the applied voltage. In particular, as the amount of N$_2$ admixture increases, the propagation velocity of the discharge in the tube first increases and then decreases, as observed in experiments. To explain these results, a detailed analysis of the kinetic scheme of He-N$_2$ mixtures with various amounts of N$_2$ is presented. The influence of other parameters as the initial preionization level, the tube material and the shape of the applied voltage are also discussed.\\[4pt] [1] T. Darny, E. Robert, S. Dozias and JM. Pouvesle, Proceedings of GD2014 [Preview Abstract] |
Wednesday, November 5, 2014 1:45PM - 2:00PM |
KW2.00002: Production of Energetic Active-Oxygen Species at Atmospheric Pressure by Linear Microplasma Arrays Wilson Rawlins, Kristin Galbally-Kinney, Steven Davis, Alan Hoskinson, Jeffrey Hopwood Linear arrays of stripline resonators operated at microwave frequencies and low powers provide spatially and temporally continuous micro-discharges with high E/N at atmospheric pressure. When implemented in a discharge-flow reactor, these microplasmas excite metastable singlet molecular oxygen and dissociate oxygen molecules to produce atomic oxygen, with efficiencies comparable to conventional microwave resonant cavities at low pressures. At elevated pressure, production of atomic oxygen leads to prompt formation of ozone immediately downstream of the discharge exit. We have observed and quantified the production of O$_{\mathrm{2}}$(a $^{\mathrm{1}}\Delta )$ metastables and O$_{\mathrm{3}}$ in the effluent of linear microplasma arrays for O$_{\mathrm{2}}$/He, O$_{\mathrm{2}}$/Ar, O$_{\mathrm{2}}$/N$_{\mathrm{2}}$/He, and O$_{\mathrm{2}}$/N$_{\mathrm{2}}$/Ar mixtures as functions of pressure, gas flow rate, and species mixing ratio. We compare results for single-array microplasmas, where the discharge products are formed in a small volume and entrained into the bulk flow, and overlapping dual-array microplasmas which process larger gas flow volumes. [Preview Abstract] |
Wednesday, November 5, 2014 2:00PM - 2:15PM |
KW2.00003: High Frequency Self-pulsing Microplasmas John Lassalle, William Pollard, David Staack Pulsing behavior in high-pressure microplasmas was studied. Microplasmas are of interest because of potential application in plasma switches for robust electronics. These devices require fast switching. Self-pulsing microplasmas were generated in a variable-length spark gap at pressures between 0 and 220 psig in Air, Ar, N$_{2}$, H$_{2}$, and He for spark gap lengths from 15 to 1810 $\mu$m. Resulting breakdown voltages varied between 90 and 1500 V. Voltage measurements show pulse frequencies as high as 8.9 MHz in argon at 100 psig. These findings demonstrate the potential for fast switching of plasma switches that incorporate high-pressure microplasmas. [Preview Abstract] |
Wednesday, November 5, 2014 2:15PM - 2:30PM |
KW2.00004: Conversion of carbon dioxide to carbon monoxide using non-thermal radio-frequency microplasmas at atmospheric pressure James Dedrick, James Comerford, Zaenab Abd-Allah, Kari Niemi, Deborah O'Connell, Michael North, Timo Gans The conversion of carbon dioxide to carbon monoxide using non-thermal plasmas offers the potential to provide a sustainable and efficient source of carbon monoxide that is widely used in industry. To maximise conversion efficiency, a non-thermal microplasma source is developed to operate at 40.68 MHz in helium while minimising the potential for arcing. Operation in argon is also achieved and this offers the possibility for the future upscaling of production. Measurements of the concentration of carbon monoxide in the effluent are undertaken using Fourier transform infrared spectroscopy and combined with electrical measurements to estimate the efficiency of conversion with respect to variations in the applied voltage and inlet gas composition. The production of carbon monoxide concentrations greater than 1000 ppm (using a 1\% carbon dioxide admixture in helium) facilitates the use of this method for simple chemical reactions including the generation of carbonyl functionalised molecules. [Preview Abstract] |
Wednesday, November 5, 2014 2:30PM - 2:45PM |
KW2.00005: Air-Plasma Bullets Propagating Inside Microcapillaries and in Ambient Air Deanna A. Lacoste, Anne Bourdon, Koichi Kuribara, Keiichiro Urabe, Sven Stauss, Kazuo Terashima We report on the characterization of air-plasma bullets formed inside microcapillary tubes and in ambient air, obtained without the use of inert or noble gases. The bullets are produced by nanosecond discharges, applied at 1 kHz in a dielectric barrier discharge configuration. The anode consists of a tungsten wire with a 50-$\mu $m diameter, centered in the microcapillary, while the cathode is a silver ring, fixed on the outer surface of the fused silica tube. The gap distance is kept constant at 1.35 mm. The microcapillary is fed with a 4-sccm flow of air at atmospheric pressure. In the tubes and in ambient air, the propagation of air plasma bullets is observed. The temporal evolution of the bullet propagation has been studied with the aid of an ICCD camera. The effect of the applied voltage (from 5.2 to 8.2 kV) and the inner diameter of the microcapillaries (from 100 to 500 $\mu$m) on the discharge dynamics are investigated. Inside the tubes, while the topology of the bullets seems to be strongly dependent on the diameter, their velocity (on the order of 1 to 5x10$^{5}$ ms$^{-1})$ is only a function of the applied voltage. In ambient air, the air-plasma bullets propagate at a velocity of 1.25x10$^{5}$ ms$^{-1}$. Possible mechanisms for the propagation of air-plasma bullets in ambient air are discussed. [Preview Abstract] |
Wednesday, November 5, 2014 2:45PM - 3:00PM |
KW2.00006: High pressure micro glow discharge: Detailed approach to gas temperature modeling Mostafa Mobli, Tanvir Farouk High pressure micro plasma discharge has been the center of interest in recent years, unlike low pressure discharges; gas heating is an important factor in these discharges. A Dirichlet temperature boundary condition (iso-thermal) which is the most commonly used, is unable to capture the cathode and anode wall temperature temporal changes, effects of materials thermal characteristics and also forces an artificial cooling of the discharge. To overcome this inadequacy a conjugate heat transfer (CHT) model has been implemented which is found to resolve the gas temperature predictions both in the volume and the electrode surfaces more accurately. The implemented CHT model increases the overall computational overhead due to resolution of the temperature field in the solid phase, hence a novel temperature boundary condition has been proposed that resolves a temporally evolving electrode surface temperature without implicitly solving the temperature in the solid phase. Comparison with the experimental results shows that these two new approaches are able to predict an agreeable gas temperature distribution. The effect of pressure on the discharge characteristics also has been studied. [Preview Abstract] |
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