Bulletin of the American Physical Society
70th Annual Gaseous Electronics Conference
Volume 62, Number 10
Monday–Friday, November 6–10, 2017; Pittsburgh, Pennsylvania
Session SR2: Plasmas in Liquids II |
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Chair: Tanvir Farouk, University of South Carolina Room: Duquesne |
Thursday, November 9, 2017 1:30PM - 1:45PM |
SR2.00001: Electrical Breakdown of Weakly-Conductive Liquids and Transition to a Supercritical Fluid. Skye Elliott, Sergey Leonov This experimental study reveals the high-voltage pulsed electrical breakdown of weakly-conductive liquid (MeOH) trapped in a dielectric test cell. It is considered a three-phase process with (1) mm-scale streamers propagation, (2) formation of a highly-conductive channel, and (3) transition of the discharge in liquid to in a supercritical fluid. Typical test conditions are: voltage applied U?10kV; electrical current I?100A; initial pressure P$=$1bar; maximal pressure within supercritical fluid P\textgreater 100bar. The diagnostics include: electrical probes, fast camera imaging, schlieren visualization of hydrodynamic processes, laser tracking of interfaces, optical emission spectroscopy. The sequence of plasma formation and supercritical fluid generation were shown to be highly sensitive to electrode configuration and applied voltage, with lower voltages yielding a two-step delayed breakdown. A non-ideal plasma state is considered with electron density Ne\textgreater 3e19 cm-3 measured by Stark broadening of H$\alpha $ line. Study of mechanisms of electric breakdown and discharge dynamics in supercritical fluids is a fundamental challenge and promises well-recognized practical benefits, such as a fuel injection technique, protection against deadly breakdowns in electrically-insulating liquids, etc. [Preview Abstract] |
Thursday, November 9, 2017 1:45PM - 2:00PM |
SR2.00002: Self-organization and Electrolyte Ion Mass Transport Processes with Chemistry in 1 ATM DC Glows Yao Kovach, Maria Garcia, John Foster In plasma physics, self-organization is observed in phenomena ranging from plasmoid formation in low pressure, RF plasmas to large-scale, and magnetized structures observed on the surface of the sun. Of recent interest is the puzzling information of self-organization patterns on the surface of liquid anodes in 1 ATM DC glows. While these patterns are of academic interest in regards to understanding collective phenomena, the appearance of the patterns may play an important role in the sub-surface liquid phase chemistry, driving convection and inducing thermal gradients. In this current work, a new, complex, star-shaped structure with round edges was observed with a copper sulfate electrolyte. The pattern was not observed with sodium chloride solutions. This observation suggests that electrolyte ion mass or perhaps ionization state may play a key role in deterring overall pattern shape. In order to understand the role of the transport of electrolyte ions from liquid to the gas phase on discharge maintenance, and pattern formation, spectroscopic analysis of the halo surrounds the main plasma column for multiple electrolytes are studied as a function of discharge conditions. [Preview Abstract] |
Thursday, November 9, 2017 2:00PM - 2:30PM |
SR2.00003: Understanding the Plasma-Liquid Interface: Progress and Challenges Invited Speaker: John Foster The interaction of plasma with liquid water occurs at a phase boundary layer, which includes gas, a water vapor layer, and the liquid itself. A host of physical and chemical processes are active at this interface making it a rich multiphase physics problem. These processes ultimately give rise to changes in the bulk liquid. Such induced changes are the basis for a number of emerging technologies and applications such as plasma-based water treatment and plasma medicine. The nature of the physical processes and ensuing chemistry that ``activates'' the liquid water, which is believed to originate at the interface, is not well understood. Ongoing experimental and computational efforts however are making progress towards the formulation of a consistent picture of the role of the plasma liquid interface in driving chemistry in solution. Here we survey the current state of understanding regarding the interfacial region including electrohydraulic forces that can lead to fluid dynamical effects resulting in enhanced radical distribution as well as chemistry driven by direct plasma interaction with liquid water. In particular, we review recent results from single and 2-D bubble studies that have yielded insight into mechanisms of radical transport into solution as a function of discharge type present in the bubble. Complex mass transport and induced chemistry generated in DC atmospheric pressure glows with liquid electrode resulting from plasma self-organization is also not well understood. Insight into the physical mechanism underlying both self-organization and its role in radical transport in these systems as inferred from recent experiments is also discussed. The implications of these findings, the understanding gaps along with measurement and modeling needs for continued progress, and the connection of this understanding with technologies with a plasma liquid underpinning are also commented upon. [Preview Abstract] |
Thursday, November 9, 2017 2:30PM - 2:45PM |
SR2.00004: Simultaneous particle image velocimetry (PIV)-Schlieren photography of fluid flow in liquid induced by plasma-driven interfacial forces Janis Lai, John Foster Understanding the transport of plasma-derived reactive species into bulk liquid is crucial for effective plasma-based water purification and other environmental applications. Physical and chemical interactions at the plasma-liquid interface region drive flow in the bulk liquid. The mechanisms of such flow are not well-understood. A 2-D plasma-in-liquid apparatus is used to study this interface region to understand the plasma-driven fluid dynamics. Previous shadowgraphs showed density gradients in the bulk liquid, while particle image velocimetry (PIV) measurements showed the velocity shear at the interface region. These measurements indicate the presence of fluid instabilities. Using simultaneous PIV-Schlieren photography, the interplay effect of such instabilities observed in the bulk liquid is investigated to better understand the plasma-driven forces at the interface, such as possible contribution of Marangoni flow. [Preview Abstract] |
Thursday, November 9, 2017 2:45PM - 3:00PM |
SR2.00005: Chemical reactions induced by plasma in contact with the solution containing halide ions: importance of ion distribution at gas-liquid interface for plasma-liquid interaction Kosuke Tachibana, Koichi Yasuoka Plasma in contact with liquid is widely studied for the research of water purification, nanoparticle synthesis, and so on. However, plasma-liquid interaction has not been fully understood. In order to deepen the understanding of the plasma-liquid interaction, we are focusing on ion distribution at gas-liquid interface and using halide ions of chloride and iodide ions. That is because these ions have similar chemical properties but different distributions at the gas-liquid interface. There is a paper reporting that chloride ions exist in a region a little away from the gas-liquid interface while iodide ions gather at the gas-liquid interface. In order to investigate the importance of the ion distribution at the gas-liquid interface, we irradiated a DC plasma to 2.1 mol/L NaCl and NaI solution. The DC plasma was generated between a metal pin electrode and water surface in argon atmosphere, and the current was regulated at 2 mA. Though the DC plasma could not oxidize chloride ions into chlorine in the 2.1 M NaCl solution within 600 s, the plasma was able to oxidize iodide ions into iodine in the 2.1 M NaI solution within 20 s. The experimental results have shown that the ion distribution at gas-liquid interface can play an important role in the plasma-liquid interaction. [Preview Abstract] |
Thursday, November 9, 2017 3:00PM - 3:15PM |
SR2.00006: Electrostatic Debye layer formed at a plasma-liquid interface David Go, Paul Rumbach, Jean Pierre Clarke Many of the new applications of low-temperature plasma in medicine and material synthesis rely on the direct interaction of plasma with an aqueous media. In this work, we derive and experimentally test an analytic model for the electrostatic Debye layer formed at a plasma-liquid interface [1]. Our theoretical model combines the Gouy-Chapman theory of aqueous electrolytes with a simple parabolic band model for the plasma sheath, and it gives closed form expressions for the electric field and charge distribution at the interface. It also predicts the plasma current density as a function of the solution ionic strength, which we experimentally confirmed using a liquid anode plasma. Fitting the model to the experimental data yields a plasma electron density on the order of 10$^{\mathrm{19}}$ m$^{\mathrm{-3}}$ and an electric field on the order of 10$^{\mathrm{4}}$ V/m on the liquid side of the interface. Importantly, this work clearly shows that the plasma behavior and the electrostatics of the plasma-liquid interface are highly dependent on the ionic strength of the aqueous solution. [1] P. Rumbach, J. P. Clarke, D. B. Go, \textit{Phys. Rev. E}, 95, 053203 (2017). [Preview Abstract] |
Thursday, November 9, 2017 3:15PM - 3:30PM |
SR2.00007: Interactions between water droplets and atmospheric pressure plasmas Juliusz Kruszelnicki, Amanda M. Lietz, Mark J. Kushner Atmospheric pressure plasmas are being studied for their potential application in water purification and agriculture. Transfer of plasma produced reactivity to the micro-droplets is potentially efficient due to the high surface area to volume ratio. We present results from a modeling study of the interactions between water micro-droplets and dielectric barrier discharges. The modeling is the plasma hydrodynamics simulator, \textit{nonPDPSIM}. Spherical water droplets (5-20 $\mu $m) were placed into a 2 mm gap between dielectric-covered electrodes. For spherical water droplets ($\varepsilon_{\mathrm{r}}\approx $80), dielectric polarization results in local electric field enhancement at the poles of the droplet. During the discharge, this enhancement increases the electron temperature near the poles, which can launch ionization waves (IW) from the droplet. Since the IW interaction time is short compared to the dielectric relaxation time of the droplet, charge deposition occurs at the boundary, leading to an initial anisotropy in the species produced in the droplet. Large droplets depleted the local gas-phase densities of reactive species, which leads to a radius-dependent saturation of densities and pH. Liquid-phase saturation densities of reactive species strongly depends on their Henry's Law constants, $h$. Low-$h$ species, such as O$_{\mathrm{3}}$, saturate rapidly invariant of the droplet size, whereas high-$h$ species (e.g., H$_{\mathrm{2}}$O$_{\mathrm{2}}$, NO$_{\mathrm{2}}$, N$_{\mathrm{2}}$O$_{\mathrm{5}})$ do not saturate and become transport limited in getting reactants to the droplet. [Preview Abstract] |
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