Bulletin of the American Physical Society
75th Annual Gaseous Electronics Conference
Volume 67, Number 9
Monday–Friday, October 3–7, 2022;
Sendai International Center, Sendai, Japan
The session times in this program are intended for Japan Standard Time zone in Tokyo, Japan (GMT+9)
Session IR2: Plasma Liquid Interaction II |
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Chair: Nozomi Takeuchi, Tokyo Institute of Technology Room: Sendai International Center Sakura 2 |
Thursday, October 6, 2022 10:00AM - 10:30AM |
IR2.00001: Electric wind and water surface stabilization under impingement of an atmospheric pressure plasma jet Invited Speaker: Wonho Choe An electric wind or ionic wind is a neutral gas flow that occurs in weakly ionized gases due to the electrohydrodynamic force generated by the charged particle drag as a result of the momentum transfer from charged particles to neutrals (Nature Comm. 9 (2018) 371). In atmospheric pressure plasmas, although the convective flow of neutrals by electric winds can significantly contribute to the transport of radicals, it has not been considered so far and must be considered. For gas-liquid two phase systems, such as water under impingement of a plasma jet, these electric winds also give rise to many interesting physical phenomena. Gas jets can create dimple-like depressions in the liquid surface. As the gas jet speed increases, the cavity becomes unstable and starts bubbling and splashing. Our study, for the first time, revealed that an ionized gas jet blowing onto water produces a more stable interaction with the water surface compared to a neutral gas jet (Nature 592 (2021), 49). It has been found that when a plasma jet is impinged toward the water surface, deeper digging of the water surface occurs by the electric wind generated by the plasma. At the same time, the cavity undergoes a damped oscillation of about 100 Hz, which eventually becomes stable, i.e., the stability of the surface is improved despite the deeper digging of the water surface. We found that the Kelvin-Helmholtz instability becomes stabilized due to the strong electric field parallel to the water surface produced by high-speed ionization waves. The experimental observation was confirmed by computational modelling for the plasma jet and water surface. In the modelling, the plasma characteristics were analyzed by calculating the spatiotemporal change of the plasma, and the electric field near the water surface was quantitatively obtained. From this computational modelling, the experimentally identified improvement in surface stability and deepening of the water surface cavity was cross-validated. |
Thursday, October 6, 2022 10:30AM - 10:45AM |
IR2.00002: Change in surface tension of water in atmospheric pressure plasma-liquid interaction Naoki Shirai, Yuto Takamura, Takuma Kaneko, Koichi Sasaki We've demonstrated that measuring surface tension is a good way to look at the plasma–liquid contact in real-time. A method based on the dispersion relation of an acoustic capillary wave created on the water surface was used to detect surface tension. The surface tension steadily rose over time when the water surface was bombarded with the outside region of the spatial afterglow of an atmospheric-pressure plasma. During plasma irradiation, the Marangoni effect was detected, which was related to a localized rise in surface tension. After the discharge was completed, the surface tension was reduced. The fluctuation of the OH radical density in the gas phase was shown to be related to the temporary drop in surface tension. In the solution containing a trapping agent for liquid-phase OH radicals, there was no increase in surface tension. The results of these experiments imply that OH radicals enhance surface tension. The behavior of the surface tension, on the other hand, cannot be fully explained by considering solely the activity of OH radicals. We have also examined the interaction between plasma and liquids with low surface tension. |
Thursday, October 6, 2022 10:45AM - 11:00AM |
IR2.00003: Atmospheric Pressure Plasma in Contact with High-speed Water Flow for Evaluating Liquid-phase OH Transport Kazuki Takeda, Shota Sasaki, Keisuke Takashima, Toshiro Kaneko Novel applications of non-equilibrium atmospheric pressure plasmas (APPs) in a liquid or in contact with a liquid have been found in the life science field. However, much of the reactive species chemistry at the plasma-liquid interface has not been understood. Notably, short-lived species (e.g., OHaq, NxOyaq, HO2aq) has hardly characterized due to their high reactivity and non-uniformity. To break through this problem, we built an APP system with a high-speed liquid flow (over 10 m/s) through plasma. This APP system revealed very rapid OHaq decay within approximately 0.5 ms after the plasma exposure [1]. To explain the rapid decay of OHaq , we built the numerical model which assumed highly surface localized distribution of OHaq and it is consumed by the reaction with OHaq , H2O2aq, and NO2−aq. As a results, OHaq decay calculated using the numerical model was in good agreement with the experimental rapid decay. |
Thursday, October 6, 2022 11:00AM - 11:15AM |
IR2.00004: Detection of pulsed current induced by laser-induced desolvation of hydrated electrons in water jet immersed in low-pressure plasma Yoshinobu Inagaki, Koichi Sasaki Hydrated electrons are generated by plasma-liquid interaction. However, there have been limited reports on the detection of hydrated electrons in liquids interacting with plasmas. The difficulty is caused by the fact that hydrated electrons generated by the plasma irradiation are localized in a narrow region with a thickness of several nanometers below the plasma-liquid interface. To overcome the difficulty, we have developed a method to detect hydrated electrons in the interfacial region. Hydrated electrons in the interfacial region are converted to free electrons when they are irradiated with laser beam having a photon energy exceeding the desolvation energy. Free electrons produced by the desolvation are transported to the gas phase. In a previous work, we used an atmospheric-pressure helium dc glow discharge with the liquid cathode, and observed the pulsed increase in the discharge current when the liquid cathode was irradiated with the 4th harmonics of a Nd:YAG laser pulse. In the present work, we try to detect hydrated electrons in a micro water jet immersed in a low-pressure plasma. We detected the pulsed current from the plasma to the water jet when the water jet was irraditated with the 4th harmonics of a Nd:YAG laser pulse. |
Thursday, October 6, 2022 11:15AM - 11:30AM |
IR2.00005: Plasma self-organization in DC discharges with liquid anode: effect of electrode separation, liquid type and working gas Bhagirath Ghimire, Gabe Xu, Vladimir I Kolobov We study the formation of self-organized patterns (SOPs) in the vicinity of a liquid anode in atmospheric pressure DC glow discharges. The discharge is generated in a pin-to-liquid anode configuration with helium (He) flowing into open air. We investigate how the electrode separation and gas mixing influence the formation of SOPs on the surface of a distilled water (DIW) and 1% sodium chloride (NaCl). For a pin-to-liquid gap (g) of ~5 mm and 500 sccm He flow rate, the anode glow has the form of a circle on both DIW and NaCl surfaces. The diameter of this circle increases with increasing current. With increasing gap, multiple circles are first formed which finally transform into several more complex patterns. A ring formed at g = 8 mm changes to a wedge-shaped structure at g = 12 mm. Further increase of the pin-to-liquid gap makes the discharge unstable. The diameters of the patterns at all gap distances are larger for DIW than the NaCl solution. To understand effects of the gas type on the formation of SOPs on liquid anode surfaces, different gases (O2, N2 and air) were added as the surrounding gases in addition to the main He gas flow. For all gap distances, mixing He with other gases affected the formation of SOPs. For example, at g=10 mm, the wedge-shaped pattern that forms on the surface of DIW with pure He flow is transformed to a semi-circular wedge with addition of N2 or air. A similar semi-circular wedge-shaped pattern is formed at g=15 mm without any surrounding gas. Modelling some aspects of the discharge self-organization has been performed using computational tools available to the team. Comparison of simulation results with electrical and optical measurements is being conducted to clarify the nature of SOPs. The presence of electronegative gases and negative ions near the liquid anode surface and the charge transport inside the liquid anode on the pattern formation will be discussed. |
Thursday, October 6, 2022 11:30AM - 11:45AM Author not Attending |
IR2.00006: Plasma Discharge Morphology in a Thin Stream Packed Bed DBD with Turbulence Effects Roxanne Z-P Walker, John E Foster Turbulent flows in plasma discharges can provide several potential advantages for water purification applications, including enhanced surface area, local electric field enhancements, islands of trapped surface charge, and increased mixing both in the gas and liquid phases. All of these can enhance effective plasma dose as an advanced oxidation/reduction process, which is necessary to scale up plasma systems to real world applications. In the UM Packed Bed Reactor (PBR) [1], in which thin water streams serve as the packing medium, it has been observed that the discharge morphology and liquid phase chemistry are altered with changes in flow rate, corresponding to turbulence, with the same plasma electrical input. The interaction of plasma discharge with the water stream as a function of turbulence is not well understood. This work aims to characterize the discharge morphology as a function of flow rate in a single stream packed bed dielectric barrier discharge (DBD). With no plasma, laser scattering techniques along with fast imaging will be employed to understand the nature of the flow as well as gas phase mixing. With plasma on, optical emission spectroscopy and fast imaging will be used to understand the discharge morphology and plasma parameters. |
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