자료유형  

 학위논문

Control Number  

0017162815

International Standard Book Number  

9798382739458

Dewey Decimal Classification Number  

530

Main Entry-Personal Name  

Yang, Zimu.

Publication, Distribution, etc. (Imprint  

[S.l.] : University of Michigan., 2024

Publication, Distribution, etc. (Imprint  

Ann Arbor : ProQuest Dissertations & Theses, 2024

Physical Description  

180 p.

General Note  

Source: Dissertations Abstracts International, Volume: 85-12, Section: B.

General Note  

Advisor: Foster, John Edison.

Dissertation Note  

Thesis (Ph.D.)--University of Michigan, 2024.

Summary, Etc.  

요약It is known that under certain conditions, the DC atmospheric pressure plasma attachment at the liquid surface can self-organize both spatially and temporally into coherent and complex patterns, called self-organized pattern (SOP). The mechanism of SOP formation remains poorly understood. Such SOP is also observed in DC glows with metal anodes as well, taking the form of organized arrays of dot-like attachments. However, the liquid anode SOP is typically more complex. SOP formation is also subject to more complicated processes including liquid phase evaporation, fluid dynamics, sophisticated chemical reactions, species interaction, and local sheath electric field. In the community of plasma-liquid interactions, a conclusive understanding of many of these processes is still elusive due to their nonlinear nature and limited by currently available diagnostics methods. On the other hand, one can assert that the patterns are a consequence of dynamical coupling and feedback among the aforementioned processes. By unfolding this coupling and understanding the feedback pathways it may be possible to elucidate the nature of pattern formation and dynamics.In this work, multiple diagnostics were introduced to investigate the coupling processes in an atmospheric pressure DC glow discharge and plasma-liquid interface. The current-voltage (I-V) characteristics of the discharge and the corresponding shape and surface area of the self-organized pattern (SOP) were examined to correlate the changes in bulk plasma discharge properties with pattern dynamics. Various pattern morphology and the associated operating conditions necessary to realize the dynamic SOP were documented and it was found that both the oxygen entrainment and liquid properties had the most significant effect on the pattern dynamics. Specifically, a larger discharge gap or lower inert gas flow support more complex SOP dynamics and liquid conductivity was found to heavily affect the current density and attachment surface area of SOP. Schlieren imaging and control of ambient oxygen level in the air reveal that oxygen is critical for the establishment of a pattern.The importance of electronegative gas, including species such as oxygen, is then further examined through the examination of the negative ion hypothesis by laser photodetachment. Because the discharge operates in an ambient atmosphere, gases from this atmosphere can have a significant impact on gas-phase chemistry and inelastic processes taking place in the actual plasma column driven by heat and mass transfer. A gas-phase glow discharge strongly depends on gas-phase chemistry, heat, and mass transfer. By decreasing ambient oxygen concentration in a purge box, the SOP became featureless when the oxygen volume fraction dropped below ≈7%. A qualitative investigation of the gas density change by Schlieren imaging showed that discharge gap and inert flow rate strongly shape the convection boundary and thus the rate of air entrainment. In the literature, there is significant speculation that negative ions are necessary for pattern formation. It was found in this work that the mere presence of negative ions was not a sufficient condition for the appearance of SOP. Here by using detachment spectroscopy, negative ions in the discharge were detached by laser and the SOP showed no change implying that negative ions are not the cause of pattern dynamics.The coupling between the gas phase and plasma-liquid interface was further investigated by spatially resolved optical emission spectroscopy (OES). The emission map of major species in the plasma is obtained by scanning the plasma with a focusing lens and an imaging spectrometer. Gas temperatures and electron densities are estimated from the rotational temperature of nitrogen second positive system N2(C −B) and Stark broadening of Hβ line, respectively. The result of the gas temperature distribution near the liquid anode had a steep gradient which is one of the important cooling mechanisms. The corresponding change in temperature profiles is more sensitive to the gas phase heating than the variation of liquid conditions. The radial profile of electron density has a profound coupling with excited species including H(4d) and He(3d) whose productions are heavily dependent on the energetic electrons.Next, the thermodynamic and hydrodynamic processes at the plasma-liquid interface were examined via particle image velocimetry. Substantial convective flow at the plane vertical to the plasma-liquid interface was observed under SOP and driven by plasma gas heating and water evaporation at the interface. Interestingly, convection parallel to the interface is also observed and induces an unstable convective flow at a high electrical current where dynamic SOP is formed. It is assumed that this shear flow is either due to an anode sheath electric field or Marangoni flow (fluid motion due to surface tension gradient).Last, a fast, but non-trivial mass transport process at the plasma-liquid interface was observed: droplet generation was investigated via high-speed imaging cameras and OES. Unlike the droplets generated from the Taylor cone on the liquid cathode, the droplet generation from the liquid anode was observed due to gas bubbles bursting at the interface. Although it is not inherently a plasma process, the driving forces are the discharge gas heating. Additionally, these droplets can enhance the mass transport of liquid-phase species toward the gas phase. This was confirmed by OES that droplets' emissions are from salt particles in the electrolyte and excited OH radicals from the water molecule dissociation. These findings substantiate a new approach to the mass transfer from the liquid and control of discharge by dispersing plasma-activate liquid into the gas phase and chemically and ionically enriching the plasma-liquid interaction.From the aforementioned diagnostics, the couplings of pattern dynamics with gas phase operation, heat, and chemical dynamics were examined and found to provide useful insights into the SOP mechanism. In addition, this work, by using diagnostics, elucidated the complex coupling of the liquid phase to the gas phase driving discharge. At its core, the SOP problem is a manifestation of an interfacial process driven far from equilibrium-nonequilibrium thermodynamics. It is hoped that the data acquired by the suite of diagnostics in this thesis not only facilitates the understanding of SOP formation but also provides modelers with the parameters necessary to model this very complex system.

Subject Added Entry-Topical Term  

Plasma physics.

Subject Added Entry-Topical Term  

Applied physics.

Subject Added Entry-Topical Term  

Nuclear engineering.

Index Term-Uncontrolled  

Plasma-liquid interaction

Index Term-Uncontrolled  

Plasma self-organization

Index Term-Uncontrolled  

Optical emission spectroscopy

Index Term-Uncontrolled  

Atmospheric pressure

Index Term-Uncontrolled  

Jet droplets

Added Entry-Corporate Name  

University of Michigan Nuclear Engineering & Radiological Sciences

Host Item Entry  

Dissertations Abstracts International. 85-12B.

Electronic Location and Access  

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Control Number  

joongbu:657779