The term plasma actuator has now been a part of the fluid dynamics flow-control vernacular for more than a decade. A particular type of plasma actuator that has gained wide use is based on a single–dielectric barrier discharge (SDBD) mechanism that has desirable features for use in air at atmospheric pressures. For these actuators, the mechanism of flow control is through a generated body-force vector field that couples with the momentum in the external flow. The body force can be derived from first principles, and the effect of plasma actuators can be easily incorporated into flow solvers so that their placement and operation can be optimized. They have been used in a wide range of internal and external flow applications. Although initially considered useful only at low speeds, plasma actuators are effective in a number of applications at high subsonic, transonic, and supersonic Mach numbers, owing largely to more optimized actuator designs that were developed through better understanding and modeling of...

Dielectric Barrier Discharge Plasma Actuators for Flow Control

The application of strong electric fields in water and organic liquids has been studied for several years, because of its importance in electrical transmission processes and its practical applications in biology, chemistry, and electrochemistry. More recently, liquid-phase electrical discharge reactors have been investigated, and are being developed, for many environmental applications, including drinking water and wastewater treatment, as well as, potentially, for environmentally benign chemical processes. This paper reviews the current status of research on the application of high-voltage electrical discharges for promoting chemical reactions in the aqueous phase, with particular emphasis on applications to water cleaning.

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Electrohydraulic Discharge and Nonthermal Plasma for Water Treatment

Many-particle charged-particle plasma simulations using spatial meshes for the electromagnetic field solutions, particle-in-cell (PIC) merged with Monte Carlo collision (MCC) calculations, are coming into wide use for application to partially ionized gases. The author emphasizes the development of PIC computer experiments since the 1950s starting with one-dimensional (1-D) charged-sheet models, the addition of the mesh, and fast direct Poisson equation solvers for 2-D and 3-D. Details are provided for adding the collisions between the charged particles and neutral atoms. The result is many-particle simulations with many of the features met in low-temperature collision plasmas; for example, with applications to plasma-assisted materials processing, but also related to warmer plasmas at the edges of magnetized fusion plasmas. >

Particle-in-Cell Charged Particle Simulations, plus Monte Carlo Collisions with Neutral Atoms, PIC-MCC

In recent decades particular interest in applications of nonequilibrium plasma for the problems of plasma-assisted ignition and plasma-assisted combustion has been observed. A great amount of experimental data has been accumulated during this period which provided the grounds for using low temperature plasma of nonequilibrium gas discharges for a number of applications at conditions of high speed flows and also at conditions similar to automotive engines. The paper is aimed at reviewing the data obtained and discusses their treatment. Basic possibilities of low temperature plasma to ignite gas mixtures are evaluated and historical references highlighting pioneering works in the area are presented. The first part of the review discusses plasmas applied to plasma-assisted ignition and combustion. The paper pays special attention to experimental and theoretical analysis of some plasma parameters, such as reduced electric field, electron density and energy branching for different gas discharges. Streamers, pulsed nanosecond discharges, dielectric barrier discharges, radio frequency discharges and atmospheric pressure glow discharges are considered. The second part depicts applications of discharges to reduce the ignition delay time of combustible mixtures, to ignite transonic and supersonic flows, to intensify ignition and to sustain combustion of lean mixtures. The results obtained by different authors are cited, and ways of numerical modelling are discussed. Finally, the paper draws some conclusions on the main achievements and prospects of future investigations in the field.

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Plasma assisted ignition and combustion

The barrier discharge: basic properties and applications to surface treatment

The atmospheric pressure glow discharge burning in nitrogen
with small admixture of organosilicon compounds such as
hexamethyldisilazane or hexamethyldisiloxane was used for the
deposition of thin organosilicon polymer films. The properties
of the discharge were studied by means of optical emission
spectroscopy and electrical measurements. The deposited films
were characterized by atomic force microscopy, x-ray
photoelectron spectroscopy, infrared transmission measurements,
ellipsometry, depth sensing indentation technique and contact
angle measurements. The films were polymer-like, transparent in
the visible range, with uniform thickness and without pinholes.
The film hardness varied from 0.3 to 0.6 GPa depending on
deposition conditions, the elastic modulus was in the range
15-28 GPa and the surface free energy was in the range 26-45 mJ
m-2. The studied films exhibited good adhesion to the
substrate.

Deposition of thin organosilicon polymer films in atmospheric pressure glow discharge

Barrier discharges (BDs) can be operated in so-called diffuse modes. In contrast to the usual filamentary regime, which is characterized by a large number of individual microdischarges, the plasma of a diffuse BD covers the entire electrode area uniformly. Depending on the operation conditions (gas composition, amplitude and frequency of applied voltage), different diffuse modes can be investigated, namely, the atmospheric pressure Townsend discharge (APTD) and the atmospheric pressure glow discharge (APGD). The subject of the paper is the study of the transition between APTD and APGD as well as between diffuse and filamentary BD modes. Therefore, BDs were studied in the gas mixtures N2/H2, N2/He, N2/Ne and N2/Ar. It is shown that APGD in the noble gases helium and neon is formed due to high ionization rate at a comparatively low electric field, assisted by indirect ionization mechanisms involving metastable states of inert gases and nitrogen impurities, while the existence of APTD is coupled to the existence of metastable states of molecular nitrogen. Furthermore, a similar memory effect of residual surface charges on the dielectric barriers as described for filamentary BDs was observed in diffuse BDs.

The transition between different modes of barrier discharges at atmospheric pressure

The dielectric barrier discharge burning at atmospheric pressure usually has a filamentary non-homogeneous form. However, it was found that uniform dielectric barrier discharge can be generated in helium, nitrogen and in the mixture of argon with acetone under specific conditions. Such uniform discharge is called atmospheric pressure glow discharge (APGD). We studied dielectric barrier discharge burning in neon at atmospheric pressure and we found that the APGD can also be generated in neon. We measured the electrical characteristics of APGD in neon for different voltages and frequencies of power supply and different gas flows. We found that higher gas flow stabilizes the APGD and we determined the area of parameters in which the APGD burns. The images of discharges were recorded by a video camera and emission optical spectra were measured by a spectrometer. The properties of the discharges in neon were compared with the properties of discharges burning in argon and in the mixture of neon with argon.

https://iopscience.iop.org/article/10.1088/0022-3727/34/11/322/pdf

Atmospheric pressure glow discharge in neon

Diffuse dielectric barrier discharges in neon and helium at
atmospheric pressure were studied. The discharges were
generated between two metal electrodes, both covered by an
alumina layer and driven by ac voltage of frequency 10 kHz. The
discharge gap was 2.2 mm and 5 mm, respectively. The discharges
were investigated by electrical measurements and by temporally
and spatially resolved optical emission spectroscopy. The
experimental results revealed similar discharge behaviour in
both gases being considered. Although the discharges were
ignited at slightly different electric field strengths, their
evolutions were found to be similar. At maximum discharge
current the spatial light intensity distribution was
characterized by the formation of a cathode fall. A difference
was observed in the magnitudes of the current density only. In
addition to the regime with a single discharge pulse per
voltage half period T/2, a discharge mode with two and more
subsequent current pulses per T/2 (also referred to as the
pseudoglow discharge regime in the literature) was obtained due
to an increase in the voltage amplitude or an admixture of
nitrogen.

https://iopscience.iop.org/article/10.1088/0963-0252/15/1/002/pdf

Comparative study of diffuse barrier discharges in neon and helium

An atmospheric pressure glow discharge (APGD) was used for
surface modification of polyethylene (PE) and polypropylene
(PP). The discharge was generated between two planar metal
electrodes, with the top electrode covered by a glass and the
bottom electrode covered by the treated polymer sample. The
discharge burned in pure nitrogen or in nitrogenhydrogen or
nitrogenammonia mixtures. The surface properties of both
treated and untreated polymers were characterized by scanning
electron microscopy, atomic force microscopy, surface free
energy measurements and x-ray photoelectron spectroscopy. The
influence of treatment time and power input to the discharge on
the surface properties of the polymers was studied. The ageing
of the treated samples was investigated as well. The surface of
polymers treated in an APGD was homogeneous and it had less
roughness in comparison with polymer surfaces treated in a
filamentary discharge. The surface free energy of treated PE
obtained under optimum conditions was 54mJm2 and the
corresponding contact angle of water was 40; the surface free
energy of treated PP obtained under optimum conditions was 53
mJm2 and the contact angle of water 42. The maximum decrease in
the surface free energy during the ageing was about 10%.

David Trunec

Papers

Deposition of thin organosilicon polymer films in atmospheric pressure glow discharge

The transition between different modes of barrier discharges at atmospheric pressure

Atmospheric pressure glow discharge in neon

Comparative study of diffuse barrier discharges in neon and helium

Surface modification of polyethylene and polypropylene inatmospheric pressure glow discharge