3,858 research outputs found
Fully Coupled Simulation of the Plasma Liquid Interface and Interfacial Coefficient Effects
There is a growing interest in the study of coupled plasma-liquid systems
because of their applications to biomedicine, biological and chemical
disinfection, agriculture, and other areas. Without an understanding of the
near-surface gas dynamics, modellers are left to make assumptions about the
interfacial conditions. For instance it is commonly assumed that the surface
loss or sticking coefficient of gas-phase electrons at the interface is equal
to 1. In this work we explore the consequences of this assumption and introduce
a couple of ways to think about the electron interfacial condition. In one set
of simulations we impose a kinetic condition with varying surface loss
coefficient on the gas phase interfacial electrons. In a second set of
simulations we introduce a Henry's law like condition at the interface in which
the gas-phase electron concentration is assumed to be in thermodynamic
equilibrium with the liquid-phase electron concentration. It is shown that for
a range of electron Henry coefficients spanning a range of known hydrophilic
specie Henry coefficients, the gas phase electron density in the anode can vary
by orders of magnitude. Varying reflection of electrons by the interface also
has consequences for the electron energy profile. This variation in anode
electron density and energy as a function of the interface characteristics
could also lead to significant variation in near-surface gas chemistries when
such reactions are included in the model; this could very well in turn affect
the reactive species impinging on the liquid surface. We draw the conclusion
that in order to make more confident model predictions about plasma-liquid
systems, finer scale simulations and/or new experimental techniques must be
used to elucidate the near-surface gas phase electron dynamics
Momentum, Heat, and Neutral Mass Transport in Convective Atmospheric Pressure Plasma-Liquid Systems and Implications for Aqueous Targets
There is a growing interest in the study of plasma-liquid interactions with
application to biomedicine, chemical disinfection, agriculture, and other
fields. This work models the momentum, heat, and neutral species mass transfer
between gas and aqueous phases in the context of a streamer discharge; the
qualitative conclusions are generally applicable to plasma-liquid systems. The
problem domain is discretized using the finite element method. The most
interesting and relevant model result for application purposes is the steep
gradients in reactive species at the interface. At the center of where the
reactive gas stream impinges on the water surface, the aqueous concentrations
of OH and ONOOH decrease by roughly 9 and 4 orders of magnitude respectively
within 50 m of the interface. Recognizing the limited penetration of
reactive plasma species into the aqueous phase is critical to discussions about
the therapeutic mechanisms for direct plasma treatment of biological solutions.
Other interesting results from this study include the presence of a 10 K
temperature drop in the gas boundary layer adjacent to the interface that
arises from convective cooling and water evaporation. Accounting for the
resulting difference between gas and liquid bulk temperatures has a significant
impact on reaction kinetics; factor of two changes in terminal aqueous species
concentrations like HO, NO, and NO are observed if the
effect of evaporative cooling is not included
Applications of plasma-liquid systems : a review
Plasma-liquid systems have attracted increasing attention in recent years, owing to their high potential in material processing and nanoscience, environmental remediation, sterilization, biomedicine, and food applications. Due to the multidisciplinary character of this scientific field and due to its broad range of established and promising applications, an updated overview is required, addressing the various applications of plasma-liquid systems till now. In the present review, after a brief historical introduction on this important research field, the authors aimed to bring together a wide range of applications of plasma-liquid systems, including nanomaterial processing, water analytical chemistry, water purification, plasma sterilization, plasma medicine, food preservation and agricultural processing, power transformers for high voltage switching, and polymer solution treatment. Although the general understanding of plasma-liquid interactions and their applications has grown significantly in recent decades, it is aimed here to give an updated overview on the possible applications of plasma-liquid systems. This review can be used as a guide for researchers from different fields to gain insight in the history and state-of-the-art of plasma-liquid interactions and to obtain an overview on the acquired knowledge in this field up to now
From submicrosecond-to nanosecond-pulsed atmospheric-pressure plasmas
We have developed a time-hybrid computational
model to study pulsed atmospheric-pressure discharges and compared
simulation results with experimental data. Experimental
and computational results indicate that increasing the applied
voltage results in faster ignition of the discharge and an increase
in the mean electron energy, opening the door to tunable plasma
chemistry by means of pulse shaping. Above a critical electric field
of ~2 kV/mmfor ~1-mm discharges, pulsed plasmas ignite right
after the application of an externally applied voltage pulse. Despite
the large pd value (30–300 torr · cm) and the high applied electric
field, the discharges are found to be streamer free in a desirable
glowlike mode. The comparison of the time evolution of the mean
electron kinetic energy as a function of the pulse rise time suggests
that a fast rise time is not necessarily the best way of achieving
high mean electron energy
High-voltage nanosecond pulses in a low-pressure radiofrequency discharge
An influence of a high-voltage (3-17 kV) 20 ns pulse on a weakly-ionized
low-pressure (0.1-10 Pa) capacitively-coupled radiofrequency (RF) argon plasma
is studied experimentally. The plasma evolution after pulse exhibits two
characteristic regimes: a bright flash, occurring within 100 ns after the pulse
(when the discharge emission increases by 2-3 orders of magnitude over the
steady-state level), and a dark phase, lasting a few hundreds \mu s (when the
intensity of the discharge emission drops significantly below the steady-state
level). The electron density increases during the flash and remains very large
at the dark phase. 1D3V particle-in-cell simulations qualitatively reproduce
both regimes and allow for detailed analysis of the underlying mechanisms. It
is found that the high-voltage nanosecond pulse is capable of removing a
significant fraction of plasma electrons out of the discharge gap, and that the
flash is the result of the excitation of gas atoms, triggered by residual
electrons accelerated in the electric field of immobile bulk ions. The
secondary emission from the electrodes due to vacuum UV radiation plays an
important role at this stage. High-density plasma generated during the flash
provides efficient screening of the RF field (which sustains the steady-state
plasma). This leads to the electron cooling and, hence, onset of the dark
phase
Controlled production of atomic oxygen and nitrogen in a pulsed radio-frequency atmospheric-pressure plasma
International audienceRadio-frequency driven atmospheric pressure plasmas are efficient sources for the production of reactive species at ambient pressure and close to room temperature. Pulsing the radio-frequency power input provides additional control over species production and gas temperature. Here, we demonstrate the controlled production of highly reactive atomic oxygen and nitrogen in a pulsed radio-frequency ( ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn001.gif] 13.56 MHz) atmospheric-pressure plasma, operated with a small ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn002.gif] 0.1 % air-like admixture ( ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn003.gif] \rm N_2 / ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn004.gif] \rm O_2 at ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn005.gif] 4:1 ) through variations in the duty cycle. Absolute densities of atomic oxygen and nitrogen are determined through vacuum-ultraviolet absorption spectroscopy using the DESIRS beamline at the SOLEIL synchrotron coupled with a high resolution Fourier-transform spectrometer. The neutral-gas temperature is measured using nitrogen molecular optical emission spectroscopy. For a fixed applied-voltage amplitude (234?V), varying the pulse duty cycle from 10% to 100% at a fixed 10?kHz pulse frequency enables us to regulate the densities of atomic oxygen and nitrogen over the ranges of ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn006.gif] (0.18±0.03) ? ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn007.gif] (3.7±0.1)× 10^20 ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn008.gif] \rm m^-3 and ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn009.gif] (0.2±0.06) ? ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn010.gif] (4.4±0.8) × 10^19 ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn011.gif] \rm m^-3 , respectively. The corresponding 11?K increase in the neutral-gas temperature with increased duty cycle, up to a maximum of ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn012.gif] (314±4) K, is relatively small. This additional degree of control, achieved through regulation of the pulse duty cycle and time-averaged power, could be of particular interest for prospective biomedical applications
Integrated design of atmospheric pressure non-equilibrium plasma sources for industrial and biomedical applications
In this dissertation are reported the most relevant results obtained during my three years Ph.D. project. An open-air plasma source has been developed to treat plastic and metallic films typically used in food packaging manufacturing. Among others, the DBD configuration was chosen due to its many advantages such as high intensity and uniformity of the treatment, possibility of operating in ambient air as well as ease of scale up.
Biological experiments were performed to assess the microbial reduction induced by the plasma treatment. Different operative conditions have been tested in order to identify the most efficient configuration and two distinct behaviours have been observed: low-power density treatment allowed to achieve microbial inactivation values below log 2 independently on treatment time; high-power density treatment where the microbial reduction grew with increasing treatment time.
Subsequently, the plasma discharge has been characterized by means of three investigation methods: thermal, electrical and optical absorption spectroscopy (OAS) analysis. The thermal and electrical analyses were employed to identify the best dielectric materials for food packaging manufacturing purposes. Once defined the optimal DBD configuration, OAS was used to measure the absolute concentration of ozone and nitrogen dioxide. Results showed that at low-power density the chemistry is governed by ozone; while at high-power density ozone is consumed by the poisoning effect and only nitrogen dioxide is detectable.
Lastly, a numerical simulation has been used to deeper investigate the chemistry governing the plasma discharge; by means of PLASIMO a global model and a fluid model were implemented
Plasma medicine: an introductory review
This introductory review on plasma health care is intended to
provide the interested reader with a summary of the current status of this
emerging field, its scope, and its broad interdisciplinary approach, ranging
from plasma physics, chemistry and technology, to microbiology, biochemistry,
biophysics, medicine and hygiene. Apart from the basic plasma processes
and the restrictions and requirements set by international health standards,
the review focuses on plasma interaction with prokaryotic cells (bacteria),
eukaryotic cells (mammalian cells), cell membranes, DNA etc. In so doing, some
of the unfamiliar terminology—an unavoidable by-product of interdisciplinary
research—is covered and explained. Plasma health care may provide a fast and
efficient new path for effective hospital (and other public buildings) hygiene—
helping to prevent and contain diseases that are continuously gaining ground
as resistance of pathogens to antibiotics grows. The delivery of medically
active ‘substances’ at the molecular or ionic level is another exciting topic
of research through effects on cell walls (permeabilization), cell excitation
(paracrine action) and the introduction of reactive species into cell cytoplasm.
Electric fields, charging of surfaces, current flows etc can also affect tissue in
a controlled way. The field is young and hopes are high. It is fitting to cover
the beginnings in New Journal of Physics, since it is the physics (and nonequilibrium
chemistry) of room temperature atmospheric pressure plasmas that
have made this development of plasma health care possible
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