共查询到20条相似文献,搜索用时 0 毫秒
1.
Wenxia Pan Wenhong Zhang Wei Ma Chengkang Wu 《Plasma Chemistry and Plasma Processing》2002,22(2):271-283
Argon DC plasma jets in stable laminar flow were generated at atmospheric pressure with a specially designed torch under carefully balanced generating conditions. Compared with turbulent jets of short length with expanded radial appearance and high working noise, the laminar jet could be 550 mm in length with almost unchanged diameter along the whole length and very low noise. At gas feeding rate of 120 cm3/s, the jet length increases with increasing arc current in the range of 70–200 A, and thermal efficiency decreases slightly at first and then leveled off. With increasing gas flow rate, thermal efficiency of the laminar jets increases and could reach about 40%, when the arc current is kept at 200 A. Gauge pressure distributions of the jets impinging on a flat plate were measured. The maximum gauge pressure value of a laminar jet at low gas feeding rate is much lower than that of a turbulent jet. The low pressure acting on the material surface is favorable for surface cladding of metals, whereas the high pressure associated with turbulent jets will break down the melt pool. 相似文献
2.
Recently, much attention has been paid to gas discharges producing nonthermal plasma because of many potential benefits in industrial applications. Historically, past work focused on Dielectric Barrier (silent) Discharges (DBD) and pulse-periodical corona discharges. Recently, a number of new different discharge techniques succeeded in producing stable gas discharge at atmospheric pressure. Among these are repetitively pulsed glow discharge; continuous glow discharge in a gas flow; hollow-cathode atmospheric pressure discharge; RF and microwave (MW) discharges. Several new variants of the DBD have been demonstrated over a rather wide range of frequencies. All these forms of gas discharge are characterized by a strong nonequilibrium plasma state. We attempt to classify these discharges with respect to their properties, and an overview of possible applications is made. Conditions for the existence of homogenous and filamentary forms of each of the discharge types are discussed. 相似文献
3.
Wenxia Pan Xian Meng Chengkang Wu Xi Chen 《Plasma Chemistry and Plasma Processing》2006,26(4):335-345
The generation, jet length and flow-regime change characteristics of argon plasma issuing into ambient air have been experimentally examined. Different torch structures have been used in the tests. Laminar plasma jets can be generated within a rather wide range of working-gas flow rates, and an unsteady transitional flow state exists between the laminar and turbulent flow regimes. The high-temperature region length of the laminar plasma jet can be over an order longer than that of the turbulent plasma jet and increases with increasing argon flow rate or arc current, while the jet length of the turbulent plasma is less influenced by the generating parameters. The flow field of the plasma jet has very high radial gradients of plasma parameters, and a Reynolds number alone calculated in the ordinary manner may not adequately serve as a criterion for transition. The laminar plasma jet can have a higher velocity than that of an unsteady or turbulent jet. The long laminar plasma jet has good stiffness to withstand the impact of laterally injected cold gas and particulate matter. It could be used as a rather ideal object for fundamental studies and be applied to novel materials processing due to its attractive stable and adjustable properties. 相似文献
4.
Nithiphat Teerakawanich Varakorn Kasemsuwan Kulsawasd Jitkajornwanich Weerawoot Kanokbannakorn Siwapon Srisonphan 《Plasma Chemistry and Plasma Processing》2018,38(4):817-830
By exploiting the physical effect of a highly nonuniform localized electric field and electron-initiated impact ionization on space charge, we generated homogeneous nonthermal plasma under ambient atmosphere. We evaluated the physical characteristics and evolution of microcorona discharge-induced nonthermal atmospheric plasma (NAP) based on a point-to-plane electrode in open air with two distinct configurations. High-voltage pulses were employed as the primary power source of corona discharge generation to reveal the fundamental mechanism, polarity effect and feasibility of using NAP for organic surface modification. Consequently, we employed NAP to modify the surface of rice (Oryza sativa L.) seeds to improve their wettability. The surface modification of the rice seeds was investigated via water apparent contact angle (ACA) and water imbibition (WI) measurements. The ACA and WI measurements revealed not only the improvement in the wetting properties but also the mutual relationships between and limitations of ACA and WI analysis. We found that the WI time reached saturation after a certain treatment time, called the threshold treatment time. Because vacuum conditions are not required, well-established NAP technology will garner interest in many fields, ranging from the life, environmental, and biomedical sciences to solid-state electronics applications. 相似文献
5.
High Energy Chemistry - It has been shown that plasma treatment of the surface of a polytetrafluoroethylene film in nonthermal plasma of atmospheric-pressure glow discharge makes it possible to... 相似文献
6.
High Energy Chemistry - A change in the surface properties of polytetrafluoroethylene films by treatment in nonthermal nonequilibrium plasma generated by atmospheric-pressure plasma jets has been... 相似文献
7.
Zen Shungo Abe Tetsuya Teramoto Yoshiyuki 《Plasma Chemistry and Plasma Processing》2019,39(5):1203-1210
Plasma Chemistry and Plasma Processing - The synthesis of Mg3N2, a new safe ammonia carrier, by the nitridation of MgO using a simple plasma process is proposed and demonstrated. Recently, ammonia... 相似文献
8.
Modeling study is performed to reveal the momentum and heat/mass transfer characteristics of a turbulent or laminar plasma
reactor consisting of an argon plasma jet issuing into ambient air and interacting with a co-axially counter-injected argon
jet. The combined-diffusion-coefficient method and the turbulence-enhanced combined-diffusion-coefficient method are employed
to treat the diffusion of argon in the argon–air mixture for the laminar and the turbulent regimes, respectively. Modeling
results presented include the streamline, isotherm and argon mass fraction distributions for the cases with different jet-inlet
parameters and different distances between the counter-injected jet exit and the plasma torch exit. It is shown that there
exists a quench layer with steep temperature gradients inside the reactor; a great amount of ambient air is always entrained
into the plasma reactor; and the flow direction of the entrained air, the location and shape of the quench layer are dependent
on the momentum flux ratio of the plasma jet to the counter-injected cold gas. Two quite different flow patterns are obtained
at higher and lower momentum flux ratios, and thus there exists a critical momentum flux ratio to separate the different flow
patterns and to obtain the widest quench layer. There exists a high argon concentration or even ‘air-free’ channel along the
reactor axis. No appreciable difference is found between the turbulent and laminar plasma reactors in their overall plasma
parameter distributions and the quench layer locations, but the values of the critical momentum flux ratio are somewhat different. 相似文献
9.
10.
Impact of Nonthermal Atmospheric Plasma on the Structure of Cellulose: Access to Soluble Branched Glucans 下载免费PDF全文
Joakim Delaux Prof. Carmen Ortiz Mellet Christine Canaff Dr. Elodie Fourré Dr. Cédric Gaillard Dr. Abdellatif Barakat Prof. José M. García Fernández Dr. Jean‐Michel Tatibouët Dr. François Jérôme 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(46):16522-16530
We have investigated the effect of non‐thermal atmospheric plasma (NTAP) on the structure of microcrystalline cellulose. In particular, by means of different characterization methods, we demonstrate that NTAP promotes the partial cleavage of the β‐1,4 glycosidic bond of cellulose leading to the release of short‐chain cellodextrins that are reassembled in situ, preferentially at the C6 position, to form branched glucans with either a glucosyl or anhydroglucosyl terminal residue. The ramification of cellulosic chain induced by NTAP yields branched glucans that are soluble in DMSO or in water, thus opening a straightforward access to processable glucans from cellulose. Importantly, the absence of solvent and catalyst considerably facilitates downstream processing as compared to (bio)catalytic processes which typically occur in diluted conditions. 相似文献
11.
The excitation capability of an argon microwave plasma flame expanded at atmospheric pressure has been studied. For this purpose, argon with different proportions of nitrogen was introduced at the end of the expanded flame, where the population densities of the atomic argon levels were still high enough. Optical emission spectra allowed the identification of different excited species in the plasma. When argon containing nitrogen was added at the end of the plasma flame, all argon lines emitted in this region were highly quenched, emission due to species containing nitrogen (NH, CN) was enhanced and a noticeable increase in the emission of N2 (C 3Πu ? B 3Πg) was observed. On the contrary, the weak emission of $ {\text{N}}_{2}^{ + } \left( {B^{ 2} \sum_{u}^{ + } - X^{ 2} \sum_{g}^{ + } } \right) $ was scarcely affected. According to these results it is possible to conclude that metastable argon atoms from the expanded flame are the main energy carriers when generating N2 reactive species in this plasma zone. 相似文献
12.
CHENH.G. XIEK.C. 《高等学校化学研究》2004,20(4):446-451
A Computational Fluid Dynamics (CFD) model was formulated for DC arc hydrogen/argon plasma jet re-actors used in the process of the thermal H2/Ar plasma pyrolysis of coal to acetylene. In this model, fluid flow, convective heat transfer and conjugate heat conductivity are considered simultaneously. The error caused by estimating the inner-wall temperature of a reactor is avoided. The thermodynamic and transport properties of the hydrogen/argon mixture plasma system, which are usually expressed by a set of discrete da-ta, are fitted into expressions that can be easily implemented in the program. The effects of the turbulence are modeled by two standard k-ε equations. The temperature field and velocity field in the plasma jet reactor were calculated by employing SIMPLEST algorithm. The knowledge and insight obtained are useful for the design improvement and scale-up of plasma reactors. 相似文献
13.
Yamada Motoki Wahyudiono Machmudah Siti Kanda Hideki Goto Motonobu 《Plasma Chemistry and Plasma Processing》2020,40(4):985-1000
Plasma Chemistry and Plasma Processing - Non-equilibrium pulsed discharge plasma using a gas–liquid slug flow in a glass column as a plasma reactor is developed and applied to methylene blue... 相似文献
14.
Wen-Chao Zhu Bai-Rong Wang Hai-Ling Xi Yi-Kang Pu 《Plasma Chemistry and Plasma Processing》2010,30(3):381-389
Decontamination of the VX surrogate (malathion) by the atmospheric pressure radio-frequency plasma jet (APPJ) was investigated.
Optical emission spectroscopy was used to identify the active species and measure the neutral gas temperature. The effects
of RF input power and exposing time on the decontamination efficiency and neutral gas temperature were investigated. The thermal
effect and volatilization could be ignored from the APPJ decontamination mechanism in our processing conditions. The degradation
products were identified by gas chromatograph coupled with mass spectrometers (GC–MS). Besides the trace amount of the oxidation
product (malaxon), the main degradation products were formed by breaking the S–C bond of malathion. In the end, the main degradation
mechanism was drawn out. 相似文献
15.
Effect of Cold Atmospheric Plasma Jet Associated to Polyene Antifungals on Candida albicans Biofilms
Lady Daiane Pereira Leite Maria Alcionia Carvalho de Oliveira Mariana Raquel da Cruz Vegian Aline da Graa Sampaio Thalita Mayumi Castaldelli Nishime Konstantin Georgiev Kostov Cristiane Yumi Koga-Ito 《Molecules (Basel, Switzerland)》2021,26(19)
The increasing incidence of antifungal resistance represents a great challenge in the medical area and, for this reason, new therapeutic alternatives for the treatment of fungal infections are urgently required. Cold atmospheric plasma (CAP) has been proposed as a promising alternative technique for the treatment of superficial candidiasis, with inhibitory effect both in vitro and in vivo. However, little is known on the association of CAP with conventional antifungals. The aim of this study was to evaluate the effects of the association between CAP and conventional polyene antifungals on Candida albicans biofilms. C. albicans SC 5314 and a clinical isolate were used to grow 24 or 48 h biofilms, under standardized conditions. After that, the biofilms were exposed to nystatin, amphotericin B and CAP, separately or in combination. Different concentrations of the antifungals and sequences of treatment were evaluated to establish the most effective protocol. Biofilms viability after the treatments was compared to negative control. Data were compared by One-way ANOVA and post hoc Tukey (5%). The results demonstrate that 5 min exposure to CAP showed more effective antifungal effect on biofilms when compared to nystatin and amphotericin B. Additionally, it was detected that CAP showed similar (but smaller in magnitude) effects when applied in association with nystatin and amphotericin B at 40 µg/mL and 60 µg/mL. Therefore, it can be concluded that the application of CAP alone was more effective against C. albicans biofilms than in combination with conventional polyene antifungal agents. 相似文献
16.
M. Boselli V. Colombo E. Ghedini M. Gherardi R. Laurita A. Liguori P. Sanibondi A. Stancampiano 《Plasma Chemistry and Plasma Processing》2014,34(4):853-869
The fluid-dynamic characterization by means of Schlieren high-speed imaging of the effluent region of a single electrode plasma jet is presented. The plasma source is powered by a high-voltage generator producing pulses with nanosecond rise time. Time evolution of fluctuations generated in a free flow regime and when the jet is impinging on substrates of different geometries (plain substrates, Petri dishes, etc.) and materials (metal, dielectric covered metal, polystyrene) has been investigated. Plasma ignition causes fluid-dynamic instabilities moving in the direction of the jet flow and correlated with the high-voltage pulses: for low pulse repetition frequency (PRF) (<125 Hz), the movement of the turbulent front between two voltage pulses can be tracked, whereas for higher PRF (1,000 Hz) the flow is completely characterized by turbulent eddies in the effluent region, without relevant changes between subsequent voltage pulses. When the jet is impinging on a substrate, turbulent fronts propagate over the surface starting from the gas impinging zone. 相似文献
17.
Plasma Chemistry and Plasma Processing - In this work, we have studied the influences of electrode geometrical shapes on the optical properties of two non-thermal atmospheric pressure plasma jets,... 相似文献
18.
Lotfy Khaled Al-Harbi Nadi Awad Abd El-Raheem Hany 《Plasma Chemistry and Plasma Processing》2019,39(4):897-912
Plasma Chemistry and Plasma Processing - The possibility to improve the germination characterization of the wheat seeds by cold atmospheric nitrogen plasma jet treatment was report. Spectroscopic... 相似文献
19.
C. E. Nwankire V. J. Law A. Nindrayog B. Twomey K. Niemi V. Milosavljević W. G. Graham D. P. Dowling 《Plasma Chemistry and Plasma Processing》2010,30(5):537-552
Plasma diagnostics of atmospheric plasmas is a key tool in helping to understand processing performance issues. This paper
presents an electrical, optical and thermographic imaging study of the PlasmaStream atmospheric plasma jet system. The system
was found to exhibit three operating modes; one constricted/localized plasma and two extended volume plasmas. At low power
and helium flows the plasma is localized at the electrodes and has the electrical properties of a corona/filamentary discharge
with electrical chaotic temporal structure. With increasing discharge power and helium flow the plasma expands into the volume
of the tube, becoming regular and homogeneous in appearance. Emission spectra show evidence of atomic oxygen, nitric oxide
and the hydroxyl radical production. Plasma activated gas temperature deduced from the rotational temperature of nitrogen
molecules was found to be of order of 400 K: whereas thermographic imaging of the quartz tube yielded surface temperatures
between 319 and 347 K. 相似文献
20.
Gabriela de Morais Gouvêa Lima Aline Chiodi Borges Thalita Mayumi Castaldelli Nishime Gabriela de Fatima Santana-Melo Konstantin Georgiev Kostov Marcia Pinto Alves Mayer Cristiane Yumi Koga-Ito 《Molecules (Basel, Switzerland)》2021,26(18)
Due to the limitations of traditional periodontal therapies, and reported cold atmospheric plasma anti-inflammatory/antimicrobial activities, plasma could be an adjuvant therapy to periodontitis. Porphyromonas gingivalis was grown in blood agar. Standardized suspensions were plated on blood agar and plasma-treated for planktonic growth. For biofilm, dual-species Streptococcus gordonii + P. gingivalis biofilm grew for 48 h and then was plasma-treated. XTT assay and CFU counting were performed. Cytotoxicity was accessed immediately or after 24 h. Plasma was applied for 1, 3, 5 or 7 min. In vivo: Thirty C57BI/6 mice were subject to experimental periodontitis for 11 days. Immediately after ligature removal, animals were plasma-treated for 5 min once—Group P1 (n = 10); twice (Day 11 and 13)—Group P2 (n = 10); or not treated—Group S (n = 10). Mice were euthanized on day 15. Histological and microtomography analyses were performed. Significance level was 5%. Halo diameter increased proportionally to time of exposure contrary to CFU/mL counting. Mean/SD of fibroblasts viability did not vary among the groups. Plasma was able to inhibit P. gingivalis in planktonic culture and biofilm in a cell-safe manner. Moreover, plasma treatment in vivo, for 5 min, tends to improve periodontal tissue recovery, proportionally to the number of plasma applications. 相似文献