The dynamics of a low-power (<40 W) rotating gliding arc in atmospheric pressure argon sustained by a homemade dual DC power supply between a conical cathode and a grounded sleeve anode and forced ...into motion by the combined action of a vortex gas flow (<26.3 SLPM) and axial magnetic field (~0.043-0.122 T) was studied. High-speed imaging and electrical diagnostics were used to gain an understanding of the projected arc length, position of the attachment point on the central cathode, and frequency of arc rotation. The electrical signals revealed a glow-type mode of operation, which characteristically low current and high voltage. The square root dependency of the rotating arc frequency on the applied current predicted by a simplified model considering the gas vortex drag and Lorentz forces was confirmed with measurements. Rotation frequencies in the ~100-300 Hz range with average projected arc lengths of 4-8 mm creating a large stabilized reactive volume were obtained. We further demonstrated that the Lorentz force acting on the rotating gliding arc is equivalent to the hydrodynamic drag caused by an argon flow rate of ~8 SLPM for this device configuration.
Abstract
The 2022 Roadmap is the next update in the series of Plasma Roadmaps published by
Journal of Physics
D with the intent to identify important outstanding challenges in the field of ...low-temperature plasma (LTP) physics and technology. The format of the Roadmap is the same as the previous Roadmaps representing the visions of 41 leading experts representing 21 countries and five continents in the various sub-fields of LTP science and technology. In recognition of the evolution in the field, several new topics have been introduced or given more prominence. These new topics and emphasis highlight increased interests in plasma-enabled additive manufacturing, soft materials, electrification of chemical conversions, plasma propulsion, extreme plasma regimes, plasmas in hypersonics, data-driven plasma science and technology and the contribution of LTP to combat COVID-19. In the last few decades, LTP science and technology has made a tremendously positive impact on our society. It is our hope that this roadmap will help continue this excellent track record over the next 5–10 years.
Renewable alternative energy sources are required to decrease or eliminate the use of environmentally unfriendly fossil fuels. Hydrogen produced by electrolysis has been identified as one such ...renewable energy carrier. In the current work, Ni nanoparticle (NP)-decorated multiwall carbon nanotube (MWCNT) electrocatalyst cathodes are prepared by a simple two-step procedure. MWCNTs are grown on stainless steel meshes by thermal-chemical vapour deposition (t-CVD) and then decorated with Ni NPs by pulsed laser ablation (PLA). The morphological and electrochemical properties of the produced Ni NP/MWCNT cathodes were characterized through electron microscopy and linear Tafel polarization (LTP)/electrochemical impedance spectroscopy (EIS), respectively. SEM and TEM imaging revealed that the Ni NPs deposited by PLA are on the order of 4 nm in diameter with a narrow size distribution. The LTP measurements showed that the electrocatalytic activity of the Ni NP/MWCNT cathodes towards the hydrogen evolution reaction (HER) is dependent on PLA time and shows a maximum at tPLA = 40 min. EIS measurements revealed that the HER response is characterized by a two time constants process representing HER kinetics and adsorption of hydrogen.
•Ni NPs were deposited onto MWCNTs in a single step dry process.•The electrocatalytic activity of Ni NP/MWCNT in terms of hydrogen evolution is dependent on the NP loading.•The Ni NP/MWCNT electrocatalysts show a significant increase in electrocatalytic activity relative to a bulk Ni plate.
Nanofluids-engineered colloidal suspensions in base liquids-have captivated the interest of researchers over the last two decades for various existing as well as emerging technological applications. ...The main impetus for the synthesis of such novel nanocomposite liquids is the potential to alter properties of the base liquid, such as its viscosity, thermal conductivity, and surface tension, and to introduce specific optical and magnetic properties. Numerous studies suggest trends and explanations for the effects associated with the addition of nanoparticles, and that deviation from the base liquid properties are dependent on nanoparticle concentration. However, there remains a certain ambiguity in the available literature. The wetting behavior and surface tension of nanofluids are particular examples where highly conflicting results exist. In this study, we used multi-walled carbon nanotubes (MWCNTs) functionalized by plasma treatment and dispersed in reverse osmosis water and 99% anhydrous ethanol. Our observations reveal that the surface tension and wetting behavior of the stable aqueous and ethanol-based nanofluids containing plasma functionalized MWCNTs are unaffected by the MWCNT loading up to 120 (0.012) and ∼210 (0.021) ppm (vol%), respectively. The ethanol-based MWCNT nanofluids allowed us to extend the study to higher loadings, and a linear increase of the surface tension past ∼200 ppm was observed. Conversely, nanofluids containing non-functionalized or surfactant-stabilized MWCNTs show drastically different contact angle values when compared to the base liquids even at very low concentrations (less than 100 ppm). We demonstrate that the stability of nanofluid and method of stabilization are crucial parameters in determining the wetting behavior of nanofluids.
The performance of a nanosecond repetitively pulsed discharge for CH4 reforming is studied at atmospheric pressure for temperatures ranging from 300 to 700 K. The high-voltage pulser used is capable ...of producing a voltage pulse with an amplitude of 14 kV and a duration of 40 ns at a repetition frequency of 10 kHz. The discharge energy per pulse is varied in a range from 462 J to 2.47 mJ. The rotational temperature is estimated by fitting synthetic to experimental spectra. Experiments at pulsing frequency of 1 kHz led to temperature profiles that remain unchanged along the axial direction of the reactor. For pulse frequencies between 2-10 kHz, the average temperature of the filament rises from 507 to 777 K. Emission from C2(A-X) is compared to emission from CH(A-X) along the reactor axis and with respect to the energy input. It is found that as the energy input increases, so does the emission from C2(A-X), turning the discharges green rather than blue. Results from CH4 conversion show that the inlet gas temperature has negligible effect on reforming performance. Higher values of energy per pulse improve conversion and energy efficiency. However, increasing the pulse frequency leads to the best performance enhancement with a maximum slope of 0.53% and 0.24% per kJ · mol−1 for conversion and energy efficiency, respectively. The maximum conversion and energy efficiencies were 68.2% and 25.6%, respectively, measured in a CH4-air mixture.
As a measure to increase the heat transfer from a surface, the application of nanofluids made up of nanoparticles stably dispersed in traditional coolants is considered. Researchers have succeeded in ...preparing nanofluids, that remain stable when stored in glass vials for long periods of time. However, it is still not known whether these nanofluids remain stable in the presence of metals, which is inevitable to use them in industrial heat exchangers. In this article, we show that an ethanol-based nanofluid containing oxygen functionalized multi-walled carbon nanotubes remained stable for more than one year when in contact with copper and when boiled. We investigated the reason for this observation by measuring individual particle size with atomic force microscopy, solvent diffusion co-efficient by nuclear magnetic resonance spectroscopy and molecular interactions by Fourier transform infra-red spectroscopy. We understood that the exceptional stability of the ethanol-based nanofluid is due to the strong hydrogen bonding and polar interactions between the ethanol molecules and the oxygen-containing functional groups on functionalized carbon nanotubes. When tested for heat transfer enhancement, the stable ethanol-based nanofluid gave a 7% rise in cooling rate compared to that with pure ethanol.
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This article addresses the issue of metallic nanoparticle suspension (nanofluid) stabilization without the use of traditional surface-stabilizing agents such as surfactants. A dual plasma process for ...the single-step synthesis of a copper–ethylene glycol nanofluid is presented. The process uses a combination of low-pressure pulsed cathodic arc erosion to generate metal nanoparticles and in-flight radio-frequency glow discharge plasma functionalization for surface stabilization. The surface-stabilized nanoparticles are collected
in situ by a falling film of ethylene glycol, the vapours of which are used for plasma functionalization. Little to no agglomeration is observed in the suspension, although this process is shown to occur when the produced suspensions are heated to temperatures well beyond the range of effectiveness of typical surfactants. This thermally induced agglomeration is demonstrated to be fully reversible. The stability of the suspension is confirmed by UV–Vis absorption spectrometry and electron microscopy. The particles synthesized are also shown to be re-dispersible in aqueous media. Though no heat transfer enhancement was observed due to the low nanoparticle loading, this study demonstrates for the first time that high temperature-stable nanofluids containing metal nanoparticles can be synthesized in a single-step, without manipulation outside the controlled synthesis environment and without the post-addition of surfactants.
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► Stabilization of nanoparticles suspensions (nanofluids) without using surfactants. ► Single-step synthesis, functionalization and collection of metal nanoparticles. ► Thermal stability over a larger temperature range than surfactants. ► Any agglomeration occurring at high temperatures is fully reversible.
A miniature atmospheric pressure glow discharge plasma torch was used to detach cells from a polystyrene Petri dish. The detached cells were successfully transplanted to a second dish and a ...proliferation assay showed the transplanted cells continued to grow. Propidium iodide diffused into the cells, suggesting that the cell membrane had been permeabilized, yet the cells remained viable 24 h after treatment. In separate experiments, hydrophobic, bacteriological grade polystyrene Petri dishes were functionalized. The plasma treatment reduced the contact angle from 93 deg to 35 deg , and promoted cell adhesion. Two different torch nozzles, 500 mum and 150 mum in internal diameter, were used in the surface functionalization experiments. The width of the tracks functionalized by the torch, as visualized by cell adhesion, was approximately twice the inside diameter of the nozzle. These results indicate that the miniature plasma torch could be used in biological micropatterning, as it does not use chemicals like the present photolithographic techniques. Due to its small size and manouvrability, the torch also has the ability to pattern complex 3D surfaces.
A method for the incorporation of immobile oxygen-containing functional groups onto multi-walled carbon nanotubes (MWCNTs) rooted in a metallic substrate for supercapacitor (SC) application is ...presented. Direct growth on the current collector (a 316 stainless steel (SS) mesh) offers the benefit of minimal MWCNT agglomeration, avoidance of using binder, and maintaining the 3-dimensional nanostructure. MWCNTs are grown by thermal-chemical vapour deposition (t-CVD) using SS as substrate and functionalized using an Ar/C2H6/O2 glow discharge. When used as a binder-free SC electrode, these functionalized MWCNTs (f-MWCNTs) show excellent surface stability and large specific capacitance values. At low charging/discharging current densities (0.2mAcm−2 or 3A g−1), a specific capacitance of 288±10F g−1 is achieved. The material shows good rate capability up to charging/discharging current density of 10mAcm−2 (37A g−1) and displays excellent reversibility. Consequently, these new binder-free f-MWCNT SC electrodes are excellent candidates for future investigations of MWCNT-based SC electrodes.
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