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Showing papers on "Atmospheric pressure published in 2011"


Journal ArticleDOI
25 Jan 2011-ACS Nano
TL;DR: In this paper, the thermal conductivity of a graphene monolayer grown by chemical vapor deposition and suspended over holes with different diameters ranging from 2.9 to 9.7 μm was measured in vacuum, thereby eliminating errors caused by heat loss to the surrounding gas.
Abstract: Using micro-Raman spectroscopy, the thermal conductivity of a graphene monolayer grown by chemical vapor deposition and suspended over holes with different diameters ranging from 2.9 to 9.7 μm was measured in vacuum, thereby eliminating errors caused by heat loss to the surrounding gas. The obtained thermal conductivity values of the suspended graphene range from (2.6 ± 0.9) to (3.1 ± 1.0) × 103 Wm−1K−1 near 350 K without showing the sample size dependence predicted for suspended, clean, and flat graphene crystal. The lack of sample size dependence is attributed to the relatively large measurement uncertainty as well as grain boundaries, wrinkles, defects, or polymeric residue that are possibly present in the measured samples. Moreover, from Raman measurements performed in air and CO2 gas environments near atmospheric pressure, the heat transfer coefficient for air and CO2 was determined and found to be (2.9 +5.1/−2.9) and (1.5 +4.2/−1.5) × 104 Wm−2K−1, respectively, when the graphene temperature was heat...

498 citations


Journal ArticleDOI
TL;DR: In this article, a green synthesis of 2,5-furandicarboxylic acid, one of the most important chemical building blocks from biomass, viaoxidation of 5-hydroxymethylfurfural has been demonstrated using hydrotalcite-supported gold nanoparticle catalyst in water at 368 K under atmospheric oxygen pressure without addition of homogeneous base.

391 citations


Journal ArticleDOI
TL;DR: In this article, an atmospheric pressure chemical vapor deposition (CVD) method was developed for the growth of large-area graphene on catalytic metal substrates, which is potentially more cost-effective and compatible with industrial production than approaches based on synthesis under high vacuum, and the results showed that field effect transistors fabricated from CVD graphene made with the optimized process had room temperature hole mobilities that are a factor of 2−5 larger than those measured for samples grown on as-purchased Cu foil with larger methane concentration.
Abstract: The growth of large-area graphene on catalytic metal substrates is a topic of both fundamental and technological interest. We have developed an atmospheric pressure chemical vapor deposition (CVD) method that is potentially more cost-effective and compatible with industrial production than approaches based on synthesis under high vacuum. Surface morphology of the catalytic Cu substrate and the concentration of carbon feedstock gas were found to be crucial factors in determining the homogeneity and electronic transport properties of the final graphene film. The use of an electropolished metal surface and low methane concentration enabled the growth of graphene samples with single layer content exceeding 95%. Field effect transistors fabricated from CVD graphene made with the optimized process had room temperature hole mobilities that are a factor of 2−5 larger than those measured for samples grown on as-purchased Cu foil with larger methane concentration. A kinetic model is proposed to explain the observed...

301 citations


Journal ArticleDOI
TL;DR: A set of diagnostic methods to obtain the plasma parameters including power dissipation, gas temperature and electron density is evaluated for an atmospheric pressure helium or argon radio frequency (RF) plasma needle for biomedical applications operated in open air as mentioned in this paper.
Abstract: A set of diagnostic methods to obtain the plasma parameters including power dissipation, gas temperature and electron density is evaluated for an atmospheric pressure helium or argon radio frequency (RF) plasma needle for biomedical applications operated in open air. The power density of the plasma is more or less constant and equal to 1.3 ? 109?W?m?3. Different methods are investigated and evaluated to obtain the gas temperature. In this paper the gas temperatures obtained by rotational spectra of OH(A?X) and (B?X) are compared with Rayleigh scattering measurements and measurements of the line broadening of hydrogen and helium emission lines. The obtained gas temperature ranges from 300 to 650?K, depending on the gas. The electron densities are estimated from the Stark broadening of the hydrogen ? and ? lines which yield values between 1019 and 1020?m?3. In the case of helium, this is an overestimate as is shown by a power balance from the measured power density in the plasma jet. The obtained plasma parameters enable us to explain the radial contraction of the argon plasma compared with the more diffuse helium plasma. The accuracy of all considered diagnostics is discussed in detail.

226 citations


Journal ArticleDOI
TL;DR: In this article, the authors present new experimental measurements of the laminar flame velocity of components of natural gas, methane, ethane, propane, and n-butane as well as of binary and tertiary mixtures of these compounds proposed as surrogates for natural gas.
Abstract: This paper presents new experimental measurements of the laminar flame velocity of components of natural gas, methane, ethane, propane, and n-butane as well as of binary and tertiary mixtures of these compounds proposed as surrogates for natural gas. These measurements have been performed by the heat flux method using a newly built flat flame adiabatic burner at atmospheric pressure. The composition of the investigated air/hydrocarbon mixtures covers a wide range of equivalence ratios, from 0.6 to 2.1, for which it is possible to sufficiently stabilize the flame. Other measurements involving the enrichment of methane by hydrogen (up to 68%) and the enrichment of air by oxygen (oxycombustion techniques) were also performed. Both empirical correlations and a detailed chemical mechanism have been proposed, the predictions being satisfactorily compared with the newly obtained experimental data under a wide range of conditions.

184 citations


Journal ArticleDOI
01 Sep 2011-Carbon
TL;DR: In this paper, a liquid-precursor-based atmospheric pressure CVD synthesis provides a new route for simple, inexpensive and safe growth of graphene thin-films using ethanol as the precursor.

182 citations


Journal ArticleDOI
TL;DR: In this article, a simplified model for multi-component droplet heating and evaporation is generalised to take into account the coupling between droplets and the ambient gas, where the effects of interaction between the droplets are also considered, leading to noticeably better agreement between the predictions of the model and the experimentally observed average droplet temperatures.

147 citations


Journal ArticleDOI
01 Aug 2011-Fuel
TL;DR: In this article, the effect of low air pressure on the combustion characteristics and puffing flame frequency of pool fires, ethanol and n-heptane pool fires were performed using 15 square burners of various size in both Lhasa (altitude: 3650m; air pressure: 65 kPa) and Hefei (altitudes: 24 m, air pressure): 100.8 kPa.

137 citations


Journal ArticleDOI
TL;DR: In this article, a pulsed discharge in an inhomogeneous electric field at a pressure of 1 atm for varying voltage pulse parameters was reported. But the amplitude of voltage pulses applied to point-to-plane and point-point gaps was 12-140 kV and the full width at half maximum was 1-40 ns.
Abstract: This letter reports on experimental studies of a pulsed discharge in an inhomogeneous electric field at a pressure of 1 atm for varying voltage pulse parameters. The amplitude of voltage pulses applied to point-to-plane and point-to-point gaps was 12–140 kV and the full width at half maximum was 1–40 ns. It is shown that in a wide range of experimental conditions, a diffuse discharge is ignited due to preionization of the gap by runaway electrons and x-rays. With all gaps, the runaway electrons are produced in response to electric field amplification near the electrodes and in the gap.

137 citations


Journal ArticleDOI
TL;DR: In this article, the etching capability of an atmospheric pressure plasma jet is shown, where a variety of polymers [e.g., polyethylene and poly (ether ether ketone)] was exposed to pure argon and argon/oxygen plasma.
Abstract: The impact of atmospheric pressure plasma on surfaces, in particular its potential application of modification and decontamination of different materials has been intensively investigated. In this study, the etching capability of an atmospheric pressure plasma jet is shown. A variety of polymers [e.g., polyethylene and poly (ether ether ketone)] was exposed to pure argon and argon/oxygen plasma. The influence of the oxygen admixture (up to 1%) and of the jet-nozzle to substrate distance on the etch rate of chemically different polymers was explored. Particular attention was applied on the feasible use of atmospheric pressure plasma on biofilm removal. For that reason a theory was postulated with each polymer representing a model compound of bacterial cells. The etch rates were obtained by determination of the mass loss and etch profiles after plasma exposure. The experiments showed that reactive oxygen species play an important role in the polymer removal which results in etch rates of 50 up to 300 nm · s ―1 depending on the polymeric material. These high etch rates imply that non-thermal atmospheric plasma jets could be used for removal of organic material including micro-organisms from surfaces.

129 citations


Journal ArticleDOI
TL;DR: In this paper, a one-dimensional fluid model for a dielectric barrier discharge in methane, used as a chemical reactor for gas conversion, is developed, which describes the gas phase chemistry governing the conversion process of methane to higher hydrocarbons.
Abstract: A one-dimensional fluid model for a dielectric barrier discharge in methane, used as a chemical reactor for gas conversion, is developed. The model describes the gas phase chemistry governing the conversion process of methane to higher hydrocarbons. The spatially averaged densities of the various plasma species as a function of time are discussed. Besides, the conversion of methane and the yields of the reaction products as a function of the residence time in the reactor are shown and compared with experimental data. Higher hydrocarbons (C2Hy and C3Hy) and hydrogen gas are typically found to be important reaction products. Furthermore, the main underlying reaction pathways are determined.

Journal ArticleDOI
01 Jan 2011
TL;DR: In this article, an experimental and computational study was conducted on the propagation of flames of saturated butanol isomers, and the experiments were performed in the counterflow configuration under atmospheric pressure, unburned mixture temperature of 343 K, and for a wide range of equivalence ratios.
Abstract: An experimental and computational study was conducted on the propagation of flames of saturated butanol isomers. The experiments were performed in the counterflow configuration under atmospheric pressure, unburned mixture temperature of 343 K, and for a wide range of equivalence ratios. The experiments were simulated using a recent kinetic model for the four isomers of butanol. Results indicate that n-butanol/air flames propagate somewhat faster than both sec-butanol/air and iso-butanol/air flames, and that tert-butanol/air flames propagate notably slower compared to the other three isomers. Reaction path analysis of tert-butanol/air flames revealed that iso-butene is a major intermediate, which subsequently reacts to form the resonantly stable iso-butenyl radical retarding thus the overall reactivity of tert-butanol/air flames relatively to the other three isomers. Through sensitivity analysis, it was determined that the mass burning rates of sec-butanol/air and iso-butanol/air flames are sensitive largely to hydrogen, carbon monoxide, and C1–C2 hydrocarbon kinetics and not to fuel-specific reactions similarly to n-butanol/air flames. However, for tert-butanol/air flames notable sensitivity to fuel-specific reactions exists. While the numerical results predicted closely the experimental data for n-butanol/air and sec-butanol/air flames, they overpredicted and underpredicted the laminar flame speeds for iso-butanol/air and tert-butanol/air flames respectively. It was demonstrated further that the underprediction of the laminar flame speeds of tert-butanol/air flames by the model was most likely due to deficiencies of the C4-alkene kinetics.

Journal ArticleDOI
TL;DR: In this paper, a detailed computational modeling study of a luminous plasma jet discharge is presented, where the dynamics of streamer propagation, its dependence on the diffusional mixing layer between helium and air species, and the role of photoionization are discussed.
Abstract: A luminous plasma jet is produced when helium gas issuing into atmospheric pressure ambient air is excited by high voltage nanosecond pulsing of a dielectric covered electrode. A detailed computational modeling study of such a discharge is presented. The dynamics of streamer propagation, its dependence on the diffusional mixing layer between helium and air species, and the role of photoionization are discussed.

Journal ArticleDOI
TL;DR: In this article, the authors used a 3D climate model to simulate the CO2 atmosphere of a terrestrial planet on an 8-day orbit around an M 3 dwarf and its apparent infrared emission as a function of its orbital phase.
Abstract: Context. Although transit spectroscopy is a very powerful method for studying the composition, thermal properties, and dynamics of exoplanet atmospheres, only a few transiting terrestrial exoplanets will be close enough to allow significant transit spectroscopy with the current and forthcoming generations of instruments. Thermal phase curves (variations in the apparent infrared emission of the planet with its orbital phase) have been observed for hot Jupiters in both transiting and nontransiting configurations, and have been used to put constraints on the temperature distribution and atmospheric circulation. This method could be applied to hot terrestrial exoplanets. Aims. We study the wavelength and phase changes of the thermal emission of a tidally-locked terrestrial planet as atmospheric pressure increases. We address the observability of these multiband phase curves and the ability to use them to detect atmospheric constituents. Methods. We used a 3D climate model (GCM) to simulate the CO2 atmosphere of a terrestrial planet on an 8-day orbit around an M 3 dwarf and its apparent infrared emission as a function of its orbital phase. We estimated the signal to photon-noise ratio in narrow bands between 2.5 and 20 μm for a 10 pc target observed with a 6 m and a 1.5 m telescope (respectively the sizes of JWST and EChO). Results. Atmospheric absorption bands produce associated signatures in what we call the variation spectrum. Atmospheric windows probing the near surface atmospheric layers are needed to produce large, observable phase-curve amplitudes. The number and transparency of these windows, hence the observability of the phase curves and the molecular signatures, decreases with increasing pressure. Planets with no atmosphere produce large variations and can be easily distinguished from dense absorbing atmospheres. Conclusions. Photon-noise limited spectro-photometry of nearby systems could allow us to detect and characterize the atmosphere of nontransiting terrestrial planets known from radial velocity surveys. Two obvious impediments to these types of observations are the required photometric sensitivity (10 −5 ) over the duration of at least one orbit (8-days in the studied case) and the intrinsic stellar variability. However, overcoming these obstacles would give access to one order of magnitude more targets than does transit spectroscopy.

Journal ArticleDOI
TL;DR: In this paper, the authors introduce the general properties of low-temperature atmospheric pressure plasma devices for biomedical applications and explain recently reported simulation results, such as gas mixture composition, driving frequency and voltage, and function shape of sinusoidal and pulsed power.
Abstract: As interest has increased in the interaction between low-temperature plasmas and living cells or organic materials, the role of modelling and simulation of atmospheric pressure plasmas has become important in understanding the effects of charged particles and radicals in biomedical applications. This review paper introduces the general properties of low-temperature atmospheric pressure plasma devices for biomedical applications and explains recently reported simulation results. Control parameters of atmospheric pressure plasmas, such as gas mixture composition, driving frequency and voltage and the function shape of sinusoidal and pulsed power, are considered through both a review of previous findings and new simulation results in order to improve plasma properties for given purposes. Furthermore, the simulation or modelling techniques are explained along with surface interactions of the plasma for the future development of simulation codes to study the interaction of plasmas with living cells. (Some figures in this article are in colour only in the electronic version)

Journal ArticleDOI
TL;DR: In this paper, nano-particle enhanced ionic liquids (NEILs) have been shown to increase the heat capacity of the IL with no adverse side effects to the ILs thermal stability and, only at high nanoparticle loading, are the IL physical properties affected.
Abstract: Interest in capturing the energy of the sun is rising as demands for renewable energy sources increase. One area of developing research is the use of concentrating solar power (CSP), where the solar energy is concentrated by using mirrors to direct the sunlight towards a collector filled with a heat transfer fluid (HTF). The HTF transfers the collected energy into pressurized steam, which is used to generate energy. The greater the energy collected by the HTF, the more efficent the electrical energy production is, thus the overall efficiency is controlled by the thermal fluid. Commercial HTFs such as Therminol{reg_sign} (VP-1), which is a blend of biphenyl and diphenyl oxide, have a significant vapor pressure, especially at elevated temperatures. In order for these volatile compounds to be used in CSP systems, the system either has to be engineered to prevent the phase change (i.e., volatilization and condensation) through pressurization of the system, or operate across the phase change. Over thirty years ago, a class of low-melting organic compounds were developed with negligible vapor pressure. These compounds are referred to as ionic liquids (ILs), which are organic-based compounds with discrete charges that cause a significant decrease in their vapor pressure. As amore » class, ILs are molten salts with a melting point below 100 C and can have a liquidus range approaching 400 C, and in several cases freezing points being below 0 C. Due to the lack of an appreciable vapor pressure, volatilization of an IL is not possible at atmospheric pressure, which would lead to a simplification of the design if used as a thermal fluid and for energy storage materials. Though the lack of a vapor pressure does not make the use of ILs a better HTF, the lack of a vapor pressure is a compliment to their higher heat capacity, higher volummetric density, and thus higher volumetric heat capacity. These favorable physical properties give ILs a pontential advantage over the current commerically used thermal fluids. Also within the past decade nanofluids have gained attention for thermal conductivity enhancment of fluids, but little analysis has been completed on the heat capacity effects of the nanoparticle addition. The idea of ILs or nanofluids as a HTF is not new, as there are several references that have proposed the idea. However, the use of ionic liquid nanofluids containing nanomaterials other than carbon nanotubes has never before been studied. Here, for the first time, nano-particle enhanced ILs (NEILs) have been shown to increase the heat capacity of the IL with no adverse side effects to the ILs thermal stability and, only at high nanoparticle loading, are the IL physical properties affected. An increase of volumetric heat capacity translates into a better heat transfer fluid as more energy is stored per volumetric unit in the solar concentrating section, thus more efficency in increased steam pressure. Results show that the properties of the NEIL are highly dependant on the suspended nanomaterial and careful materials selection is required to fully optimize the nanofluid properties.« less

Journal ArticleDOI
TL;DR: Improvements in detecting amines and ammonia from a smog chamber were evident due to improvements in AmPMS background determination; notably dimethyl amine and its OH oxidation products were followed along with impurity ammonia and other species.
Abstract: An instrument to detect gaseous amines and ammonia is described, and representative data from an urban site and a laboratory setting are presented. The instrument, an Ambient pressure Proton transfer Mass Spectrometer (AmPMS), consists of a chemical ionization and drift region at atmospheric pressure coupled to a standard quadrupole mass spectrometer. Calibrations show that AmPMS sensitivity is good for amines, and AmPMS backgrounds were suitably determined by diverting sampled air through a catalytic converter. In urban air at a site in Atlanta, amines were detected at subpptv levels for methyl and dimethyl amine which were generally at a low abundance of <1 and ∼3 pptv, respectively. Trimethyl amine (or isomers) was on average about 4 pptv in the morning and increased to 15 pptv in the afternoon, while triethyl amine (or isomers or amides) increased to 25 pptv on average in the late afternoon. The background levels for the 4 and 5 carbon amines and ammonia were high, and data are very limited for these ...

Journal ArticleDOI
01 Jan 2011
TL;DR: In this article, a micro-flow reactor with a controlled temperature profile was used to investigate the ignition and combustion characteristics of a stoichiometric gaseous n-heptane/air mixture.
Abstract: Ignition and combustion characteristics of a stoichiometric gaseous n -heptane/air mixture were investigated using a micro flow reactor with a controlled temperature profile which smoothly ramped from room temperature to ignition temperature. At atmospheric pressure condition, normal stable flames in high mixture flow velocity region, unstable flames with repetitive extinction and ignition (FREI) in intermediate velocity region, and stable weak flames in low velocity region were experimentally observed. Especially at low velocity condition, distinct two luminous weak flames and one broaden luminous zone were observed. Gas sampling and analysis were conducted to interpret this phenomenon and it was supposed that those luminous flames consist of three-stage oxidation process. Computational results also showed that there are co-existing three heat-release-rate peaks in the flow direction at low velocity condition, which qualitatively supported the experimental observations. From the concentration profiles of the species, these three reactions are confirmed so-called cool, blue and hot flames, respectively. In addition, the effect of pressure on the three-stage oxidation process was examined by conducting experiments and computations at high pressure conditions. With an increase of pressure, the first and second weak flames were intensified and the third flame was weakened. Moreover, the position of the first and second weak flames shifted to low temperature side with the increase of pressure. Consequently, the first and second flames in the three-stage oxidation process become more significant at higher pressure conditions.

Journal ArticleDOI
TL;DR: In this article, an array of filtered photomultipliers was used to enable optical pyrometry and evaluate the molecular AlO emission of spherical aluminum powder burning in atmospheric pressure O2/N2 gas mixtures with the oxygen concentrations of 10, 15, and 21% (air).

Journal ArticleDOI
TL;DR: Using molecular beam mass spectroscopy, time-resolved measurements of the ionic species in the plasma plume of an atmospheric-pressure helium microplasma jet are made for a range of excitation frequencies (5, 10 and 25 kHz) and source-instrument orifice distances (1, 7 and 11 mm).
Abstract: Using molecular beam mass spectroscopy, time-resolved measurements of the ionic species in the plasma plume of an atmospheric-pressure helium microplasma jet are made for a range of excitation frequencies (5, 10 and 25 kHz) and source–instrument orifice distances (1, 7 and 11 mm). Ionic species can only be observed in the visible plasma plume, with the main positive species being (65.26%) and (21.11%), and a few percentages of N+, O+, NO+and He+. For the negative ions, the majority species are (22.68%), (H2O) (10.49%) and a large range of minority species observed, namely , , , and clusters, , , (CO3) and . The flux of ions created from air species, such as NO+ and , is seen to be maximized at a distance of several millimeters from the nozzle, whereas the He+ concentration continually decreases with distance from the exit orifice. The time-resolved measurements (time resolution down to 2 µs) show that positive ions appear twice in one full period of the voltage waveform, correlated directly with positive and negative current peaks. The rise and fall times of the positive ions are typically tens of μs. In contrast, the appearance of negative ions is correlated only with the negative part of discharge current, with one main peak in the detected ionic flux seen per cycle. The rise time of the negative ions is about 10 µs, independent of mass; however, we observed longer decay times, from 100 to 150 µs, increasing with mass. With increased driving frequency, the time modulation in the ionic fluxes is reduced, particularly for the negative species that show almost constant fluxes at 25 kHz throughout the cycle. The observations can be understood through a simple picture of the interaction of the He jet and the moist ambient air. The results indicate that the discrete plasma 'bullets' and their afterglow tail, that forms the jet, carry an associated positive or negative current depending on the time of their creation in the voltage cycle.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated two hypothetical feedbacks that can destabilize climate on planets in synchronous rotation and identified a new pathway by which habitable-zone planets can undergo rapid climate shifts and become uninhabitable.
Abstract: Feedbacks that can destabilize the climates of synchronously rotating rocky planets may arise on planets with strong day-night surface temperature contrasts. Earth-like habitable planets maintain stable surface liquid water over geologic time. This requires equilibrium between the temperature-dependent rate of greenhouse-gas consumption by weathering, and greenhouse-gas resupply by other processes. Detected small-radius exoplanets, and anticipated M-dwarf habitable-zone rocky planets, are expected to be in synchronous rotation (tidally locked). In this paper, we investigate two hypothetical feedbacks that can destabilize climate on planets in synchronous rotation. (1) If small changes in pressure alter the temperature distribution across a planet's surface such that the weathering rate goes up when the pressure goes down, a runaway positive feedback occurs involving increasing weathering rate near the substellar point, decreasing pressure, and increasing substellar surface temperature. We call this feedback enhanced substellar weathering instability (ESWI). (2) When decreases in pressure increase the fraction of surface area above the melting point (through reduced advective cooling of the substellar point), and the corresponding increase in volume of liquid causes net dissolution of the atmosphere, a further decrease in pressure will occur. This substellar dissolution feedback can also cause a runaway climate shift. We use an idealized energy balance model to map out the conditions under which these instabilities may occur. In this simplified model, the weathering runaway can shrink the habitable zone and cause geologically rapid 103-fold atmospheric pressure shifts within the habitable zone. Mars may have undergone a weathering runaway in the past. Substellar dissolution is usually a negative feedback or weak positive feedback on changes in atmospheric pressure. It can only cause runaway changes for small, deep oceans and highly soluble atmospheric gases. Both instabilities are suppressed if the atmosphere has a high radiative efficiency. Our results are most relevant for atmospheres that are thin, have low greenhouse-gas radiative efficiency, and have a principal greenhouse gas that is also the main constituent of the atmosphere. ESWI also requires land near the substellar point, and tectonic resurfacing (volcanism, mountain-building) is needed for large jumps in pressure. These results identify a new pathway by which habitable-zone planets can undergo rapid climate shifts and become uninhabitable.

Journal ArticleDOI
TL;DR: In this paper, an atmospheric pressure plasma jet generated in Ar with water vapor is investigated, and it is shown that an increase in the water content results in a decrease in the input power and asymmetry of the current waveform on positive and negative half-periods of the applied voltage.
Abstract: An atmospheric pressure plasma jet generated in Ar with water vapor is investigated. It is shown that an increase in the water content results in a decrease in the input power and asymmetry of the current waveform on positive and negative half-periods of the applied voltage. Space-resolved spectroscopy with a resolution of 1 mm and an imaging technique are applied for the characterization of the afterglow and investigation of the influence of water content on plasma properties. The rotational temperature of the jet is determined by simulation of the OH radical emission spectrum, transition A 2Σ+(v = 0) → X 2Π(v = 0). It is revealed that the temperature of the discharge increases from 450 K (Ar) up to 850 K with an increase in the water content up to 7600 ppm. Generation of the discharge in mixtures of argon with water vapor at a concentration of 350 ppm results in a maximal yield of OH radicals that can be useful in plasma jet applications. Preliminary tests of polypropylene surface modification are carried out in order to estimate the influence of water content on the results of treatment.

Journal ArticleDOI
TL;DR: In this article, an atmospheric-pressure helium plasma jet operating in the bullet/streamer mode has been studied using optical emission spectroscopy, and the electric field strength distribution is measured using Stark polarization spectrograms of He I 492.19nm line.
Abstract: Atmospheric-pressure helium plasma jet operating in the bullet/streamer mode has been studied using optical emission spectroscopy. Electric field strength distribution is measured using Stark polarization spectroscopy of He I 492.19 nm line. It is shown that the electric field is almost constant along the jet axis. Measured electric field distribution is in agreement with theoretical predictions of streamer propagation in helium jets at atmospheric pressure. Obtained radial distribution of the axial electric field shows that the ring-shaped structure of the light emission is a consequence of such electric field distribution.

Journal ArticleDOI
TL;DR: The chars were highly carbonised, especially at the higher pressures, and provided thermally stable materials, and the phenols could provide useful platform chemicals and products.

Journal ArticleDOI
TL;DR: In this article, the effect of ozone on the burning velocity of premixed methane-air flames at atmospheric pressure and room temperature was investigated using a dielectric barrier discharge device, and its quantity was fixed equal to 5 g/Nm3 in air.
Abstract: New experimental results were obtained to better assess the effect of ozone on the burning velocity of premixed methane–air flames at atmospheric pressure and room temperature. Ozone was produced using a dielectric barrier discharge device, and its quantity was fixed equal to 5 g/Nm3 in air (2369 ppm of ozone). Measurements were performed using a Bunsen burner. Simultaneous to flame height measurements, a 1D Rayleigh scattering system was set up to investigate the impact of ozone on the thermal flame structure. The experimental results showed that the partial conversion of molecular oxygen into ozone has a moderate positive effect on the burning velocity of methane–air flames, confirming previous measurements in the literature. The injection of 5 g/Nm3 of ozone in air increased the burning velocities by ca. 0.8–1.3 cm/s (ca. 3–8%). The oxidation of methane in the presence or absence of ozone was modeled using a detailed chemical kinetic scheme taken from the literature, to which an ozone submechanism was ...

Journal ArticleDOI
TL;DR: In this article, a camera-based temperature measurement with accurate evaluation of emissivity from experiment was shown that the surface temperature has to reach Tv to initiate the melt surface deformation, which is the first experimental evidence for the frequently used assumption that deep keyhole welding requires surface temperature over Tv.
Abstract: Recoil pressure is the principal driving force of molten metal in laser processing in the intensity range 10−1–102 MW cm−2. It is thus essential to estimate the recoil pressure in order to describe physical processes or to carry out numerical simulations. However, there exists no quantitative estimation of the recoil pressure near the boiling temperature (Tv), which is particularly important in the welding process. In this study we experimentally investigated the recoil pressure of pure iron around Tv. The main interest was to determine the threshold surface temperature to start deformation of melt surface. Using camera-based temperature measurement with accurate evaluation of emissivity from experiment, it was shown that the surface temperature has to reach Tv to initiate the melt surface deformation. This result provides the first experimental evidence for the frequently used assumption that a deep keyhole welding requires surface temperature over Tv. It is indicated also that, in normal gas-assisted laser cutting process, the recoil pressure hardly contributes to material ejection when the surface temperature is lower than Tv, as opposed to the commonly believed presumption.

Journal ArticleDOI
TL;DR: In this article, the authors showed that if the membrane is compressible, total pressure in the pore and the thermal resistance of the membrane will change and affect the performance of membrane.

Journal ArticleDOI
TL;DR: In this paper, a theoretical analysis was performed for the head-on collision of two identical droplets in a gaseous environment, with the attendant bouncing and coalescence outcomes, for situations in which the extent of droplet deformation upon collision is comparable to the original droplet radius, corresponding to O(1) −O(10) of the droplet Weber number.
Abstract: A theoretical analysis was performed for the head-on collision of two identical droplets in a gaseous environment, with the attendant bouncing and coalescence outcomes, for situations in which the extent of droplet deformation upon collision is comparable to the original droplet radius, corresponding to O(1)–O(10) of the droplet Weber number. The model embodies the essential physics that describes the substantial amount of droplet deformation, the viscous loss through droplet internal motion induced by the deformation, the dynamics and rarefied nature of the gas film between the interfaces of the colliding droplets, and the potential destruction and thereby merging of these interfaces due to the van der Waals attraction force. The theoretical model was applied to investigate collisions involving hydrocarbon and water droplets at sub- and superatmospheric pressures. The results agree well with previous experimental observations in that as the Weber number increases in the range of O(1)–O(10), collision of hydrocarbon droplets at one atmospheric pressure results in the nonmonotonic coalescence-bouncing-coalescence transition, that while bouncing is absent for water droplets at atmospheric pressure, it occurs at higher pressures, and that while bouncing is observed for hydrocarbon droplets at atmospheric pressure, it is absent at lower pressures.

Journal ArticleDOI
TL;DR: A stable air surface barrier discharge device for large-area sterilization applications at room temperature was proposed in this article, which may result in visually uniform plasmas with the electrode area scaled up or down to the required size.
Abstract: This letter reports a stable air surface barrier discharge device for large-area sterilization applications at room temperature This design may result in visually uniform plasmas with the electrode area scaled up (or down) to the required size A comparison for the survival rates of Escherichia coli from air, N2 and O2 surface barrier discharge plasmas is presented, and the air surface plasma consisting of strong filamentary discharges can efficiently kill Escherichia coli Optical emission measurements indicate that reactive species such as O and OH generated in the room temperature air plasmas play a significant role in the sterilization process

Journal ArticleDOI
TL;DR: In this article, the authors performed an assessment using data collected by a field-portable FTIR spectrometer, which was positioned to view a fixed IR source placed at the other end of an IR-transparent cell filled with the gases of interest, whose target concentrations varied by more than two orders of magnitude.
Abstract: . When compared to established point-sampling methods, Open-Path Fourier Transform Infrared (OP-FTIR) spectroscopy can provide path-integrated concentrations of multiple gases simultaneously, in situ and near-continuously. The trace gas pathlength amounts can be retrieved from the measured IR spectra using a forward model coupled to a non-linear least squares fitting procedure, without requiring "background" spectral measurements unaffected by the gases of interest. However, few studies have investigated the accuracy of such retrievals for CO2, CH4 and CO, particularly across broad concentration ranges covering those characteristic of ambient to highly polluted air (e.g. from biomass burning or industrial plumes). Here we perform such an assessment using data collected by a field-portable FTIR spectrometer. The FTIR was positioned to view a fixed IR source placed at the other end of an IR-transparent cell filled with the gases of interest, whose target concentrations were varied by more than two orders of magnitude. Retrievals made using the model are complicated by absorption line pressure broadening, the effects of temperature on absorption band shape, and by convolution of the gas absorption lines and the instrument line shape (ILS). Despite this, with careful model parameterisation (i.e. the optimum wavenumber range, ILS, and assumed gas temperature and pressure for the retrieval), concentrations for all target gases were able to be retrieved to within 5%. Sensitivity to the aforementioned model inputs was also investigated. CO retrievals were shown to be most sensitive to the ILS (a function of the assumed instrument field-of-view), which is due to the narrow nature of CO absorption lines and their consequent sensitivity to convolution with the ILS. Conversely, CO2 retrievals were most sensitive to assumed atmospheric parameters, particularly gas temperature. Our findings provide confidence that FTIR-derived trace gas retrievals of CO2, CH4 and CO based on modeling can yield results with high accuracies, even over very large (many order of magnitude) concentration ranges that can prove difficult to retrieve via standard classical least squares (CLS) techniques. With the methods employed here, we suggest that errors in the retrieved trace gas concentrations should remain well below 10%, even with the uncertainties in atmospheric pressure and temperature that might arise when studying plumes in more difficult field situations (e.g. at uncertain altitudes or temperatures).