Flowing Gas Stream Research Articles

대기압 플라즈마 제트의 기체 유량에 대한 방전 특성

대기압 플라즈마 제트 장치의 유량 변화에 대한 플라즈마 방전 특성을 실험적으로 조사하고 이를 유체역학적으로 해석하였다. 유리관에 주입되는 아르곤 기체의 유량 변화에 대한 레이놀즈 수(Re)로 결정되는 기체 흐름의 형태 변화와 베르누이 정리에 의한 압력 변화가 플라즈마 발생에 영향을 준다. 유리관 내부에 발생하는 플라즈마의 길이 변화의 실험을 통하여, 아르곤 기체에 대한 레이놀즈 수가 Re<2,000이면 층류이고, Re>4,000이면 난류가 형성된다. 이는 일반 유체에서 알려진 결과와 일치한다. 층류에서 유량의 증가로 플라즈마의 길이가 증가한다. 층류와 난류의 전환 영역에서 플라즈마의 길이는 줄어든다. 난류 영역에서는 방전 기체의 흐름이 불규칙함으로서 방전 경로가 흐트러져 플라즈마 칼럼의 길이가 매우 짧아지고 급기야 플라즈마가 소멸된다. 층류에서 주입 유량의 증가로 유리관 내의 유속이 증가하면, 베르누이 정리에 의하여 유리관 내부의 압력이 낮아진다. 관내의 압력이 낮아지면, 파센 법칙에 의하여 관내의 전기장의 세기가 증가하여 방전 전압이 낮아진다. 따라서 주입 유량이 증가하면, 동일한 구동 전압에서 유리관에 발생하는 플라즈마의 길이는 길어진다. 층류의 방전은 유리관 밖에서도 층류의 흐름이 일정 길이로 유지되므로 시료 표면에 조사되는 플라즈마 빔의 직경은 유리관의 직경 이하로 유지된다. The influence of gas flow on the plasma generation in the atmospheric plasma jet is described with the theory of hydrodynamics. The plasma discharge is affected by the gas-flow streams with Reynolds number (Re) as well as the gas pressure with Bernoulli's theorem according to the gas flow rate inserted into the glass tube. The length of plasma column is varied with the flow types such as the laminar flow of Re<2,000 and the turbulent flow of Re>4,000 as it has been known in a general fluid experiments. In the laminar flow, the plasma column length is increased as the increase of flow rate. Since the pressure in the glass tube becomes low as the increase of flow velocity by the Bernoulli's theorem, the breakdown voltage of plasma discharge is reduced by the Paschen's law. Therefore, the plasma length is increased as the increasing flow rate with the fixed operation voltage. In the transition of laminar and turbulent flows, the plasma length is decreased. When the flow becomes turbulent as the flow rate is increasing, the plasma length becomes short and the discharge is shut down ultimately. In the discharge of laminar flow, the diameter of plasma beam exposed on the substrate surface is kept less than the glass diameter, since the gas flow is kept to the distinct distance from the nozzle of glass tube.

Observations of ionic species produced in an atmospheric pressure pulse-modulated RF plasma needle

Pulse-modulated generation of atmospheric pressure plasma promises lower operating temperatures and enhanced energy efficiencies compared with those generated using continuous excitation. In this study, the effect of pulse modulation on the ionic content of a radio-frequency helium plasma needle was explored using molecular beam mass spectrometry (MBMS). In all cases reported the pulse repetition frequency was held constant at 6 kHz while the duty cycle and distance between the plasma needle and MBMS were varied from 30% to 90% and 4 mm to 10 mm, respectively. Decreasing the duty cycle was seen to enhance the negative ion flux to the MBMS and yields a clear shift to higher masses for positive ion species. Time-resolved ion intensity measurements (5 µs resolution) demonstrated that negative ions were created almost exclusively in the pulse off-time while positive ions were generated mainly in the on-time. The ions detected were also seen to change as the distance between the sampling orifice and tip of the plasma needle increased, highlighting the effect of different ion mobilities in the flowing gas stream and the presence of an extended cooler afterglow region. The results suggest that there is a possibility of tailoring the ionic plasma chemistry through pulsed modulation, increasing the versatility of the already widely studied plasma needle device.

Evaluation and comparison of different models for asphaltene particle deposition in flow streams

Asphaltene deposition in the wellbore is a frequent problem in certain oil fields that may yield serious operational challenges, safety hazards, and an overall decrease in production efficiency. These particulates are entrained in the flowing fluid from the reservoir or generated in the wellbore flow. The asphaltene precipitation is a function of pressure, temperature, and fluid composition. Considering the existence of asphaltene in the oil, the accurate prediction of those solid particle deposition is necessary to design production facilities and to optimize well performance.A great deal of research has been conducted to study the dynamic aspects of solid particles fouling inside a pipe. However, those studies have mostly been applied in engineering fields other than petroleum. In this paper, firstly we discuss the mechanisms for solid particle deposition, including particle momentum and mass transfer as well as particle re-entrainment. Afterwards we describe important particulate deposition models and compare them using different sets of experiments published in the literature. In one set, deposition of iron particles in the gas flow is investigated and in the other, deposition of asphaltene in the oil flow is considered.Our results show that the deposition models that were studied in this work satisfactorily agree with experimental data. They are also applicable for modeling asphaltene deposition in crude oils as well as other particle deposition in gas flow streams.

Dynamic Modelling for a Trickle-Bed Reactor Using the Numerical Inverse Laplace Transform Technique

Abstract Experimental evaluation and dynamic modelling were presented for the transient behavior of a trickle bed reactor in which gas and liquid streams flow downwards through a bed of catalyst particles. One-dimensional dynamic mathematical model has been described to study the gas-liquid-solid process in which the gas phase (Ar) with the tracer (SO2) is treated as a continuum. The physical model has been analyzed, including the formulation of initial and boundary conditions and the description of the solution methodology. An experimental procedure to measure the concentrations of the tracer (SO2) has been performed. The concentration measurements for this tracer (SO2) were performed in a fixed be reactor on trickling flow of the gas phase for a range of operating conditions. The gas-liquid mass transfer (kgl) coefficient, liquid-solid mass transfer (kls) coefficient, gas holdup (hg) and partial wetting efficiency (fe) were chosen as the hydrodynamic parameters of the proposed mathematical model. Such parameters have been optimized with the experimental measurents of the tracer (SO2) at the exit of the trickle-bed reactor. The optimized parameters hg, kgl, kls and fe were calculated simultaneously using the equation (51) with minimization of the objective function. Results of the mathematical model was presented and compared to the two experimental cases. Each above parameters were correlated using empirical correlations.

Progress with a gas-accepting ion source for Accelerator Mass Spectrometry

The National Ocean Sciences AMS (NOSAMS) facility at Woods Hole Oceanographic Institution has developed a novel, gas-accepting microwave-plasma ion-source. The source is a key component of a compact Accelerator Mass Spectrometry (AMS) system built for the analysis of 14C in a continuously flowing gas stream. The gas source produces carbon currents from a stream of CO 2 with currents typical of a traditional graphite source. Details of the gas source, including ion current achieved, optimal flow rate, efficiency, and memory are presented. Additionally, data obtained from coupling a gas chromatograph to the source shown. Details about ion optics are presented separately [1].

Extraction of Gaseous VOCs Using Passive Needle Trap Samplers

ABSTRACTGaseous toluene, ethylbenzene and o-xylene (TEX) were extracted by using the divinylbenzene (DVB) particle of 60–80 mesh as a sorbent packed in series of needle trap samplers (NTS). The feasibility of using this self-designed DVB-NTS as a diffusive time-weighted average (TWA) sampler for occupational hygiene applications was evaluated by examining extended sampling periods of 4–12 hr. Additionally, the NTS was compared in terms of extraction efficiency by simultaneously using the 75 μm Carboxen/polydimethylsiloxane-solid phase microextration (Carboxen/PDMS-SPME) fiber for sampling TEX. Experimental results indicated that, regardless of static (in a bulb) or dynamic samplings (in a flowing gas stream), the packed DVB-NTS achieved higher TEX extraction rates (ng VOCs/min) than those of 75 μm Carboxen/PDMS-SPME fiber. The decreasing rates of extracting TEX for SPME fiber were 24–34% and 28–36% as NTS performed during the sampling periods of 240 and 480 min, respectively. Typically, the maximum VOC adsorption capacities per mg DVB were measured as 5.692 μg toluene, 7.669 μg ethylbenzene and 5.199 μg o-xylene. During the sampling period of 12 hr, the DVB-NTS extracted 1600–1800 ng of individual TEX components from a continuously flowing air stream, in which the gas flow rate equals 200 mL/min. We recommend the badgelike or penlike NTS as an alternative passive sampler to the legal active sampling method 1501, National Institute of Occupational Safety and Health (NIOSH), owing to its small size and high extraction capacity of TEX.

Selective Retardation of Perfume Oil Evaporation from Oil-in-Water Emulsions Stabilized by Either Surfactant or Nanoparticles

We have used dynamic headspace analysis to investigate the evaporation rates of perfume oils from stirred oil-in-water emulsions into a flowing gas stream. We compare the behavior of an oil of low water solubility (limonene) and one of high water solubility (benzyl acetate). It is shown how the evaporation of an oil of low water solubility is selectively retarded and how the retardation effect depends on the oil volume fraction in the emulsion. We compare how the evaporation retardation depends on the nature of the adsorbed film stabilizing the emulsion. Surfactant films are less effective than adsorbed films of nanoparticles, and the retardation can be further enhanced by compression of the adsorbed nanoparticle films by preshrinking the emulsion drops.

A COMMON SOURCE OF ACCRETION DISK TILT

Many different system types retrogradely precess, and retrograde precession could be from a tidal torque by the secondary on a misaligned accretion disk. However, a source to cause and maintain disk tilt is unknown. In this work, we show that accretion disks can tilt due to a force called lift. Lift results from differing gas stream supersonic speeds over and under an accretion disk. Because lift acts at the disk's center of pressure, a torque is applied around a rotation axis passing through the disk's center of mass. The disk responds to lift by pitching around the disk's line of nodes. If the gas stream flow ebbs, then lift also ebbs and the disk attempts to return to its original orientation. To first approximation, lift does not depend on magnetic fields or radiation sources but does depend on mass and the surface area of the disk. Also, for disk tilt to be initiated, a minimum mass transfer rate must be exceeded. For example, a $10^{-11}M_{\odot}$ disk around a 0.8$M_{\odot}$ compact central object requires a mass transfer rate greater than $\sim10^{-13}$M$_{\odot}$yr$^{-1}$, a value well below known mass transfer rates in Cataclysmic Variable Dwarf Novae systems that retrogradely precess and that exhibit negative superhumps in their light curves and a value well below mass transfer rates in protostellar forming systems.

THREE-DIMENSIONAL DOPPLER TOMOGRAPHY OF THE RS VULPECULAE INTERACTING BINARY

Three-dimensional Doppler tomography has been used to study the H$\alpha$ emission sources in the RS Vulpeculae interacting binary. The 2D tomogram of this binary suggested that most of the emission arose from the cool mass losing star with additional evidence of gas flowing close to the predicted trajectory. However, the 3D tomogram revealed surprising evidence of a more pronounced gas stream flow at high $V_z$ velocities from -240 to -360 km s{$^{-1}$}. This behavior is most likely caused by magnetic activity on the cool star since the central velocity plane, defined by $V_z$ = 0 km s{$^{-1}$}, should be coincident with the orbital plane of the binary if the flow is dominated by gravitational forces only. RS Vul has been detected as both an X-ray and a radio source, and it is possible that the RS Vul gas stream may have been deflected by magnetic field lines. This flow is distinctly different from that found in the streamlike state of U CrB, in which the gas flow was confined mostly to the central velocity plane.

Carbon-Based Honeycomb Monoliths for Environmental Gas-Phase Applications

Honeycomb monoliths consist of a large number of parallel channels that provide high contact efficiencies between the monolith and gas flow streams. These structures are used as adsorbents or supports for catalysts when large gas volumes are treated, because they offer very low pressure drop, short diffusion lengths and no obstruction by particulate matter. Carbon-based honeycomb monoliths can be integral or carbon-coated ceramic monoliths, and they take advantage of the versatility of the surface area, pore texture and surface chemistry of carbon materials. Here, we review the preparation methods of these monoliths, their characteristics and environmental applications.

Effect of Plasma Gas Flow Direction on Hydrophilicity of Polymer by Small Zone Cold Plasma Treatment and Hydrophobic Plasma Treatment

Plasma treatment is the most popular surface modification process of polymers. A small cold plasma zone treatment is an important modification technique in modern industry. In this study, the effect of gas flow direction on plasma treatment was investigated. In order to decrease the plasma zone area, we added a separate cylinder to surround the upper electrode. The separate cylinder is effective in limiting the plasma discharge area, and we could find a light and dark area in the vacuum chamber. After O2 plasma treatment, the result shows that only PP nonwoven in the discharge area became hydrophilic, but the other position away from the plasma zone was not affected. The water adsorption of PP nonwoven increased from 34.8% to 537.4%. When the sample is further from the plasma zone, near the up stream of gas flow, the surface property is less hydrophilic. The water contact angle analysis of PS and glass shows the same results as those of PP nonwoven. But PET in plasma zone or dark zone (plasma zone: 75° to 31°, dark zone: 75° to 52°) both show hydrophilic property. The wettability effect in the dark zone may be due to the UV-light irradiation in the process of plasma excitation.

Acoustic levitator for structure measurements on low temperature liquid droplets

A single-axis acoustic levitator was constructed and used to levitate liquid and solid drops of 1-3 mm in diameter at temperatures in the range -40 to +40 degrees C. The levitator comprised (i) two acoustic transducers mounted on a rigid vertical support that was bolted to an optical breadboard, (ii) an acoustic power supply that controlled acoustic intensity, relative phase of the drive to the transducers, and could modulate the acoustic forces at frequencies up to 1 kHz, (iii) a video camera, and (iv) a system for providing a stream of controlled temperature gas flow over the sample. The acoustic transducers were operated at their resonant frequency of approximately 22 kHz and could produce sound pressure levels of up to 160 dB. The force applied by the acoustic field could be modulated to excite oscillations in the sample. Sample temperature was controlled using a modified Cryostream Plus and measured using thermocouples and an infrared thermal imager. The levitator was installed at x-ray beamline 11 ID-C at the Advanced Photon Source and used to investigate the structure of supercooled liquids.

Methane steam reforming in a microchannel reactor for GTL intensification: A computational fluid dynamics simulation study

The integration of the steam reforming and combustion of methane in a catalytic microchannel reactor has been simulated by computational fluid dynamics (CFD). Two models including 4 or 20 square microchannels of 20 mm of length and 0.7 mm of side have been developed. It has been assumed that a thin and homogeneous layer of an appropriate catalyst has been uniformly deposited onto the channels walls. The kinetics of the steam reforming of methane (SRM), water-gas shift (WGS) and methane combustion in air have been incorporated into the models. This has allowed simulating the effect of the gas streams space velocities, catalyst load, steam-to-carbon (S/C) ratio and flow arrangement on the microreformer performance. The results obtained illustrate the potential of microreactors for process intensification: complete combustion of methane is achieved at gas hourly space velocities (GHSV) as high as 130,000 h −1. As concerns the SRM, methane conversions above 97% can be obtained at high GHSV of 30,000 h −1 and temperatures of 900–950 °C. Under these conditions selectivity for syngas is controlled by the WGS equilibrium.

THREE-DIMENSIONAL DOPPLER IMAGES OF THE DISKLIKE AND STREAMLIKE STATES OF U CORONAE BOREALIS

The three-dimensional (3D) Radioastronomical Approach to Doppler tomography has been used to study the H? emission sources in U Coronae Borealis. These 3D tomograms provide greater resolution than the projected two-dimensional version and highlight the jetlike gas flows in the V z direction transverse to the orbital plane. In this paper, the 3D tomograms are compared at two distinct epochs when U CrB was in the disklike state (1993 data) and the streamlike state (1994 data). Both states display a prominent emission source, the circumprimary bulge, which is produced when the gas stream strikes the photosphere of the mass gainer. This source is detected within Vz = ?150 km s?1, and demonstrates that the bulge is not confined to the orbital plane although it achieves a maximum strength near Vz = 0 km s?1. Other emission sources include the stream-star and stream-disk shocks and a Localized Region (LR) where the circling disk material strikes the incoming gas stream. The LR has V z velocities of 200-500 km s?1 in the disklike state. The disk emission is seen over a range of V z velocities, and there is evidence that the disk is inclined to the orbital plane or may have two arms. The gas stream flows along its predicted trajectory in the streamlike state, and a comparison with the disklike state suggests that the gas stream has a higher density than the disk in both states of this binary.

The glow and no glow zone effect on surface wettability modified in O 2 or hexamethyldisilazane cold plasma treatment

Small cold plasma zone treatment is an important modification technique in modern industry. In this study, the effect of gas flow direction on plasma treatment was investigated. In order to decrease the plasma zone area, we added a separate cylinder to surround the upper electrode. Separate cylinder is effective to limit plasma discharge area, and we could find a light and dark area in the vacuum chamber. After O 2 plasma treatment, the result shows that only PP non-woven in the discharge area became hydrophilic, but other position away from the plasma zone was not affected. The water adsorption of PP non-woven increased from 34.8% to 537.4%. When sample is more far from the plasma zone, near the up stream of gas flow, the surface property is less hydrophilic. Water contact angle analysis of PS and glass shows the same results as those of PP non-woven. But PET in plasma zone or dark zone (plasma zone: 75–31°, dark zone: 75–52°) both shows hydrophilic property. The wettability effect in dark zone may be due to the UV-light irradiation in the process of plasma excitation.

Production of Calcium Phosphate Particles from Marine Wastes by Gas Jet Assisted Laser Heating

There are many manufacturing techniques to form metallic particles with certain size and properties. The laser heating method has been successfully applied to generate metallic particles when a supersonic gas flow is assisting this process. The metallic target is heated, melted and vaporised and micro-particles are carried away by a gas flow stream. The high-velocity gas is used to solidificate molten particles and to condensate the metallic vapour resulting in the formation of fine particles. Several attempts were carried out for the production of metallic particles by laser supersonic heating method, obtaining spherical micro-particles (1- 50 "m) of copper, steel, or aluminium. This work presents the application of this method to generate particles from fish bone, in order to obtain a material with a composition close to the inorganic part of the bones. A pulsed Nd:YAG laser has been used to obtain calcium phosphate micro- and nanoparticles. Microparticles size ranges from 10 to 100"m, whereas the nanoparticles have diameters as small as 2 nm. High resolution transmission electron microscopy (HRTEM) allowed us to identify the nanoparticles as whitlockite.

Localization of CsI Radioaerosols from the gas phase using various filtration elements

The behavior of 137Cs131I radioaerosols, yielded by CsI evaporation from a Pt healer into argon or air, during their localization with aqueous solutions and various filtration materials [filters based on Petryanov fabric (from here on, Petryanov filter), “while band” paper filter, and TRUMEM metallic membrane filter] was studied. The degree of localization of 137Cs131I radioaerosols was examined in relation to the amount of sublimed 137Cs131I, the number of bubblers in the system, the size of the nozzle in the bubbling system, and the gas stream flow rate. The efficiency of localization of 137Cs131I radioaerosols with a 10-layer stack of Petryanov filters from the gas stream with and without bubbling system was estimated. It was found that, at the stream velocity of 2–3 cm s−1, a 10-layer stack of Petryanov filters with the total thickness of 3 cm takes up ca. 97% of total 137Cs131I sublimed from the Pt heater. It was shown that the bubbling system does not affect the efficiency of localization of 137Cs131I radioaerosols by Petryanov filters but only favors decrease of the aerosol load on these filters. Electron-microscopic examination of the particle-size distribution of the CsI aerosols penetrating through aqueous solutions was carried out, and various filtration materials (Petryanov filter and “white band” paper filter) were tested.

Effect of Plasma Gas Flow Direction on Hydrophilicity of Polymer by Small Zone Cold Plasma Treatment

Plasma treatment is the most popular surface modification process of polymer. Small cold plasma zone treatment is an important modification technique in modern industry. In this study, the effect of gas flow direction on plasma treatment was investigated. In order to decrease the plasma zone area, we added a separate cylinder to surround the upper electrode. Separate cylinder is effective to limit plasma discharge area, and we could find a light and dark area in the vacuum chamber. After O2 plasma treatment, the result shows that only PP non‐woven in the discharge area became hydrophilic, but other positions away from the plasma zone were not affected. The water adsorption of PP non‐woven increased from 34.8% to 537.4%. When sample is more far from the plasma zone, near the up stream of gas flow, the surface property is less hydrophilic. Water contact angle analysis of PS and glass shows the same results as those of PP non‐woven. But PET in plasma zone or dark zone (plasma zone: 75° to 31°, dark zone: 75° to 52°) both shows hydrophilic property. The wettability effect in dark zone may be due to the UV‐light irradiation in the process of plasma excitation.

Pore Corrosion Model for Gold-Plated Copper Contacts

The goal of this study is to model the electrical response of gold plated copper electrical contacts exposed to a mixed flowing gas stream consisting of air containing 10ppb H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S at 30degC and a relative humidity of 70%. This environment accelerates the attack normally observed in a light industrial environment (essentially a simplified version of the Battelle class 2 environment). Corrosion rates were quantified by measuring the corrosion site density, size distribution, and the macroscopic electrical resistance of the aged surface as a function of exposure time. A pore corrosion numerical model was used to predict both the growth of copper sulfide corrosion product which blooms through defects in the gold layer and the resulting electrical contact resistance of the aged surface. Assumptions about the distribution of defects in the noble metal plating and the mechanism for how corrosion blooms affect electrical contact resistance were needed to close the numerical model. Comparisons are made to the experimentally observed number density of corrosion sites, the size distribution of corrosion product blooms, and the cumulative probability distribution of the electrical contact resistance. Experimentally, the bloom site density increases as a function of time, whereas the bloom size distribution remains relatively independent of time. These two effects are included in the numerical model by adding a corrosion initiation probability proportional to the surface area along with a probability for bloom-growth extinction proportional to the corrosion product bloom volume. The cumulative probability distribution of electrical resistance becomes skewed as exposure time increases. While the electrical contact resistance increases as a function of time for a fraction of the bloom population, the median value remains relatively unchanged. In order to model this behavior, the resistance calculated for large blooms has been weighted more heavily.

Study of adsorption deposition of xenon in an industrial unit for processing ASU tail streams

Results are presented for studying the deposition stage in an industrial unit of the adsorption type intended for extracting xenon from “dirty oxygen” taken from air separation units (ASU). Calculation relationships are proved under industrial conditions that were obtained as a result of studies in a laboratory unit. The following parameters of low-temperature deposition of xenon from a stream of so-called dirty oxygen are varied: adsorption temperature, linear gas stream flow rate in an adsorber and xenon content in the gas mixture.