NH3 dissociation along the gas flow lines of Ar–NH3 dielectric barrier discharges and its effects on global and local properties

The micro-discharge properties and evolution in a 2D array of integrated coaxial microhollow dielectric barrier discharges are studied by using highly time-resolved electrical and optical diagnostics. The study is focused on the effect of the gas flow rate and gas residence time on discharge properties. The investigated integrated coaxial microhollow discharge geometry allows operating the discharge at exceptionally small residence times, which can be equal to or even smaller than the discharge period, at reasonable gas flow rates. The gas flow has an impact on gas heating, residual humidity, pre-ionization density and the densities of excited and reactive species produced by previous discharges. A unique voltage–charge plot is obtained with elongated periods without discharge activity. A very significant effect of flow on NO emission is observed that relates to the impact of flow on the NO production in these micro-discharges. Using the emission intensities of molecular bands of the second positive system of nitrogen and the first negative system of the nitrogen ion, effective reduced electric field strengths are obtained with a maximum equal to 870 Td. The reduced electric field decreases with increasing gas flow rate. This behavior is consistent with the reduction of the overall discharge intensity due to a reduced amount of charges present in the discharge gap. Both the flow rate and a reduction in water impurity changing the ion mobility can be responsible for the different effective electric field distributions at the highest and no flow conditions.

Liquid loading is a major problem in the natural gas industry, in which gas production is limited by the accumulation of liquids in the well tubing. Liquid loading can be prevented by the injection of surfactants at the bottom of the well. The surfactants cause the liquid in the well to foam, thereby changing the gas-liquid flow in the well. The flow is characterized by the TPC (Tubing Performance Curve), which relates the average pressure gradient in the tubing to the gas flow rate. This work has two main goals: (i) To improve the understanding of the effect of surfactants on gas-liquid flow in pipes, which we characterize by a change in the generalised TPC. The generalised TPC relates the average pressure gradient to the gas and liquid flow rates in the pipe. (ii) To provide subsidies for the development of simple physically-based models for the effect of surfactants on gas-liquid flow. We performed experiments in intermediate-scale pipes (lengths of 12 m to 18 m and diameters of 34 mm, 50 mm, and 80 mm) with air and water at atmospheric conditions, without and with surfactants. Multiple parameters, that also vary between different gas wells in the field, were varied: the gas and liquid flow rates, the pipe diameter, the pipe inclination, the surfactant type and the surfactant concentration. We performed a visualisation of the flow without and with surfactants to obtain qualitative results on the effect of surfactants on the flow morphology, and we related these results to quantitative measurements of the generalised TPC and the liquid holdup. The behaviour of the generalised TPC is to a large extent determined by the transition between annular flow and churn flow. In annular flow without surfactants, at large gas flow rates, the water is present in a film along the pipe wall and in entrained droplets in the gas core; the water always moves upwards, which leads to a relatively regular flow morphology. In the churn flow regime, which occurs at low gas flow rates, the liquid film reverses, as the interfacial friction between the gas and the liquid, which drags the liquid upwards, no longer exceeds the gravitational force on the film. This leads to a complex flow morphology, a large liquid holdup and a large pressure gradient. Surfactants cause the formation of foam through the hydrodynamics of the flow. The foam decreases the density and increases the volume of the film at the wall. This changes the balance between the interfacial friction and the gravitational force, which shifts the transition between churn flow and annular flow to lower gas flow rates. As a result, the generalised TPC is changed by the surfactants, leading to a decrease in the pressure gradient at low gas flow rates. An optimum surfactant concentration exists that results in the largest reduction of the pressure gradient. This concentration increases with increasing film thickness; therefore, it increases with decreasing gas flow rate, increasing liquid flow rate, increasing pipe diameter, and decreasing inclination from horizontal. Qualitatively, these results are unaffected by the type of surfactant that is used. From the results obtained in this work, we qualitatively understand the effect of surfactants on the gas-liquid flow, and we understand why surfactants are able to deliquify gas wells. However, a physically-based model is required to translate the results obtained in this work in a quantitative way to the large-scale gas wells. Such a model requires a characterization of the foaming behaviour of the surfactant-liquid mixture using a small-scale setup. We determined that a small-scale sparging setup, often used in the gas industry, is not suitable, because the hydrodynamics in the sparging setup differ too much from the hydrodynamics of annular flow and churn flow. A small-scale shaking test, in which the hydrodynamics more closely resemble churn flow, shows more potential to characterize the foaming behaviour of the surfactants in the context of gas-liquid flows.

The removals of NO x by low temperature plasma produced from gas-liquid two phase dielectric barrier discharge(DBD) were investigated, also studied the major particles information of gas-liquid two phase DBD by emission spectroscopy, and analyzed effects of peak voltage, gas residence time, gas flow rate and NO x initial concentration to the removal of NO x . The results show that OH radicals spectral intensity of gas-liquid two phase DBD is far more than plate plate electrode DBD, so it is more adapt to the removal of NO x . Increasing the peak voltage and gas residence time is good for reduction of NO x , increasing gas flow rate and NO x initial concentration have inhibitory effect on NO x removal. The results have a guiding significance on the application of NO x removal by low temperature plasma.

Previous research has revealed the uniqueness-facilitation effect in the multiple object tracking (MOT) task: simple distinct identities and surface features of moving targets could facilitate attentional tracking. By adapting compound stimuli, the present study investigated whether the global or local properties played the main role in the uniqueness-facilitation effect in the MOT task. The uniqueness of local properties, of global properties or of both local and global properties were considered. Observers’ tracking performance in alternative conditions were compared with that in the homogeneous condition wherein all stimuli have identical local and global properties. Results from two experiments suggest that the global properties played the key role in facilitating tracking. The distinctiveness of local properties can also facilitate tracking with global properties being homogeneous. However, when the stimuli’s global properties are distinct from each other—whether the local properties being unique or not—observers’ tracking performance can achieve the same level as that in the unitary-uniqueness condition wherein the moving objects were distinct unitary letters. These results revealed a global superiority effect in the MOT task. Finally, the facilitation effects of the global and local properties might depend on the stimulus sparsity. When the compound stimuli had fewer local elements, the uniqueness facilitation effect on tracking decreased.

Atmospheric pressure corona discharges are industrially employed to treat large areas of commodity polymer sheets by creating new surface functional groups. The most common processes use oxygen containing discharges to affix oxygen to hydrocarbon polymers, thereby increasing their surface energy and wettability. The process is typically continuous and is carried out in a web configuration with film speeds of tens to hundreds of cm s−1. The densities and relative abundances of functional groups depend on the gas composition, gas flow rate and residence time of the polymer in the discharge zone which ultimately determine the magnitude and mole fractions of reactive fluxes to the surface. In this paper, results are discussed from a two-dimensional computational investigation of the atmospheric pressure plasma functionalization of a moving polypropylene sheet in repetitively pulsed He/O2/H2O discharges. O and OH typically initiate surface processing by hydrogen abstraction. These species are regenerated during every plasma pulse but are also largely consumed during the inter-pulse period. Longer-lived species such as O3 accumulate over many pulses and convect downstream with the gas flow. Optimizing the interplay between local rapid reactions, such as H abstraction which occurs dominantly in the discharge zone, and non-local slower processes, such as surface–surface reactions, may enable the customization of the relative abundance of surface functional groups.

Caractérisation de décharges à barrières diélectriques atmosphériques et sub-atmosphériques et application à la déposition de couches d"oxyde de silicium

A novel process for oxygen absorption from air using hollow fiber gas-liquid membrane contactor

Dielectric barrier discharge (DBD) under atmospheric pressure is usually characterized with a large number of streamer discharge filaments. So its applications are greatly limited due to the non-uniform discharge mode. Nowadays, most research efforts are being focused on how to achieve the uniform DBD, and results show that there are many ways to improve the non-uniformity of the discharge, one of which is the introduction of flowing gas into the discharge gap at controllable flow rates. However, the mechanism of gas flow on discharge mode on DBD is still not understood clearly. This paper presents a coaxial DBD plasma jet, in which a powered electrode covered by polytetrafluorethylene (PTFE) is fastened in the center of a quartz glass tube, and a copper strip as grounded electrode is wrapped outside the tube. The device is operated under atmospheric pressure with an intermediate frequency sinusoidal resonant power supply. Argon (99.999%) is employed as the working gas, and its flow rate is measured and controlled through a flow meter within the range of 0–25 L/min. The influence of different gas flow rates on the discharge mode is investigated and the mechanism is analyzed. From the discharge photos, it can be seen that the discharge is generated inside the tube and the plasma is blown out by the gas flow to form a plasma jet. When the flow rate is relatively slower, there are obvious discharge filaments near the tube nozzle, which can also be confirmed through the waveform of the discharge current characterized by many current pulses per half cycle of the applied voltage. The faster the gas flows, the fewer the discharge filaments are, and the more homogeneous discharge is obtained. At a certain gas flow rate, together with the lowest breakdown voltage value, the discharge mode presents a glow like state. It can be concluded that the faster flowing argon can take more heat generated in the discharge away, which can induce the thermal stability of discharges and prevent the transition the Townsend discharge to a filamentary discharge effectively. Besides, there is the distortion of applied electric field caused by the wall charge accumulated on the surface of dielectric and the space charge moving towards electrodes in the discharge gap. When the argon flows through the gap at different rates, the spatial distribution of wall charges and space charge is influenced. The faster the argon flows, the less wall charges and space charge accumulates, and the more homogeneous the discharge presents.

Numerical simulation for mass transfer characteristics of CO2 capture in a rotating packed bed

Effect of microchannel junction angle on two-phase liquid-gas Taylor flow

This paper reports the absorption of SO2 in a transversal flow hollow fiber membrane contactor (HFMC) using water at 27 °C. Experimental results show that gas and liquid flow rates can be regulated independently without causing operational failures in the HFMC. High SO2 removal efficiencies could be achieved at water flow rates from 194 and 463 mL min−1, gas flow rates between 8276 and 18073 mL min−1, and the inlet SO2 concentration of 2000 ppm. The SO2 removal efficiency increased with increasing liquid flow rate and decreasing gas flow rate. The overall volumetric gas phase mass transfer coefficient \( (K_{G} a) \) of the HFMC is in the range of \( 10^{ - 3} \;{\text{mol}}\;{\text{s}}^{ - 1} \;{\text{m}}^{ - 3} {\text{Pa}}^{ - 1} \). It is higher than that of conventional wet SO2 scrubbers although water is used in HFMC while effective alkaline absorbents are used in the compared reactors. It indicates that the HFMC is superior in SO2 absorption over conventional absorbers.

PurposePowder bed fusion processes are common due to their ability to build complex components without the need for complex tooling. While additive manufacturing has gained increased interest in industry, academia and government, flaws are often still generated during the deposition process. Many flaws can be avoided through careful processing parameter selections including laser power, hatch spacing, spot size and shielding gas flow rate. The purpose of this paper is to study the effect of shielding gas flow on vapor plume behavior and on final deposition quality. The goal is to understand more fully how each parameter affects the plume and deposition process.Design/methodology/approachA filtered-photodiode based sensor was mounted onto a commercial EOS M280 machine to observed plume emissions. Three sets of single tracks were printed, each with one of three gas flow rates (nominal, 75% nominal and 50% nominal). Each set contained single-track beads deposited atop printed pedestals to ensure a steady-state, representative build environment. Each track had a set power and speed combination which covered the typical range of processing parameters. After deposition, coupons were cross-sectioned and bead width and depth were measured. Finally, bead geometry was compared to optical emissions originating in the plume.FindingsThe results show that decreasing gas flow rate, increasing laser power or increasing scan speed led to increased optical emissions. Furthermore, decreasing the gas cross-flow speed led to wider and shallower melt pools.Originality/valueTo the best of the authors’ knowledge, this paper is among the first to present a relationship among laser parameters (laser power, scan speed), gas flow speed, plume emissions and bead geometry using high-speed in situ data in a commercial machine. This study proposes that scattering and attenuation from the plume are responsible for deviations in physical geometry.

1,4-Dichlorobenzene (1,4-DCB) is a carcinogen. Therefore, the purification of gases from the vapor of this substance is an urgent task. In this work, we studied the vapor decomposition of 1,4-dichlorobenzene under the action of a dielectric barrier discharge (DBD) of atmospheric pressure in oxygen. The range of specific discharge powers was 0.6–1.7 W/cm3, concentrations of 2,4-DCB was 0.076–0.382 mg/l, and gas flow rate was 1–3 cm3/s. The concentrations of 1,4-DCB and its decay products were measured using chromatography, spectrophotometry, fluorometry, and some others. It was found that the kinetics of decomposition (the dependence of the concentration of 1,4-DCB on the gas residence time) obeys the first-order kinetic equation with a rate constant of about 0.13 s−1. The decomposition products were carboxylic acids, aldehydes, CO2, and Cl2. CO2 yield is 75% of total carbon content in system. The decomposition process is accompanied by the formation of a polymer film on the reactor walls. The composition of the film was characterized by the EDX method and FTIR. The elemental composition of the film was C:O:Cl = 1:2.1:0.1. FTIR spectra showed that the film contains a significant amount of functional groups of carboxylic acids. The results demonstrated that DBD is an effective tool to remove 1,4-DCB. The process is characterized by the following indicators. The maximum degree of decomposition reaches 90%. The energy yield of decomposition is 2.7 × 10−3 molecules per 100 eV, and specific input energy is 15 kJ/l.

The mechanism of flow of air and water through packed glass fibres has been studied. Pressure drops and liquid hold ups were measured as a function of gas and liquid flow rates and the packing characteristics. It has been found that the pressure difference measured is dependent upon the history of previous gas and liquid flow rates in the bed. The liquid hold up is defined entirely by the gas and liquid flow rates. An analysis of the flow mechanism shows that the capillary forces interact with the fluid pressures in the bed. For example an increase in gas flow rate followed by a reduction to the same flow rate has been shown to reduce the resistance of the bed to gas flow even though the liquid flow rate is unchanged. A measure of the irreversibility of the flow operation is suggested.

The DBD (Dielectric Barrier Discharge) is well known for its great advantages in various kinds of industrial applications and has been widely used in manufacturing process including flat panel displays, thin films and semiconductor packaging. There has been enormous progress on DBD source development and diagnostics to suit these different purposes. At the same time, there are increasing needs for moderate and efficient remote plasma sources in order to avoid electrical damage from microarcs or high energy ion collisions. To this end, a stable remote plasma using an extended DBD source having a stable effective discharge area of 550mm × 40mm was investigated. The electron temperature was measured from a Boltzmann plot based a PLTE (Partial Local Thermodynamic Equilibrium) model and electron density measured from linewidth broadening of H β line, with hydrogen insertion for comparison of the direct discharge region in between electrodes and the remote plasma region. The capacitance of DBD electrode as well as discharge energy and discharge power has been investigated with V-Q Lissajous analysis. Surface treatment of glass and polypropylene with various applied voltage and gas flow rates were studied. Combining optical and electrical diagnostics and surface analysis results on treated samples, the atmospheric plasma source for in-line processing was characterized.