Gas Mixing Process Research Articles

Experimental study on characteristics of air entrainment and distribution of void fraction in surf zone

The study of breaking wave-induced air bubble flows near the seashore is a great challenge. The process of air entrainment is highly complex and air bubbles evolution takes place over a wide range of spatial and temporal scales. Surf wave breaking can generate strong turbulence and entrain a large amount of air in the water and produce many air bubbles with different lifetimes. It is a typical two-phase flow involving water and air. The evolution and transport of wave-induced air bubbles can significantly affect coastal structures with respect to impact intensity, seawater-air exchange, sediment transport and wave energy dissipation. Studying the characteristics of wave-induced air bubbles in the nearshore wave breaking zone has important theoretical value and scientific significance. A better understanding of this process is also important to improving engineering practice and environmental protection in the nearshore region. Past studies have been focused on the transport law of the wave-induced air bubbles and the related statistics of air bubbles involved in the wave breaking process. Due to the complexity of water and gas mixing processes and the difficulty of the corresponding measurements, the prior research mainly focused on the formation and distribution of wave-induced air bubbles and their relationship with wave energy dissipation. However, quantitative research on how air bubble characteristics vary with different wave parameters still lacks in-depth discussion. This work presents a wave tank experiment to fully understand the void fraction distribution and its relationship with prominent wave parameters during the air entrainment process during surf wave breaking. Spatial and temporal variations of air entrainment and void fraction evolutions are recorded by an air bubble measuring system and high speed camera, respectively. The main factors affecting the distribution of void fraction are determined. The experimental data demonstrates that the distribution of void fraction is closely related to the water depth, prominent wave parameters and distance from the wave breaking location. We discuss the spatial and temporal evolution of the void fraction and derive an empirical formula to predict the void fraction by introducing two factors named C 0 and k 1. The factor k 1 is inversely proportional to wave height and C 0 varies with the wave steepness, relative water depth and dimensionless horizontal position. The empirical formula is used to analyze the relationship between each wave parameter and the distribution of void fraction. Experimental results show that the maximum void faction was close to 20% at the water surface and that the maximum penetration depth of air bubbles was close to 5 cm below the still water surface. As the water depth increased, void faction varied with e-index. Results of this work can be used to analyze and predict the spatiotemporal distribution of the void fraction in wave breaking zone and provide a good reference for further study of air bubble transport during surf wave breaking.

Thermal Analyses of Active-Cooled Strut in RBCC Engine

Fuel-injection strut is an efficient way to increase the depth of fuel penetration and strengthen the mixing process of hot gas in supersonic combustor. With a validated numerical model, this article analyzed the effects of leading edge's radius, wall thickness and mass flow distribution on cooling efficiency of fuel-injection strut and proposed an optimizing strategy for active-cooled strut. Results showed that the larger radius of leading edge not only decreased the heat flux on the leading edge, but also has a negative effect on the aerodynamic performance of strut; and a thinner wall could enhance the cooling efficiency and uniformize the temperature distribution of the wedge; furthermore, the flow distribution of inlet coolant had a significant impact on the heat transfer and flow processes, an optimized way of flow distribution was obtained by comparing three different ways of distribution.

Investigation of geochemical characteristics of hydrocarbon gas and its implications for Late Miocene transpressional strength — A study in the Fangzheng Basin, Northeast China

We have assessed the genetic types of hydrocarbon gas in the Fangzheng Basin by analyzing the effects of geologic settings on gas generation, kerogen types in source rocks, gas compositions, stable carbon isotopes of individual alkanes, and biomarkers in gas-associated oil. The primary compounds of source rocks in the Eocene Xinancun Formation and Paleocene Wuyun Formation are found as type II and III kerogens, respectively. The hydrocarbon gas in the Fangzheng Basin can be classified into three families. Family I is affected by biodegradation, and it is dry gas generated from low-maturity lacustrine mudstones (i.e., oil-prone source rocks) of the Xinancun Formation. Family II is coal-derived wet gas accompanied by oil, and it is typically generated by type III kerogen of mudstones in coal measures of the Wuyun Formation. Family III is mixed-type wet gas whose primary compound is oil-associated gas, and it is mainly generated by type II kerogen in the Xinancun Formation and partly from type III kerogen in the Wuyun Formation in the Daluomi (DLM) Uplift. The family I and II hydrocarbon gases are located in the Zhuozhugang (ZSG) Sag. Family III hydrocarbon gas was formed in the mixing process of different genesis gas through the active faults because the late Miocene transpressional strength of uplift in the DLM Uplift was more intense than that in the ZSG Sag after the development of increased accommodation space coeval with intrabasinal rifting before Oligocene.

ON THE NATURE OF HYDROSTATIC EQUILIBRIUM IN GALAXY CLUSTERS

ABSTRACT In this paper, we investigate the level of hydrostatic equilibrium (HE) in the intracluster medium of simulated galaxy clusters, extracted from state-of-the-art cosmological hydrodynamical simulations performed with the Smoothed-Particle-Hydrodynamic code GADGET-3. These simulations include several physical processes, among which are stellar and active galactic nucleus feedback, and have been performed with an improved version of the code that allows for a better description of hydrodynamical instabilities and gas mixing processes. Evaluating the radial balance between the gravitational and hydrodynamical forces via the gas accelerations generated, we effectively examine the level of HE in every object of the sample and its dependence on the radial distance from the center and on the classification of the cluster in terms of either cool-coreness or dynamical state. We find an average deviation of 10%–20% out to the virial radius, with no evident distinction between cool-core and non-cool-core clusters. Instead, we observe a clear separation between regular and disturbed systems, with a more significant deviation from HE for the disturbed objects. The investigation of the bias between the hydrostatic estimate and the total gravitating mass indicates that, on average, this traces the deviation from HE very well, even though individual cases show a more complex picture. Typically, in the radial ranges where mass bias and deviation from HE are substantially different, the gas is characterized by a significant amount of random motions ( ), relative to thermal ones. As a general result, the HE-deviation and mass bias, at a given distance from the cluster center, are not very sensitive to the temperature inhomogeneities in the gas.

Numerical simulation of hydrodynamic and gas mixing processes in underground hydrogen storages

The storage of hydrogen in underground reservoirs comprises a potential solution for balancing the fluctuating energy production from wind and solar power plants. In this concept, electrolysers are used to transform excessively produced electrical energy into chemical energy in the form of hydrogen. The resulting large volumes of hydrogen are temporarily stored in subsurface formations purely or in mixture with other gases. In times of high energy demand, the chemical energy is transformed back into electricity by fuel cells or engine generators. Key aspects in the development period and the subsequent cyclic operations of such a storage are the hydrodynamic behavior of hydrogen and its interaction with residual fluids in the reservoir. Mathematically, the behavior can be described by a compositional two-phase flow model with water and gas as phases and all relevant chemical species as components (H2, H2O, CH4, CO2, N2, H2S, etc.). The spatial variation of the gas phase composition between injected and initial gas leads to density and viscosity contrasts which influence the displacement process. The mixing of gases with different compositions is governed by molecular diffusion or mechanical dispersion dependent on the flow velocity. In the present paper, a numerical case study in a depleted gas reservoir was performed. The storage was charged with hydrogen for 5 years. Subsequently, 5 years of seasonal cyclic operation were simulated to predict injection and production rates, pressure response and composition of the produced gas stream .

High-density plasma etching characteristics of indium–gallium–zinc oxide thin films in CF4/Ar plasma

Abstract We investigated the etching process of indium–gallium–zinc oxide (IGZO) thin films in an inductively coupled plasma system. The dry etching characteristics of the IGZO thin films were studied by varying the CF 4 /Ar gas mixing ratio, RF power, DC-bias voltage, and process pressure. We determined the following optimized process conditions: an RF power of 700 W, a DC-bias voltage of − 150 V, and a process pressure of 2 Pa. A maximum etch rate of 25.63 nm/min for the IGZO thin films was achieved in a plasma with CF 4 /Ar(= 25:75), and the selectivity of IGZO to Al and TiN was found to be 1.3 and 0.7, respectively. We determined the ionic composition of the CF 4 /Ar plasma using optical emission spectroscopy. Analysis of chemical reactions at the IGZO thin film surfaces was performed using X-ray photoelectron spectroscopy.

Influence of concentration distribution of hydrogen in air on measured flammability limits

There is a clear difference between exiting data on the measured flammability limits of hydrogen-air mixture. The non-uniformity of concentration distribution of hydrogen in air is a contributor to deviations of the upper flammability limit (UFL) and the lower flammability limit (LFL) measured in different experiments. This paper presents a numerical model to simulate the gas mixing process from start to stability, to predict the concentration distribution, and to research the influence of concentration distribution of hydrogen in air on measured UFLs and LFLs. The commercial software package Fluent was used to carry out the numerical simulation for the concentration distribution of hydrogen in air in the vessels with length-to-diameter ratios (L: D) of 1:1, 3:1, 5:1 and 7:1 respectively. Based on the numerical simulation and analysis, the influence of concentration distribution on measured flammability limits was demonstrated for hydrogen in air in the vessel. It is found that the deviations of measured flammability limits of hydrogen in air are the minimum in the vessel with length-to-diameter ratio of 1:1, and augment with the augmentation of vessel length-to-diameter ratio. Moreover, it is presented that the deviations of measured flammability limits of hydrogen in the center of the vessel are lower than that in the top and the bottom.

An analytical model of claw rotor profiles and working process model with the mixing process for claw vacuum pumps

Claw rotor profiles play an important role on performances of claw vacuum pumps. In this paper, an analytical model of claw rotor profiles, including profile equations, design methods, geometric theories and profile meshing relationships is established; and a working process model with the particular gas mixing process for claw vacuum pumps is also built in order to reveal characteristics of the mixing process. The mixing process, which includes phenomena of gas over compression, gas expansion and mixing, new chamber generation, chamber separation and merge, is investigated in detail. Numerical simulations of working process consisting of the suction, mixing, compression and discharge process are carried out to exhibit flow fields and analyze the thermodynamic process for claw vacuum pumps. The presented flow domain distributions give a good understanding about their physical process. The study results are beneficial to performance evaluations of different types of profiles and designs of novel claw rotor profiles with high performances.

Improvement of a Gas Intake Device and a Gas Mixing Study in a Large‐Scale Vessel

AbstractGas mixing is a common process in chemical engineering. For actual industrial manufacturing of chemicals, most reactions commonly run in reactors or reaction vessels with large volumes (over 10 m3). In order to simulate a gas mixing process in a sealed reactor, and finally to improve the mixing effect between the gases, here the mixing process between methane and air in a reaction vessel with a volume of 10 m3 was studied via several approaches. Several specific evaluation indexes, including the mixing degree, the maximum concentration difference, and the mixing time, were obtained and recorded to evaluate the mixing effect on the gases. After a series of experiments targeting the determination of the size and pressure difference values of the gas intake device, the mixing effect between methane and air was finally optimized. The mixing degree was found to reach 0.97 within 1 h of monitoring, and the mixing time was decreased by 1700 % from the original situation.

Secondary microbial gas formation associated with biodegraded oils from the Liaohe Basin, NE China

A suite of oils and associated gases from the Liaohe Basin NE China, which have similar maturity and source rock origin but with varying degrees of biodegradation, have been analyzed for the molecular compositions of oil and gas as well as for the isotopic values. Isotopic compositions of the gas samples show wide variation (δ13C1 from −55.4‰ to −36.8‰, δ13C2 from −39.4‰ to −28.5‰, δ13C3 from −31.9‰ to −16.4‰ and δ13n-C4 from −26.6‰ to −20.4‰). Most gas samples display clear geochemical evidence of alteration by biodegradation, with relatively high dryness (C1/C1–4>0.97), high ratios of isobutane/n-butane (0.4–1.8) and C2/C3 (0.3–42.3). The carbon isotopic compositions of wet gas components (C3 and C4) in the biodegraded gases are heavier than these in non-biodegraded gases with Δδ13C (C3−C2) of up to 13.4‰, but methane and ethane isotope signatures are variably heavier or lighter than those in non-biodegraded gases. Carbon dioxide contents and isotopic values provide evidence for gas origins. Gases with isotopically heavy carbon dioxide (δ13C>+2‰), and isotopically light methane (δ13C<−50‰) indicate that secondary microbial methane was generated from CO2 reduction under anaerobic conditions. Gases with isotopically heavy methane (>−45‰), together with heavy carbon dioxide (>+8‰), probably indicate a high degree of CO2 conversion to methane under later stages of secondary microbial methane generation. We speculate that the presence of isotopically heavy methane (>−45‰) and isotopically light carbon dioxide (<−8‰) may be indicative of anaerobic methane oxidation but much additional work is needed to evaluate that.It seems likely that most of the variations in isotopic signatures of gases related to biodegraded oil can be described by various sequential biodegradation, carbon dioxide reduction and gas mixing processes. Methanogenesis through carbon dioxide reduction does not necessarily produce isotopically depleted methane. The methane becomes richer in 13C when a large fraction of carbon dioxide is reduced to methane, resulting in newly generated methane that is sometimes heavier than the original thermogenic methane. Anaerobic methane oxidation may exist in the present case study. Mixing of newly generated methane with thermogenic methane already in place in the reservoir, coupled with anaerobic methane oxidation, can result in very complicated isotopic signatures. Care should be taken when gas isotopic values were applied for source and maturity assessment.

Novel Fiber-Optic Sensing System for Detection of Methane

Based on DFBLD (Distributed Feedback Laser Diode) and harmonic detection technique, a novel fiber-optic methane detection system is constructed. The system can be applied to broad-range concentration detection of methane. Based on the approximation express of the law of Beer-Lambert, detection of methane with various concentration from 0% to 20% is completed using subtraction of background and ratio processing method, as the atmosphere surroundings are treated as background noise. The direct absorption spectra for various concentration is measured using GRIN gas cell, combined with DFBLD. The R5 line of the 2v3 band of methane is selected as the absorption peak. The system is tested online during gas mixing process and the linear relationship between system indication and concentration variation is validated. Also the stability and dynamic response characteristics are confirmed by the experiments. The sensitivity of the system can be adjusted according to the concentration level of various field environments by changing the prism distance using step motor. In the range of 0% to 20% the sensitivity of methane detection can arrive at 0.001%. So the system can be applied to various application fields and adopted as monitoring instruments for coalmine tunnel and natural pipeline.

Surface reaction effects on dry etching of IGZO thin films in N2/BCl3/Ar plasma

We were experimented the etching process of indium gallium zinc oxide (IGZO) thin films in an inductively coupled plasma. The dry etching characteristics of the IGZO thin films was studied by varying the N2/BCl3/Ar gas mixing ratio, RF power, DC-bias voltage, and process pressure. We determined the optimized process conditions that were as follows: a RF power of 700W, a DC-bias voltage of −150V, and a process pressure of 15mTorr. The minimum etch rate of the IGZO thin film was 38.1nm/min in N2/BCl3/Ar=(3:10:10sccm) plasma, and the selectivities of IGZO for Al and TiN were 0.26 and 0.38, respectively. From XPS analyses, the chemical reactions on the IGZO thin films were explained. From AFM and FESEM images, we found the etch conditions for the smooth surface and vertical sidewall conditions.

Numerical simulation of carbon dioxide injection for enhanced gas recovery (CO2-EGR) in Altmark natural gas field

This paper studied the CO2-EGR in Altmark natural gas field with numerical simulations. The hydro-mechanical coupled simulations were run using a linked simulator TOUGH2MP-FLAC3D. In order to consider the gas mixing process, EOS7C was implemented in TOUGH2MP. A multi-layered 3D model (4.4 km × 2 km × 1 km) which consists of the whole reservoir, caprock and base rock was generated based on a history-matched PETREL model, originally built by GDF SUEZ E&P Deutschland GmbH for Altmark natural gas field. The model is heterogeneous and discretized into 26,015 grid blocks. In the simulation, 100,000 t CO2 was injected in the reservoir through well S13 within 2 years, while gas was produced from the well S14. Some sensitivity analyses were also carried out. Simulation results show that CO2 tends to migrate toward the production well S14 along a NW–SE fault. It reached the observation wells S1 and S16 after 2 years, but no breakthrough occurred in the production well. After 2 years of CO2 injection, the reservoir pressure increased by 2.5 bar, which is beneficial for gas recovery. The largest uplift (1 mm) occurred at the bottom of the caprock. The deformation was small (elastic) and caprock integrity was not affected. With the injection rate doubled the average pressure increased by 5.3 bar. Even then the CO2 did not reach the production well S14 after 2 years of injection. It could be concluded that the previous flow field was established during the primary gas production history. This former flow field, including CO2 injection/CH4 production rate during CO2-EGR and fault directions and intensity are the most important factors affecting the CO2 transport.

The Applied Research of Decoupling Control Algorithm in Gas Mixing Process

It is difficult to get satisfied effects using conventional instruments to control the caloric value of the mixed-gas. A hybrid intelligent control strategy is presented in this paper in order to solve the coupling problem that exists between the calorific value control and pressure control. This strategy partitions the whole control system into gas–pressurized machine’s post pressure control loop and control loop of pressure decoupling .In the former decoupling control loop, in order to realize the stability of the calorific value and restrain the fluctuation of the mixing pressure, a decoupling controller is designed by combining the fuzzy control and the expert control. The result of real-time control showed the method obviously enhanced the control accuracy and reduced the undulation of pressure and calorific value and fulfilled the request of customer.

Effect of Dry Etching of TiO2 Thin Films Using Inductively Coupled Plasma

In this study, the effect of the dry etching of titanium dioxide (TiO2) thin films was investigated with addition of O2 to BCl3/Ar plasma. The maximum etch rate of TiO2 thin films and the selectivity of TiO2 to SiO2 were 100 nm/min and 1.07 in O2/BCl3/Ar (= 3:4:16 sccm) plasma, respectively. In addition, the etch rate and selectivity were measured as functions of the etching parameters, such as the gas mixing ratio, RF power, DC-bias voltage, and process pressure. The chemical state on the etched surface of TiO2 thin films were investigated by the x-ray photoelectron spectroscopy. To determine the re-deposition and reorganization of residues on the surface, the surface morphology and roughness of TiO2 thin films were examined by the atomic force microscopy.

Dry Etching Characteristics of Bi0.5(Na0.82K0.18)0.5TiO3 Thin Films in Inductively Coupled Plasma

The etch process of the Bi0.5(Na0.82K0.18)0.5TiO3(BNKT) thin films were performed in BCl3/Ar plasma. We investigated the etching characteristics of BNKT thin films and the selectivity of BNKT to SiO2 in inductively coupled plasma (ICP) system. The best etch rate of BNKT thin films was 27.8 nm/min in BCl3/Ar (4:16 sccm) plasma. In addition, the etch rate was investigated as functions of the gas mixing ratio, RF power, DC-bias voltage, and process pressure. From the x-ray photoelectron spectroscopy (XPS) data analysis, we were assumed that the byproducts were generated on the surface of the BNKT thin films during etching process. The surface morphology of the BNKT thin films was observed by atomic force microscopy (AFM). We determined the ionic composition of BCl3/Ar plasma using optical emission spectroscopy (OES).

Langmuir circulation inhibits near‐surface water turbulence

In the surface ocean, breaking waves are a major source of air bubbles and turbulent kinetic energy. During the presence of a consistent surface wind, these wave‐generated bubbles, along with other surface material like seaweed or foam, can be drawn into long rows along the surface. Driving this organization is Langmuir circulation, a phenomenon in which the wind and waves cause surface waters to rotate helically, moving like a wire wrapped around a pole in the windward direction. These spiral currents oscillate between clockwise and counterclockwise rotations, such that in some places the surface waters are pushed together and in others they are pulled apart. Researchers have previously found that at sites of convergence the bubbles produced by breaking waves are pushed to depths of 15 meters or more, with important implications for air‐sea gas mixing and other processes.

Numerical simulation on mixing process of ejecta and gas

Ejecta mixing takes place at the interface between metal and gas under shock loading, i.e., the transport process of ejecta from metal surface appears in the gas. In this paper, adopting disperse particles instead of the initial ejecta, we simulate the ejection mixing process according to two-phase flow of gas and particle. We give the numerical results of the evolution process of the mixing, and analyze the effects of initial gas pressure and particle size on the mixing zone. The pneumatic break is observed from the numerical simulations, which can lead to evident reduction of the particle and then become an important factor affecting the evolution of mixture; also, our simulations are consistent with the corresponding measurements, showing that the gas and particle two-phase flow model is an effective method to simulate the ejection mixing.

Decoupling Control of Gas Mixing Based on Fuzzy-Single Neuron Adaptive PID

The gas mixing pressuring and calorific value control of gas mixing process have the characteristics of strong coupling, nonlinear, uncertainty and large time-varying. If the calorific value of mixing gas is unstable in gas pressurization station, the quality and quantity of iron and steel production will be affected. In this paper, an compound decoupling control method of fuzzy-single neuron adaptive PID is proposed according to the mixing gas pressure and calorific value decoupling control, the fuzzy decoupling controller is used to realize the initial adjustment of mixing gas and pressure, which has the characteristics of rapidity and anti-interference performance. The fine adjustment work of control process is completed by the secondary adjustment of adaptive PID controller of single neuron, the design of controller has the ability of parameter self-learning, and the simulation results show that this design scheme has a better dynamic performance than traditional PID scheme to verify the feasibility of this method.

Dry etching characteristics of HfAlO 3 thin films in BCl 3/Ar plasma using inductively coupled plasma system

In this study, we monitored the HfAlO 3 etch rate and selectivity to SiO 2 as a function of the etch parameters (gas mixing ratio, RF power, DC-bias voltage, and process pressure). A maximum etch rate of 52.6 nm/min was achieved in the 30% BCl 3/(BCl 3 + Ar) plasma. The etch selectivity of HfAlO 3 to SiO 2 reached 1.4. As the RF power and the DC-bias voltage increased, the etch rate of the HfAlO 3 thin film increased. As the process pressure decreased, the etch rate of the HfAlO 3 thin films increased. The chemical state of the etched surfaces was investigated by X-ray Photoelectron Spectroscopy (XPS). According to the results, the etching of HfAlO 3 thin films follows the ion-assisted chemical etching mechanism.