Gas Flow Characteristics Research Articles

Calculation of thermodynamic characteristics of gas flows in concentrated fire vortices

The article presents the results of numerical simulation of gas flows in free fire vortices. The fundamental possibility of physical modeling of the occurrence of concentrated fire vortices is presented in a series of experimental studies carried out at the Joint Institute for High Temperatures of the Russian Academy of Sciences. In the model of a compressible continuous medium for the complete system of Navier-Stokes equations, an initial-boundary-value problem is proposed that describes complex three-dimensional unsteady flows of viscous compressible heat-conducting gas in ascending swirling heat fluxes. Using explicit difference schemes and the proposed initial-boundary conditions, approximate solutions of the Navier-Stokes system of equations are constructed and the thermodynamic characteristics of three-dimensional unsteady gas flows are numerically determined. The calculation results showed that in the process of formation of fiery vortices, it is formally possible to distinguish several stages. The calculations of the thermodynamic characteristics of gas flows during heating of the underlying surface by several local sources showed that the selected mathematical model under the corresponding initial and boundary conditions allows numerical experiments to describe the arising of complex unsteady three-dimensional flows.

Gas Flow and Heat Transfer in an Enclosure Induced by a Sinusoidal Temperature

The heat transfer and flow characteristics of rarefied gas confined within a square cavity are investigated. The cavity upper-wall is subjected to a symmetrical sinusoidal temperature with respect to its midline. Two cases are considered, one of them is that the bottom and two sidewalls are kept adiabatic, while in the other, all the enclosure walls are considered diffusely reflecting. Kinetically, the gas is simulated with the direct simulation Monte Carlo method (DSMC) in the slip and transition regimes. The DSMC results are compared with the Navier-Stokes-Fourier equation, with second order boundary conditions of velocity slip and temperature jump, (NSF) in the slip regime. Main outcomes are presented as velocity streamlines overlaid on temperature contours and macroscopic parameters plots. The Knudsen number (Kn) increase shows other vortices, beside the two classical ones that appear in the hydrodynamic and slip regime. The normal heat flux about the sinusoidally heated wall is strengthened by the flow in DSMC rather than that predicted by NSF method. Good agreement is observed between the NSF theory and DSMC method in the early slip regime, but when Kn=0.1 the NSF approach breaks down to show the secondary counter rotating eddies illustrated by the DSMC method.

Calculation of gas velocities in concentrated fire vortices

The article presents the results of numerical modeling of the generation of free fire vortices in laboratory conditions without the use of special swirling devices. The fundamental possibility of physical modeling of the occurrence of concentrated fire vortices is described in a series of experimental studies conducted under the supervision of A. Yu. Varaksin, corresponding member of the RAS. In the model of compressible continuous medium for the complete system of Navier-Stokes equations, an initial-boundary-value problem is proposed that describes complex three-dimensional unsteady flows of viscous compressible heat-conducting gas in ascending swirling heat flows. Using explicit difference schemes and the proposed initial-boundary conditions, approximate solutions of the complete system of Navier-Stokes equations are constructed and the velocity characteristics of three-dimensional unsteady gas flows initiated by local heating of the underlying surface by nineteen heat sources are numerically determined.

CFD Analysis of Gas Flow Characteristics and Residence Time Distribution in a Rotating Spherical Packing Bed

Rotating packed beds (RPBs) have attracted widespread attention due to their high mass transfer efficiency. In this paper, gas flow characteristics in a rotating spherical packing bed (RSPB) were i...

Microscopic Imaging Spray Diagnostics under High Temperature Conditions: Application to Urea–Water Sprays

The quantitative investigation of droplet laden turbulent flows at high temperature conditions is of great importance for numerous applications. In this study, an experiment was set up for investigation of evaporating urea–water sprays, which are relevant for the effective reduction of nitrogen oxide emissions of diesel engines using Selective Catalytic Reduction. A shadowgraphy setup is pushed to its limits in order to detect droplet diameters as small as 4 m and droplet velocities up to 250 m / s . In addition, the operating conditions of the gaseous flow of up to 873 K and 0 . 6 M Pa are an additional challenge. Due to the high temperature environment, image quality is prone to be compromised by Schlieren effects and astigmatism phenomena. A water-cooled window and an astigmatism correction device are installed in order to correct these problems. The results to be presented include characteristics of the turbulent gas flow as well as detailed spray characteristics at different positions downstream of the atomiser. It is demonstrated that the velocity of the gas can be approximated by the velocity of the smallest detectable droplets with sufficient accuracy. Furthermore, the statistical analysis of velocity fluctuations provides data for predicting the turbulent dispersion of the droplets.

Numerical Analysis of the Influence of Atmospheric Plasma Gun Structure on Plasma Flow

To investigate the gun structure influence on gas flow characteristics during plasma spraying process, a simplified 3-D computing model was developed to calculate the multi-physical properties of the gun. The geometric model included cathode and anode, and electrodes boundary layers. Besides the temperature of ions and electrons was treated separately. In other words, the model used a two-temperature plasma model, which took into account ionization and recombination reactions of ions and electrons, the plasma flow inside the spray gun was studied. From the calculation results, decreasing of gun throat diameter caused the increase of velocity and decreasing of temperature. The change of velocity behaved a linear relationship with diameters, while temperature decreasing slowed down when the diameters reached a certain value. The research will provide theoretical guidance for the optimal design of spray gun.

1D-3D coupling algorithm for unsteady gas flow analysis in pipe systems

Numerical analysis of intake and exhaust systems in diesel engines has been used to reduce harmful emissions from them. An unsteady gas flow analysis in 3D format of the intake and exhaust systems was inefficient due to the need for a high-resolution workstation and enormous time for analysis. Therefore, a 1D-3D coupling algorithm was developed to resolve this issue. The algorithm was based on the method of characteristics coded in the C language for ID, and utilized ANSYS FLUENT R15.0, a commercial computation fluid dynamics program for 3D. The 1D-3D coupling method employed a User-Defined Function to share the computation between ID and 3D. Numerical analyses of unsteady gas flow in a pipe system were performed under four conditions including ID, 3D, 1D-3D and 3D-1D coupling. As a result, the characteristics of gas flow including pressure and velocity distributions were similar and the calculation time of 1D-3D coupling model was 11.46 times faster than in 3D. Therefore, the proposed algorithm was strongly expected to enhance the results and shorten the calculation time.

A CFD study of wet gas metering over-reading model under high pressure

The venturi flow meter is increasingly being preferred in multiphase flow measurement because of its shorter upstream and downstream straight sections, less influenced by the flow pattern and relatively small pressure loss. However, when the venturi is used for wet gas measurement, the over-reading phenomenon occurs due to the presence of a small amount of liquid. Many scholars have established over-reading models to correct the measured values of wet gas. Regrettably, the applicability of these over-reading models under actual high pressure operating conditions has not been verified. Therefore, this review focuses on numerical simulation of the flow of wet gas in the venturi tube under high pressure conditions (11MPa/13MPa/15 MPa). The discrete phase model (DPM) and the standard k-ε model was employed in this review. The simulations results reveals the flow characteristics of wet gas in venturi tube, which includes the flow field distributions, droplet concentration distributions and wall pressure profile distributions, and indicates that the over-reading values increases with the increase of Lockhart-Martinelli parameters and gas volume flow rate, but decreases with the increase of pressure. Moreover, the ISO model has the best performance under high pressure conditions.

The effect of gas migration on the deformation and permeability of coal under the condition of true triaxial stress

The dynamic characteristics of gas flow are often not considered in a true triaxial stress environment, making the simulation test hard to meet the requirement for coal and gas outburst in reality. To solve this issue, we investigated the deformation and gas flow characteristics of coal-like briquette under true triaxial stress conditions using self-developed triaxial servo-controlled seepage equipment for fluid-solid coupling of coal containing methane. Analysis of the experimental data revealed the relationship of coal body’s stress to strain as well as the relationship of their permeability. The results showed that in the conventional triaxial and true triaxial compression seepage tests, the relationship of stress-strain-permeability varies at different stages. The stress-strain curves in the whole stress-strain process of coal show a trend of decrease after increase, while the permeability-strain curves show a trend of increase after decrease. There is a “stress-sensitive zone” in the influence of the intermediate principal stress on the minimum permeability of the coal. The gas pressure promotes the “fluctuation” strain of the coal body, resulting in an instantaneous increase in the strain rate. The research provides the experimental basis for studying the permeability of coal body in the true triaxial stress environment.

Experimental study on flow characteristics of gas transport in micro- and nanoscale pores

Gas flow behavior in porous media with micro- and nanoscale pores has always been attracted great attention. Gas transport mechanism in such pores is a complex problem, which includes continuous flow, slip flow and transition flow. In this study, the microtubes of quartz microcapillary and nanopores alumina membrane were used, and the gas flow measurements through the microtubes and nanopores with the diameters ranging from 6.42 μm to 12.5 nm were conducted. The experimental results show that the gas flow characteristics are in rough agreement with the Hagen-Poiseuille (H-P) equation in microscale. However, the flux of gas flow through the nanopores is larger than the H-P equation by more than an order of magnitude, and thus the H-P equation considerably underestimates gas flux. The Knudsen diffusion and slip flow coexist in the nanoscale pores and their contributions to the gas flux increase as the diameter decreases. The slip flow increases with the decrease in diameter, and the slip length decreases with the increase in driving pressure. Furthermore, the experimental gas flow resistance is less than the theoretical value in the nanopores and the flow resistance decreases along with the decrease in diameter, which explains the phenomenon of flux increase and the occurrence of a considerable slip length in nanoscale. These results can provide insights into a better understanding of gas flow in micro- and nanoscale pores and enable us to exactly predict and actively control gas slip.

Multiscale analysis of flow patterns in the dense‐phase pneumatic conveying of pulverized coal

AbstractFour typical flow patterns in the vertical pipe of the dense‐phase pneumatic conveying of pulverized coal were obtained, namely packed bed flow, plug flow, churn flow and less dense phase flow. The electrical capacitance tomography (ECT) was used for space–time multiscale analysis. Firstly, Daubechies second order wavelet transform and rescaled range analysis(R/S) were applied for the scientific multiscale decompositions. The multiscale frequency range is that the microscale signal is d1–d5 (2.1875, 70.0000) Hz, the mesoscale signal is d6 and d7 (0.5469, 2.1875) Hz and the macroscale signal is d8–d11 (0.0342, 0.5469) Hz. The multiscale ECT signal characteristics of pure gas flow, particle–wall friction, and particle–particle collision were determined by experiments. The multiscale ECT signal energy matrix is proposed, based on the multiscale energy structure characteristics. Control mechanisms and multiscale statistical rules of four typical flow patterns are obtained. This study provides theoretical support for the study of flow pattern transformation of dense‐phase pneumatic conveying.

Flow Field Characteristics in the Combustion Space of a Float Glass Furnace with Co-combustion of Heavy Oil and Petroleum Coke

A numerical simulation was carried out for the combustion space of a float glass furnace in which the heavy oil and petroleum coke were co-fired. The characteristics of gas flow in the combustion space and its influence on the temperature distribution were analyzed. The research shows that after the combustion air coming from inlet 2 to inlet 6 respectively enters the flame space, it flows toward the outlet, and forms a relatively straight “flame” after the fuel is completely burned, eventually forming five high-temperature zones with wide coverage; when the flue gas generated by the combustion reaches the outlet, a part of the flue gas from inlet 2 to inlet 4 is deflected to the left, and a recirculation zone is formed above the batch material zone at the left end, and the O2 is diluted, so that the fuel at No. 2 zone is not sufficiently burned, resulting in a temperature region being significantly lower than other regions; A part of the flue gas at No. 5 and No. 6 is deflected to the right, forming a recirculation zone above the clarification zone at the right end, so that the combustion at No. 7 is insufficient, resulting in a lower temperature zone at that place, but the influence is weaker than that at No. 1, so the temperature peak at No. 7 is slightly higher than that at No. 1.

The hydrogen flow characteristics of the multistage hydrogen Knudsen compressor based on the thermal transpiration effect

Multistage hydrogen Knudsen compressor based on the thermal transpiration effect has very exciting prospect for the hydrogen transmission in the micro devices. Understanding of the hydrogen flow characteristic is the key issue for the designs and applications of the hydrogen energy systems. Firstly, the numerical models of the multistage hydrogen Knudsen compressor are established. The distributions of the rarefaction, velocity and temperature at different stages of the hydrogen flow are calculated and presented. Moreover, the dimensional pressure increases of the hydrogen gas flow are analyzed, and the flow behaviors in the microchannel and the connection channel are discussed. Secondly, the numerical simulation at different connection channel height is implemented, and the hydrogen gas flow characteristics in the connection are analyzed. Especially, the performances of the pressure drop in the connection channel under different channel heights are studied, and the hydrogen gas compression characteristics of different cases are compared and discussed. Also, the effect of the connection channel height on the hydrogen gas pressure increase in the microchannel is investigated. The studies presented in this paper could be greatly beneficial for the hydrogen detection and transmission.

Flow characteristics of supersonic gas passing through a circular micro-channel under different inflow conditions**Project supported by the National Natural Science Foundation of China (Grant No. 11802264) and the Natural Science Foundation of Jiangsu Province, China (Grant No. BK20180896).

Gas flow in a micro-channel usually has a high Knudsen number. The predominant predictive tool for such a micro-flow is the direct simulation Monte Carlo (DSMC) method, which is used in this paper to investigate primary flow properties of supersonic gas in a circular micro-channel for different inflow conditions, such as free stream at different altitudes, with different incoming Mach numbers, and with different angles of attack. Simulation results indicate that the altitude and free stream incoming Mach number have a significant effect on the whole micro-channel flow field, whereas the angle of attack mainly affects the entrance part of micro-channel flow field. The fundamental mechanism behind the simulation results is also presented. With the increase of altitude, thr free stream would be partly prevented from entering into micro-channel. Meanwhile, the gas flow in micro-channel is decelerated, and the increase in the angle of attack also decelerates the gas flow. In contrast, gas flow in micro-channel is accelerated as free stream incoming Mach number increases. A noteworthy finding is that the rarefaction effects can become very dominant when the free stream incoming Mach number is low. In other words, a free stream with a larger incoming velocity is able to reduce the influence of the rarefaction effects on gas flow in the micro-channel.

Experimental Simulation of the Zones Characteristics Considering Oily Bubble Behavior During in Situ Combustion

A linear combustion tube experiment with halfway fire extinguishing was utilized to reconstruct the combustion region distributions based on apparent characteristics of burnt oil-bearing quartz, temperature profile, and oil saturation field distribution between a gas injection well and a production well, etc. The gas composition and fluid composition in each region could be obtained. Following, a high-temperature-high-pressure visualization system was utilized to simulate experimentally the flue-gas flow in the crude oil. A flow characteristics simulation using such process parameters as system injected fluid composition and temperature condition based on the above test results of the combustion tube was conducted. The characteristics of each region were qualitatively described, the flow characteristics of the flue gas was visualized, and the oil bubble enhancement mechanism causing crude oil movement with flue gas was semiquantitatively determined. The results of the combustion tube simulation showed tha...

Numerical modeling of aerosol deposition process

Aerosol Deposition (AD) method is an emerging coating process for deposition of ceramic particles for industrial applications such as MEMS, fuel cells, optical devices and radio frequency components. In this process, various parameters such as nozzle geometry, powder size and type, pressure inside the deposition chamber, and carrier gas flow rate have significant influence on the in-flight particle behavior before impact, and therefore, on the coating properties. In this study, a two-way coupled Eulerian-Lagrangian model is used to study the effects of gas flow rates and substrate location on the gas flow characteristics, bow shock near the substrate, and more importantly on the particle velocity and trajectory upon impact. The study is carried out with a rectangular sonic nozzle. To validate our simulations, locations of the Mach disks in highly under-expanded free-jet conditions are compared with the theoretical and experimental results in the literature. Two different computational geometries are utilized; a 2D planar and a quarter slice of 3D. It is found that, for the rectangular nozzle, the 3D geometry produces more accurate results and can capture the axis-switching phenomenon. Moreover, it is observed that the gas flow structure as well as the in-flight particle behavior obtained from 2D and 3D geometries are almost identical before the Mach disk. In addition, two different drag expressions are employed and it is shown that the influence of Mach and Knudsen numbers on particle behavior in vacuum condition is significant.

Study of Channel-Induced Convective Mass Transport in a PEMFC Using Limiting Current Method

In a proton exchange membrane fuel cell (PEMFC), oxygen transport is a critical limitation for operating at high current density due to sluggish Oxygen Reduction Reaction (ORR). Total oxygen transport resistance includes losses from channel, diffusion media, and catalyst layer. This study focuses on studying the effect of flowfield design on total oxygen transport resistance with the assist of limiting current diagnostic tool. The limiting current method is an in-situ experimental tool to study dry and wet oxygen transport resistances by varying oxygen concentration. In addition, a commercial finite element simulation software, COMSOL Multiphysics, is employed to elucidate gas flow characteristics in the channel and diffusion media. In this work, we designed and fabricated a novel three-dimensional channel and compared with a baseline straight rectangular channel as shown in Figure 1. The novel 3-D channel has converging-diverging nozzle like design. Therefore, the oxygen gas is being directed in and out of the diffusion media when entering and exiting the throat area, respectively. In addition, the alternating nature of the neighboring channel enables cross flow through the diffusion media. As confirmed by the Comsol simulation, convective gas flux is induced inside the diffusion media rather than pure diffusion mechanism observed in conventional channel design (Figure 1a). All fuel cell tests were done with baseline materials, which consist of wet-proofed Toray-H-060 coated with microporous layer and NR211 membrane electrode assembly from Ion Power. The limiting current results show that the novel 3-D channel design has significant lower total oxygen transport resistance compared to conventional straight channel design under both dry and wet conditions. As a result, 3-D channel design shows much improved fuel cell performance under wet operating condition. Detail experimental and simulation results will be shared at the conference. Figure 1

FORMATION OF THE SUPERSONIC HETEROGENEOUS STREAMS IN THE GASDYNAMIC ACCELERATORS WITH GREAT ELONGATION

The present article describes results of the experimental and theoretical investigation of gas dynamics and heat exchange in the course of a supersonic flow of the gas-powder mixture within the axially symmetric gas-dynamic accelerators, which have small critical cross-sections (dcritical from 1 to 3 mm) and substantial elongation (L/dcritical from 70 to 200). The necessity of performance of such investigations was determined by two aspects. The first is the development of the innovative technologies with the purpose of formation of the heat-resistant coatings and other coatings with various functions and necessary properties (formation of such coatings with the help of supersonic heterogeneous streams). The second is the creation of the supersonic heterogeneous streams, which are required for the development of experimental investigations of processes of the erosive and corrosive wear of structural components of the high-speed air vehicles, which conduct flights in atmospheric anomalies (rain clouded sky and dust-in-air conditions). This study describes the entire cycle of the experimental investigations, which were performed with the purpose of construction of the more reliable mathematical model of flow of the nonisentropic heterogeneous streams in the gas-dynamic accelerators with great elongation. The viscous gas flow parameters were calculated using the classical model of a flat boundary layer. The value of the characteristics of the carrier gas flow, the dispersion of particles and their material for accelerating particles in a heterogeneous flow were found out. The study showed that the design of gasdynamic micro accelerators must be carried out taking into account the increase in the thickness of the boundary layer along the walls of the particle accelerator. In addition, this article presents a more detailed description of gas dynamics of flow and heat exchange of the heterogeneous mixtures within supersonic gasdynamic accelerators with mass concentration of the powder particles ("К-phase") in the stream up to 15%.

Optimal design for real-time quantitative monitoring of sand in gas flowline using computational intelligence assisted design framework

Abstract Global demand for oil and gas is still increasing rapidly. The direct consequence of this is the increased operating pressure amid concerns over increasing sand production. According to the Society of Petroleum Engineers (SPE), 70% of the world's hydrocarbon reserves are contained in reservoirs situated on unconsolidated formations. Given the reality of these formations, sand production will certainly be a problem of significant concern particularly during the later life of the fields when they become more ‘mature’. However, to monitor sand and optimise its production for improved recovery and safety, life extension and economy of the fields and ensured reliability, the automatic detection and prediction of sand flow characteristic measurements; sand flow rate (SFR), sand concentration (SC), line pressure drop (PD), and gas velocity (GV), has become an important research topic of great interest. Despite this importance, discussion of the topic is still lacking in the literature. This paper proposes a novel and robust architecture of intelligent real-time sand flow characteristic measurement using an acoustic sensor and computational intelligence assisted design (CIAD) framework. It fully incorporates acoustic signal processing and analysis, prediction algorithms and optimisation algorithms in the design. Acoustic features based on acoustic signal processing techniques are extracted to reduce the dimensionality of the acoustic signals. A classical Artificial Neural Network (ANN) is used to model the non-linear relationships between the acoustic signal characteristics and the flow characteristics measurands. In addition, the ANN algorithm adapts its weights and biases using the Grey Wolf Optimiser (GWO) through minimisation of the cost function during the training phase. Preliminary results obtained on a laboratory test rig demonstrate that an acoustic sensor coupled with CIAD may provide simple and robust practical solution to the measurement problem of particle-laden gas flow characteristics in real-time.

Numerical analysis of the momentum and heat transfer in an atmospheric pressure dielectric barrier discharge

In this paper, the momentum and heat transfer between charged particles and neutral particles in a needle-to-plane dielectric barrier discharge reactor with Ar as the working gas are simulated. In this simulation, the heat transfer from ions to the neutral atom is described by the interaction term between ions and atoms. Detailed discharge reaction mechanisms are considered in the simulation including metastable atom. The Navier-Stokes equation is solved in combination with the Poisson equation and the charged particles drift-diffusion equations. The interrelation between the gas discharge and the gas flow characteristics are preliminary revealed. In particular, when the streamer strikes the cathode, the maximum gas temperature can reach 1026 K, and the high temperature area is concentrated in a confined space around the needle cathode tip with a thickness of 0.01 mm and a diameter of 0.1 mm. Then, the temperature change decreases to 400 K in 1 μs. Induced by the discharge, the pressure perturbation of the gas can exceed 6×104 Pa at 1.1 μs, and an expanding wave is created. The propagation velocity of the expanding wave is close to the sound velocity. The forward velocity decreases from approximately 120 m/s at 1.1 μs to 5.5 m/s at 4.4 μs. The inverted velocity remains at approximately 5 m/s. The number density for the neutral particles has a minimum value, which is approximately 8×1024 m-3, in the sheath as well as changes in the expanding wave propagation in the plasma bulk.