Identifying the enhancement mechanism of Al/MoO_(3) reactive multilayered films on the ignition ability of semiconductor bridge using a one-dimensional gas-solid two-phase flow model

Energetic Semiconductor bridge(ESCB)based on reactive multilayered films(RMFs)has a promising application in the miniature and intelligence of initiator and pyrotechnics device.Understanding the ignition enhancement mechanism of RMFs on semiconductor bridge(SCB)during the ignition process is crucial for the engineering and practical application of advanced initiator and pyrotechnics devices.In this study,a one-dimensional(1D)gas-solid two-phase flow ignition model was established to study the ignition process of ESCB to charge particles based on the reactivity of Al/MoO_(3) RMFs.In order to fully consider the coupled exothermic between the RMFs and the SCB plasma during the ignition process,the heat release of chemical reaction in RMFs was used as an internal heat source in this model.It is found that the exothermal reaction in RMFs improved the ignition performance of SCB.In the process of plasma rapid condensation with heat release,the product of RMFs enhanced the heat transfer process between the gas phase and the solid charge particle,which accelerated the expansion of hot plasma,and heated the solid charge particle as well as gas phase region with low temperature.In addition,it made up for pressure loss in the gas phase.During the plasma dissipation process,the exothermal chemical reaction in RMFs acted as the main heating source to heat the charge particle,making the surface temperature of the charge particle,gas pressure,and gas temperature rise continuously.This result may yield significant advantages in providing a universal ignition model for miniaturized ignition devices.

Near-source characteristics of two-phase gas-solid outbursts in roadways

Coal and gas outbursts compromise two-phase gas-solid mixtures as they propagate as shock waves and flows from their sources.Propagation is influenced by the form of the outburst,proximity to source,the structure and form of the transmitting roadways and the influence of obstacles.The following characterizes the propagation of coal and gas outbursts as two-phase gas-solid flows proximal to source where the coupled effects of pulverized coal and gas flows dominate behavior.The characteristics of shock wave propagation and attenuation were systematically examined for varied roadway geometries using experiments and numerical models.The results demonstrate that the geometry of roadway obstructions is significant and may result in partial compression and sometimes secondary overpressurization in blocked and small comer roadways leading to significant attenuation of outburst shock waves.The shock waves attenuate slowly in both straight and abruptly expanding roadways and more significantly in T-shaped roadways.The most significant attenuation appears in small angle comers and bifurcations in roadways with the largest attenuation occurring in blocked roadways.These results provide basic parameters for simplifying transport in complex roadway networks in the far-field,and guidance for the design of coal and gas outburst prevention facilities and emergency rescue.

Numerical simulation of the gas-solid two-phase flow inside the multi-channel nozzle for the surface nanocrystallization induced by the ultrasonic particulate peening

Using a gas-solid two-phase model(a discrete phase model),the authors investigated the flow field inside the multi-channel nozzle for surface nanocrystallization(SNC)induced by the ultrasonic particulate peening(USPP).By computation,the velocity fields of both the gas and the solid phases were simulated and the track of the solid phase was analyzed in detail.It can be found that the velocities of the two phases are able to reach an ultrasonic level;meanwhile,the dispersion width of the solid phase at the nozzle exit is less than that of the gas phase.When particle diameters are less than 5 μm,there is a decreasing trend in the dispersion width of the solid phase with an increase in particle diameters.The trend becomes stable as the particle diameters are greater than 5 μm;in the meantime,the distribution of solid particles is near the axis of the jet flow.The optimal standoff distance between the nozzle and the substrate in the process of USPP is about 120 mm.Simulation results can help improve the design of mass-production-oriented multi-channel nozzles for SNC induced by USPP.

Particle modulations to turbulence in two-phase round jets

The particle modulations to turbulence in round jets were experimentally studied by means of two-phase velocity measurements with Phase Doppler Anemometer （PDA）. Laden with very large particles, no significant attenuations of turbulence intensities were measured in the farfields, due to small two-phase slip velocities and particle Reynolds number. The gas-phase turbulence is enhanced by particles in the near-fields, but it is significantly attenuated by the small particles in the far-fields. The smaller particles have a more profound effect on the attenuation of turbulence intensities. The enhancements or attenuations of turbulence intensities in the far-fields depends on the energy production, transport and dissipation mechanisms between the two phases, which are determined by the particle prop- erties and two-phase velocity slips. The non-dimensional parameter CTI is introduced to represent the change of turbulence intensity.

Numerical Simulation of the Gas-solid Two-phase Flows in a Precalciner

The gas-solid two-phase flous of the precalciner were simulated by different multiphase models,such as mixture model,the Enderium model,including mixture and dispersed,and discrete phase model（DPM）,The results of the different multiphase models were analyzed and compared.showing the rationality of the diffusion and mixture of the cenment raic meals and coal poroder some extent Moreover,the results also shose the rationality of the given inlets parameters of actual process of the precalciner.

PREDICTIONS OF 3-D STRONGLY SWIRLING GAS-SOLID TWO-PHASE FLOW WITH GAS COMBUSTION

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NUMERICAL MODELING OF TURBULENTEVAPORATING GAS-DROPLET TWO-PHASE FLOWS IN AN AFTERBURNER DIFFUSOR OF TURBO-FAN JET ENGINES

The two-dimensional turbulent evaporating gas-droplet two-phase flows in an afterburner diffusor of turbo-fan jet engines are simulated by the k-ε turbulence model and the particle trajectory model. Comparison of predicted gas velocity and temperature distributions with experimental results for the cases without liquid spray shows pretty good agreement. Gas-droplet two-phase flow predictions give plausible droplet trajectories, fuel-vapor concentration distribution, gas-phase velocity and temperature field in presence of liquid droplets. One run of computation with this method is made for a particular afterburner. The results indicate that the location of the atomizers is not favorable to flame stabilization and combustion efficiency. The proposed numerical modeling can also be adopted for optimization design and performance evaluation of afterburner combustors of turbo-fan jet engines.

A Numerical Sirnulation of Gas-Particle Two-Phase Flow in a Suspension Bed Using DifFusion Flux Model

A mathematical modei of two-dimensional turbulent gas-particle twophase flow based on the modified diffusion flux modei (DFM) and a numerical simulation method to analyze the gas-particle flow structures are developed. The modified diffusion flux modei, in which the acceleration due to various forces is taken into account for the calculation of the diffusion velocity of particles, is applicable to the analysis of multi-dimensional gas-particle two-phase turbulent flow. In order to verify its accuracy and efficiency, the numerical simulation by DFM is compared with experimental studies and the prediction by k-ε-kp two-fluid modei, which shows a reasonable agreement. It is confirmed that the modified diffusion flux modei is suitable for simulating the multi-dimensional gas-particle two-phase flow.

Deduction and Validation of an Eulerian-Eulerian Model for Turbulent Dilute Two-Phase Flows by Means of the Phase Indicator Function-Disperse Elements Probability Density Function

A statistical formalism overcoming some conceptual and practical difficulties arising in existing two-phase flow (2PHF) mathematical modelling has been applied to propose a model for dilute 2PHF turbulent Hows. Phase interaction terms with a clear physical meaning enter the equations and the formalism provides some guidelines for the avoidance of closure assumptions or the rational approximation of these terms. Continuous phase averaged continuity, momentum, turbulent kinetic energy and turbulence dissipation rate equations have been rigorously and systematically obtained in a single step. These equations display a structure similar to that for single-phase flows. It is also assumed that dispersed phase dynamics is well described by a probability density function (pdf) equation and Eulerian continuity, momentum and fluctuating kinetic energy equations for the dispersed phase are deduced. An extension of the standard k-e turbulence model for the continuous phase is used. A gradient transport model is adopted for the dispersed phase fluctuating fluxes of momentum and kinetic energy at the non-colliding, large inertia limit. This model is then used to predict the behaviour of three axisymmetric turbulent jets of air laden with solid particles varying in size and concentration. Qualitative and quantitative numerical predictions compare reasonably well with the three different sets of experimental results, studying the influence of particle size, loading ratio and flow confinement velocity.

Effects of the nozzle structure and fluidized gas composition on the gas-particle two-phase jet characteristic in a powder fuel scramjet

The interaction between nozzle design and fluidization gas composition significantly influences the dynamics within a powder fuel scramjet's combustion chamber.To investigate this relationship,an experimental study utilized high-speed shadow imaging technology to explore the macroscopic aspects of powder fuel injection.The investigation examined various convergence angles,nozzle throat lengths,and fluidized gas compositions.Key findings include:During jet development,powder fuel initially concentrates near the axis,with non-convergence angle nozzles exhibiting longer concentrated distribution periods than convergence angle conditions.Decreasing nozzle convergence angles lead to increased penetration distance,frontal velocity,and radial diffusion distance during the initial stages of jet development.Additionally,stable jet shapes show larger divergence angles as nozzle convergence angle decreases,with the largest divergence angle observed atα=60°.In the initial 0-7 ms of jet development,the powder fuel jet demonstrates greater penetration distance and frontal velocity under certain conditions.Moreover,penetration distance and frontal velocity increase with throat length from 7 to 20 ms,accompanied by changes in divergence angles.Specifically,at a throat length(l)of 2 mm,the near-field divergence angle measures 46.50°,and the far-field divergence angle is 22.25°.Conversely,at l=8mm,the near-field divergence angle is 33.49°,and the far-field divergence angle is 23.21°.The fluidization gas composition minimally affects jet penetration distance and frontal velocity during the initial 0-3 ms.However,due to hydrogen's low density,hydrogen/powder fuel jets exhibit shorter distances and velocities compared to nitrogen/powder fuel jets.Hydrogen fluidization also results in larger divergence angles,particularly in the near field.These findings underscore the importance of nozzle design and fluidization gas composition in optimizing scramjet performance and efficiency.

LBE-DEM coupled simulation of gas-solid two-phase cross jets

This paper establishes a lattice Boltzmann equation-discrete element method (LBE-DEM) coupled simulation method under the Eulerian-Lagrangian framework at first, and applies it to simulating a two-dimensional gas-solid two-phase cross jet. The gas phase is simulated by the lattice-Boltzmann method via the TD2G9 model; the solid phase is traced by the Lagrangian method and the inter-particle collision is calculated by the DEM method. Three values of the Stokes number St=10, 25, and 50 are simulated under the same mass loading. This paper focuses on the characteristics of vortex structure, particle distribution, and the reverse-flow/rebounding rate in cross jets. We analyze the characteristics of fluid vortex motion, particle cluster distribution, rebounding rate of particles and the influencing factors for them. The results show the existence of joint distribution of discrete clusters and discrete particles in cross jets. Meanwhile, it shows that a larger concentration of particles in the early stage of jet evolution or a smaller Stokes number under the same mass loading can produce a larger rebounding rate. However, the rebounding rate of particles at the late stage, in general, is stable.

Critical Stokes Number for Gas-Solid Flow Erosion of Wind Turbine Airfoil

Wind turbine blades are inevitable to be eroded in wind-sand environment,so it is crucial to identify the flow conditions under which the erosion happens.Here,the effect of the sand diameter on wind turbine airfoil is first investigated.When the sand diameter is less than 3μm,the sands will bypass the airfoil and no erosion occurs.When the sand diameter is larger than 4μm,the sand grains collide with the airfoil and the erosion happens.Thus,there must be a critical sand diameter between 3μm and 4μm,at which the erosion is initiated on the airfoil surface.To find out this critical value,aparticle Stokes number is introduced here.According to the range of the critical sand diameter mentioned above,the critical value of particle Stokes number is reasonably assumed to be between 0.007 8and 0.014.The assumption is subsequently validated by other four factors influecing the erosion,i.e.,the angle of attack,relative thickness of the airfoil,different series airfoil,and inflow velocity.Therefore,the critical range of Stokes number has been confirmed.

Large-eddy Simulation of Bubble-Liquid Confined Jets

The Large-eddy simulation (LES) with two-way coupling is used to study bubble-liquid two-phase confined multiple jets discharged into a 2D channel.The LES results reveal the large-eddy vortex structures of both liquid flow and bubble motion,the shear-generated and bubble-induced liquid turbulence,and indicate much stronger bubble fluctuation than that of the liquid,the enhancement of liquid turbulence by bubbles.Both shear and bubble-liquid interaction are important for the liquid turbulence generation in the case studied.

PARALLEL ADAPTIVE SIMULATION OF A PLUNGING LIQUID JET

This paper is concerned with three-dimensional numerical simulation of a plunging liquid jet. The transient processes of forming an air cavity around the jet, capturing an initially large air bubble, and the break-up of this large toroidal-shaped bubble into smaller bubbles were analyzed. A stabilized finite element method （FEM） was employed under parallel numerical simulations based on adaptive, unstructured grid and coupled with a level-set method to track the interface between air and liquid. These simulations show that the inertia of the liquid jet initially depresses the pool＇s surface, forming an annular air cavity which surrounds the liquid jet. A toroidal liquid eddy which is subse- quently formed in the liquid pool results in air cavity collapse, and in turn entrains air into the liquid pool from the unstable annular air gap region around the liquid jet.

Numerical simulation of slurry jets using mixture model

Slurry jets in a static uniform environment were simulated with a two-phase mixture model in which flow-particle interactions were considered. A standard k-e turbulence model was chosen to close the governing equations. The computational results were in agreement with previous laboratory measurements. The characteristics of the two-phase flow field and the influences of hydraulic and geometric parameters on the distribution of the slurry jets were analyzed on the basis of the computational results. The calculated results reveal that if the initial velocity of the slurry jet is high, the jet spreads less in the radial direction. When the slurry jet is less influenced by the ambient fluid （when the Stokes number St is relatively large）, the turbulent kinetic energy k and turbulent dissipation rate e, which are relatively concentrated around the jet axis, decrease more rapidly after the slurry jet passes through the nozzle. For different values of St, the radial distributions of streamwise velocity and particle volume fraction are both self-similar and fit a Gaussian profile after the slurry jet fully develops. The decay rate of the particle velocity is lower than that of water velocity along the jet axis, and the axial distributions of the centerline particle streamwise velocity are self-similar along the jet axis. The pattern of particle dispersion depends on the Stokes number St. When St = 0.39, the panicle dispersion along the radial direction is considerable, and the relative velocity is very low due to the low dynamic response time. When St = 3.08, the dispersion of particles along the radial direction is very little, and most of the particles have high relative velocities along the streamwise direction.

Large eddy simulation of a particle—laden turbulent plane jet

Gas solid two-phase turbulent plane jet is applied to many natural s it uations and in engineering systems. To predict the particle dispersion in the ga s jet is of great importance in industrial applications and in the designing of engineering systems. A large eddy simulation of the two-phase plane jet was con d ucted to investigate the particle dispersion patterns. The particles with Stokes numbers equal to 0 0028, 0 3, 2 5, 28 (corresponding to particle diameter 1 μm , 10 μm, 30 μm, 100 μm, respectively) in \%Re\%=11 300 gas flow were studied. The simulation results of gas phase motion agreed well with previous experimental re sults. And the simulation results of the solid particles motion showed that part icles with different Stokes number have different spatial dispersion; and that p articles with intermediate Stokes number have the largest dispersion ratio.

CFD Simulation of Dilute Gas-Solid Flow in 90^oSquare Bend

Gas-solid two-phase flow in a 90? bend has been studied numerically. The bend geometry is squared cross section of (0.15 m × 0.15 m) and has a turning radius of 1.5 times the duct's hydraulic diameter. The solid phase consists of glass spheres having mean diameter of 77 μm and the spheres are simulated with an air flowing at bulk velocity of 10 m/s. A computational fluid dynamic code (CFX-TASCflow) has been adopted for the simulation of the flow field inside the piping and for the simulation of the particle trajectories. Simulation was performed using Lagrangian particle-tracking model, taking into account one-way coupling, combined with a particle-wall collision model. Turbulence was predicted using k-ε model, wherein additional transport equations are solved to account for the combined gas-particle interactions and turbulence kinetic energy of the particle phase turbulence. The computational results are compared with the experimental data present in the literature and they were found to yield good agreement with the measured values.

Gas-solid flow field numerical simulation of different feeding and returning formations of flue-gas circulating fluidized bed

3D Euler double-fluid model was applied and three different feedstocks and reverts formations were simulated. By calculating and analyzing the state of gas and solid fluxion in absorber using three different methods of the feedstocks and reverts in recirculating fluidized bed, described the behavior of gas and solid through the gas-phase velocity, turbulence intensity, gas-solid sliding velocity, and density of particles. The results show that the feedstocks and reverts enters into absorption tower through two symmetrical feedings and are mixed with flue gas. Based on the respective analysis of each model and the com- parison analysis of the three models, this paper drew conclusions. The turbulence intensity of absorption tower is high, gas-solid sliding speed is big, and granule concentration near the axis is high, which has advantages for desulfurization and im- proving the utilization rate of absorbent.

Mixing effects of high-speed jets in gas-solid riser and downer reactors

For the high-temperature and short-contact time gas-solid reaction process,riser and downer are considered appropriate reactors.To realize an intensive and complete mixing of reactants with catalysts,the feed raw is always introduced in the form of high-speed jets.In this study,in order to investigate the mixing effects of different types of high-speed jets in riser and downer,traceable ozone is injected with the high-speed feed jets to react with catalyst particles.By detecting the decomposition of ozone,the gas-solid mixing and reaction in riser and downer under the influence of both co-current and counter-current injections are analyzed.The relative ozone concentration is used to reflect the location reaction extent and its radial nonuniformity index is proposed to compare the results in riser and downer.It is found that the jet influence zone in downer provides a relatively better environment for the mixing of feed jets with catalysts.In the riser,introduction of counter-current injections could improve the uniformity of gas-solid mixing in the initial contact region of feed with catalysts.

Transportation characteristics of gas-solid two-phase flow in a long-distance pipeline

In this study, experiments on fly ash conveying were carried out with a home-made long-distance positive-pressure pneumatic conveying system equipped with a high performance electrical capacitance tomography system to observe the transient characteristics of gas-solid two-phase flow. The experimen- tal results indicated that solids throughput increased with increasing solids-gas ratio when the conveying pipeline was not plugged. Moreover, the optimum operating state was determined for the 1000 m long conveying pipeline with a throttle plate of 26 orifices. At this state the solids throughput was about 12.97 t/h. Additionally, the transportation pattern of fly ash gradually changed from sparse-dense flow to partial and plug flows with increasing conveying distance because of the conveying pressure loss, These experimental results provide important reference data for the development of pneumatic conveying technology.