Two-phase Gas-particle Research Articles

An Open-Source Code for High-Speed Non-Equilibrium Gas–Solid Flows in OpenFOAM

This paper details the development and verification tests of an open-source code named hy2LPTFoam intended for solving high-speed non-equilibrium gas-particle flows in OpenFOAM. The solver, based on hy2Foam for high-speed non-equilibrium gas flow, integrates multiple particle force models, heat transfer models, the diffusion-based smoothing method, and the MPPIC method. The verification tests incorporate interactions between shock waves and particle curtains with varying particle volume fractions, a JPL nozzle generating a two-phase gas–particle flow, and a Mars entry body with two particle inflow mass fractions. The tests yield good physical agreement with numerical and experimental data from the literature.

МЕТОДЫ ПРОЕКТИРОВАНИЯ ПНЕВМАТИЧЕСКИХ СИСТЕМ

In this paper, the parameters of a two-phase heterogeneous gas-particle flow (for example, “airseed”) are shown using the example of mathematical modeling of technological processes of a pneumatic system of a grain seeder. It is proposed to apply the mechanics of two-phase gas-particle flow to the theoretical description of the processes of motion and distribution of solid particles in pneumatic systems. The results of the study establish the possibility of using these methods to analyze and optimize the pneumatic system of grain seeders. Practical and theoretical methods were used to determine the air flow and speed of movement of seeds of various crops in pneumatic systems of grain drills. The values of the seed resistance coefficients necessary for mathematical modeling of the technical processes of the pneumatic system are also presented. The research will make it possible to effectively simulate the operation of the pneumatic system of the sowing complex using the mechanics of two-phase flows and computational fluid dynamics methods.

Dusty Gas Flow past Bodies under Scattering of Rebounded Particles

Two-phase gas-particle flow over a flat plate of finite thickness in a channel at a high subsonic velocity and supersonic transverse flow past a cylinder are considered. The leading edge of the plate is wedge-shaped or represents a smooth bluntness of constant radius. The wedge surface and the front bluntness are specified both smooth and rough. The roughness is modeled by a two-dimensional profile based on an experiment. Spherical particles and a mixture of particles in the form of ellipsoids of revolution, rectangular prisms, prisms with flat-cut vertices, and tetrahedrons are considered. The parameters of each of the forms vary. The impact interaction model proposed earlier and consistent with the experimental data on the coefficients of restitution of the center-of-mass velocity is used to determine the translational and rotational velocities of non-spherical particles after rebound. Along with monosized particles, a dispersed phase with a spread of particles in size is considered. The role of the studied factors of random nature which affect the flow pattern and the dispersed phase parameters is found.

On the Structure of a Viscous Shock-Front in a Two-Phase Gas–Particle Medium

On the Structure of a Viscous Shock-Front in a Two-Phase Gas–Particle Medium

Numerical Simulation of the Flow in Two-Phase Supersonic Underexpanded Gas–Particle Jets Exhausting into a Slotted Submerged Space

A simplified 2D model for calculating two-phase gas–particle flows in a slot space has been developed. The model can be used for fast calculation and estimation of supersonic-flow parameters in the slot space. Using this model, a numerical simulation of the flow in two-phase gas–particle supersonic jets exhausting into a submerged slot space bounded by two parallel disks was performed. The presence of particles led to the splitting of the gas jet into an internal two-phase jet and an external gas jet. In the present study, we investigated the structure of a two-phase jet as dependent on the spacing between the disks for conditions of cold spraying. A new effect was found in the flow at a small spacing between the disks (of the order of 0.2 mm) and a high-velocity internal two-phase gas–particle jet was formed. The distribution of the concentration of particles in the particle jet proved to be essentially non-uniform, with a caustic formed at the upper jet boundary.

Numerical study on powder fuel injection characteristics of powder fuel scramjet

Powder fuel injection is an attractive technique for powder fuel scramjets and plays an important role in numerically investigating the particle velocity and concentration distribution in powder fuel injection. In this study, the coupled model of computational fluid dynamics-discrete element method (CFD-DEM) was used to simulate the flow of aluminium powder in the nozzle. Firstly, the flow field characteristics of gas-phase and two-phase gas-particle were compared. The results show that the particle disturbance has a great influence on the convection field, in which the maximum velocity of gas-phase is reduced by 47.15%, the acceleration distance is shortened by 34.18%, and the minimum velocity is reduced by 41.48%. Secondly, particle velocity and concentration distributions under different nozzle convergence angles were compared, and their correlations with the nozzle convergence angle, particle collision, and gas-particle drag force were identified. The results show that as increase in convergence angle of the nozzle, both the number of particle collisions in the nozzle and expansion angle of the particle jet at the nozzle exit have increased, while the particle velocity at the nozzle exit has decreased. The overall simulation results and analyses provide a new reference for the flow mechanism of the fuel injection process and the design of a powder conveying system for a powder fuel scramjet.

A new approach in reducing sand deposition on railway tracks to improve transportation

Abstract Aeolian particle transport involves uplift from the ground, dispersion and deposition back to the surface. Integrated effects of these processes, in general, are of great importance for a wide range of reasons mostly because of their unwanted deposition on the railway tracks, environmental impact, degradation of air quality and risks to human health. In sandy dry lands Aeolian sand accumulation on railway tracks is a major problem, since it directly affects safety of railway transportation, apart from decreasing the speed in railway transportation. The most common methods for preventing sand deposition on railway tracks like, building galleries (Gallery is a short length tunnel-shape cover which is built and installed over the railway track to avoid sand deposition. It is commonly applied in regions which are more probable of sand storm.), fences or increasing plant varieties around railway are restricted to special situations and not as effective. Efficient prevention of sand deposition is a great challenge that requires a comprehensive knowledge of wind-sand flow behavior. In the present study, an efficient 2D and 3D CFD model for simulation of two-phase gas-particle problems, as the sandy air flow, is developed. Conventional methods for preventing sand deposition on the railway track as well as an innovative method for avoiding sand deposition are presented and their effectiveness is evaluated by the proposed CFD model. It has been shown both by the CFD model and the accomplished empirical works that galleries cannot prevent sand deposition effectively. Instead, the innovative proposed method is proved to reduce sand deposition near the embankment, along with decreasing sand content of flowing wind.

Numerical simulation of reactive gas-particle flow in a solar jet spouted bed reactor for continuous biomass gasification

Solar steam gasification of beech wood biomass in a novel solar conical jet spouted bed reactor was studied. A 3D numerical model of the reactive two-phase gas-particle flow was developed and the model was experimentally validated. The cavity-type solar reactor was operated in both direct and indirect heating configurations at a constant wall temperature of 1200 °C with a biomass feeding rate that varied from 1.2 g/min to 2 g/min. Experiments showed that directly heating the particles increases the H2 yield and the carbon conversion efficiency. The Computational Fluid Dynamics (CFD) model was developed to thoroughly investigate the biomass conversion process inside the conical jet spouted bed subjected to direct or indirect solar irradiations. The desired vigorous cyclic flow pattern of the biomass particles was accurately predicted by the model with peak particles velocity of 2 m/s in the spout region. The maximum temperature reached by the indirectly-irradiated particles is about 1200 °C while it is above 1500 °C when considering directly-irradiated particles. Direct heating thus increases both particles gasification rates and carbon conversion efficiency. Furthermore, simulations reveal that the reaction zone temperature is 100 °C higher for the direct heating configuration. This promotes the H2 formation at the expense of CH4. The steam oxidant concentration, gas products distribution and particles trajectories inside the cavity were also investigated to identify improvement strategies for enhancing the phase mixing and the gas/solid residence time.

On the Strong Spherical Shock Waves in a Two-Phase Gas–Particle Medium

In this paper, power series solutions for strong spherical shocks of time dependent variable energy propagating in a two-phase gas-particle medium are presented taking into consideration the power series solution technique (Sakurai in J Phys Soc Jpn 8:662-669,1953; Freeman in J Phys D Appl Phys 2(1):1697-1710,1968). Assuming the medium to be a mixture of a perfect gas and small solid particles, the power series solutions are obtained in terms of M^-2, where M is the upstream Mach number of shock. This investigation presents an overview of the effects due to an increase in (i) the propagation distance from the inner expanding surface and, (ii) the dust loading parameters on flow-field variables such as the velocity of fluid, the pressure, the density, and also on the speed of sound, the adiabatic compressibility of mixture and the change-in-entropy behind the strong spherical shock front.

Influence of offset angle of mid-secondary air nozzles on gas-particle flow characteristics in a furnace.

A three-component particle-dynamics anemometer was used to measure the characteristics of two-phase gas-particle flows in a primary air nozzle using a gas/particle two-phase test facility. The jet trajectory of primary air velocities, Reynolds stress and particle concentration profiles were obtained. Based on this, the advantages and disadvantages of increasing the offset angle were analyzed to optimize performance. The results show that gas-particle slippage is not noticeable in the furnace, even though the mid-secondary air offset angle changes. Within the jet's free developing zone, the location of the peak concentration does not change with the mid-secondary air offset angles. Properly enlarging the offset angle of mid-secondary air nozzles will delay the mixing of the secondary air into the primary-air-and-coal mixture and realize horizontal-staged combustion in a furnace. It also can enhance the stability of airflow and form a better blended jet tail, meanwhile reducing the vortex at the back-fire side and avoiding a short circuiting of the airflow. It is favorable for increasing combustion efficiency and preventing slagging and high-temperature corrosion.

Numerical tracking of sorbent particles and distribution during gas desulfurization in pulverized coal-fired furnace

Furnace sorbent injection for sulfur removal from flue gas presents a challenge, as the proper process optimization is of crucial importance in order to obtain both high sulfur removal rates and good sorbent utilization. In the simulations a two-phase gas-particle flow is considered. Pulverized coal and calcium-based sorbent particles motion is simulated inside of the boiler furnace. It is important to determine trajectories of particles in the furnace, in order to monitor the particles heat and concentration history. A two-way coupling of the phases is considered ? influence of the gas phase on the particles, and vice versa. Particle-to-particle collisions are neglected. Mutual influence of gas and dispersed phase is modeled by corresponding terms in the transport equations for gas phase and the equations describing the particles turbulent dispersion. Gas phase is modeled in Eulerian field, while the particles are tracked in Lagrangian field. Turbulence is modeled by the standard k-? model, with additional terms for turbulence modulation. Distribution, dispersion and residence time of sorbent particles in the furnace have a considerable influence on the desulfurization process. It was shown that, by proper organization of process, significant improvement considering emission reduction can be achieved.

CFD simulation of two-phase gas-particle flow in the Midrex shaft furnace: The effect of twin gas injection system on the performance of the reactor

In the present study a mathematical model is developed to examine the effect of dual gas injection system on the distribution of process variables and energy consumption in the Midrex shaft furnace. The developed model was constructed by considering the major chemical reactions and physical structures within the furnace and describes a counter-current moving bed reactor in which hematite pellets are reduced to sponge iron by pure hydrogen gas. Governing equations containing overall continuity, momentum, energy and mass equations are developed for both gas and solid phases in cylindrical coordinate system. Unreacted shrinking core model is implemented to simulate gas–solid reactions in the reactor. The complicated equations are solved by applying finite volume technique. The model is applied to simulate multiphase flow inside the reactor when it is equipped with one and two hydrogen gas intake ports to examine the impact of gas injection arrangement on the process variables. The radial and axial distributions of operational parameters including gas and solid temperature, fractional reduction of iron oxides and hydrogen and water vapor concentration are obtained for both cases. The results indicate that reduction degree and energy consumption are improved by utilizing dual gas injection system.

Numerical study on characteristics of turbulent two-phase gas-particle flow using multi-fluid model

The purpose of this research is to study numerically the turbulent gas-particle two-phase flow characteristics using the Eulerian-Eulerian method. A computer code is developed for the numerical study by using the k-ɛ-kp two-phase turbulent model. The developed code is applied for particle-laden flows in which the particle volume fraction is between 10−5 and 10−2 for the Stokes numbers smaller than unity. The gas and particle velocities and the particle volume fraction obtained by using this code are in good agreement with those obtained by a commercial code for the gas-particle jet flows within a rectangular enclosure. The gas-particle jet injected into a vertical rectangular 3D enclosure is numerically modeled to study the effect of the Stokes number, the particle volume fraction and the particle Reynolds numbers. The numerical results show that the Stokes number and the particle volume fraction are important parameters in turbulent gas-particle flows. A small Stokes number (St ≤ 0.07) implies that the particles are nearly at the velocity equilibrium with the gas phase, while a large Stokes number (St ≥ 0.07) implies that the slip velocity between the gas and particle phase increases and the particle velocity is less affected by the gas phase. A large particle volume fraction (αp ≥ 0.0001) implies that the effect of the particles on the gas phase momentum increases, while a small particle volume fraction (αp ≤ 0.0001) implies that the particles would have no or small effect on the gas flow field. For fixed Stokes number and particle volume fraction, an increase of the particle Reynolds number results in a decrease of the slip velocity between the gas and particle velocities.

Numerical simulation of a supersonic gas–solid flow over a blunt body: The role of inter-particle collisions and two-way coupling effects

A supersonic dusty gas flow over a blunt body is considered. The mathematical model of the two-phase gas–particle flow takes into account the inter-particle collisions and the two-way coupling effects. The carrier gas is treated as a continuum, the averaged flow field of which is described by the complete Navier–Stokes equations with additional source terms modeling the reverse action of the dispersed phase. The dispersed phase is treated as a discrete set of solid particles, and its behavior is described by a kinetic Boltzmann-type equation. Particles impinging on the body surface are assumed to bounce from it. Numerical analysis is carried out for the cross-wise flow over a cylinder. The method of computational simulation represents a combination of a CFD-method for the carrier gas and a Monte Carlo method for the “gas” of particles. The dependence of the fine flow structure of the continuous and dispersed phases upon the free stream particle volume fraction α p∞ and the particle radius r p is investigated, particularly in the shock layer and in the boundary layer at the body surface. The particle volume fraction α p∞ is varied from a negligibly low value to the value α p∞ = 3 × 10 5 at which inter-particle collisions and two-way coupling effects are simultaneously essential. Particular attention has been given to the particles of radii close to the critical value r p∗, because in this range of particle size the behavior of the particles and their effect on the carrier gas flow are not yet completely understood. An estimate of the turbulent kinetic energy produced by the particles in the shock layer is obtained.

The role of magma composition and water content in explosive eruptions: 2. Pyroclastic dispersion dynamics

The net effect of magma composition and water content on the behavior of explosive volcanic eruptions was investigated by the use of thermofluid-dynamic models and numerical simulation. The two-phase flow models employed allowed the description of the eruptive process from the conduit entrance at the top of the magma chamber up to the pyroclastic dispersion process in the atmosphere. In this paper, vent conditions computed in the companion paper by Papale et al. [Papale, P., Neri, A., Macedonio, G., this issue. The role of magma composition and water content in explosive eruptions: I. Conduit ascent dynamics. J. Volcanol. Geotherm. Res.], as a function of magma composition and water content, are employed as boundary conditions at the crater base of the pyroclastic dispersion model. The eruptive mixture was described as a two-phase gas–particle fluid. Pyroclasts are represented as solid particles of one size whereas the gas phase consists of superheated water vapor leaving the vent and atmospheric air. Simulations were performed on physical domains extending several kilometers in both radial and vertical directions and for several minutes of real time. The results clearly show the net effects of the anhydrous magma composition, crystals, and water content on the spatial and temporal distribution of pyroclastic material during the first minutes of eruption. In detail, the results indicate a strong influence of magma composition on eruption intensity, whereas the eruptive style, i.e., the generation of Plinian, transitional, or collapsing columns, appears to be mainly controlled by the total water content of the magma, i.e., the weight fraction of water with respect to the entire magmatic mixture. The main effect of the crystals is to reduce the total water content of the mixture and lead to a less buoyant behavior of the column. As a summary, for the investigated ranges of variations, simulation results indicate a progressive change to a more collapsing behavior of the column whenever water-poorer or crystal-richer magma is erupted from the vent with the anhydrous composition of magma affecting just the intensity of the eruption. For most conditions, such a conclusion does not appear to be strongly dependent on a relatively large variation of vent diameter and, therefore, of the scale of the event. Simulation results appear to be consistent with field studies even though more complete data on specific eruptions are recommended for a more thorough comparison.

Hypersonic flow past a supersonic two-phase source

The interaction of a uniform hypersonic gas flow with a supersonic two-phase gas-particle source is considered. In the symmetry-axis neighborhood between the bow and termination shock waves, an approximate analytical solution for the carrier-phase parameters is found. On the basis of parametric numerical calculations, the behavior of the particle trajectories and the concentration distribution in the shock layers are studied for both continuum and free-molecule flow regimes around the particles. The appearance of regions with multiple intersections of the particle trajectories and the formation of "layer structures" in the particle concentration distributions (particle accumulation regions near the envelopes of the particle trajectories) are indicated. The dependence of the number of the high concentration layers on the governing parameters is studied.

Modeling of dynamics, heat transfer, and combustion in two-phase turbulent flows: 1. Isothermal flows

This paper presents a review of authors' collective works in the field of two-phase flow modeling done in the past few decades. The paper is aimed at the construction of mathematical models for simulation of particle-laden turbulent flows. A kinetic equation was obtained for the probability density function (PDF) of the particle velocity distribution in turbulent flows. The proposed kinetic equation describes both the interaction of particles with turbulent eddies of the carrier phase and particle-particle collisions. This PDF equation is used for the derivation of different schemes describing turbulent momentum transfer in the dispersed particle phase. The turbulent characteristics of the gaseous phase are calculated on the basis of the k - ε turbulence model with a modulation effect of particles on the turbulence. The constructed models have been applied to the calculation of various two-phase gas-particle turbulent flows in jets and channels as well as particle deposition in tubes and separators. For validating the theoretical and numerical results, a wide range of comparisons with experimental data from Russian and foreign sources has been done.

Modeling of dynamics, heat transfer, and combustion in two-phase turbulent flows: 2. Flows with heat transfer and combustion

The objective of this part of the paper is to summarize the information concerning the authors' works in the field of simulation of two-phase gas-particle turbulent flows with heat transfer and combustion. A kinetic equation had been derived for the probability density function (PDF) of the particle velocity, temperature, and mass distributions in turbulent flows. This PDF equation is used for the construction of the governing conservation equations of mass, momentum, and heat transfer in the dispersed particle phase. The numerical scheme incorporates two-phase fluid dynamics, convective and radiative heat transfer, and combustion. The proposed models have been applied to the calculation of various particle-laden turbulent flows in jets, combustion and gasification chambers, and furnaces.

Numerical Simulation of Two-Phase Gas-Particle Jet in a Crossflow

A particle trajectory model to simulate the mean trajectories, velocities, and densities of a particle-laden gas jet injected into a uniform cross free stream has been developed. Governing equations were derived by considering a balance between forces acting on an elementary control volume of the crossjet along the trajectories of the gas and particle phases. The effects of particle size, particle loading ratio, injection angle, and the carrier gas to free stream velocity ratio and the particle-to-carrier gas velocity ratio at the jet exit on the average characteristics were investigated in this study. The computational results of the mean particle trajectories are in good agreement with available experimental observation. The present method should be useful to predict the average properties of a two-phase gas-particle jet in a crossflow.

Application of Lumley’s Drag Reduction Model to Two-Phase Gas-Particle Flow in a Pipe

A “two-fluid model” has been incorporated with Lumley’s drag reduction model to analyze the mechanism of momentum transfer in the turbulent dilute gas-particle flow in a vertical pipe. The change of the effective viscous sublayer thickness by the presence of particles is modeled by Lumley’s theoretical model. The numerical computations of the friction factor and the pressure drop in a fully developed pipe flow are in good agreement with the corresponding experimental data for an average particle size of 15 μm. It is proved that Lumley’s model is successful in predicting the correct reduction behavior of the drag in the gas-particle flows. It has been confirmed that the effective viscous sublayer thickness for two-phase gas-particle flow is dependent on the particle relaxation time, Kolmogoroff time scale and the solids-gas loading ratio.