Gas-solid Two-phase Flow Research Articles

Ultrasonic Simulation Research of Two-Dimensional Distribution in Gas-Solid Two-Phase Flow by Backscattering Method

Ultrasonic Simulation Research of Two-Dimensional Distribution in Gas-Solid Two-Phase Flow by Backscattering Method

Mathematical Modeling of Gas-Solid Two-Phase Flows: Problems, Achievements and Perspectives (A Review)

Mathematical modeling is the most important tool for constructing theories of different kinds of two-phase flows. This review is devoted to the analysis of the introduction of mathematical modeling to two-phase flows, where solid particles mainly serve as the dispersed phase. The main problems and features of the study of gas-solid two-phase flows are included. The main characteristics of gas flows with solid particles are discussed, and the classification of two-phase flows is developed based on these characteristics. The Lagrangian and Euler approaches to modeling the motion of a dispersed phase (particles) are described. A great deal of attention is paid to the consideration of numerical simulation methods that provide descriptions of turbulent gas flow at different hierarchical levels (RANS, LES, and DNS), different levels of description of interphase interactions (one-way coupling (OWC), two-way coupling (TWC), and four-way coupling (FWC)), and different levels of interface resolution (partial-point (PP) and particle-resolved (PR)). Examples of studies carried out on the basis of the identified approaches are excluded, and they are also excluded for the mathematical modeling of various classes of gas-solid two-phase flows.

Flow irreversibility versus wear of elbow-reducer connection with gas-solid two-phase flow: A numerical study via CFD-DEM coupling method

In industry sectors, such as power, petroleum, and natural gas production, many fluids contain solid particles in gas/liquid-solid two-phase flows. Thus, resistance and wall erosion, which mainly occur at pipe resistance components, such as elbows and reducers, should be considered in the design of conveying pipelines. To examine the interaction of two resistance components, the flow irreversibility versus wear of an elbow-reducer connection with a gas–solid two-phase flow were studied via the CFD–DEM coupling method. The studied connection structures include a reducer at the elbow downstream with distances of 0, 1, and 3 pipe diameters, and a reducer at the elbow upstream with distances of 0, 1, and 3 pipe diameters. Results show that turbulence and wall entropy generation are main reasons for the total entropy generation and flow irreversibility, which are mainly distributed in the interior wall of the elbow and the pipe. The reducer located downstream of the elbow has a good inhibition effect on the fluid with a separation phenomenon. The total entropy generation and maximum erosion rate for the elbow-reducer connections are lower than that for the reducer-elbow connections. Moreover, influences of solid particle mass flow rate and particle size on partial entropy generations, including mean, turbulent, and wall entropy generations, and wall erosion were comparatively analyzed. The simulation results can provide a reference for the design of pipelines to reduce energy consumption and pipeline wear.

Measurement and CFD-DEM Simulation of Suspension Velocity of Peanut and Clay-Heavy Soil at Harvest Time

The suspension velocity is the core of the cleaning and sorting mechanisms that utilize a combination of a fan and vibrating sieve. To investigate this, various experimental subjects, such as peanuts with different kernels and clay-heavy clods in different states, were used. The experiment involved simulating the suspension velocity of materials through numerical calculations using fluid dynamics and particle discrete element coupling. The Eularian model was employed to study the coupled gas-solid two-phase flow. The experiment measured the suspension velocities of single and double kernel peanuts, which were found to be 8.34~9.40 m/s and 8.13~9.51 m/s, respectively. Under 20.4% water content and lumpy conditions, the suspension velocities of smaller clods, side by side clods, and larger clods were 12.61~14.30 m/s, 14.16~15.76 m/s and 16.44~18.72 m/s, respectively; under 20.4% water content and smaller clods, the suspension velocities of lumpy and strip of clods were 12.61~14.30 m/s, 11.90~14.13 m/s, respectively; under lumpy and smaller clods, the suspension velocity at 17.6%, 20.4%, and 23.9% water content ranged from 12.38 to 14.20 m/s, 12.61 to 14.30 m/s, and 12.62 to 14.49 m/s, respectively. The simulations showed that the suspension velocity for different types of peanuts, clod sizes, shapes, and water contents was less different from the actual experiments. Specifically, the relative errors in suspension velocity for single-kernel peanuts, double-kernel peanuts, smaller clods, side-by-side clods, larger clods, lumpy clods, strips of clods, and clods with 17.3%, 20.4%, and 23.9% water content were 1.2%, 4.1%, 0.4%, 2.0%, 4.4%, 0.4%, 5.1%, 5.4%, 0.4%, and 1.9%, respectively, compared to actual experiment measurements. The results indicate a significant difference in the suspension velocity between peanuts and clay-heavy clods, which can be distinguished from each other based on this difference. Furthermore, the simulation results have been found to be consistent with the experimental results, thus verifying the feasibility of measuring the material suspension velocity using CFD-DEM gas-solid coupling.

Analysis of gas-solid two-phase flow characteristics of mobile shot blasting machine recovery device based on CFD-DEM

The shot blasting machine recovery device is an important part of the operation of the shot blasting machine to recover solid particles and reduce environmental pollution. The recovery efficiency of solid particles has an important influence on their processing efficiency and service life. The computational fluid dynamics and discrete element method (CFD-DEM) simulation method is applied to study the gas-solid two-phase flow characteristics and solid particle recovery efficiency of shot pellet recovery unit. The results show that the simulation results of outlet and inlet wind speeds and pressures are in good agreement with the experimental data, which verifies the accuracy of the simulation model. The existence of particle phase divides the recovery pipeline into inner high-speed flow area and outer low-speed flow area, which has little influence on the air flow distribution inside the recovery bin. The results of solid particle recovery efficiency show that with the increase of incident angle, the recovery efficiency of waste particles and shot particles first decreases and then increases, and the recovery efficiency is the lowest when the incident angle is 30°. With the increase of particle formation rate, the efficiency of shot recovery first increases and then decreases. When the particle formation rate is 2000 n/s, the efficiency of shot recovery is the highest, which has little influence on the efficiency of waste recovery.

Influence of SiO2 and Al2O3 particles on erosion wear of aero-compressor blades

When helicopters take off and land in areas such as plateaus and deserts, both SiO2 and Al2O3 particles in the external environment can cause erosion wear on compressor blades, compromising helicopter safety during operation. The aim of this study is a model of a pre-1.5-stage compressor from a turboshaft engine. The experimental schemes of SiO2 and Al2O3 particle velocimetry and Ti–6Al–4V alloy erosion wear were designed to construct a Tabakoff erosion wear model. The influence of particle density and hardness on the erosion rate was deduced. The trajectories and velocities of the two types of particles were analyzed using the gas-solid two-phase flow method. The erosion pattern of the blade was investigated to determine the influence of the two-particle on the erosion rate of the blade. The results showed that Al2O3 particles produced more energy than SiO2 particles and had a higher ability to erosion materials. The maximum impact angle of both the SiO2 and Al2O3 particles on the Ti–6Al–4V alloy was 30°, and the erosion rate of Al2O3 particles at this angle was 66% higher than that of the SiO2 particles. The erosion patterns of the compressor guide, rotor, and stator blades did not vary with the particle material; however, the erosion rate caused by the Al2O3 particles on the blade was larger than that of the SiO2 particles. The maximum erosion rate on the compressor occurred at 98.5% span of the leading edge of the rotor blade, and the erosion rate generated by the Al2O3 particles at this position was 114% higher than that of the SiO2 particles. This research can provide a theoretical reference for anti-erosion protection designs and vibration characteristic analysis of aero-engine compressor blades.

Gas–solid two-phase erosion of multi-elbow relief line under supercritical condition

The Eulerian–Lagrangian method was used to establish a numerical model of a multi-elbow pipeline erosion and examine the erosion of the relief line elbow under supercritical conditions. The model was used to examine the effects of the discharge volume, sand content, and shape factor of sand on multi-elbow erosion and those of the connection length on double-elbow erosion. The erosion mechanism and law of multi-elbow lines under gas–solid two-phase flow conditions were revealed. The results indicated that the most severe erosion of the elbow occurred on the impact surface. However, the erosion area of the multi-elbow was relatively long. In a multi-elbow pipeline, the maximum erosion rate of the outlet elbow was 84 times that of the inlet elbow. For the multi-elbow pipeline, the erosion rate was related to the discharge volume, sand content, particle shape, and length of the connection between elbows. The erosion rate of the elbow at the outlet decreased gradually and stabilized with an increase in the connection length.

Measurements of particle velocity and solid concentration near the wall of a cyclone using high-speed particle shadow velocimetry

The particle velocity and solid concentration distribution in the near-wall region of a cyclone separator was experimentally studied. A series of measurement experiments were conducted based on the high-speed particle shadow velocimetry (HPSV) method. The experiment was conducted on a ϕ160 mm cyclone at an inlet velocity of 12-20 m/s and inlet concentration of 30-300 g/m3 with glass beads whose median diameter was 136.7 μm. The measured results of the microscopic particle movement demonstrate the moving behavior of the spiral particle band near the cyclone wall. It was found that the particle velocity and solid concentration are greatly different from those in and outside the particle band. The particle velocity inside the particle band can drop to 1.9 m/s, while the dispersed particle velocity outside the particle band away from the wall can reach 15.2 m/s. Along the downward movement of particle band, the particle velocity decrease and velocity fluctuation become milder, the solid concentration increases four times and reaches the highest at the cone wall. On the cross-section plane, the solid concentration decreases along the radial direction away from the wall. In the near-wall region inside particle band, the solid concentration can reach 0.004 or even higher, which is 32 times higher than the inlet solid concentration. This study helps to understand the complex gas-solid two-phase flow phenomena in cyclones.

Coal dust dispersion with the moving conveyance in a high-rise building for the mine hoist system.

The present study investigates dust generated from the unloading process in a high-rise building for the mine hoist system and analyzes dust dispersion with the moving conveyance in the building. First, the gas-solid two-phase flow in the building was investigated based on the CFD-DPM method. In particular, the moving conveyance was considered in detail and treated via thedynamic mesh technology. Then, the airflow and dust distribution were investigated in the building. The airflow and the dust concentration at selected points show good agreement with the relative results of field measurements by ourselves. It is found that the descending conveyance significantly influences the surrounding flow field and the spatial and temporal distribution of dust. Dust concentration before the dust source (2 m × 2 m) is high, which extends downward with the conveyance. Dust concentration of the lower floors increases obviously when compared with that of the condition without the movement of the conveyance. The descending velocity of the conveyance also affects the amount of PM2.5 discharged from the return air outlet. The fitting functions are provided to predict PM2.5 emissions to the surrounding atmosphere. The research results are of great significance for the improvement of the dust control system for cleaner production technology.

A hybrid safety monitoring framework for industrial FCC disengager coking rate based on FPM, CFD, and ML

This work proposed a hybrid modeling framework for the safety monitoring of coking rates in FCC (Fluidized Catalytic Cracking) disengager. The framework combines CFD (Computational Fluid Dynamics), coking FPM (First Principles Model), machine learning, and industrial data to establish a comprehensive and customizable approach. The FPM of the coking rate, including the UNIFAC condensation ratio model, the coking ratio model and the capture ratio model, are established by combustion experiments, gas-solid two-phase flow simulations and DPM (Discrete Phase Model) simulations. The capture ratio model is built to calculate the capture ratio of heavy oil droplets by each high-risk region, achieved by DPM simulation. By establishing a link between the simulated position and the DCS (Distributed Control System) sensor, the simulation results and the real-time DCS data are matching. An improved LSTM (Long Short-Term Memory) network was then established to predict the real-time temperature and pressure in the high-risk coking regions of the disengager using real-time DCS and LIMS (Laboratory Information Management System) data. The LSTM network can achieve online monitoring of coking rate by coupling FPM. This hybrid coking monitoring framework has been industrially applied and validated with an accuracy of over 90% in a continuous one-month online monitoring task, which is highly interpretable and extensible, providing refining companies with a scalable and customizable approach to monitor coking problems in FCC disengager.

Experimental study on the flow characteristics of horizontal pneumatic conveying of stiff shotcrete

The gas-solid two-phase flow of stiff shotcrete in horizontal pneumatic conveying was experimentally studied to reveal the flow characteristics of stiff shotcrete in a horizontal pipeline. Pressure data and particle flow characteristics were measured by pressure transmitter and high-speed camera, respectively. The unit pressure drop and particle flow characteristics in the steady state zone of stiff shotcrete under different air volumes of flow, water cement ratio, and pipe diameter were systematically studied. The results show that the unit pressure drop increases with the increase of the water-cement ratio; the pressure drop per unit length in the steady state zone decreases first and then increases with the growth of air volume of flow, and there is the most economical air volume of flow. Through image analysis, it is found that with the increased air volume of flow, the stiff shotcrete particles gradually transform from stratified flow to suspended flow in the pipeline. In addition, the stability of stiff shotcrete during pneumatic conveying is studied by analyzing the variation coefficient of pressure. The stability increases with the decrease of the pressure variation coefficient. This study further reveals the pneumatic conveying mechanism of stiff shotcrete, which provides essential guidance for designing a pneumatic conveying system and the experimental basis of stiff shotcrete.

Study on the Influence of Different Factors on Pneumatic Conveying in Horizontal Pipe

Aiming at the problems of high energy consumption and particle breakage in the pneumatic conveying process of large-scale breeding enterprises, in this paper, based on the theoretical calculated value of particle suspension velocity, a computational fluid model and a discrete element model are established based on computational fluid dynamics (CFD) and discrete element method (DEM). Then, through the numerical simulation of gas-solid two-phase flow, the influence of four factors of conveying wind speed, particle mass flow rate, pipe diameter, and particle size on the velocity distribution of particles in a horizontal pipe, dynamic pressure change in the pipe, pressure drop in the pipe, and solid mass concentration are studied. The results show that the k-ε turbulence model can better simulate the movement of gas-solid two-phase flow, and through the analysis of the simulation, the influence of four different factors on the conveying characteristics is obtained, which provides a scientific basis for the construction of the conveying line.

Numerical Simulation of Gas-Solid Two-Phase Heat Transfer in a Kaolin Cyclone Cooling System

The kaolin suspension calcination technology is currently gaining attention as a new process of calcining kaolin. In this paper, the cooling system of the kaolin suspension calcination process designed by CBMI Construction Co., Ltd. is simulated using ANSYS Fluent software to analyze the velocity field and temperature field of the gas–solid two-phase flow using the Eulerian model. A compiled UDF (User-Defined Function) is used to simulate the transfer of mass and heat from the downcomer tube to the different elements. The gas, coming from the gas outlet of the cyclone, enters the next level twin-cylinder cyclone in a spiral state. The results show that the airflow in the cyclone consists of an external spiral flow from the top to the bottom and an internal spiral flow from the bottom to the top. During the downward movement of the airflow, the outer spiral flow is continuously transformed into an inner cyclonic flow. The part of the airflow that rotates close to the inner cylinder is likely to become a ‘short circuit flow’, which largely affects the separation efficiency and cooling effect of the cyclone. There is evident temperature deviation and flow deviation in the twin-cylinder cyclone, which is primarily due to the high cooling air volume and high rotation of air flow coming from the gas outlet of the previous level’s cyclone. The rotation of the air flow is the main cause of the bias temperature and bias flow phenomenon in the twin-cylinder cyclone.

Coupling Characteristics of Powder and Laser of Coaxial Cone Nozzle for Laser Direct Metal Deposition: Numerical Simulation and Experimental Study.

Laser direct metal deposition (LDMD) enables not only the preparation of high-performance coatings on the surfaces of low-property materials but also the three-dimensional direct manufacturing and re-manufacturing of parts. In the LDMD process, the spatial coupling characteristics of the powder flow and the laser beam are the key factors affecting the forming quality of the cladding layer. Based on the gas-solid two-phase flow theory, a numerical model of coaxial powder feeding was established by CFD. The powder flow characteristics of the lower part of the nozzle, the powder particle motion trajectory, and the optical-powder spatial coupling morphology and law were studied, and the relationship between the powder flow morphology, laser beam, and powder utilization was explored. On this basis, the law between the optical-powder coupling characteristics and the geometric characteristics of the cladding layer is discussed in conjunction with LDMD experiments. The results show that the powder concentration scalar located in the focal plane of the laser beam can be used to visualize the optical-powder coupling morphology. When the powder feeding speed exceeds the loading capacity of the carrier gas flow, the powder concentration in the center of the spot and the powder utilization rate decrease. When the carrier gas flow rate is 4.0 L/min and the powder feeding rate is 4.0 g/min, the best utilization rate achieved is 81.4%. In addition, the H (height) of the cladding layer is more sensitive to changes in the powder concentration than the W (width). These findings provide new ideas for nozzle structure design and the optimization of LDMD parameters.

Structural design of a coaxial-jet vortex powder mixer for multi-material directed energy deposition

Directed energy deposition (DED) offers an unprecedentedly convenient and efficient additive manufacturing approach for novel alloy design. As a critical component of the novel DED system, a powder mixer plays an important role in the stable and uniform mixing of different powders. In this work, the coaxial-jet dome powder mixer (CDPM) was designed based on the convergent-jet cone powder mixer (CCPM). In order to explore a reliable multi-powder mixing mechanism, the gas-solid two-phase flow state in the mixing chamber was simulated by the large eddy simulation and discrete particle model (LES-DPM) method. In addition, the powder delivery stability and mixing uniformity of the mixer were characterized by curve fitting and image processing methods. Finally, CDPM avoids the generation of ineffective vortices that occurred in the mixing chamber. In addition, deposition experiments show that the powder mixer can ensure the uniform distribution of multiple elements in the local forming zone.

Study on Wear Properties of the Graphite-Sealing Surfaces in a Triple Eccentric Butterfly Valve Based on EDEM-Fluent Coupling

When using valves and pipes, erosion wear is a major issue. Erosion wear can result in equipment shutdown, material replacement, and other issues, as well as the failure of sealing surfaces. The depth of erosion wear is primarily determined by particle velocity, particle size, target material, and use conditions. A combination of the discrete element method (DEM) and computational fluid dynamics (CFD) was used in this study. The dynamic process of particle collision with the sealing surface is also considered. The wear depth was then calculated using Archard’s abrasive wear theory. The erosion wear process of the graphite-sealing surface by gas-solid two-phase flow medium is numerically simulated in a high-temperature triple eccentric butterfly valve using the above theory and method. The erosion wear patterns of graphite-sealing surfaces were investigated under various particle velocities, particle sizes, target materials, and service conditions. The findings indicate that particle velocity and particle size are positively related to wear rate. Soft target wear depth is greater than hard target wear depth. The wear depth decreases as the ambient temperature rises. As a result, graphite has excellent resistance to erosion and wear at high temperatures. When feeding, however, particle velocity and particle size must be considered. The erosion wears characteristics of a high temperature three eccentric butterfly valve investigated in this paper can be used to optimize erosion wear prevention.

Application of Anti-wear Technology for Water-cooled Wall of CFB Boilers

Because of its high efficiency, low pollution, energy saving and other technical advantages, CFB boiler has been rapidly promoted commercially in recent decades. However, because of its special combustion mode and high material concentration, the gas-solid two-phase flow is more complex and the wear is more serious. No matter in theoretical research or engineering practice, the problem of serious wear and tear of CFB boiler has not been completely solved. Wear is the main reason that restricts the further development of CFB boilers. The main purpose of this paper is to study the application of anti-wear technology of water-cooled wall of CFB boiler. Therefore, this paper makes a systematic study on the serious wear problem of CFB boiler, makes an accurate prediction of the serious wear area, and puts forward comprehensive anti-wear measures to slow down the wear rate and prolong the service life. Through experiment, numerical simulation and comparison with the field practice, the study shows that the wear of water wall is mainly divided into erosion wear, friction wear and high temperature atmosphere corrosion wear. Among them, the wear of water-cooled wall (WCW) is mainly erosion and friction wear, while the corrosion wear of high temperature atmosphere accelerates the speed of these two kinds of wear.

Sensitivity analysis of kinetic theory of granular flow (KTGF) and mixture models in terms of involved elemental parameters for two-phase gas-solid flow

Probing into the multiscale essence and nonlinear interactions of gas-solid flows whether in natural or industrial scale have continuously been evoking challenges in flow physics and modeling approaches. Although there are capabilities within the test bench experiments and empirical formulas to define or predict the flow characteristics in two-phase systems, the flow pattern would be still unknown, and here is where the numerical approaches thrive. Since, the corresponding non-linear equation system developed to predict the behavior of two-phase flows is intrinsically complex and makes the numerical solutions time-consuming, in this article, the sensitivity analysis of two well-known models based on the Euler-Euler approach, namely KTGF and Mixture models, is conducted in terms of continuous/dispersed shear stress and solid pressure on the accuracy, stability, and duration of solution. In the KTGF model, granular viscosity is particularly most influential term; while in the Mixture model, the numerical solution profoundly depends on the continuous phase viscosity. Moreover, it is perceived that the existence of solid pressure as a diffusive source term is consequential for the stability in the modeling process, and in high values of dispersed volume fraction, its impact on the flow behavior is distinguishable.

On cutting transport for air reverse circulation in horizontal and inclined wells

Air reverse circulation (RC) drilling has drawn considerable interest and has been adopted in tunnel drilling owing to its beneficial features. Cutting transport is a primary concern in RC drilling because poor cutting transport efficiency may lead to several problems, such as stuck pipes, excessive torque and drag, and severe bit wear. The Euler-Euler method of computational fluid dynamics simulation was applied to model the gas–solid two-phase flow in a drill pipe to determine the influence of various parameters on cutting transport. The effects of the air velocity, cutting concentration, rate of penetration (ROP), particle diameter, and inclination angle were investigated by analyzing the variation in the pressure drop, characteristics of cutting motion, and efficiency of cutting transport. The results revealed that the positive contribution of air velocity to transport efficiency was restricted. The optimal concentration of cuttings was approximately 20 %. The pressure drop, average volume fraction, and cutting migration ratio tended to be positively correlated with the ROP. An increase in the cutting diameter led to a decrease in transport efficiency. At an inclination of 30°, the least cutting transport efficiency was observed.

Numerical Study of the Erosion Distribution of Sulfur-Containing Particulate Gas in 90-Degree Gathering Elbow

The phenomenon of pipeline erosion dominated by sulfur particles has become a key research target for sulfur-containing gas-gathering pipelines. Gas-solid two-phase flow of sulfur-containing gases is simulated with a coupled CFD-DPM model in this paper. The Realizable k-ε turbulence model was used to determine the changes in the complex flow field and the Euler-Lagrange method was used to describe the specific trajectory of sulfur particles in the complex flow field. The main erosion trace distribution and the effect of secondary flow effects at the elbow were analyzed and the erosion distribution pattern was investigated for different curvature ratios, particle sizes, and pipe diameters. The results show that the formation of erosion along the tip of the V-shaped erosion trace on the outlet sidewall of the elbow may be related to secondary flow effects. The increase of the curvature ratio RD reduces the erosion intensity of the maximum erosion area, but subsequent increase will result in new secondary erosion trace near the outlet of the elbow and reach the maximum when RD = 8. Variations in particle size will have a significant effect on the extent of the erosion distribution, causing the main erosion distribution of the elbow to vary between 48.2° and 84.2°, while variations in pipeline diameter will have a lesser effect. The Stokes number can also be reduced by controlling the variation in particle size and pipe diameter to alter the force profile on the particles and reduce the erosion effect.