Multiphase Flow Field Research Articles

Numerical and experimental study of inlet velocity effects on separation performance of hydrocyclones for purifying low-grade phosphate ore

Due to the scarcity of phosphorus as a strategic resource, there is a growing trend to extract and refine low-grade phosphate ore using hydrocyclones. This study focuses on purifying low-grade phosphate ore using a hydrocyclone, with experiments conducted to obtain data on inlet velocity, mass flow rate, and pressure of inlet and outlet. These measurements assess pressure drop, separation efficiency and accuracy, thereby validating the numerical simulation outcomes. The Mixture and RSM models are used to simulate and analyze the hydrocyclone's internal multiphase flow field and performance of separation at varying inlet velocities. Findings show that an inlet velocity ranging from 6 to 7 m/s results in over 90% separation efficiency, around 90% separation accuracy, and low energy expenditure. These research findings provide theoretical guidance for low-grade phosphate ore separation and purification using hydrocyclones.

Study on the characteristics of the transient flow field under different underwater environments

The underwater muzzle transient flow field is an unsteady, multiphase complex flow field interacting with projectiles and containing various shock wave structures. The turbulent mixing of gunpowder gas and water has a significant impact on the development of the muzzle gas flow field. Moreover, the muzzle gas flow field disturbs the motion of the projectile, thereby affecting shooting accuracy. As part of this research, an unsteady multiphase flow model of the underwater muzzle transient flow field is established by combining the theories of multiphase flow and turbulent mixing. The volume of fluid model is employed to trace the two-phase interface, while the gas–liquid turbulent mixing is described by the standard k–ε turbulence model. Furthermore, the cavitation model is used to describe the cavitation phenomenon caused by the motion of the projectile. The established numerical model is validated by comparing underwater launching experimental results. Accordingly, the muzzle flow field of a 30 mm underwater gun under different water depth conditions is numerically calculated. The results demonstrate that, as the water depth increased, the gunpowder gas is exposed to relatively high water pressure during the expansion process, resulting in a continuous decrease in the core area of the gas, and the Mach disk is also increasingly closer to the muzzle. At different water depths, the diameter of the Mach disk conforms to the binomial law with time, while the displacement of the Mach disk from the muzzle increases exponentially with time.

Forecasting three-dimensional unsteady multi-phase flow fields in the coal-supercritical water fluidized bed reactor via graph neural networks

The study of three-dimensional unsteady multi-phase flows inside the coal-supercritical water fluidized bed (SCWFB) reactor coupled with fluid dynamics, heat transfer and chemical reactions usually relies on time-consuming numerical simulation. Recently, to provide quick spatio-temporal estimation of the SCWFB reactor, the data-driven deep learning techniques have been adopted to build a digital yet fast reactor forecasting model. However, due to the irregular 3D geometry, it usually uses unstructured meshes to discrete the domain of reactor and builds the corresponding simulation model, which poses difficulties for the convolutional neural networks based deep learning models. Hence, this article develops a 3D unstructured spatio-temporal forecasting model, named GraphReactorNet, via graph neural networks for learning the dynamics under multi-phase flow fields inside the SCWFB reactor. It utilizes an efficient strategy to tackle large-scale 3D transient flow graphs and proposes an effective unstructured spatio-temporal learning module to extract the underlying flow dynamics. This model is trained on data collected from the transient simulator at different conditions. Numerical experiments reveal that in comparison to the counterparts, the GraphReactorNet not only achieves accurate multi-step-ahead predictions of the multi-phase flow fields at unseen conditions, but also performs thousands of times faster than the numerical simulator.

Study on high-speed water entry process of non-rotating vehicles

The non-rotating trans-media vehicle can better adapt to the hypersonic flight conditions, but new problems in the hydrodynamic characteristics and motion stability arise during the water entry process. With the VOF multiphase model, Realizable k-ε turbulence model, and Schnerr-Sauer cavitation model, this paper establishes a simulation method of coupling the movement of non-roating body into water with multiphase flow fields based on overset grid technology, and the accuracy of the established model is verified. The simulation calculation of the oblique water entry process of the vehicle with different ratio of short axis to long axis in cross section is carried out. And the results show that although the ratio of short axis to long axis in cross section does not change the cavitation morphology, it affects the hydrodynamic and kinematic characteristics of the vehicle by influencing the relative position of the cavitation. As the ratio of short axis to long axis decreases, the motion stability of the vehicle increases gradually. However, if the ratio of short axis to long axis is too small, the drag reduction effect will be weakened, and the structure will suffer a bigger load.

Editorial: Multiphase flow in energy studies and applications—A special issue for MTCUE-2022

Establishing a clean, low-carbon, and efficient energy system is paramount for the sustainable development of industries and human society. Multiphase flows are encountered extensively in various energy applications, including transportation, conversion, and utilization of fossil, renewable, hydrogen, and nuclear energies. These flows encompass a wide range of phenomena, such as fluid flow, heat and mass transfer, combustion, and chemical reactions. However, multiphase flows are highly intricate due to the coexistence of multiple phases, states, and components, as well as the interactions among them that occur across diverse spatiotemporal scales. Consequently, both academia and industry face significant challenges in comprehending and harnessing multiphase flows. Thus, establishing connections between basic research and industrial applications in the field of multiphase flows is fundamental and indispensable for advancements in energy science and technologies.

Effect of dynamic formation of multiphase slag skin on heat transfer and magneto-hydrodynamic flow in electroslag remelting process

During the electroslag remelting (ESR) process, the effect of dynamic formation of slag skin on magneto-hydrodynamic multiphase flow and temperature field is studied using a 2-D axisymmetric model. The electromagnetic field is described by user-defined functions. The dynamic formation and distribution of multiphase slag skin, as well as the interface between slag and metal, are investigated by using the volume of fluid (VOF) model and the dynamic meshing method. Especially, the effect of slag skin/air gap on heat transfer characteristics is considered and developed by user-defined functions. The results show that the thickness of slag skin at the interface between slag and metal increases as the axial distance from free surface of slag rises, reaching a maximum of about 25 mm. With the height of ingot increasing, the thickness of slag skin drops to 17 mm. When the current changes from 2.0 kA to 3.0 KA in the ESR process, the current density, Joule heat, velocity and temperature increases. In the meanwhile, the slag skin becomes thinner and the melt pool becomes deeper. The vibration of electrode has a weak effect on the formation behavior of slag skin, and only has effects on formation of metal droplet and velocity field.

Research on multiphase flow field characteristics of underwater gun double‐tube parallel firing

AbstractThe underwater muzzle flow field formed by the double‐tube launch will interfere with each other, resulting in large changes in the characteristic parameters of the flow field and shock wave morphology. Therefore, the numerical model of three‐dimensional unsteady multiphase flow for underwater gun‐sealed launching was established. Meanwhile, an experimental platform for the underwater sealed launch was built and the rationality of the model was verified. The interior ballistic process compiled by UDF was coupled with the dynamic mesh technology, and the VOF multiphase flow model integrated with the Schnerr‐Sauer cavitation model was chosen to numerically calculate the muzzle flow field of the 30 mm underwater gun double‐tube parallel launch, and the numerical results were compared to those of the single‐tube launch. The results show that the gas is expelled from the muzzle and rapidly expands to form a gas cavity, and the “necking” phenomenon of the gas cavity occurs at 0.2 ms, while the Mach disk structure has formed. Due to the mutual interference between the flow fields formed by each tube, the diameters of the Mach disk are slightly different, and the flow field structure has a certain asymmetry in the evolution process. The core area of the shock wave is bowl‐shaped of the single‐tube launch, while it is not completely filled of the double‐tube launch. Within 0.5 ms, the diameter of the Mach disk increases monotonously when the single‐tube is launched, while it first increases and then decays by a double‐tube.

Model of multiphase flow, superheat transport, and particle capture in a steel continuous caster

A model of turbulent multiphase flow, heat transfer, and particle entrapment during continuous casting of steel is presented. The model includes the top 7m of the vertical and curved strand, and considers the effects of argon gas injection and thermal buoyancy. RANS model flow results are compared with LES. Lagrangian particle transport through the Eulerian-Eulerian multiphase flow field from the k-ɛ RANS model is based on random walk and features advanced particle capture criteria, improved from previous work by including anisotropic turbulent velocity fluctuations near the walls. Particle capture via 3 mechanisms is included: capture by solidified hooks at the meniscus, entrapment between dendrites, and engulfment by surrounding large particles. The fluid flow and bubble/inclusion capture results are validated with plant measurements, including nail board dipping tests and ultrasonic tests of particle locations, and good agreement is seen. The superheat has negligible effect on flow in the mold region but causes complex flow in the lower strand by creating multiple recirculation zones due to the thermal buoyancy. With high (30 K) superheat, this leads to less penetration, and slightly fewer and shallower capture of particles. Lower (10 K) superheat may enable significant top surface freezing, leading to very large internal defect clusters. Lower superheat also leads to deeper meniscus hooks, and more surface capture. Capture bands occur near the transition from vertical to curved, where downward liquid flow velocity balances the particle terminal velocity.

Numerical and experimental study of the effects of tangential to axial velocity ratio and structural parameters inside the nozzle on spray characteristics

Pressure swirl nozzles are widely applied in spray cooling, dust removal, and fuel injection. To better connect the nozzle structure with the internal flow to analyze their influence on spray parameters, this paper designs a nozzle structure and uses experimental measurement and computational fluid dynamics simulation methods to investigate the influence of the nozzle's tangential velocity to axial velocity ratio (vτin/vzin) and the swirl diversion channel eccentric distance (dl) on the spray parameters. A phase Doppler particle analyzer was used in the experiment study to determine the spray axial velocity (vz) and sault mean diameter (D32). In the simulation investigation, the Eulerian multiphase flow model was used to calculate the multiphase flow field of the spray. The results showed that dl and vτin/vzin both have an obviously linear relationship to the peak location (rpeak) of each spray parameter. It means that dl plays similar roles as the vτin/vzin, which can enhance the swirl strength inside the nozzle and increase the spray cone angle. The rpeak of liquid phase volume fraction (αw) and D32 of the droplet particle are always greater than the rpeak of vz. The analysis of the flow field inside the spray orifice indicates that as the vτin/vzin rises, the liquid in the nozzle orifice tends to move farther from the central axis, causing atomization to occur more upstream. This study serves as a reference for the flow analysis and structure design of the pressure swirl nozzle.

Underwater ejection multifield coupling model and response characteristics

This article presents a numerical simulation analysis of the ejection process of a rigid projectile under the coupling effect of a support structure, ejection gas and transverse flow in a launch tube. Based on the computational fluid dynamics method and nested dynamic mesh technique, the dynamic response model of the support structure is used to simulate the deformation loads of the support structure inside the tube and construct a multifield coupled model for underwater ejection. Through computational analysis, we focus on the evolution characteristics of the multiphase flow field during the ejection process, the development mechanism of the bubble at the tube outlet, and the trajectory and load response characteristics of the projectile. In addition, the effects of different launch conditions, such as transverse flow velocity and interphase heat and mass transfer effects, on the projectile ejection process are also analyzed. The results show that the established model can effectively characterise the ejection motion process of the projectile. The impact of the lateral flow causes drastic changes in the motion displacement and velocity of the projectile as well as the rotation angle and rotation angular velocity. Furthermore, the interphase heat and mass transfer effects have less influence on the ejection process of the projectile due to the temperature change of the high-temperature ejected gas caused by the intermittent interface between the bubble and the aqueous medium.

Computational Fluid Dynamics Modelling of Two-Phase Bubble Columns: A Comprehensive Review

Bubble columns are used in many different industrial applications, and their design and characterisation have always been very complex. In recent years, the use of Computational Fluid Dynamics (CFD) has become very popular in the field of multiphase flows, with the final goal of developing a predictive tool that can track the complex dynamic phenomena occurring in these types of reactors. For this reason, we present a detailed literature review on the numerical simulation of two-phase bubble columns. First, after a brief introduction to bubble column technology and flow regimes, we discuss the state-of-the-art modelling approaches, presenting the models describing the momentum exchange between the phases (i.e., drag, lift, turbulent dispersion, wall lubrication, and virtual mass forces), Bubble-Induced Turbulence (BIT), and bubble coalescence and breakup, along with an overview of the Population Balance Model (PBM). Second, we present different numerical studies from the literature highlighting different model settings, performance levels, and limitations. In addition, we provide the errors between numerical predictions and experimental results concerning global (gas holdup) and local (void fraction and liquid velocity) flow properties. Finally, we outline the major issues to be solved in future studies.

Numerical study on the impact load characteristics of a trans-media vehicle during high-speed water entry and flat turning

When a trans-media vehicle enters water at high speed and turns while flat, the vehicle is subjected to vast impact loads. The impact on the structural strength of the vehicle cannot be ignored. In this paper, based on the fluid volume multiphase flow model and dynamic mesh technology, a coupling calculation method for the multiphase flow field and trajectory of a trans-media vehicle entering water at high speed is established. The accuracy and applicability of the numerical calculation method are verified by experiments. Through the numerical simulation, the typical water-entry and flat-turning process and the water-entry process with different water-entry velocities, water-entry angles and preset rudder angles are analyzed. The results show that the phenomenon of tail-slapping oscillation occurs in the process of high-speed water entry and flat turning. Under different water-entry conditions, the impact load characteristics of the vehicle are basically different, but the water-entry process is stable overall.

Effects of stress histories and drainage conditions on inception of strain localization in unsaturated soils

A diagnostic method to detect the inception of strain localization, which is based on the singularity of a total acoustic tensor, was developed for variably saturated soils. The effective stress approach was used to establish coupling between the multiphase fluid flow and deformation fields, while isotropic hardening/softening due to changes in suction and plastic volumetric strain were accounted for. To this end, several fundamental testing conditions were investigated, including Conventional Triaxial Compression (CTC) and Extension (CTE), Plane Strain Compression (PSC) and Extension (PSE) under drained, constant water content, and undrained loadings. It was found that, for the silty soil and stress histories considered, suction can completely prevent the onset of strain localization in undrained CTE tests and partially prevent the onset in constant water content and drained CTE tests. Furthermore, while suction can significantly affect the inception of strain localization in all PSC tests, it has almost no effect on the onset of strain localization in all PSE tests. Finally, suction affects more significantly the orientation and mode of shear bands at the inception of strain localization in extension tests than in compression tests.

Application and comparison of dynamic mode decomposition methods in the tip leakage cavitation of a hydrofoil case

The cavitation of the tip leakage vortex (TLV) induced by tip leakage has always been a difficult problem faced by turbomachinery, and its flow structure is complex and diverse. How to accurately extract the main structures that affect the cavitating flow of the TLV from the two-phase flow field is a key problem. In this study, the main mode extraction and low order mode reconstruction accuracy of the cavitation flow field of TLV downstream of National Advisory Committee for Aeronautics (NACA)0009 hydrofoil by two dynamic mode decomposition (DMD) methods are compared. The research shows that the main modes extracted by the standard DMD method contain a large number of noise modes, while the sparsity-promoting DMD eliminates the noise modes, showing obvious advantages in the reconstruction accuracy of the velocity field. The characteristics of cavitation signals are analyzed, and the cavitation signals are divided into four categories, which explains the reason why DMD methods have low reconstruction accuracy in cavitation. This study provides a theoretical basis and strong guarantee for the extraction of mode decomposition characteristics of the two-phase flow field. This is of great significance for accelerating the prediction of multiphase flow fields based on intelligent flow pattern learning in the future. Meanwhile, it also provides a new method and road for the introduction of artificial intelligence technology in future scientific research.

Anode analysis and modelling hydrodynamic behaviour of the multiphase flow field in circular PEM water electrolyzer

A numerical study of the behaviour of the multiphase flow of an anode-porous transport layer of an aqueous electrolyzer with a proton-exchange membrane (PEM) of an aqueous electrolyzer is presented. A mixture model was used to study the flow behaviour in a circular-shaped anode box to determine the efficient design of a PEM water electrolyzer. As a result of the simulation, it was found that the model pressure drop profiles obtained by computational fluid dynamics (CFD) are in good agreement with the corresponding experimental data. In addition, the performance profile was predicted considering various PEM water electrolyzer cell improvement factors compared to the Bassline model. The results of the behaviour of two-phase flows with different velocity, pressure and volume fraction profiles, as well as with porous regions in the centre, are presented, which showed a key difference in the flow profile for various inlet and outlet flow configurations. In addition, the flow volume fraction behaviour was obtained at higher and lower water and oxygen rates. Three-dimensional (3D) modelling predicted flow characteristics for three different cell configurations. In this article, we also run simulations over a wide range of flow rates. The main results of the numerical study were discussed to shed light on the design of a high-performance PEM water electrolyzer.

An Image Construction Based on the VTLF Fusion Technique for Oil–Water Two-Phase Flow of Noncontact Electrical Impedance Tomography

Electrical tomography (ET) has attracted extensive attention in the petroleum multiphase flow field due to its advantages of nonintrusion, nonradiation, and simple equipment structure. Some contactless impedance imaging methods, such as capacitively coupled electrical resistance tomography (CCERT) and phase-based dielectric spectroscopy tomography, or displacement current phase tomography (DCPT), have been studied for the parameter measurement of two-phase flow. The mentioned research mainly focuses on the separate imaging by real part, imaginary part, or phase information of the voltage/current. However, the distribution change of media in the region of interest (RoI), especially the presence of high permittivity and conductivity materials, involves the distribution change of conductivity, permittivity, and loss factor. Developing a proper image fusion technique based on the three components can provide more comprehensive image information for tomographic imaging. This article proposed an improved logic filter image fusion algorithm based on a variable threshold (VTLF), and a noncontact electrical impedance tomography (NEIT) system for imaging water–oil two-phase flow is carried out. Image reconstruction is implemented by the VTLF image fusion algorithm under different media distributions, conductivities, and excitation frequencies, and the image fusion algorithms of a weighted average (WA) and logic filter (LF) are also used for comparison. The simulation results show that the reconstructed images by the proposed fusion method of VTLF had the lowest artifacts and the highest correlation coefficient (above 0.7) compared with other methods. Also, in the experiment, the VTLF also got the best performance, so it is effective to improve the reconstruction accuracy.

A general numerical method for solid particle erosion in gas–liquid two-phase flow pipelines

A general numerical method is developed to analyse solid particle erosion in gas–liquid mixed pipeline. Tracking particle trajectories is an important intermediate step of the numerical procedure. The present numerical method considers that two factors can affect a particle's trajectory. First, a particle is randomly affected by the gas or liquid phase, and the probability of a certain phase acting is equal to the volume fraction of the phase. Second, surface tension prevents particles from entering the gas phase from the liquid phase and promotes the particles entering the liquid phase from the gas phase. The numerical procedure is well verified by comparison with the experimental data available in the literature. Seventeen cases are used to validate the predicted multiphase flow field and solid particle erosion. In addition, the movement and distribution of particles predicted by the present model are indirectly verified, and the effects of the phase volume fraction and surface tension are discussed in detail.

Simulation research on the outlet cavity features in the underwater launching process

This paper analyzes the evolution of cavity features and pressure characteristics during the underwater launching process. The improved delayed eddy simulation (IDDES), energy equation, and overlapping grid technique are adopted. In addition, validation of the numerical approach and grid independence is carried out. The evolution of the multiphase flow field and pressure fluctuations near the launcher outlet are studied. Results show that the gas mass escaping from the tube expands and contracts, eventually breaking off with a jet that acts on the tail of the vehicle after the vehicle leaves the tube. Four major pressure fluctuations occurred near the launcher outlet, the first two of which are generated by the alternate expansion and contraction of the high-pressure gas mass, while the subsequent fluctuations mainly originate from the intermittent escape of the remaining gas mass inside the tube, the magnitude of the pressure fluctuations decreases gradually. As the Froude number increases, the scale of the escaping high-pressure gas mass expands significantly, while the dissipation rate of the fused gas mass at the launch tube outlet also increases, the evolution mechanism of multiphase is more complex.

Numerical Investigation of Fine Particulate Matter Aggregation and Removal by Water Spray Using Swirling Gas Flow

In this paper, a mathematical model based on the two-fluid frame model coupled with the population balance model which considers the aggregation of particles and droplets in detail for cyclonic spray dedusting is proposed. The model is applied to study the characteristics of multiphase flow field and the effects of the gas velocity, spray volume, and particle concentration on the removal efficiency. In addition, the simulation results are verified by the experimental data. The results suggest that the turbulence kinetic energy increases near the wall as the inlet velocity increases, and the spray region increases as the spray volume increases. This is conducive to turbulent mixing of the particles and droplets, and the agglomeration efficiency of the particles is improved, so the particle size increases, and the particle removal efficiency increases to 99.7% by simulation results are within the allowable range of error (about 99-99.5% in dedusting efficiency by experimental data). As the particle concentration increases, the particle removal efficiency initially increases, then decreases and reaches the highest value at 2 g/m3, which is due to the limited adsorption efficiency of the spray droplets. The results are helpful for providing a theoretical basis for spray to promote agglomeration of particles and improving the dust removal efficiency in the swirl field.

Learning time-aware multi-phase flow fields in coal-supercritical water fluidized bed reactor with deep learning

The supercritical water fluidized bed (SCWFB) reactor has been utilized to achieve clean and efficient conversion of coal as well as the generation of hydrogen. The complicated time-aware multi-phase flow fields inside the reactor however are usually obtained via time-consuming experiments or transient numerical simulation. To this end, we propose a data-driven deep spatio-temporal sequence model, named ReactorNet, for intelligent modeling and efficient prediction of the complex time-aware multi-phase flow fields inside the SCWFB reactor. Particularly, the model employs the U-Net architecture wherein the coupled convolution module and BiConvLSTM module in a single block are stacked to simultaneously extract the multi-scale spatial and temporal features of multi-phase flow fields in the reactor. The numerical results showcase that the ReactorNet could successfully and simultaneously learn the evolution of multi-phase flow fields in the reactor under different temperature conditions, thus performing accurate multi-step-ahead prediction. The flow fields predicted by ReactorNet are not only highly consistent with the simulated results, but also hundreds of times faster than the traditional numerical simulation. In addition, the ReactorNet can carry out both reasonable spatial and temporal extrapolation and even long-term rollout prediction according to the learned evolution principle of flow fields, thus showcasing remarkable generalization ability. It is the first attempt to apply deep learning to the modeling and predicting of time-aware multi-phase flow fields inside the challenging SCWFB reactor.