•An Euler-Euler large eddy simulation (EELES) approach is developed.•First to study scale-adaptive of EELES model for predicting dispersed bubbly flow.•−25/3 law of power spectrum densities is first ...found in high frequency region.•A grid comparable to bubble size can be effective for EELES.
Euler-Euler large eddy simulation (EELES) of transient dispersed turbulent bubbly flows in a laboratory scale square cross-sectioned bubble column has been presented. The main objective is to investigate the scale-adaptive of EELES model for predicting the dispersed bubbly flows. The sub-grid modeling is based on the Smagorinsky kernel with dynamic CS constant. The bubble induced turbulence and various interfacial forces including drag, lift, and virtual mass forces are incorporated in the model. Good quantitative agreement with previous experimental measurements by a two-camera particle image velocimetry (PIV) is obtained both for the fluctuating velocities and the mean velocities. More instantaneous details of two-phase flow characteristic in the bubble column have been captured by LES, including the multi-scale vortex structures, fluctuation characteristics of liquid motion and rotating buoyancy motion of bubbles. Predicted turbulence effective viscosity by unsteady Reynolds-Averaged Navier–Stokes (RANS) approach is nearly thirty times larger than LES, the turbulent dissipation is so strong that it cannot be used to predict the multi-scale fluctuation characteristics inside the bubble column. The classical −5/3 law of power spectrum densities (PSD) of liquid vertical velocity is hold properly in the low frequency region. For high frequency region, the classical −5/3 law does not hold properly, the decay is too fast, where the slope is around −25/3. The current EELES can be effectively used for studying the transient two-phase flow when a grid comparable to the bubble diameter is used, not just for the condition that the grid size is larger than the bubble diameter.
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•A volume-of-fluid and discrete-element-method solver was implemented in OpenFOAM.•Case studies were carried out with the simulation results compared with previous experiments.•The ...solver was suitable for systems with discrete particles and distinct fluid interface.
Numerous gas–liquid–solid flows exist in chemical engineering and metallurgical processes. Numerical modeling is an important topic that can be used to improve the design and investigate the operating conditions of these processes. The complicated interphase interaction within such three-phase systems, which include free surfaces and discrete phases, poses challenges in the existing methods. We implemented a volume-of-fluid (VOF) and discrete-element-method (DEM) combined solver, which should be useful for modeling the gas–liquid–solid systems, within the OpenFOAM framework. The Du Plessis and Masliyah drag force, added mass force, and capillary force were considered for fluid–particle coupling. The VOF–DEM solver was tested in three different cases, namely, particles in pure gas, particle collision in water, and gas–liquid–solid three-phase dam break. The results were validated against previous experiments and good agreement was obtained between the simulations and the experiments, which indicates the accuracy and suitability of this VOF–DEM solver for gas–liquid–solid systems.
To obtain a better understanding the gas-steel-slag three-phase flow in ladle metallurgy with eccentric gas bubbling, both the single-plug-stirred and dual-plug-stirred water model systems were ...employed. The plume Froude number derived from the buoyancy of the bubble plume was used to characterize the plume two-phase flow. The elctrical conductivity measurement technique was applied to measure the mixing time. A video technique was used to monitor the slag eye and the open software called ImageJ was taken to quantify the slag eye area. Some experiments were carried out to determine the location of the probe in the ladle where the measured mixing times can be interpreted as the bulk mixing times. The eccentric gas injection in the ladle bottom can improve the mixing efficiency in the ladle. Shorter mixing times can be achieved by injecting gas through two porous plugs, located diametrically opposite at mid-bath radius position (α=180°). A critical gas flow rate is proposed based on the formation of slag eye. The mixing time will decreases sharply at the condition of slag eye formation and collapse alternately. The critical gas flow rate increases with increasing the slag layer thickness and decreasing the porous plug angles. Four fators effect on the slag eye area were investigated: the gas flow rate, slag layer thickness, porous plug locations and angles. A semi-empirical model was developed based on the experimental data of the present work to describe the slag eye area as a function of the heights of the two liquids and the gas flow rate. The present correlation for slag eye area was reviewed against many previous different liquid-liquid systems.
A coupled three-dimensional finite-volume computational model has been developed to simulate the transient fluid flow, heat transfer and solidification processes in a vertical-bending continuous ...casting caster. The turbulence of molten steel inside the liquid pool is calculated using the large eddy simulation (LES). The enthalpy–porosity approach is used to simulate the heat transfer and solidification of steel in the caster. Based on the fractal theory and the conservation of mass, a kind of inclusion cluster model was developed. A new criterion was developed using the user-defined functions to model the motion and entrapment of inclusion cluster in the caster based on the Lagrangian approach. Firstly, the predicted growth of solidified shell was compared with the plant measurements, and the asymmetrical flow pattern was compared with the dye-injection observations of water model experiments. Secondly, the validated model was used to predict the instantaneous motion and entrapment distribution, statistical data, escape and entrapment positions of different inclusion clusters in the caster. Many known phenomena and other new predictions were reproduced in this part, and the center inclusion band defects in the steel plates found by the UT method can be interpreted using the current model. Finally, two methods were proposed to optimize the inclusion cluster motion and entrapment in the caster.
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•Transient flow, solidification and particle transport were studied using LES.•An inclusion cluster model was developed using fractal theory and mass conservation.•A criterion was developed to model the motion and entrapment of inclusion cluster.•Predicted center inclusion band agrees well with plant ultrasonic flaw detection maps.
Gas stirring ladle is a complex three-phase reactor which contains phases whose interfaces are in different scales. The bubble-liquid interaction also leads to multi-scale eddy structures. The ...present work proposes a multi-scale mathematical model to simulate the multiphase flow in ladle, which directly captures large phase interfaces and eddies, while models sub-grid scale interfaces and eddies using respectively discrete bubble model (DBM) and one equation eddy viscosity model (OEEVM) in large eddy simulation (LES) approach. By this way, the mesh resolution can be defined relatively coarse to save computational resources. The volume of fluid (VOF) model coupled with the compressive interface capturing scheme for arbitrary meshes (CICSAM) is adopted for the slag surface, while the DBM is used for handling the dynamics of discrete bubbles. The bubble coalescence is considered using the O’Rourke’s algorithm to solve the bubble diameter redistribution and it is found that aggregation mostly occurs below 0.2 m from the inlet. Moreover, bubbles are removed after leaving the air-liquid interface and the mass is transferred to air. The flow with multi-scale eddies induced by bubble-liquid interaction is solved using LES. The slag droplet entrainment and the slag-eye size fluctuation related with the pressure fluctuation on gas inlet are well revealed. The time-averaged spout eye size and the bubble diameter evolution are validated against the experimental data. The results show that the multi-scale VOF-DBM-LES model provides an effective modeling framework to predict the intrinsically unsteady flow behaviors in ladle.
An Euler-Euler large eddy simulation (LES) of transient gas-liquid turbulence flow in a bubble column was conducted to investigate the adaptiveness of various sub-grid scale (SGS) models. The ...performance of three SGS models, respectively the standard Smagorinsky model, the wall-adapting local eddy (WALE) model and the Dynamic model, on the predictions of bubbly flow was studied. Comparison between SGS models for time-averaged and transient velocities, gas void fraction, power spectrum density (PSD), SGS turbulent dissipation, SGS turbulent kinetic energy, and Reynolds stress is conducted. The transient multi-scale irregular vortex structures, fluctuation characteristics of liquid motion and spiral floating motion of bubbles can be well captured by LES. The Dynamic model and WALE model with CW = 0.325 give reasonably better agreement with the time-averaged experimental data. The transient fluctuation behavior of gas-liquid turbulent flow can be correctly captured by the current Euler-Euler LES model, whatever the SGS model. The classical −5/3 law of PSD of vertical liquid velocity is hold properly in the low frequency region. The slope of PSD is around −25/3 at the high frequency region. The Smagorinsky model and WALE model are sensitive to the model constant, at least for the energy transfer of high frequency. The molecular dissipation is negligible compared to the SGS turbulent dissipation. The Dynamic model gives higher predictions for fluctuation amplitude and time-averaged values of both SGS turbulent dissipation rate profile and SGS turbulent kinetic energy profile than other SGS models. A certain calculation time is needed to reach the dynamic stable state in LES, and the specific time is related to the scale of the calculation model.
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•Adaptiveness of various SGS models in LES for two-phase turbulent flow is studied.•First to study SGS turbulent dissipation, SGS turbulent kinetic energy, and Reynolds stress tensor for bubbly flow.•A certain calculation time is needed to reach dynamic stability process in LES.
A transient three-dimensional (3D) model was developed to understand the role fill ratio plays in the macrosegregation induced by the magnetohydrodynamic (MHD) thermosolutal convection in the ...electroslag remelting (ESR) process. In this model, the solution of the mass, momentum, energy, and species conservation equations are simultaneously implemented by the finite volume method with full coupling of the Joule heating and Lorentz force by solving the Maxwell's equations. Anisotropic permeability was employed to describe the directional solidification. The experimental data and the simulated data demonstrated reasonable agreement. An increase in fill ratio resulted in a larger melting rate and a deeper metal pool. The maximum positive and negative segregation indexes along the ingot centerline increased from 0.16 to 0.18 and from −0.055 to −0.071 respectively when the fill ratio was varied from 0.21 to 0.60.
•A transient 3D model was developed to study macrosegregation in ESR ingots.•Anisotropic permeability was first used to model directional freezing of ESR ingots.•Two nondimensional criteria were first proposed to reveal the effects of the forces.•The effect of the fill ratio on macrosegregation in ESR ingots was clarified.
Sustainable development strategy of bastnaesite concentrates.
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•The history of the metallurgical technology for bastnaesite is summarized.•The state-of-the-art processes for ...bastnaesite concentrates are critically reviewed.•Some recently developed methods towards cleaner production are introduced.•The prospects and recommendations for bastnaesite processing are provided.•Multiple factors should be considered for sustainable development.
Considering the indispensable role of rare earth elements in the field of modern high technology, the efficient exploitation and utilization of rare earth resources is of great importance. As one of the world's major rare earth minerals, bastnaesite significantly bears on scientific development and social progress. In order to provide some reference for future research and production, this paper retraces the history of the metallurgical processes of bastnaesite concentrates and critically reviews the current commercial industrial processes. Most of these processes are chemical and energy intensive, and the discharge of large quantities of low-grade waste has a serious negative impact on the ecological environment. The recently developed methods in laboratory scale towards cleaner production are then evaluated. More improvements are still needed to further simplify the process and reduce the reliance on strong acidic and alkali chemicals as well as the demand for energy. According to these evaluations, the prospects for process optimization are discussed, and the areas where further research is needed are suggested. To achieve sustainable development of the rare earth resources in bastnaesite, it is essential for the design of ideal process to comprehensively consider environmental impact, human health, economic benefits and resource utilization efficiency.
•The removal and distribution of non-metallic inclusions in ESR process were understood.•The magnetohydrodynamic flow, heat transfer and inclusion behaviour were solved simultaneously.•The ...interaction between the melt and inclusions was described by two-way coupled Euler-Lagrange method.•The effect of diameter, density and current on the inclusion behaviour was clarified.
A transient model coupling the magnetohydrodynamic flow and heat transfer is developed to predict the removal and distribution of non-metallic inclusions in electroslag remelting process. The interaction between the melt and non-metallic inclusions was described by two-way coupled Euler-Lagrange method. Both original inclusions from electrode and newly precipitated ones with solidification were considered. The effect of current on the inclusion behaviour was also studied. The model was validated by experiments. The overall removal ratio of original inclusions 2–20 µm in diameter increases from 80.47% to 94.75%. The inclusions with 30 µm even is completely removed. A proper increase of current is conductive to the removal efficiency. In the mushy zone the drag force and buoyancy force play a major role in the entrapment and distribution of newly precipitated inclusions. The inclusion amount increases along radius, but slightly decreases when ranging from 0.9 to 1.0 radius in the solidified ingot. The buoyancy force is great enough for almost all of the 20 µm inclusions to escape from the mushy zone. The absorption ratio of inclusions into slag decreases from 50.5% to 28.7% when the current increases from 3100 A to 3700 A due to the increase of solidification rate.
The structure, vaporization behavior and crystallization of CaF
2
–CaO–Al
2
O
3
slags with different SiO
2
contents for electroslag remelting were investigated by employing the TG and DSC ...measurements in conjunction with the Raman spectroscopy measurement for linking the macroscopic physicochemical property and microstructure information. The results show that SiO
2
addition makes the depolymerized aluminate units polymerized into fully polymerized Q
Al
4
unit and Al–O–Al complex structural groups. With the SiO
2
content increasing to 6.1 mass%, the vaporization rate of fluoride increases because the SiF
4
possessing higher vapor pressure is formed and the SiO
2
addition can promote the formation of AlF
3
. As SiO
2
content is further increased to 8.6 mass%, the vaporization rate of fluoride decreases because the mass transfer becomes slower. The more complex slag structure resulted from SiO
2
addition dramatically decreases the crystallization temperature of the primary crystalline phase and the size of crystalline particles in the solidified slag.
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