Numerical simulations of a gas-particle jet through a Laval nozzle are performed using a modified point-particle Euler–Lagrange approach. By excluding the particle-occupied fluid fraction when ...solving the fluid phase equations and accounting for gas-particle and inter-particle interactions in the mathematical framework, the particle motion behaviors in gas stream and their impact on gas stream structure are studied, and the nonequilibrium dynamics of the two-phase flow are revealed by depicting the particle velocity and temperature evolution in gas stream. The results indicate that the preferential concentration of particles occurs in gas stream, resulting in nonuniform jet structure. The preferential concentration mainly occurs in nozzle divergent section and makes the local flows there lie in dense regime even if a dilute two-phase flow is predetermined. The level of the preferential concentration increases when the powder feeding rate or the particle size increases. Thus, it is necessary to consider the volumetric displacement effect of dispersed phase when modelling such a gas-particle jet system. Based on the impact of powder blowing parameters on particles motion and distribution and oxygen jet structure, the powder feeding rate no more than 2.0 kg/s and the particle size of 50 to 100
µ
m are suggested for real industrial operations.
Gas injection through the submerged entry nozzle (SEN) into the continuous casting mold can be an effective approach for preventing SEN clogging and promoting the floatation of the non‐metallic ...inclusions. However, sometimes the exposed slag eyes due to gas injection appear on the top surface of the liquid slag layer, resulting in heat losses, re‐oxidation, and nitrogen pickup in the molten steel. An Eulerian multiphase‐flow model is developed to predict the argon‐steel‐slag three‐phase flow in a slab continuous casting mold. All the phases are treated based on Eulerian approach. The mathematical model is compared with the industrial observations and the water model experiments. Both of physical and numerical results reproduce the phenomenon of the high gas concentration at the SEN exit port. Most of the argon bubbles stay below the slag layer for quite long time because the slag blocks their floatation. Furthermore, the argon bubbles would gradually gather in a dense plume while escaping through the slag layer. Scattered argon exit spots are found at the top surface of slag layer. Two main locations of the exposed slag eye are found: 1) adjacent to the SEN; 2) at the mold's mid‐section at the position where a concentrated argon plume breaches through the slag layer. The near‐SEN exposed eye occurs under any of considered conditions. The one at the mid‐section is formed when the meniscus convex reaches a critical level, been dependent on the casting conditions.
The exposed slag eyes due to gas injection appear on the top surface of the mold are studied by an Eulerian multiphase‐flow model. Two main locations of exposed slag eye are found: 1) adjacent to the SEN; 2) at the mold's mid‐section at the position where a concentrated argon plume breaches through the slag layer.
Lagrangian tracking model combined with Eulerian multi-phase model is employed to predict the time-dependent argon–steel–slag–air quasi-four-phase flow inside a slab continuous casting mold. The ...Eulerian approach is used for the description of three phases (molten steel, liquid slag, and air at the top of liquid slag layer). The dispersed argon bubble injected from the SEN is treated in the Lagrangian way. The complex interfacial momentum transfers between various phases are considered. Validation is supported by the measurement data of cold model experiments and industrial practice. Close agreements were achieved for the gas volume fraction, liquid flow pattern, level fluctuation, and exposed slag eye phenomena. Many known phenomena and new predictions were successfully reproduced using this model. The vortex slag entrapment phenomenon at the slag–steel interface was obtained using this model, some small slag drops are sucked deep into the liquid pool of molten steel. Varying gas flow rates have a large effect on the steel flow pattern in the upper recirculation zone. Three typical flow patterns inside the mold with different argon gas flow rates have been obtained: double roll, three roll, and single roll. Effects of argon gas flow rate, casting speed, and slag layer thickness on the exposed slag eye and level fluctuation at the slag–steel interface were studied. A dimensionless value of
H
ave
/
h
was proposed to describe the time-averaged level fluctuation of slag–steel interface. The exposed slag eye near the SEN would be formed when the value of
H
ave
/
h
is larger than ~0.4.
A transient three-dimensional (3D) model was developed to understand the role slag thickness plays in the formation of the metal pool in the electroslag remelting (ESR) process. In this model, the ...solution of the mass, momentum and energy conservation equations were simultaneously implemented by the finite volume method with full coupling of the Joule heating and Lorentz force by solving the Maxwell’s equations. The movement of metal droplet was described by volume of fluid (VOF) approach. Additionally, the solidification was modeled using an enthalpy-based technique, where the mushy zone was treated as a porous medium. The experiment and simulation demonstrated a reasonable agreement. The results indicate that changing the slag thickness changes the slag temperature, but not monotonically. The slag temperature drops with the slag thickness up to 60 mm, beyond which the slag temperature rises. The melt rate decreases and then increases while the cooling intensity remains unchanged. As a consequence, the maximal metal pool depth reduces from 0.081 m to 0.067 m and slightly increases to 0.074 m.
A transient three-dimensional (3D) coupled mathematical model is developed in this paper in order to explore the electromagnetic, flow, and temperature fields, as well as the solidification in the ...electroslag remelting (ESR) process. Maxwell's equations are solved by the Finite Volume Method. The Joule heating and electromagnetic force (EMF), the source terms in the energy and momentum equations, are recalculated during each iteration as function of the phase distribution. The movement of the metal droplets is described by the Volume of Fluid (VOF) approach. Additionally, the solidification of the metal is modeled by an enthalpy-based technique, where the mushy zone is treated as a porous medium with a porosity equal to the liquid fraction. The results show that the electric current tends to go through the metal droplet first. The EMF varies with the falling metal droplet, always blocking the motion of the metal droplet. The zone with the highest temperature appears under the outer radius of the inlet. A larger Joule heating density, as well as a higher average temperature of the molten slag, is obtained when the current increases. Bigger metal droplets form with more heat and momentum, resulting in a deeper liquid metal pool.
•First time to develop a transient 3D coupled mathematical model of the ESR process.•Variation of Joule heating and EMF with the falling metal droplet is demonstrated.•Asymmetrical physical fields are revealed indicating the necessity of a 3D model.•The effect of the current on the heat transfer and MHD flow is clarified.
Gas was injected into the upper part of a water model ladle shroud, producing micro-bubbles by the shearing action of the high-speed entry flow of water, combined with subsequent bubble breaking ...actions of turbulence. An impact pad was used in favor of a standard turbulence inhibitor, to maintain the integrity of the micro-bubbles, and assure their wide distribution within the tundish. The effects of these two systems on removing small inclusions were investigated, and a numerical model was developed to simulate the motion behaviors of bubbles in the tundish, considering bubble coalescence. Both the turbulence inhibitor and the impact pad performed similar on flow improvement, but the impact pad effectively restrained coalescence between bubbles, leading to a 55.3 pct drop in the average bubble size within the tundish, and generating a 53.9 pct reduction in the residual numbers of inclusions below 51
μ
m diameter, by contrast with the turbulence inhibitor data. The impact pad fits well with gas bubbling for deep cleaning the liquid steel in tundish.
The cement-bonded corundum castables are often subjected to great temperature gradient in the service process of purging plugs for refining ladle. The mechanical properties of such castables are of ...particular interest in the serviceability and the safety of purging plug, which are significantly influenced by the microstructures including the amount, size and morphology of materials. The reported cement contents in compounds of purging plugs are generally low or ultralow, which inevitably limits the adjustable range of the mechanical properties enhancement by regulating their microstructures. In the present research, a serial of comprehensive experiments have been carried out, including the high cement contents (10–15 wt%), so as to further understand the role of cement content on the microstructural evolution and mechanical properties of castables. It is found that the phase compositions and microstructure can be optimized through adjusting the cement content in corundum castables. When the cement content is below 10 wt%, the hexagonal flake CA6 grains are platelet-shaped both in the matrix and at the border of the aggregates, their amount and size increase and distributions are more uniformly with cement content. When the cement content is above 10 wt%, small amount of granular crystals CA2 are detected in matrix, and CA6 crystals transform to equiaxial morphologies after cement content of 10 wt%. This research also provides quantitative relationship between the mechanical properties of the castables and the cement content. Castables with cement content of 10 wt% contain most hexagonal flake CA6 crystals, so that they have the highest CMOR and HMOR after heating at 1600 °C. However, CMOR decreases after cement content of 10 wt% due to the porosity and volumetric expansion from the formation of in-situ CA6 and CA2.
The current study developed a coupled computational model to simulate the transient fluid flow, solidification, and particle transport processes in a slab continuous-casting mold. Transient flow of ...molten steel in the mold is calculated using the large eddy simulation. An enthalpy-porosity approach is used for the analysis of solidification processes. The transport of bubble and non-metallic inclusion inside the liquid pool is calculated using the Lagrangian approach based on the transient flow field. A criterion of particle entrapment in the solidified shell is developed using the user-defined functions of FLUENT software (ANSYS, Inc., Canonsburg, PA). The predicted results of this model are compared with the measurements of the ultrasonic testing of the rolled steel plates and the water model experiments. The transient asymmetrical flow pattern inside the liquid pool exhibits quite satisfactory agreement with the corresponding measurements. The predicted complex instantaneous velocity field is composed of various small recirculation zones and multiple vortices. The transport of particles inside the liquid pool and the entrapment of particles in the solidified shell are not symmetric. The Magnus force can reduce the entrapment ratio of particles in the solidified shell, especially for smaller particles, but the effect is not obvious. The Marangoni force can play an important role in controlling the motion of particles, which increases the entrapment ratio of particles in the solidified shell obviously.
Purging plugs are widely used in the secondary refining process, and its service life determines the downtime and usage efficiency of the whole ladle. This study focuses on comparing the heat ...transfer and thermomechanical behaviour of purging plug with different slits to obtain the reason for the long service life of purging plug by thermal-structure coupling method. The numerical results showed that the moderation of temperature distribution is achieved by changing the slit shape and the reasonable arrangement of the circular slits. Furthermore, the circular slits can alleviate the stress concentration phenomena, and circular slits are better for decreasing the axial stress in the purging plug, which occurred at the position located 0.323 m above the bottom face, and its distance from the centre is 0.04 m.
A generalized three dimensional mathematical model, which adopted the Euler-Lagrange approach, has been developed for the motion of inclusions in a continuous casting tundish with channel type ...induction heating. The inclusion trajectories were obtained by numerical solution of the motion equation including gravity, buoyancy, drag, lift, added mass, Brownian, electromagnetic pressure and thermophoretic forces. Besides, the collision and coalescence of inclusions and adhesion to the lining solid surfaces were also taken into account. The Brownian, Stokes and turbulent collision were clarified, separately. Then the effect of induction heating power on the inclusion behavior was demonstrated. A reasonable agreement between the experimental observation and numerical results was obtained. The results indicate that the electromagnetic pressure force significantly promotes the removal of inclusions, especially for the bigger inclusion. Although the thermophoretic force goes against the removal of inclusions, its influence is negligibly small. The removal ratio of inclusions in the tundish with induction heating increases from 67.45% to 96.43%, while the power varies from 800 kW to 1200 kW. The collision and coalescence should be included when model the inclusion motion, because it can promote the removal of inclusion. The turbulent and Brownian collision becomes more active with the increasing power, while the Stokes collision is just opposite.
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