Visualization of bubble coalescence in bubble chains rising in a liquid metal

Abstract Gas–liquid flows inside the submerged entry nozzle (SEN) of a slab mold and its influence in the flow field in the mold were studied using video recording, mathematical simulations and particle image velocimetry (PIV) approaches. Bubbly and annular flows in the SEN yield structurally-uncoupled and structurally coupled flows in mold, respectively. High gas loads (ratio of mass flux of gas and mass flux of liquid) at high casting rates lead to increases of bubble population and bubbles sizes due to coalescence processes whose rate exceeds that of their breakup. The presence of gas bubbles or gas layers inside the SEN lead to periodical twisting of the liquid flow that induces biased flows through both ports yielding uneven flows in the mold. A multiphase mathematical model predicts acceptably well the flow dynamics of two-phase flows inside the SEN.

Dynamics of two-phase downward flows in submerged entry nozzles and their influence on the two-phase flow in the mold

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.

Physical and Numerical Modeling of Exposed Slag Eye in Continuous Casting Mold using Euler–Euler Approach

X-ray radiography has proved to be an efficient and powerful tool for the visualization of two-phase flows in non-transparent fluids, in particular in liquid metals. This paper presents a validation of the X-ray radiography by comparing measurements in water with corresponding results obtained by optical methods. For that purpose Ar bubbles were injected through a single orifice. The measurements results are compared in terms of bubble size, bubble shape and velocity. Furthermore, visualization experiments were performed in the eutectic alloy GaInSn where the image contrast between the liquid phase and the gas bubble is much stronger. Some obvious differences of the bubble dynamics in water and GaInSn are discussed.

Validation of X-ray radiography for characterization of gas bubbles in liquid metals

We present an experimental study on the formation and behavior of a liquid metal bubbly flow arising from a downward gas injection through a top submerged lance (TSL). A visualization of the bubble dynamics was achieved by the X-ray radiography combined with high-speed imaging. The experiments were carried out in a parallelepiped container (144 × 144 × 12 mm3) using GaInSn, a ternary alloy that is liquid at room temperature. The gas flow rate Qgas was adjusted in a range between 0.033 and 0.1 L/s. Three different injection positions were considered with respect to the submergence depth L. X-ray images allow for a characterization of the flow regimes and provide the properties of the individual bubbles such as size, shape, and trajectory. Formation and entrainment of smaller gas bubbles are observed at the free surface. These small bubbles can be trapped in the fluid for a long time by recirculation vortices. Bubble size distributions are determined for different Qgas. The bubble detachment frequency is measured as a function of Qgas and L. The results are compared with previously published data for water. The X-ray radiography offers an effective method for determining the local void fraction and allows for an estimation of the bubble volume.

X-ray Radioscopic Visualization of Bubbly Flows Injected Through a Top Submerged Lance into a Liquid Metal

We present an experimental study concerned with investigations of the two-phase flow in a mock-up of the continuous casting process of steel. A specific experimental facility was designed and constructed at HZDR for visualizing liquid metal two-phase flows in the mold and the submerged entry nozzle (SEN) by means of X-ray radioscopy. This setup operates with the low melting, eutectic alloy GaInSn as model liquid. The argon gas is injected through the tip of the stopper rod into the liquid metal flow. The system operates continuously under isothermal conditions. First results will be presented here revealing complex flow structures in the SEN widely differing from a homogeneously dispersed bubbly flow. The patterns are mainly dominated by large bubbles and large-area detachments of the liquid metal flow from the inner nozzle wall. Various flow regimes can be distinguished depending on the ratio between the liquid and the gas flow rate. Smaller gas bubbles are produced by strong shear flows near the nozzle ports. The small bubbles are entrained by the submerged jet and mainly entrapped by the lower circulation roll in the mold. Larger bubbles develop by coalescence and ascend toward the free surface.

Visualization of Liquid Metal Two-phase Flows in a Physical Model of the Continuous Casting Process of Steel

The invention concerns a method for producing a metal coating on a moving ferromagnetic strip (2) which consists in causing the strip (2) to pass substantially vertically in a metal coating bath (1) contained in a crucible (10), causing it to pass through a slot (13) provided in the base of the crucible, and in adjusting the transverse position of the strip using magnetic forces generated for example by electromagnets (20) placed above the crucible and produced on said strip, on either side thereof, the intensity of the magnetic forces respectively applied on each face of the strip being determined so as to maintain the strip in a predetermined transverse position.

Method and device for continuously producing a metal surface coating on a moving sheet metal

Pour realiser un revetement metallique sur une bande ferromagnetique (2) en defilement, on fait passer la bande (2) sensiblement verticalement dans un bain du metal de revetement (1) contenu dans un creuset (10), en la faisant passer par une fente (13) menagee dans le fond du creuset, et on regle la position transversale de la bande au moyen de forces magnetiques generees par exemple par des electroaimants (20) places au-dessus du creuset et exercees sur la dite bande, de chaque cote de celle-ci, l'intensite des forces magnetiques appliquees respectivement sur chaque face de la bande etant determinee de maniere a maintenir la bande dans une position transversale predeterminee.

Procede et dispositif de realisation en continu d'un revetement de surface metallique sur une tole en defilement

Inductor (8,8') width (li) is less than internal width (lc) of the recirculation channel (5).

Galvanizing equipment for steel band advancing vertically upward through molten zinc bath, has inductors occupying less width than recirculation channel

Procede de revetement au trempe d'une bande d'acier (16) en defilement dans un bain liquide (9) de metal, tel que du zinc, ou d'alliage metallique contenu dans un bac (15), selon lequel on eloigne de la surface de la bande (16) les mattes qui sont formees au cours du revetement et flottent a la surface (10) du bain (9), au moyen d'au moins un inducteur (11-15), caque inducteur (11-15) produisant un champ electromagnetique glissant oriente selon une direction donnee et generant une force magnetomotrice, l'ensemble desdites forces magnetomotrices deplacant lesdites mattes en direction d'un recipient (19) charge de les recueillir et/ou en direction d'une zone (25) de la surface (10) du bain (9) d'ou elles sont evacuees, caracterise en ce que, pour au moins un desdits inducteurs (11-15), on inverse par intermittence ladite direction de son champ electromagnetique glissant de maniere a modifier les ecoulements des mattes a l'interieur du bac (15). Installation pour sa mise en uvre.

Marc Anderhuber

Papers

Visualization of Liquid Metal Two-phase Flows in a Physical Model of the Continuous Casting Process of Steel

Method and device for continuously producing a metal surface coating on a moving sheet metal

Procede et dispositif de realisation en continu d'un revetement de surface metallique sur une tole en defilement

Galvanizing equipment for steel band advancing vertically upward through molten zinc bath, has inductors occupying less width than recirculation channel

Procédé de revêtement au trempé d'une bande d'acier et installation pour sa mise en oeuvre