MODELING OF MULTISCALE AND MULTIPHASE PHENOMENA IN MATERIAL PROCESSING

Abstract In order to demonstrate how CFD can help scientists and engineers to better understand the fundamentals of engineering processes, a number of examples are shown and discussed. The paper will cover (i) special aspects of continuous casting of steel including turbulence, motion and entrapment of non-metallic inclusions, and impact of softreduction; (ii) multiple flow phenomena and multiscale aspects during casting of large ingots including flow induced columnar-toequiaxed transition and 3D formation of channel segregation; (iii) multiphase magneto hydrodynamics during electro-slag remelting; and (iv) melt flow and solidification of thin but large centrifugal castings

A Numerical Investigation on the Electrochemical Behavior of CaO and Al2O3 in the ESR Slags

Field structures including electromagnetic, concentration of ions, and flow fields in an ESR-like process composed of a graphite crucible containing a molten slag, air, and an iron electrode are computed. Both CaF2-(mass pct 2) CaO and CaF2-(mass pct 2) Al2O3 slags are examined. Tertiary current distribution is calculated. Therefore, polarization overpotential and Faradic reactions at metal-slag interface are considered using Tafel law, whereas transport of ions in the bulk of slag is determined through Nernst-Planck equations. The main goal is to shed light on the invisible phenomena such as magnetohydrodynamics caused by transport of ions, electrical conductivity of CaF2-based slag using additives (e.g., CaO or Al2O3), and the role of complexation of ions (e.g., AlO33-) in the molten slag applied to the ESR. An explanation is given for the observation of higher oxygen content in the metal using Al2O3 than that using equivalent amount of CaO in the CaF2-based slag of a DC-operated ESR

A Parametric Study of the Vacuum Arc Remelting (VAR) Process: Effects of Arc Radius, Side-Arcing, and Gas Cooling

Main modeling challenges for vacuum arc remelting (VAR) are briefly highlighted concerning various involving phenomena during the process such as formation and movement of cathode spots on the surface of electrode, the vacuum plasma, side-arcing, the thermal radiation in the vacuum region, magnetohydrodynamics (MHD) in the molten pool, melting of the electrode, and solidification of the ingot. A numerical model is proposed to investigate the influence of several decisive parameters such as arc mode (diffusive or constricted), amount of side-arcing, and gas cooling of shrinkage gap at mold-ingot interface on the solidification behavior of a Titanium-based (Ti-6Al-4V) VAR ingot. The electromagnetic and thermal fields are solved in the entire system including the electrode, vacuum plasma, ingot, and mold. The flow field in the molten pool and the solidification pool profile are computed. The depth of molten pool decreases as the radius of arc increases. With the decreasing amount of side-arcing, the depth of the molten pool increases. Furthermore, gas cooling fairly improves the internal quality of ingot (shallow pool depth) without affecting hydrodynamics in the molten pool. Modeling results are validated against an experiment

A volume of fluid (VOF) method to model shape change during electrodeposition

A novel volume of fluid (VOF) based approach is proposed to simulate the transient shape change of deposit front during electrodeposition considering secondary current distribution. Transport phenomena such as electrolyte potential, electric current density, and fluid flow of electrolyte are computed. The presented algorithm comprises computation of the exact VOF interface area as well as proposed modeling equations to accurately handle transport phenomena within the deposit. Based on the modeling results, it is essential to minimize the overshoot of electric current near the singularity between the cathode and insulator in the beginning stages of electrodeposition to achieve a relatively uniform thickness of the deposit layer in electroforming process. The results are validated against existing mathematical solutions

Investigation of effect of electrode polarity on electrochemistry and magnetohydrodynamics using tertiary current distribution in electroslag remelting process

Transport phenomena including the electromagnetic, concentration of ions, flow, and thermal fields in the electroslag remelting (ESR) process made of slag, electrode, air, mold, and melt pool are computed considering tertiary current distribution. Nernst-Planck equations are solved in the bulk of slag, and faradaic reactions are regarded at the metal-slag interface. Aiming at exploring electrochemical effects on the behavior of the ESR process, the calculated field structures are compared with those obtained using the classical ohmic approach, namely, primary current distribution whereby variations in concentrations of ions and faradaic reactions are ignored. Also, the influence of the earth magnetic field on magnetohydrodynamics in the melt pool and slag is considered. The impact of the polarity of electrode, whether positive, also known as direct current reverse polarity (DCRP), or negative, as known as direct current straight polarity (DCSP), on the transport of oxygen to the ingot of ESR is investigated. The obtained modeling results enabled us to explain the experimental observation of higher oxygen content in DCSP than that of DCRP operated ESR process

Influence du champ magnétique sur l'écoulement généré par un disque tournant dans une cavité fermée (application à la corrosion des aciers par l'eutectique liquide Pb-17Li)

GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Volume-Averaged Modeling of Multiphase Flow Phenomena during Alloy Solidification

The most recent developments and applications in volume-averaged modeling of solidification processes have been reviewed. Since the last reviews of this topic by Beckermann and co-workers [Applied Mech. Rev. 1993, p. 1; Annual Rev. Heat Transfer 1995, p. 115], major progress in this area has included (i) the development of a mixed columnar-equiaxed solidification model; (ii) further consideration of moving crystals and crystal dendritic morphology; and (iii) the model applications to analyze the formation mechanisms of macrosegregation, as-cast structure, shrinkage cavity and porosity in different casting processes. The capacity of computer hardware is still a limiting factor. However, many calculation examples, as verified by the laboratory casting experiments, or even by the casting processes at a small industrial scale, show great application potential. Following the trend of developments in computer hardware (projection according to Moore’s law), a full 3D calculation of casting at the industry scale with the multiphase volume-averaged solidification models will become practically feasible in the foreseeable future

Vyšetřování možných příčin přídavného kroudícího momentu na kormidle jachty

The present article deals with investigation of possible causes of the additional torque on the yacht’s rudder. One of the most important aspect for design of yachts are the symmetric conditions of all parts, which are located under water level and concentricity of the ship’s screw, rudder and keel relative to the hull. These symmetric and concentricity conditions have a major impact on the resulting dynamic properties of the ships. They have either substantial impact on the overall efficiency of installed engine and ship’s screw. As the result of poorly designed above mentioned parts, there can be an unsolicited additional torque on the yacht’s rudder and higher consumption of the fuel. Last but not least of these problems leads to poor controllability and discomfort within steering. This article is focused on the investigation of possible causes of the additional torque on the yacht’s rudder.Tento článek se zabývá vyšetřování možných příčin přídavného momentu na kormidle jachty. Jedním z nejdůležitějších aspektů při konstrukci jachet je symetrie všech částí, které jsou umístěny pod hladinoujsou a souosost lodního šroubu, ormidla a kýlu vzhledem k trupu lodi. Tyto podmínky symetrie a soustřednosti mají významný vliv na výsledné dynamické vlastnosti lodí. Mají dopad na celkovou účinnost instalovaného motoru a lodního šroubu. Důsledem nepřesné výroby výše uvedených komponent může být přídavný moment na kormidle jachty a vyšší spotřeba paliva. Současně s tím dochází ke špatné ovladatelnosti lodi a nepohodlí při řízení lodi. Tento článek je zaměřen na zkoumání možných příčin přídavného momentu na kormidle jachty