Thorvald Abel Engh

Fluid dynamics in bubble stirred ladles: Part I. experiments

Air is supplied through a porous plug placed in the center axis of a cylindrical perspex-water model of a ladle. A Laser-Doppler system is employed to measure radial and axial mean and fluctuating velocities. Velocities in the two-phase bubbly region can also be determined. Velocities are measured near the bottom, half-way up, and near the free surface. It is shown that the bubbles contribute to production of turbulence. The ladle has recirculation zones near the bottom, where the mean velocities are very low. Close to the free surface the radial mean and turbulent velocities are high, promoting mass transfer through the interface. The present measured velocity profiles cannot be reduced to a single profile by employing similarity scaling.

Wetting of pure aluminium on graphite, SiC and Al2O3 in aluminium filtration

Abstract The wettability of pure aluminium on filter materials and on inclusions is believed to be an important factor affecting the filtration of aluminium. The contact angles of molten aluminium on alumina, SiC and graphite were measured under 10−8 bar high vacuum in the temperature range of 1000–1300 °C. To describe the wetting behaviour of the Al on ceramic at lower temperatures used in filtration and casting aluminium, a semi-empirical calculation was employed. The calculated contact angles at 700 °C were around 97° for alumina, 92° for vitreous graphite, 126° for single- and poly-crystal graphite, and 79° for single crystal SiC, respectively. This indicates that aluminium does not wet alumina or graphite (or Al4C3) around the casting temperature, but wets SiC at this temperature. Thus a priming height is required for aluminium to infiltrate an alumina filter. Increasing temperature can also improve the wettability of Al on ceramic.

Vacuum Evaporation of Pure Metals

Theories on the evaporation of pure substances are reviewed and applied to study vacuum evaporation of pure metals. It is shown that there is good agreement between different theories for weak evaporation, whereas there are differences under intensive evaporation conditions. For weak evaporation, the evaporation coefficient in Hertz-Knudsen equation is 1.66. Vapor velocity as a function of the pressure is calculated applying several theories. If a condensing surface is less than one collision length from the evaporating surface, the Hertz-Knudsen equation applies. For a case where the condensing surface is not close to the evaporating surface, a pressure criterion for intensive evaporation is introduced, called the effective vacuum pressure, peff. It is a fraction of the vapor pressure of the pure metal. The vacuum evaporation rate should not be affected by pressure changes below peff, so that in lower pressures below peff, the evaporation flux is constant and equal to a fraction of the maximum evaporation flux given by Hertz-Knudsen equation as 0.844

Wetting behavior of aluminium and filtration with Al2O3 and SiC ceramic foam filters

\dot{n}_{\hbox{Max} }

Plant Scale Investigation of Liquid Aluminum Filtration by Al2O3 and SiC Ceramic Foam Filters

. Experimental data on the evaporation of liquid and solid metals are included.

Influence of Coating and De-Coating on the Coalescence of Aluminium Drops in Salt

Abstract Silicon is the material most commonly used in the manufacturing of photovoltaic (PV) cells. In the current study, laboratory experiments of purification of solar cell silicon materials through filtration are carried out. Inclusion removal from silicon was investigated. The purpose is to achieve clean silicon materials for solar cells. Silicon samples and filter samples were analyzed using microscope observation, EPMA, and X-ray detection. Silicon nitride (Si3N4) and silicon carbide (SiC) particles are the main non-metallic inclusions present in top-cut silicon scrap. Almost all inclusions larger than 10 μm can be removed from silicon by the porous foam filter. In mass fraction, more than 90% inclusions are removed. Si3N4particles are mainly removed on the top surface of the filter, and SiC particles are mainly removed by entering the pores and attaching to the filter material. SiC inclusions are not only simply attached on the surface of the filter material, but are found also inside the filter material. There are SiC bridges near the filter materials. These bridges may fill the spaces between filter material, and this will further retard inclusions passing through the filter. Three-dimensional turbulent fluid flow and inclusion motion in the filter was calculated. Both experimental observation and fluid flow simulation indicate that most of the inclusions are entrapped at the upper part of the filter.

Oxidation of Manganese-Containing Aluminum Alloys Studied by SEM

The wetting behavior between liquid aluminium and substrates made from industrial Al2O3 and SiC based ceramic foam filters (CFF) was investigated. The same CFF filters were also tested in plant scale filtration experiments. The wetting experiment results show that the SiC based filter material is better wetted by liquid aluminium than the Al2O3 based filter material. This indicates that the improved wetting of aluminium on a filter material is an advantage for molten metal to infiltrate the filter during priming. Also, better wetting of Al-filter might increase the removal efficiency of inclusions during filtration due to better contact between filter and metal. Non-wetted inclusions are easier to be removed.

Oxidation of Manganese-Containing Aluminum Alloys

Removal of Na by an “active” AlF3 filter seemed to be so efficient that all the sodium was removed in the present experiments. The removal of Na is considered to be limited by the resistance in the melt boundary layer only. However this is not the case for calcium. For calcium to be transfered into the AlF3, resistance in the filter grains has to be taken into account in addition to the resistance in the melt boundary layer. This was indicated by the total mass transfer coefficient of only 4x10-5 m/s. A kinetic model was derived that can describe the removal of Ca from molten aluminum in an “active” AlF3 filter by deep bed filtration following first order kinetics.