Sponsored by: LMD Aluminum Committee
Program Organizer: Ms Fiona J Stevens, Comalco Research and Technology, Comalco Research Centre, PO Box 316, Thomastown, Victoria 3074, Australia
Wednesday, AM Room: A9
February 7, 1996 Location: Anaheim Convention Center
Session Chairperson: Martin Segatz, VAW Aluminium-Technologie GmbH, Friedrich - Woehler - Str.2, 53117 Bonn, Germany
A STUDY OF BATH VELOCITY DISTRIBUTION IN A 3-D WATER MODEL: J.J. Chen, Xianchun Shen, B.J. Welch, Chemical & Materials Engineering Department, The University of Auckland, Private Bag 92019, Auckland, New Zealand; M.P. Taylor, New Zealand Aluminium Smelter, Private Bag 90110, Invercargill, New Zealand
A probe consisting of a sphere and an embedded thermocouple was used for measuring point velocities in a 3-D air-water model. Prior to testing in the model, the probe was calibrated in a water flow channel. Results measured in a full-scale 3-D model covering various parts of the cell including various positions of the anode/anode ledge slot and the anode/sidewall gap will be reported. Flow directions may also be detected using this measurement technique.
A HYDRODYNAMIC MODEL FOR THE BATH FILM BETWEEN METAL AND SIDE LEDGE IN ALUMINUM CELLS: Torstein Hansen, Kemal Nisancioglu, Department of Electrochemistry, Norwegian Institute of Technology, N-7034 Trondheim, Norway; AsbjØrn Solheim, SINTEF Materials Technology, N-7034 Trondheim, Norway
Existence of a thin bath film between the side ledge and metal has been suggested to affect heat and mass transfer in aluminum cells. The present mathematical model, based on the simultaneous solution of the equations of momentum, energy and mass transfer shows that such a film can be maintained by surface-tension driven flow along the metal-film interface, provided that the bottom sludge is more acidic than the top electrolyte. The film contributes to the resistance against heat flow between the metal and the side ledge. Moreover, the variation in the xs AlF3 and Al203 concentrations along the film leads to decreasing liquidus temperature and increasing heat flux in the vertical position toward the bottom of the cell.
A WATER-MODEL STUDY OF THE LEDGE HEAT TRANSFER IN AN ALUMINIUM CELL: John J.J. Chen, Chuck C. Wei, Chemical & Materials Engineering Department, The University of Auckland, Private Bag 92019, Auckland, New Zealand; Anthony Ackland, Comalco Research Centre, PO Box 316 Thomastown Victoria 3074, Australia
A heat transfer probe was developed for studying the ledge heat transfer in a full-scale 3-D air-water model. Quantitative measurements were conducted to determine the bath/ledge heat transfer characteristics at various positions and different operating conditions. A similitude analysis was carried out to relate the measured point results to data available in the literature. A suggested range of heat transfer coefficients for the reduction cell is presented. Variation of the heat transfer due to anode bottom inclination and position on the side ledge relative to the anode slot as well as in the vertical direction, were also examined.
A STUDY OF THE SURFACING BUBBLES SPEED IN A PHYSICAL MODEL REPRESENTING THE LAYER OF LIQUID COAL PITCH: Begunov A.I., Yakovleva A.A., Irkutsk State Technical University; Irkutsk, Lermontov Str., 83, Russia
Many plants in Russia operate cells with self-baking anodes. Gas and fluid dynamic processes, occurring in the formation of anodes under the electrolysis conditions, influence the volume of cancer causing hydrocarbonic wastes and they were not sufficiently investigated. This paper investigates the motion specifics of gas bubbles, penetrating from the baked part of the anode and barbotting through the layer of liquid anodic paste. A model has been used, in which paraffine represents pitch, both having very similar thermal and physical properties. The column of the liquid part of the anode is modelled to its original size and with the similar vertical distribution of temperatures. The speed of gas bubbles, surfacing in the model medium, has been studied and the numerical values of the coefficients of resistance for the surfacing of bubbles have been determined.
10:10 am BREAK
ELECTRIC FIELDS IN THE ELECTROLYTES OF ALUMINIUM CELLS: A.I. Begunov, I.S. Grinberg, V.N. Kulkov, Irkutsk State Technical University; Irkutsk, Lermontov Str., 83, Russia
By means of physical modelling the electric fields for an aluminium cell have been constructed for the operating modes with a stable wall freeze and bottom freeze, with the anode effect and with a bottom freeze without a wall one. The bottom freeze, projecting over the metal surface, increases the voltage of the electric field and the current density on the wall plate when the distribution over the electrodes is unchanged. When the bottom freeze length doubles, there arises a redistribution of the current shares between the side and bottom surfaces of the anode, leading to the decrease of the load on the side surface. The electric field at different stages of anode effect development has been investigated. When the anode bottom conducting surface share changes from 0,016 to 0,025, there occurs a sharp redistribution of current from the side surface of the anode to the bottom one.
FINITE ELEMENT MODELLING FOR STRUCTURAL ANALYSIS OF CATHODE CASINGS: Mohammad M. Megahed, Dept Mechanical Design & Production, Cairo University, Egypt; Hesham S. Sayed, Structural Engineering Dept, Cairo University, Egypt; Mohammed M. Hasan and Shaher A. Mohammad, Aluminium Co of Egypt, Nagi-Hammadi, Egypt
In order to conduct parametric studies of design changes, a desirable prerequisite of the F.E model is the ease by which design changes can be evaluated. In this paper, three levels of F.E models are built for a certain design of cathode casing; viz. two types of simplified models and a detailed F.E model. The first simplified model employs a combination of shell elements and 3-d beam elements connected by rigid-bar elements to simulate welding between shell and stiffeners. The second model employs a larger number of shell elements together with 3-d truss and/or beam elements to represent beam webs. In the third F.E model, the whole casing structure including all beam flanges and webs is represented by much larger number of thin shell elements. Compared to the all-shell detailed model, simplified models allow quick and reasonably accurate assessment to be made of the effects of various spatial arrangements of different sizes of beam stiffeners on overall cathode stresses and deformations. The simplified models have been successfully used to conduct design improvement studies which resulted in weight reduction by about 7% while improving its structural performance significantly. This result is confirmed by conducting non-linear F.E analysis.
ASSESSMENT OF CATHODE SWELLING PRESSURE USING INVERSE NONLINEAR FINITE ELEMENT TECHNIQUE: Hesham S. Sayed, Structural Engineering Dept, Cairo University, Egypt; Mohammad M. Megahed, Dept Mechanical Design & Production, Cairo University, Egypt. Hamad H. Omar and Ismael M. Ismael, Aluminium Co of Egypt, Nagi-Hammadi, Egypt
The paper presents a new technique to determine the magnitudes of swelling pressures acting on the sidewalls of cathode casings. A nonlinear finite element model for the cathode structure is developed taking into consideration the material non-linearity effect and influence of temperature on mechanical properties of steel. A system identification technique (inverse problem) is used to estimate the swelling pressure by solving the forward non-linear problem in conjugate with the deformation field measurements of side walls of an operating cathode. The outcome of the inverse problem revealed that the proposed technique is efficient and can capture the essential features of the swelling phenomenon and the cathode structure response using a simple field deformation measurements.
THE FURTHER STUDIES ON CALCULATION METHOD OF MAGNETIC FIELD IN ALUMINIUM REDUCTION CELL: Li Guohua, Li Dexiang and Li Dianfeng, Department of Nonferrous Metallurgy of Northeastern University, Shengyang, 110006, China
On the basis of the theory of using two scalar potentials method for
calculation magnetic fields in aluminium reduction cells, we developed an
applied software. In the paper, the function blocks of the software are
described and some key problems in using this software for calculation magnetic
fields in reduction cells are introduced. The software has been debugged step
by step and taken cold simulated test in laboratory. The results show that the
method and software are very good. In the paper, the result using this software
for calculation magnetic field in a certain industry cell is also given.
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