Mathematical Modeling of Fluid Flow in a Water Physical Model of an Aluminum Degassing Ladle Equipped with an Impeller-I
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automotive applications are commonly produced by foundry processes which include a refining stage where dissolved hydrogen and other impurities are removed from the melt through the injection of inert gases. This refinement operation determines to a great extent the quality of the product, and it must be optimized with the final objective of producing high quality castings as in the case of automobile and aerospace parts. The presence of dissolved hydrogen in the melt may be detrimental to the physical and mechanical properties of the aluminum castings due to the porosity associated with this gas.[1] To remove the gas from liquid aluminum, inert gas injection into the aluminum melt through a rotating impeller-injector is the most efficient technology, EUDOXIO RAMOS GO´MEZ, formerly Graduate Student with the Metallurgical Engineering Department, Facultad de Quı´ mica, UNAM, Edificio ‘‘D’’, Circuito de los Institutos s/n, Cd. Universitaria, C.P. 04510 Mexico, DF, Mexico, is now Numerical Simulation Consultant with Cavendish, Mexico, DF, Mexico. ROBERTO ZENIT, Researcher, is with the Materials Research Institute, UNAM, Cd. Universitaria, C.P. 04510 Mexico, DF, Mexico. CARLOS GONZA´LEZ RIVERA and MARCO A. RAMI´REZ-ARGA´EZ, Professors, are with the Metallurgical Engineering Department, Facultad de Quı´ mica, UNAM. Contact e-mail: [email protected] GERARDO TRA´PAGA, Professor, is with the Centro de Investigacio´n y de Estudios Avanzados del IPN, Unidad Quere´taro, Libramiento Norponiente 2000, Fracc. Real de Juriquilla, C.P. 76230 Juriquilla, Queretaro, Mexico. Manuscript submitted June 4, 2012. Article published online December 14, 2012. METALLURGICAL AND MATERIALS TRANSACTIONS B
one which has been employed in industry for decades.[2] This degassing technique reduces hydrogen concentrations to levels below 0.05 mL H/100 g of Al (0.12 wt pct H).[3] Employment of the impeller in the refining of aluminum has the main objective of promoting good stirring in order to improve mixing, which helps to increase the kinetics of gas, impurity and inclusion removal. Sieverts,[4] Ransley and Neufeld,[5] and Opie and Grand[6] set the base to understand the phenomena occurring during degassing of aluminum based on thermodynamics and the transport phenomena. Due to the opacity of aluminum and the aggressive conditions of temperature during the degassing operation, mathematical and water physical models represent useful tools to understand, control, optimize, and redesign the process. The first mathematical models developed to calculate the rate of hydrogen removal from liquid aluminum melts were based on global mass balances of hydrogen that include the degasification kinetics by defining a global mass transfer coefficient, and as a result of this balance, an ordinary differential equation is derived representing the change of hydrogen concentration in the melt with time.[7,8] At the end of the twentieth century, numerical simulations of fluid flow in stirred ladles were made considering steady state conditions, and the momentum transfer from the
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