Many authors have pointed out that the steel superficial quality strongly depends on the operating conditions at the continuous caster mold. The analysis of the dynamic behavior of the fluid inside the mold Submerged Entry Nozzle (SEN) was done in this work by means of numerical simulations. In this work, the tundish sliding nozzle was not included. The results of two different turbulence models, the K-e and the Large Eddy Simulations (LES) models were compared. In simulations with both models, the velocity magnitude at 24 points inside the SEN was recorded every 0.001 s. The power spectrum of the results obtained with the LES turbulence model shows that the behavior inside the SEN is periodic. This behavior is compared with that obtained in physical simulations.KEY WORDS: continuous casting; fundamental frequencies; K-e turbulence model; LES turbulence model; submerged entry nozzle.ISIJ International, Vol. 46 (2006), No. 8, pp. 1183No. 8, pp. -1191 water model was employed. The mathematical model was solved using a commercial Computational Fluid Dynamics (CFD) software. Three different flow velocity conditions were simulated. To accomplish the dynamic analysis of the fluid inside the SEN, 24 monitoring points were defined. Several velocity magnitude time series were obtained for each monitoring point. Through a frequency analysis of the time series, it was found that jets at ports have periodic behavior which changes with SEN inlet flow velocity. Finally, it was found that the periodic frequencies obtained with mathematical simulations are similar to that measured in physical simulations. System DescriptionThe SEN geometry importance on the flow patterns inside the mold has been recognized long time ago. For instance, the SEN geometry in thin-slab continuous casting is very different to that used in the standard slab casting. 16,17) To compare the results of numerical simulations of this work with physical simulations reported in a previous work, 9) a pool-type SEN represented schematically in Fig. 1 was used. Additionally, the SEN dimensions correspond to a 1 : 1/3 scaled water model and are reported in Table 1. A bifurcated SEN with two exit ports was chosen, because this type is used commonly in actual casting and most of the numerical simulations of the fluid inside the SEN have been done using this geometry.In this work, the internal geometries of the bore and ports were assumed cylindrical. Nozzles with squared and cylindrical ports have been studied mathematically using the K-e turbulence model elsewhere. 10,12) These works have concluded that no significant differences between them were observed. The purpose of the port angle is to direct the molten steel jet into the mold cavity properly. The effect of the port angle on the flow pattern inside the mold has been widely studied. 10,12) In this work, downward ports were used. The port angle was 15 deg. This angle is commonly used at industry.Several configurations of the SEN bottom are used in actual casting. The most usual designs includes flat, pointed...

The flow patterns prevailing at the free-surface in a water model of a slab continuous casting mold using several water flow rates and entry nozzle submergence depths are experimentally and numerically studied in this work. The experimental study was carried out using an one-third scale cold water model, constructed in accordance with the Froude similarity criterion. Water level measurements were carried out with ultrasonic distance sensors and recorded in a computer. Numerical simulations were made with a commercial computational fluid dynamics software. It was found that free-surface oscillations are composed by several periodic components. There exists a fundamental periodic frequency of 1.2 Hz. Besides, there exist two other frequencies of 1.8 and 2.1 Hz whose contribution to the free surface dynamic behavior depend on the spatial position and on the process parameters, namely, the volumetric flow rate and the submerged entry nozzle (SEN) submergence depth. In accordance with the obtained results, several recommendations about operating policies of actual industrial casters are made.KEY WORDS: free surface velocity; mold flow; power density spectrum; slab continuous casting; submerged entry nozzle.well-known Navier-Stokes equations, which in vectorial form are expressed as follows 8,10) Given that the experiments are carried out isothermally, the energy equation is not considered. The K-e turbulence model was selected for mathematical modeling, which is described by the following expressions: ... (4) In the above equations K is the turbulent kinetic energy, e is dissipation rate of K. s K , s e , C 1 and C 2 are constants whose values are 1.0, 1.3, 1.44 and 1.92 respectively.8) The fluid viscosity must be corrected for turbulence in the Navier-Stoke equations employing an effective viscosity m eff ϭm l ϩm t , where m l is the laminar viscosity and m t is the turbulent viscosity. The latter can be determined as follows: (5) where C m ϭ0.09 is a constant. The boundary conditions in the mathematical model were those recommended by Thomas et al. 8) and are as follows: Inlet turbulence parameters at the inlet were Kϭ0.044 m 2 s Ϫ2 and eϭ1.00 m 2 s Ϫ3. At the outlet, the boundary condition was fixed in such a way that the mass balance was satisfied.A commercial CFD software was employed for numerical solving of the above mathematical model. A two-dimensional mesh with 32 500 nodes was created with a time step of 0.001 s. A personal computer with 1 GB of RAM memory and 3.0 GHz CPU was utilized for the numerical simulations. A run for 70 s of real time required a CPU time of approximately 5 h. In order to track the free surface profile, two-phase flow was considered and the Volume-of-fluid (VOF) model 10) was chosen for tracking of the air-water interface. Physical ModelingA plastic one-third scale water model was designed and constructed in accordance with the Froude similarity criterion. Froude criterion guarantees that the water model is similar to the industrial caster mold from the geometrical and dynamical...

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Peirce-Smith converters (PSC) are chemical reactors where copper matte reacts with air. A conventional PSC is a long horizontal cylinder where air is injected laterally into the cooper bath through submerged tuyeres. In these PSC, air is injected at high velocities to obtain an adequate mixing of the copper bath and to avoid tuyere blockage. An alternative PSC configuration uses top blowing of air accompanied by gentle nitrogen bottom stirring. In this work, the direct bottom injection of air at low inlet velocity was studied by means of transient multiphase 3D CFD numerical simulations considering three blowing conditions. The ?-? turbulence model and the volume of fluid model (VOF) were used in order to model the turbulent nature of the flow and to deal with the multiphase flow. Special attention was paid to the air bubbles formation and its effect on the copper bath mixing. The dynamic behavior of turbulent kinetic energy and the average velocity of the copper matte were analyzed. The numerical simulations suggest that the relationship between air inlet velocity and bath mixing is non linear. However, using the air bottom injection at low velocities, the obtained copper bath nominal velocity is similar to that reported in a conventional PSC.

This paper proposes a Markov observation based model, where the transition matrix is formulated using air quality monitoring data for specific pollutant emissions, with the primary objective to analyze the corresponding stationary distributions and evaluate sceneries for the air quality impact of pollution control policies. The model is non predictive and could be applied to every source of pollutant emissions included in air monitoring data. Two cases of study are presented, ozone and sulfur, over central zone of Mexico City for a seven years span from 2000 to 2006. For presentation purposes each year were divided in two semesters. In ozone case, the stationary distribution for both semesters shows a probability diminution of the higher ozone concentrate levels, with tendency to "piston effect". In the sulfur case, the first semester displays an oscillatory behavior with a little tendency to diminution of the higher sulfur concentrate levels, the second semester had decreasing probabilities of the higher sulfur levels. The results support an small improvement of air quality and then a favorable evaluation of the diverse pollution control policies that had been implemented in Mexico City over the last several years. Keywords ResumenEn este trabajo se propone un modelo de Markov basado en observaciones, donde la matriz de transición se formula empleando información del monitoreo de la calidad del aire para ciertos contaminantes específicos, con el objetivo principal de analizar las distribuciones estacionarias correspondientes y evaluar escenarios del impacto de las medidas de control anticontaminantes de la calidad del aire. El modelo no es predictivo y puede aplicarse a cualquier fuente de emisiones contaminantes incluidas en el sistema de monitoreo ambiental. Se presentan dos casos de estudio, ozono y azufre, sobre la zona central de la Ciudad de México para un intervalo de siete años del 2000 al 2006. Para propósitos de presentación, cada año se dividió en dos semestres. En el caso del ozono, la distribución estacionaria para ambos semestres mostró una disminución en la probabilidad de ocurrencia de los niveles de alta concentración de ozono, con cierta tendencia al "efecto pistón". En el caso del azufre, el primer semestre mostró un comportamiento oscilatorio con una pequeña tendencia a la disminución de los niveles de alta concentración y en el segundo semestre disminuyeron las probabilidades de altos niveles de azufre. Los resultados establecen una ligera mejoría en la calidad del aire y por lo tanto una evaluación favorable de las diversas medidas de control de contaminantes que han sido implementadas en la Ciudad de México en losúltimos años.Palabras clave: Cadenas de Markov; distribución estacionaria; contaminación del aire; emisiones de azufre; emisiones de ozono; Ciudad de México.Mathematics Subject Classification: 60J20, 91B76.