Water Physical Model Research Articles

Power characteristics and mass transfer of rotor injectors in a water physical model of an aluminum degassing ladle

A comparative experimental study of a physical model of a stirred ladle for a rotor-injector aluminum degassing system in the turbulent regime has been carried out. A quantitative analysis of the gaseous oxygen mass transfer to the water in a physical model is performed by evaluating the power consumption and mass transfer capacity employing the typical methods used in mechanically stirred tanks. Three rotor injector devices were compared, including two conventional designs and one new rotor design. The rotors were evaluated as a function of the rotational speed and gas flow rates. The conventional rotors exhibited similar performance, while the new design consumed more power when operating at high gassing flow rates and rotational speeds resulting in a higher breakup rate of bubbles and promoting a better formation of tiny bubbles, which are better distributed over the entire ladle. This behavior avoids bubbles rising freely to the free surface; so that the gas hold-up increases leading to an improved mass transfer capacity when using this rotor-injector. The results reported in this work agreed with previously reported works in the literature.

Utilization of the Planar Laser-Induced Fluorescence Technique (PLIF) to Measure Temperature Fields in a Gas-Stirred Ladle

A 1/17th water physical model of a 200-ton steel ladle furnace with a single gas injection was used to simulate bath heating using a single burner to mimic the heat flux due to electric arcs in the industrial steel ladle. Two phases were considered, using water to simulate the molten steel and air to simulate the argon injection at a flow rate of 1.54 NL min−1. The planar Laser-Induced Fluorescence (PLIF) technique was for the first time experimentally implemented to measure temperature fields in a longitudinal plane of the gas-stirred ladle model. PLIF employs a laser source of 532-nm wavelength to light water seeded with rhodamine B, which emits fluorescence depending on its temperature, after a complex calibration is made. Next, the fluorescence is captured by a camera with a 550-nm wavelength filter. The PLIF measurements were validated by local thermocouple measurements at five different locations in the measurement plane. Temperature fields measured by PLIF are in good agreement with those obtained locally by thermocouples, so the PLIF technique can be used to measure temperature fields with the advantage of getting a complete temperature contour field, in contrast to point values of temperatures with thermocouples. Experiments were carried out to study the thermal mixing for two common tuyere positions, i.e., axisymmetric and eccentric (mid-radius) positions. Results on the injection mode show that axisymmetric gas injection is a more efficient heat transfer configuration between the burner and the liquid phase than is the symmetric injection mode for the particular heating configuration studied in this work.

Simulation of Bubble Behavior in a Water Physical Model of an Aluminum Degassing Ladle Unit Employing Compound Technique of Rotary Blowing and Ultrasonic

A two-dimensional volume of fluid (VOF) model was developed to simulate the behavior of bubbles in a physical model of the aluminum degassing unit employing the compound technique of rotary blowing and ultrasonic. The effect of rotation speed on bubble behavior under rotating flow field, and the effects of ultrasonic parameters including the amplitude, length, and position of ultrasonic end-face on bubble behavior under compound field were analyzed according to the simulation results, respectively. The experiment shows the simulation results for the bubble shape and trajectory agree well with the experimental observations. Under single rotating flow field, the rotation speed has a strong impact upon bubble trajectory and the optimal speed is 450 rpm. Under compound field, ultrasonic can increase the number of broken bubbles, and push bubbles to further area, which is beneficial to strengthen the bubble distribution and improve the degassing effect. The appropriate amplitude, length, and position of ultrasonic end-face are 23 μm, 50 mm, and 185 mm.

Physical and Mathematical Modeling of Metal-Slag Exchanges in Gas-Stirred Ladles

AbstractLadle refining plays a key role in achieving the quality of the steel since in this reactor temperature and chemical composition is adjusted, elimination of non-metallic inclusions is performed, and also deoxidation and desulphurization are operations taking place in the refining process. Specifically, the metal-slag mass exchanges have not received much attention through scientific studies. In this work, a rigorous study on the mass exchange between metal and slag is presented through a scaled water physical model. In the model, thymol (playing the role of a solute such as sulfur) is added to the water (playing the role of steel) and silicon oil (playing the role of slag) picks up the thymol, while the ladle is agitated with the central injection of gas. The evolution of thymol concentration in time was measured. Also, a mathematical model was developed and cast into the commercial CFD code Fluent Ansys to represent the fluid flow phenomena and the mass transfer through the solution of the continuity equation, the turbulent momentum conservation equations and the species mass conservation equation. There is a good agreement between the measured and the computed results regarding the thymol concentration evolution in water and consequently the mathematical model was validated regarding the mass species metal-slag exchanges and it may be used to study metal-slag exchanges in the steel ladle such as deoxidation or desulphurization.

Design of a rotor for aluminum degassing assisted by physical and mathematical modeling

ABSTRACTRecent studies on aluminum degassing [1, 2] show that although the impeller speed and the gas flow rate are important process variables in terms of the productivity and operational costs, the impeller design is also a key design parameter influencing the productivity and the quality of the aluminum in foundry shops. In this work, an improved design of an impeller is tested through a water physical model and mathematical modeling and its performance is compared against commercial designs of impellers. A full-scale water physical model of a batch aluminum degassing unit was used to test the impellers by using the same operating conditions (580 rpm and 40 liters per minute) and by performing deoxidation from water by purging nitrogen into the water saturated with oxygen (similar to the dehydrogenation). A mathematical model based on first principles of mass and momentum conservation equations was developed and solved numerically in the commercial CFD code ANSYS Fluent to describe the hydrodynamics of the system with the objective of explaining the deoxidation kinetics observed in the experiments. It has been found that the new impeller design shows a better performance than the commercial designs in terms of degassing kinetics for the conditions used in this study, which is explained since the new design promotes a flow dynamics that increases the pumping effect, creating a bigger pressure drop and fluid flow patterns which help to drag and distribute more evenly the bubbles in the entire ladle than the commercial designs.

Effect of the Impeller Design on Degasification Kinetics Using the Impeller Injector Technique Assisted by Mathematical Modeling

A mathematical model was developed to describe the hydrodynamics of a batch reactor for aluminum degassing utilizing the rotor-injector technique. The mathematical model uses the Eulerian algorithm to represent the two-phase system including the simulation of vortex formation at the free surface, and the use of the RNG k-ε model to account for the turbulence in the system. The model was employed to test the performances of three different impeller designs, two of which are available commercially, while the third one is a new design proposed in previous work. The model simulates the hydrodynamics and consequently helps to explain and connect the performances in terms of degassing kinetics and gas consumption found in physical modeling previously reported. Therefore, the model simulates a water physical model. The model reveals that the new impeller design distributes the bubbles more uniformly throughout the ladle, and exhibits a better-agitated bath, since the transfer of momentum to the fluids is better. Gas is evenly distributed with this design because both phases, gas and liquid, are dragged to the bottom of the ladle as a result of the higher pumping effect in comparison to the commercial designs.

Comparison of the hydrodynamic performance of rotor-injector devices in a water physical model of an aluminum degassing ladle

The hydrodynamic performance of a stirred ladle, for an aluminum degassing system in turbulent regime, is analyzed experimentally. This study explores the dynamic flow features due to the bubble dispersion on the gas–liquid flow. Diverse impellers with geometrical differences are tested with the purpose of comparing the influence in the flow behavior. Three rotor-injector devices are compared, including two conventional designs and one new rotor design. The rotor performance is evaluated at two gas flow rates. The velocity fields are investigated in a water physical model under flow conditions similar to those encountered in the degassing process of molten aluminum. The particle image velocimetry (PIV) technique is employed to obtain the velocity fields during the degassing process. In such a way, instantaneous measurements of the water flow field for gassed and ungassed conditions were obtained. Considering the two gassing conditions, it is found that the flow patterns changed drastically with all the rotors tested. Moreover, the turbulent flow field results showed significant differences under gassing and ungassed conditions. Here, it is demonstrated that the rotor geometries strongly affect the distribution of turbulent intensities. It was found that the new rotor exhibits the better performance under gassed conditions, showing high turbulent intensities, producing a higher gas breakup rate and promoting the formation of small bubbles that can be easily distributed over the entire ladle. This is due to its asymmetrical geometry, as is exposed in the present analysis.

Physical Modelling Of The Steel Flow In RH Apparatus

Abstract The efficiency of vacuum steel degassing using RH methods depends on many factors. One of the most important are hydrodynamic processes occurring in the ladle and vacuum chamber. It is always hard and expensive to determine the flow character and the way of steel mixing in industrial unit; thus in this case, methods of physical modelling are applied. The article presents the results of research carried out on the water physical model of RH apparatus concerning the influence of the flux value of inert gas introduced through the suck legs on hydrodynamic conditions of the process. Results of the research have visualization character and are presented graphically as a RTD curves. The main aim of such research is to optimize the industrial vacuum steel degassing process by means of RH method.

Ultrasound imaging measurement of submerged topography in the muddy water physical model

The real-time, accurate measurement of submerged topography is vital for the analysis of riverbed erosion and deposition. This paper describes a novel method of measuring submerged topography in the B-scan image obtained using an ultrasound imaging device. Results show the distribution of gray values in the image has a process of mutation. This mutation process can be used to adaptively track the topographic lines between riverbed and water, based on the continuity of topography in the horizontal direction. The extracted topographic lines, of one pixel width, are processed by a wavelet filtering method. Compared with the actual topography, the measurement accuracy is within 1 mm. It is suitable for the real-time measurement and analysis of all current model topographies with the advantage of good self-adaptation. In particular, it is visible and intuitive for muddy water in the movable-bed model experiment.

Two-Phase CFD Model of the Bubble-Driven Flow in the Molten Electrolyte Layer of a Hall–Héroult Aluminum Cell

A two-phase computational fluid dynamics (CFD) model has been developed to simulate the time-averaged flow in the molten electrolyte layer of a Hall–Heroult aluminum cell. The flow is driven by the rise of carbon dioxide bubbles formed on the base of the anodes. The CFD model has been validated against detailed measurements of velocity and turbulence taken in a full-scale air–water physical model containing three anodes in four different configurations, with varying inter-anode gap and the option of slots. The model predictions agree with the measurements of velocity and turbulence energy for all configurations within the likely measurement repeatability, and therefore can be used to understand the overall electrolyte circulation patterns and mixing. For example, the model predicts that the bubble holdup under an anode is approximately halved by the presence of a slot aligned transverse to the cell long axis. The flow patterns do not appear to be significantly altered by halving the inter-anode gap width from 40 to 20 mm. The CFD model predicts that the relative widths of center, side, and end channels have a major influence on several critical aspects of the cell flow field.

Mathematical modeling of aluminum degassing by the impeller injector technique validated by a physical modeling

ABSTRACTA mathematical model is developed to describe deoxidation of water in a physical model of a batch aluminum degassing reactor equipped with the rotor-injector technique, assuming that deoxidation kinetics of water is similar to dehydrogenization of liquid aluminum. Degassing kinetics is described by using mass transport and mass balance principles by assuming that degassing kinetics can be characterized by a mass transfer coefficient, which depends on the process variables. The transport coefficient and the average bubble diameter are estimated with correlations reported in the literature for similar gas-injection systems. The water physical model helped to validate the mathematical model and to perform a process analysis by varying: 1) Gas flow rate (20 and 40 l/min); and 2) Impeller’s angular velocity (290 and 573 rpm). Results from the model agree well with measurements of deoxidation kinetics at low impeller rotating speeds. At high rotating speeds the model is still valid but less reliable because it does not take into account the formation of the vortex at the free surface. Nevertheless, the model provides predictions of the influence of every operating parameter and it can be used as a good approximation for real systems.

Physical Modeling of Fluid Flow in Ladles of Aluminum Equipped with Impeller and Gas Purging For Degassing

In the current study a transparent water physical model was developed to study fluid flow and turbulent structure of aluminum ladles for degassing treatment with a rotating impeller and gas injection. Flow patterns and turbulent structure in the ladle were measured with the particle image velocimetry technique. The effects of process parameters such as rotor speed, gas flow rate, and type of rotor on the flow patterns and on the vortex formation were analyzed using this model, which control degassing kinetics. In addition, a comparison between two points of gas injection was performed: (a) conventional gas injection through the shaft and (b) a “novel” gas injection technique through the bottom of the ladle. Results show that the most significant process variable on the stirring degree of the bath was the angular speed of the impeller, which promotes better stirred baths with smaller and better distributed bubbles. A gas flow rate increment is detrimental to stirring. Finally, although the injection point was the less-significant variable, it was found that the “novel” injection from the bottom of the ladle improves the stirring in the ladle, promotes a better distribution of bubbles, and shows to be a promising alternative for gas injection.

Mathematical Modeling of Fluid Flow in a Water Physical Model of an Aluminum Degassing Ladle Equipped with an Impeller-Injector

In this work, a 3D numerical simulation using a Euler–Euler-based model implemented into a commercial CFD code was used to simulate fluid flow and turbulence structure in a water physical model of an aluminum ladle equipped with an impeller for degassing treatment. The effect of critical process parameters such as rotor speed, gas flow rate, and the point of gas injection (conventional injection through the shaft vs a novel injection through the bottom of the ladle) on the fluid flow and vortex formation was analyzed with this model. The commercial CFD code PHOENICS 3.4 was used to solve all conservation equations governing the process for this two-phase fluid flow system. The mathematical model was reasonably well validated against experimentally measured liquid velocity and vortex sizes in a water physical model built specifically for this investigation. From the results, it was concluded that the angular speed of the impeller is the most important parameter in promoting better stirred baths and creating smaller and better distributed bubbles in the liquid. The pumping effect of the impeller is increased as the impeller rotation speed increases. Gas flow rate is detrimental to bath stirring and diminishes the pumping effect of the impeller. Finally, although the injection point was the least significant variable, it was found that the “novel” injection improves stirring in the ladle.

Experimental Study on Mixing in Gas-Stirred Ladles with and without the Slag Phase through a Water Physical Model

ABSTRACTA 1/6th gas–stirred water physical model of a 140 ton steel ladle is used to evaluate mixing in air–water and air–water–oil systems to model argon–steel and argon–steel–slag systems respectively. Thickness of the slag layer is kept constant at 0.004 m. The effect of the gas flow rate (7, 17, and 37 l/min), plug position (0, 1/3, ½, and 2/3 of the ladle radius, R), and number of plugs (1, 2, and 3) on mixing time is also analyzed in this work. Gas is injected at the bottom of the ladle under several plug configurations varying both position and number of plugs. Chemical uniformity of 95% is selected as mixing criterion. Mixing times are experimentally determined when a tracer is suddenly injected into the ladle and the model is instrumented with a pH meter to track the time evolution of the tracer concentration (NaOH 1 M solution) in a given location inside the ladle. Process conditions for best mixing in both water–gas and water-gas–slag systems are: a single plug located at 2/3 of the ladle radius with a gas flow rate of 17 l/min.

Study of Aluminum Degasification with Impeller-Injector Assisted by Physical Modeling

ABSTRACTA full-scale water physical model of a degassing unit is built and used to evaluate the performance of several impeller designs. Four impeller designs are tested: a) one smooth not commercial impeller for reference purposes, b) a commercial design by FOSECO®, called standard impeller in this work, c) a commercial design by FOSECO® with notches, and d) a new design proposed in this work. Since the physical model is easy and safe to operate, a full experimental design is performed to evaluate the effect of the most important process variables, such as impeller rotating speed, gas flow rate, impeller design and the point of gas injection (a conventional gas injection through the shaft and a novel method of injecting gas through the bottom of the ladle) on the kinetics of oxygen desorption of water which is similar to dehydrogenation of liquid aluminum. The new design of impeller proposed in this work shows the best performance in degassing of all impellers tested in this study. It is found that the rotor speed and its design are the most significant variables affecting degassing kinetics, and therefore the analysis of the existing commercial impeller designs may be useful to optimize the fluid dynamics of the process, which in turn would increase efficiency and productivity of the process. Finally, the novel gas injection method through the bottom, proposed by our own group, presents slightly faster degassing kinetics than the conventional injection of purge gas in the conventional way through the impeller.

Effect of Slag on Mixing Time in Gas-Stirred Ladles Assisted with a Physical Model

ABSTRACTA 1/6th water physical model of a 140 tons gas-stirred steel ladle is used to evaluate mixing times (τm at 95% of chemical uniformity) in a two phase system without slag (air-water) and in a more realistic three phase system (air-water-oil) to simulate the argon-steel-slag system and quantify the effect of the slag layer on the mixing time. Slag layer is kept constant at 0.004 m. Mixing times are estimated through measured changes in pH due to the addition of a tracer (NaOH 1 M). The effect of the following variables on the mixing time is evaluated for a single injector: gas flow rate (7, 17 y 37 l/min) and the injector position (R/r= 0, 1/3, ½, 2/3 and 4/5). Experimental results obtained in this work show good agreement when compared against mixing time correlations reported by Mazumdar for the two phase air-water case (no slag considered). Another comparison is done using the new concept called “effective bath height” proposed by Barati, where the mixing time is a function of the size of the slag layer since this layer dissipates part of the total amount of stirring energy introduced into the ladle by the injection of gas. Agreement is not good in this case. Finally, an estimation of the percentage of the stirring energy dissipated by the slag is computed, including other factors that govern the dissipation of stirring energy. Percentage of energy dissipated by the slag is found to be between 2.7 to 12 % depending on the process conditions.

Novel Degasification Design for Aluminum Using an Impeller Degasification Water Physical Model

A full scale water physical model of an aluminum degassing crucible was built to analyze the effect of changing the point of gas injection, from the conventional location, through the shaft, to an injection underneath impeller, on the performance of three rotor designs, based on the oxygen kinetic elimination from water by N2 injection, similar to hydrogen removal from liquid aluminum, under different degassing conditions. Results show that the point of gas injection plays an important role in the kinetics and efficiency of the degassing operation. The use of gas injection underneath the impeller increases notoriously the efficiency of the degassing processes.

Physical Modelling of an Aluminium Degassing Operation with Rotating Impellers—A Comparative Hydrodynamic Analysis

A hydrodynamic study of aluminum degassing by the rotating impeller technique was developed through experimental measurements obtained in a water physical model stirred with different impellers and air injection. The purpose of the work was to better understand degassing operation in molten aluminum through the analysis of the hydrodynamics of the system. Particle image velocimetry (PIV) was employed to measure flow patterns and turbulence characteristics of the ladle as a function of process and design variables, such as: a) impeller rotating speed (536 and 800 rpm), b) air flow rate (3 liters/min and 0 l/min), c) geometric design of the different impellers (impeller “A” made of a solid disc, impeller “B” with lateral nozzles and an impeller “C” with notches), where impellers “B” and “C” represent commercial designs. Impellers “B” and “C” presented similar flow behavior, with radial projection and pumping effect, while impeller “A” developed different flow patterns. By increasing the angular speed and the complexity of the impeller, stirring and turbulence increased through the entire ladle, while the vortex intensity grew. Gas injection modified the liquid flow patterns reducing the magnitude of the velocity in the liquid, and significantly increasing turbulence in the ladle.

Mathematical Modeling of Impingement of an Air Jet in a Liquid Bath

AbstractPhysical and mathematical modeling of jet-bath interactions in electric arc furnaces represent valuable tools to obtain a better fundamental understanding of oxygen gas injection into the furnace. In this work, a 3D mathematical model is developed based on the two phase approach called Volume of Fluid (VOF), which is able to predict free surface deformations and it is coded in the commercial fluid dynamics software FLUENTTM. Validation of the mathematical model is achieved by measurements on a transparent water physical model. Measurements of free surface depressions through a high velocity camera and velocity patterns are recorded through a Particle Image Velocimetry (PIV) Technique. Flow patterns and depression geometry are identified and characterized as function of process parameters like distance from nozzle to bath, gas flow rate and impingement angle of the gas jet into the bath. A reasonable agreement is found between simulated and experimental results.

Numerical Simulation of Fluid Flow and Mixing in Gas-Stirred Ladles

In this work air injection into a water physical model of an industrial steel ladle was simulated. Calculations were developed based on a multiphase Eulerian fluid flow model involving principles of conservation of mass, momentum, and chemical species for both phases to predict turbulent flow patterns and mixing times for centric and eccentric injections. Effects of gas flow rate, injector position, number of injectors, and geometry of ladle on mixing time were analyzed. Optimum injection conditions are: single injector at 2/3 of radius and high gas flow rates. Quantitative correlation of mixing time as a function of main process variables was obtained.