Fluid flow in filling ladles

The fluid flow generated during the course of tapping operations from Basic Oxygen Furnaces was analyzed. Mathematical models of the filling process were developed, and their predictions checked with experimental values obtained using a one-tenth scale model of the ladle. Reasonable agreement was achieved. Based on the full scale predictions, it is suggested that the magnitude of flow velocities are technologically significant in terms of their effect on ferro-alloy immersion times and recoveries. Formerly a Research Associate at McGill University.     

Turbulent Flow in Filling Ladles

The fluid flow patterns generated during the course of tapping operations from Basic Oxygen Furnaces have been analyzed using two mathematical models of the filling process. The present work is mainly concerned with the application of the κ — ∈ turbulent flow model to describe recirculatory flow in filling ladles. Predicted velocity fields were quite similar to those based on the laminar flow model and both models provided predictions which checked reasonably closely with experimental values using a one tenth scale model. Based on the full scale predictions, it is suggested that the magnitude of flow velocities are technologically significant in terms of their effect on ferro-alloy immersion times.     

Numerical Computational Fluid Dynamics-Based Models of Ultraviolet Disinfection Channels

Various numerical modeling approaches, all based on computational fluid dynamics (CFD) solutions for the flow field, are studied for an ultraviolet disinfection system in which the lamps are oriented perpendicular to the flow direction. A two-dimensional model assumption is made in all simulations, for which turbulent flow solutions were obtained with commercial CFD software (FIDAP). Two modeling approaches were studied. A continuum Eulerian approach was taken in formulating an appropriate advection–diffusion equation which is solved for the viable micro-organism concentration. Alternatively, a Lagrangian approach, in which particles are numerically introduced into the flow and their trajectories through a spatially varying field of ultraviolet intensities were computed, was also investigated. The effect of modeling unsteady-flow features associated with vortex shedding and motion on the extent of disinfection was examined by comparing time-averaged results based on an unsteady-flow continuum model with the results from an analogous simulation assuming a steady flow. Under the steady-flow assumption, differences between predictions of the Eulerian continuum approach and the Lagrangian particle-trajectory approach were also considered. Both modeling approaches yielded similar predictions over a range of loadings, and tended to underestimate the extent of disinfection when compared to measurements at the pilot scale.     

Authoritarianism and reactions to "sputniks."

"This study investigated the relationship between authoritarianism, as measured by an F scale, and changing or retaining predictions following a natural influence event. Following Sputnik I, college Ss made forced-choice predictions… about which nation is most likely to get to the moon first. The same prediction was again elicited following Sputnik II. Among Ss who initially favored the U. S., those who did not change their prediction… received significantly higher scores on the F scale than did those who changed their initial predictions." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Heat Flow and Solidification Modeling of Industrial Scale,Ingot Casting Operation

A model, based on the concept of effective thermal conductivity, was developed to study thermal fields and the resultant solidification behavior of large, round, industrial size ingots. In this, flow and turbulence phenomena during mold filling as well as subsequent solidification were not modeled explicitly but their influence was accounted for by artificially raising the thermal conductivity of solidifying steel. Thus, a conduction like equation embodying a conjugate approach was applied to simultaneously predict the evolution of temperature fields in the mold as well as in the solidifying ingot following teeming. Prior to comparing model predictions against industrial scale measurements, sensitivity of calculations to grid size, time step height, convergence criterion etc. were rigorously assessed. Similarly, modeling of interfacial resistance, chemical reactions and heat effects in the hot top as well as their influence on predicted results were evaluated computationally. Embodying mixed thermal boundary conditions (free convection + radiation) at the mold wall, temperature fields during solidification of two different industrial large ingots were predicted numerically. Parallely, mold wall temperature was monitored as a function of time and surface temperature of ingot was measured at the instant of mold stripping using hand held, radiation pyrometers. Incorporating relevant operating conditions (viz., mold dimensions and size, ingot and hot top dimensions and material, initial mold and liquid temperature etc.) into the calculation scheme, predictions were made via a computational procedure developed in-house and results thus obtained were compared against equivalent industrial scale measurements. Very reasonable agreement between the two was demonstrated.     

Sex differences in predicting final examination grades: The influence of past performance, attributions, and achievement motivation.

43 male and 41 female undergraduates reported their high school and last semester GPAs, their 1st and 2nd midterm grades, and their final exam predictions. Ss also rated the influence that ability, effort, task difficulty, and luck had on their performances and completed Mehrabian's achievement motivation scale. Regression analyses provided support for the attribution model of achievement expectations. All Ss used ability to explain their successes; however, males attributed failures to lack of effort while females often used luck to explain their performances. Although both sexes earned equal midterm scores and predicted similar final grades, males based their predictions solely on the 2 midterms. Females' predictions were significantly affected by both midterm performance and achievement motivation. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Experimental and mathematical investigation of the fluid flow inside and below a 1/4 scale air model of a flash smelting burner

Single-phase turbulent fluid flow inside and below a burner model was studied to better understand the fluid flow processes occurring inside and below flash smelting burners. The effect of Reynolds number and temperature on the axial velocity profiles in a 1/4 scale experimental air model of a jet flow burner and shaft were investigated. Laser Doppler anemometry (LDA) was used to determine the mean and fluctuating axial velocity components within and below this burner. Also experimentally determined were the pressure profiles along the length of the burner and shaft and the inlet air and wall temperature profiles. In the experiments, the Reynolds number range was approximately 60,600 to 76,100, which was in the turbulent flow regime. A mathematical model was used to simulate axisymmetric two-dimensional air flow through a jet flow burner and shaft for Reynolds numbers of 60,000 to 304,000. The axial velocity predictions of the high axial velocity region and surrounding region in the shaft were in reasonable agreement with the axial velocity experimental results. Recommendations are made for the improvement of the design of flash smelting burners.     

Dynamics and control of solidification of molten metal flows

A solidified layer on the inside of a cooled flow channel can be used to control the flow rate of molten material through that channel. This concept can be used for flow rate control of molten furnace products in the metallurgical industry. In this study, internal solidification of molten metal flows has been modeled mathematically for both steady-state and dynamic cases. The model predicted solidified layer thickness and metal flow rate. Experimental verification of the mathematical model was obtained using molten tin. Novel design features of the experimental apparatus included the use of boiling heat transfer and the vertical mounting of the cooling section. Engineering knowledge regarding the design, operation, and control of a pilot scale (24 kg/s) molten metal circuit was obtained during the construction, commissioning, and operation of the experimental apparatus. Experimental results for tin flow rate from the experimental apparatus were within experimental error of the predictions of the mathematical model.     

Heat transfer and fluid flow phenomena in electroslag refining

A mathematical formulation has been developed to represent the electromagnetic force field, fluid flow and heat transfer in ESR units. In the formulation, allowance has been made for both electromagnetically driven flows and natural convection; furthermore, in considering heat transfer the effect of the moving droplets has been taken into account. The computed results have shown that the electromagnetic force field appears to be the more important driving force for fluid motion, although natural convection does affect the circulation pattern. The movement of the liquid droplets through the slag plays an important role in transporting thermal energy from the slag to the molten metal pool, although the droplets are unlikely to contribute appreciably to slag-metal mass transfer The for-formulation presented here enables the prediction of thermal and fluid flow phenomena in ESR units and may be used to calculate the electrode melting rates from first principles. While a detailed comparison has not yet been made between the predictions based on the model and actual plant scale measurements, it is thought that the theoretical predictions are consistent with the plant-scale data that are available.     

Defensiveness as a factor in sex differences in anxiety.

Hypotheses involving defensiveness as a rationale for explaining sex differences in scores on anxiety questionnaires were investigated. Instruments differentially susceptible to the influence of defensiveness, the Structured-Objective Rorschach Test (SORT) and the Taylor MA scale were used in gathering data from 236 college students enrolled in a general psychology course. The following results were obtained: the relation between the MA scale and SORT was not higher for females (contrary to predictions); MA scale scores were higher for females (as predicted) while SORT scores were higher for males (no difference predicted); and no relation between either the SORT or the MA scale and grade-point average was found (contrary to predictions). The results appeared to fit an acquiescence rationale better than a defensiveness rationale, and it was argued that this hypothesis merits further research. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Safety of carotid ligation and its role in the management of intracranial aneurysms

By using measurements of cerebral blood flow and internal carotid artery pressure it is possible to select patients in whom carotid ligation can be performed with a very low risk of post-operative cerebral ischaemia. A study has been carried out in 100 patients comparing this method with clinical predictions of the type used in aneurysm surgery based on age of the patient, arterial hypertension, time from latest subarachnoid haemorrhage, and neurological status on a modified Botterell scale. These clinical factors were found to be of little value in predicting which patients would and would not develop cerebral ischaemia after carotid occlusion.     

Experimental evaluation of two simple thermal models using transient temperature analysis

Thermal models are used to predict temperature distributions of heated tissues during thermal therapies. Recent interest in short duration high temperature therapeutic procedures necessitates the accurate modelling of transient temperature profiles in heated tissues. Blood flow plays an important role in tissue heat transfer and the resultant temperature distribution. This work examines the transient predictions of two simple mathematical models of heat transfer by blood flow (the bioheat transfer equation model and the effective thermal conductivity equation model) and compares their predictions to measured transient temperature data. Large differences between the two models are predicted in the tissue temperature distribution as a function of blood flow for a short heat pulse. In the experiments a hot water needle, approximately 30 degrees C above ambient, delivered a 20 s heating pulse to an excised fixed porcine kidney that was used as a flow model. Temperature profiles of a thermocouple that primarily traversed the kidney cortex were examined. Kidney locations with large vessels were avoided in the temperature profile analysis by examination of the vessel geometry using high resolution computed tomography angiography and the detection of the characteristic large vessel localized cooling or heating patterns in steady-state temperature profiles. It was found that for regions without large vessels, predictions of the Pennes bioheat transfer equation were in much better agreement with the experimental data when compared to predictions of the scalar effective thermal conductivity equation model. For example, at a location r approximately 2 mm away from the source, the measured delay time was 10.6 +/- 0.5 s compared to predictions of 9.4 s and 5.4 s of the BHTE and ETCE models, respectively. However, for the majority of measured locations, localized cooling and heating effects were detected close to large vessels when the kidney was perfused. Finally, it is shown that increasing flow in regions without large vessels minimally perturbs temperature profiles for short exposure times; regions with large vessels still have a significant effect.     

Mathematical Modelling of Water Sampler Filling

Steel samples taken from ladles or tundishes during the steel making process can be of significant importance when monitoring the inclusion size and distribution. In order to preserve the original size and distributions of inclusions in the extracted samples, it is important to avoid their collisions and coagulations inside samplers during filling. Thus, it is necessary to investigate the flow during a sampling process to make sure that this is minimized. In addition, it is important to study the turbulence characteristics, since it is known to influence the inclusion growth. This study presents mathematical modelling of sampler filling using water as a media and experimental results for verification. The study focuses on a lollipop‐shaped sampler since it is one of the most common in the industry. The sampler is filled from an inlet pin located at the bottom centre of the main body. In addition, two different turbulence models, the realizable k‐ε model and Wilcox k‐ω model, were used to study the flow pattern in the sampler. The predictions were compared to experimental results obtained by Particle Image Velocimetry (PIV) measurements. It was found that the flow field predictions using the Wilcox k‐ω model agreed best with the flow field obtained by PIV measurements. Furthermore, it was illustrated that the Wilcox k‐ω model can be used for predictions of the different flow regions as well as the positions of the centres of vortexes which are located near the free surface. Thus, it is concluded that the Wilcox k‐ω model can be used in the future to predict the filling of steel samplers.     

Fractionation and Segregation of Suspended Particles Using Acoustic and Flow Fields

The exploratory research of applying an acoustic standing wave to a sediment flow stream to fractionate and segregate particles was investigated. Using fundamental physics of particles in an acoustic field, a mathematical model was developed to calculate trajectories of deflected particles due to the application of acoustic standing waves. Then at the bench scale, the above technology was implemented by building a flow chamber with two transducers at opposite ends to generate an acoustic standing wave. The technology was evaluated using uniform size silicon dioxide and silicon carbide particle suspensions in de-ionized water. Due to the acoustic force field, SiO2 particles migrated toward the pressure nodes at half wavelength intervals at an optimum frequency of 333 kHz and 40 W power. Dark lines representing particle columns were formed after the application of the acoustic field, which was recorded in videotape. However, due to the small particle size of SiO2, particle trajectories could not be recorded, hence the slightly larger sized SiC was used to track particle trajectories. The displacements of SiC particles due to an acoustic force were compared with the mathematical model predictions. For input power level between 3.0 and 5.0 W, the experimental data were comparable to mathematical model predictions. Also, from the experimental data it was possible to develop a relationship between input power and acoustic energy in the resonance chamber. Hence based on preliminary results it can be concluded that the acoustic field can be used either to segregate or fractionate fine particles.     

Heat transfer and fluid flow phenomena in electroslag refining

A mathematical formulation has been developed to represent the electromagnetic force field, fluid flow and heat transfer in ESR units. In the formulation, allowance has been made for both electromagnetically driven flows and natural convection; furthermore, in considering heat transfer, the effect of the moving droplets has been taken into account. The computed results have shown that the electromagnetic force field appears to be the more important driving force for fluid motion, although natural convection does affect the circulation pattern. The movement of the liquid droplets through the slag plays an import-ant role in transporting thermal energy from the slag to the molten metal pool, although the droplets are unlikely to contribute appreciably to slag-metal mass transfer. The for-formulation presented here enables the prediction of thermal and fluid flow phenomena in ESR units and may be used to calculate the electrode melting rates from first principles. While a detailed comparison has not yet been made between the predictions based on the model and actual plant scale measurements, it is thought that the theoretical predictions are consistent with the plant-scale data that are available. Presently on leave from Institute of Chemical Engineering and Technology, Punjab University, Lahore-1, Pakistan.     

Calibration and Verification of a 2D Hydrodynamic Model for Simulating Flow around Emergent Bendway Weir Structures

The predictive capability of a two-dimensional (2D)-hydrodynamic model, the finite-element surface water modeling system (FESWMS), to describe adequately the flow characteristics around emergent bendway weir structures was evaluated. To examine FESWMS predictive capability, a sensitivity analysis was performed to identify the flow conditions and locations within the modeled reach, where FESWMS inputs for Manning’s n and eddy viscosity must be spatially distributed for to better represent the river bed flow roughness characteristics and regions where the flow is highly turbulent in nature. The sensitivity analysis showed that high flow conditions masked the impact of Manning’s n and eddy viscosity on the model outputs. Therefore, the model was calibrated under low flow conditions when the structures were emergent and had the largest impact on the flow pattern and model inputs. Detailed field measurements were performed under low flow conditions at the Raccoon River, Iowa for model calibration and verification. The model predictions were examined for both spatially averaged and distributed Manning’s n and eddy viscosity model input values within the study reach for an array of emergent structures. Spatially averaged model inputs for Manning’s n and eddy viscosity provided satisfactory flow depth predictions but poor velocity predictions. Estimated errors in the predicted values were less than 10% for flow depth and about 60% for flow velocity. Distributed Manning’s n and eddy viscosity model inputs, on the contrary, provided both satisfactory flow depth and velocity predictions. Further, distributed inputs were able to mimic closely the recirculation flow pattern in the wake region behind the bendway weir structures. Estimated errors in the predicted values were less than 10 and 25% for flow depth and velocity, respectively. Overall, in the case of distributed model inputs, FESWMS provided satisfactory results and allowed a closed depiction of the flow patterns around the emergent bendway weirs. These findings suggest that 2D models with spatially distributed values for Manning’s n and eddy viscosity can adequately replicate the velocity vector field around emergent structures and can be valuable tools to river managers, except in cases when detailed three-dimensional flow patterns are needed. The study was limited to the examined low flow conditions, and more field data, especially under high flow conditions, are necessary to generalize the findings of this study regarding the model prediction capabilities.     

Hydraulic Jet Control for River Junction Design of Yuen Long Bypass Floodway, Hong Kong

The Yuen Long Bypass Floodway (YLBF) was designed to collect flows from the Sham Chung River (SCR) and the San Hui Nullah (SHN) and to serve as a diversion channel of the Yuen Long Main Nullah (YLMN). Under a 200-year return period design condition, the floodway was designed (1) to divert a flow of approximately 38?m3/s from the supercritical YLMN flow and (2) to convey a total combined flow of 278?m3/s to downstream within acceptable flood levels. The success of the design depends critically on complicated junction flow interactions that cannot be resolved by 1D unsteady flow models. These features include the supercritical-subcritical flow transition at the San Hui-Floodway (SHN-YLBF) junction and the diversion of part of the supercritical flow from the Main Nullah (YLMN). A laboratory Froude scale physical model was constructed to study water stages and flow characteristics in the floodway and to investigate optimal design arrangements at channel junctions and transitions. This paper summarizes the main features of the unique river junction network, in particular the use of the hydraulic jet principle at the SHN-YLBF junction to lower flood levels. In addition, a numerical flow model is employed to study flow details at the river junctions. The model is based on the general 2D shallow water equations in strong conservation form. The equations are discretized using the total variation diminishing finite-volume method which captures the discontinuity in hydraulic jumps. The numerical model predictions are well supported by the laboratory data, and the theoretical and experimental results offer useful insights for the design of urban flood control schemes under tight space constraints.     

Effects of tundish size,tundish design and casting flow rate on fluid flow phenomena of liquid steel

Fluid dynamics of liquid steel in continuous casting tundishes is closely related to tundish volume and geometry, existence of flow control devices and steel flow rate. To study this complex interaction physical and mathematical models were used in the present work. The first one was based in a 1/3 scale water model with injection of tracers and the second one on the solution to the steady state-turbulent Navier-Stokes equations using the K-ε [1] approximation for the turbulent viscosity. When the tundish size is increased from 30 t to 50 t the tracer indicates a strong bypassing in the second case. The mathematical predictions indicate very high fluid velocities along the tundish bottom in agreement with the experimental findings. The employment of turbulence inhibitors promotes a counter-flow that surrounds the incoming stream jet of liquid from the inlet nozzle with steel displacing itself, after leaving this zone, along the upper free surface of the liquid. The addition of well designed baffles complements the action of the turbulence inhibitor to obtain a higher volume fraction under a plug flow pattern giving a softer flow of liquid steel. Besides, the positioning of baffles inside a tundish should be performed according to the steel flow rate.     

A comparative experimental and numerical study to investigate the relative merits of convectors and “C” inserts in cooling cold-rolled coils

The coil cooling and storage unit (CCSU) is used to cool cold-rolled coils to the temper rolling temperature after the annealing cycle is over at the batch annealing furnace (BAF) in a cold rolling mill (CRM). In the CCSU, the coils are kept on the cooling bases for any fixed time irrespective of the grade and tonnage. Therefore, the need for a mathematical model to accurately predict the cooling time of the coils was felt. The current study involves experimental and numerical analysis of a stack of coils with respect to heat transfer and fluid flow. A comparative study was carried out to ascertain the relative merits of convectors and “C” inserts (CIs) in the cooling the coils. The air flow distribution for the case of different convectors and CIs was measured by means of a full scale physical model. Two different mathematical models were applied to model the fluid flow and flow distribution through the stack of coils. The first flow model uses the hydraulic resistance concept for estimating the air flow rate distribution, whereas the second flow model uses commercial computational fluid dynamics (CFD) software and predicts the velocity distribution in the flow path between two coils in a stack. The predictions from these two models compare well with the experimental data. The flow models were used to calculate the average heat-transfer coefficient in different flow passages in a stack. The heat-transfer coefficients thus obtained were used to tune and validate a two-dimensional transient heat-transfer model of coils. The heat-transfer model predicts the cooling time of coils accurately and also suggests a possible reduction of cooling time if CIs are used in place of convectors.     

The interaction of a DC transferred arc with a melting metal: Experimental measurements and mathematical description

Experimental measurements are reported on the transient development of temperature profiles in a hemispherical metal anode onto which a DC plasma jet is impinging. The main process variables were the arc current, the electrode separation, and the argon flow rate. These experimental measurements were compared with the predictions of a mathematical model, which involved the statement of the turbulent heat and fluid flow equations in the plasma, coupled to the heat flow in the testpiece through the boundary conditions. The experimental measurements were in reasonable agreement with the predictions, and convective heat transfer was found to be dominant in the heat exchange between the plasma and the anode.