Modelling of air ingress and pressure distribution in ladle shroud system for continuous casting of steel

The pressure distribution and fluid flow profiles whithin the slide gate and shroud nozzle for the continuous casting of steel have been investigated using a full scale water model and a CFD (computational fluid dynamics) model. The water modelling has shown that a large quantity of air can be drawn into the liquid stream if there is any breakdown of the seals in the vicinity of the slide gate. The 3-dimensional numerical solution for highly turbulent flow has predicted the pressure distribution and velocity profile within the slide gate and shroud. Based on the experimental and numerical modelling, it has been shown that cavitation can occur near the slide gate during ladle teeming. This can be a source for erosion of the refractories. Improvements to the design of the ladle shroud system are recommended.     

Bubble Entrainment and Distribution in a Model Spillway with Application to Total Dissolved Gas Minimization

This paper focuses on an experimental study of the two-phase flow downstream of a laboratory model fish bypass. Experiments were performed on a 1:24 scale laboratory model of a fish bypass under consideration for construction at Wanapum Dam, on the Columbia River in Washington. The model was operated at the design condition of skimming flow regime and at the possible off-design plunging and surface jump regimes. Void fraction data were collected using an optical phase detection probe on a three-dimensional grid, and the phase indicator function was recorded at selected locations. It was found that in the laboratory model, the skimming flow regime effectively prevents bubbles from reaching deep into the tailrace, resulting in a considerably lower void fraction than plunging and surface jump regimes. For this geometry, the surface jump regime entrains air deeper than the plunging regime. To observe trends, the instantaneous source of total dissolved gas was estimated for the three regimes using the model data and several simplifying assumptions. Time distributions of the indicator function are also reported.     

Vortex Plate for Enhancing Particle Settling

The feasibility of enhancing suspended solids settling by using the newly proposed vortex plates in clarifiers, instead of conventional smooth lamellae, was studied using computational fluid dynamics (CFD) modeling and laboratory experiments in which suspended particles were mimicked by crushed walnut shells and glass beads. The vortex plate was formed by attaching perpendicular ribs to the plate, forming slots of 25×25?mm (depth×width) and placing the plate parallel to the longitudinal clarifier axis at an angle of 60° from the horizontal. Rib walls were placed either in vertical planes, perpendicular to the clarifier longitudinal axis, or were slightly sloping in the main flow direction (20° about the vertical). Three hydraulic concepts were explored with respect to enhancing suspended particle settling: (1) the use of flow energy to generate steady vortices inside the slots and thereby entrain particles into the slots, where they would be sheltered from the fast horizontal flow and could settle without much hindrance; (2) enhancing the particle settling by increasing the contact surface area and thereby reducing the length of travel of settling particles; the same principle is used in conventional lamellar settlers but the surface area of a vortex plate is three times that of a smooth lamella; and (3) increasing the particle collision frequency within the swirling flow inside slots to prompt particle flocculation. The CFD modeling and experimental observations confirmed the formation of strong vortices in the parallel slots of the vortex plate. Such vortices entrained the passing by particles and retained some of them in slots, which provided a quiescent settling zone. Both the simulation and measured results indicated that the vortex plate contributed to a slightly improved removal of suspended particles. A CFD particle tracking model was applied to clarifiers with two vortex plates or two smooth plates and indicated that the vortex plate removed about 8% more particles than the smooth plate. In laboratory tests with plate arrays, the vortex plate array also contributed to better particle removals, especially for slower settling particles and larger inflow rates (by up to 26%).     

Development of a 3D Filling Model of Low-Pressure Die-Cast Aluminum Alloy Wheels

A two-phase computational fluid dynamics model of the low-pressure die-cast process for the production of A356 aluminum alloy wheels has been developed to predict the flow conditions during die filling. The filling model represents a 36-deg section of a production wheel, and was developed within the commercial finite-volume package, ANSYS CFX, assuming isothermal conditions. To fully understand the behavior of the free surface, a novel technique was developed to approximate the vent resistances as they impact on the development of a backpressure within the die cavity. The filling model was first validated against experimental data, and then was used to investigate the effects of venting conditions and pressure curves during die filling. It was found that vent resistance and vent location strongly affected die filling time, free surface topography, and air entrainment for a given pressure fill-curve. With regard to the pressure curve, the model revealed a strong relation between the pressure curve and the flow behavior in the hub, which is an area prone to defect formation.     

Numerical Simulations of Efficiency of Curb-Opening Inlets

The geometry of highway pavement and drainage inlets, especially cross slope, longitudinal slope, and local depression and transition length, usually determine the highway surface drainage capacity. In this study, a three-dimensional computational fluid dynamics (CFD) software, FLOW-3D, is used to develop models simulating unsteady, free-surface, shallow flow through curb-opening inlets, thereby demonstrating that an advanced CFD model can be used as a virtual laboratory to evaluate performance (i.e., inlet efficiency) of curb-opening inlets with different geometry conditions. Predicted intercepted flow and inlet efficiency agree well with laboratory measurements. Flow simulations were extended to smaller cross slopes for which laboratory tests were not conducted but which can occur in a highway transition.     

Computational and Experimental Study of Surcharged Flow at a 90° Combining Sewer Junction

Combining sewer junctions with a lateral inflow at 90° angle are commonly used in our sewer systems. A computational fluid dynamics (CFD) model based on Ansys CFX 10.0 was established to simulate fully surcharged flow at a 90° combining sewer junction. The model was carefully assessed by comparing its results with the measurements of detailed physical experiments. Good agreement was obtained between results of the computational model and of the laboratory experiments. The computational model was proved to be capable of simulating surcharged combining junction flow in the aspects of water depth, energy losses, velocity distributions, and turbulence. The verified CFD model was also used to investigate air entrainment and effects of the size of the junction chamber on the flow. Such CFD models can be used to optimize the design of sewer junctions and will also be useful in studying sediment transport at sewer junctions.     

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.     

基于单相LBM模拟大平板反重力充型过程

采用单相格子Boltzmann方法研究大平板的反重力充型过程,该模型不需考虑气相格子的变化,从而提高了计算效率.针对该方法,本文新提出了一种权重系数重新分配的方法来处理格点中的液相排出及分配问题.首先用该模型计算了单浇口条件下的大平板型腔反重力充填过程,以相同参数下的高速相机成像的水力充填实验为参照,数值模拟的流场特征及流体形态与实验结果吻合良好.另外,还采用线速度分布云图,并提出了自由表面的高度差判据来分析充型过程中的流场区域特征和流体平稳程度.在此基础上,继续用该模型研究了双浇口和圆柱扰流条件下的大平板反重力充型过程.双浇口条件下由于浇道间的互相影响,流场中形成的漩涡多于单浇口;圆柱扰流条件下的充填方式会降低流体的晃动程度,提高充型的稳定性.      

Three-Dimensional CFD-Population Balance Simulation of a Chemical Vapor Synthesis Reactor for Aluminum Nanopowder: Nucleation, Surface Growth, and Coagulation

A chemical vapor synthesis (CVS) process for synthesizing aluminum nanopowder as a reactant for various hydrogen-storage materials was simulated using a mathematical technique that combines computational fluid dynamics (CFD) with the population balance model. In this process, aluminum powder is produced by reacting aluminum chloride with magnesium in the vapor phase. The CFD model solves the three-dimensional (3-D) turbulent governing equations of fluid flow, heat and mass transfer, and chemical kinetics in a multiphase domain. The population balance model incorporates nucleation, surface growth, and coagulation. The nucleation rate is computed using an expression from the classical nucleation theory. The growth rate is obtained by the combined effect of vapor condensation and coagulation. A comparison of the model predictions with the available experimental data showed good agreement under different operating conditions without the need of adjustable parameters. According to the results, the final particle size is determined by particle coagulation in this particular CVS process. The new model proposed in this article can be applied to other similar systems with confidence even without the need of any experimental data and can be used for scale-up of the process.     

基于商用CFD软件的双层皮幕墙热工性能模拟程序的开发

Double-skin facade （DSF） is widely used in commercial buildings for its excellent performance in saving energy. But it＇s very difficult for the ordinary designers to predict the thermal performance of DSF due to the complexity of the energy transmitting through the DSF and the difficulty of manipulating the complicated commercial CFD （computational fluid dynamic） simulation software. This paper take an effort in the foundation of the DSF analysis code with VC ＋ ＋ 6. 0 based on the commercial CFD software. This code is complied to analyze and predict the thermal behaviorof the ‘standard＇geometry natural ventilation DSF. The analyzer can gain the thermal behavior and the air flow characteristics of DSF after entered the relevant parameters of the model. This code gives the designer a tool to make quick design decisions in analyzing and optimizing DSF.     

Case Study of an Application of a Computational Fluid Dynamics Model to the Forebay of the Dalles Dam, Oregon

A proposal for facilitating the downstream migration of juvenile fish at The Dalles Dam, Ore. calls for blocking the upper 12.3?m of turbine intakes by J-shaped steel panels (blocked trashracks). These trashracks are expected to reduce velocity near the powerhouse that is responsible for entraining juveniles into the turbine intake flow. A three-dimensional computational fluid dynamics model was used to investigate the forebay hydraulics for the existing and proposed configurations of the intakes. Velocity data from a 1:40 scale physical model and a field program were utilized for model validation. In general, agreements between computed velocities and data were within the variability of field measurements. The model results confirmed the development of low velocity zones adjacent to the powerhouse. Further, the flow field created by the proposed trashracks could aid juveniles in swimming to the downstream end of the powerhouse where the fish bypass system is located.     

Validation of a Three-Dimensional Computational Fluid Dynamics Model of a Contact Tank

A three-dimensional (3D) computational fluid dynamics (CFD) model of a contact tank is presented in this paper. The model results are compared against 3D velocities and flow through curve (FTC) data, representing a tracer concentration profile, from a 1:8 scale physical model. The objective is to demonstrate that CFD models can simulate both the FTC and the 3D velocity field quite well. Simultaneous validation of velocities and FTC is important in ascertaining the predictive capabilities of CFD models, as physical model studies indicate that different baffle arrangements can lead to similar FTCs. Therefore, a good prediction of only FTC, as presented in previous 3D CFD model studies, does not necessarily imply a correct simulation of the flow field.     

Three-dimensional coupled fluid-structure simulation of pericardial bioprosthetic aortic valve function

A computational, three-dimensional coupled fluid-structure dynamics model was developed for a generic pericardial aortic valve in a rigid aortic root graft with physiologic sinuses. Valve geometry was based on that of the natural valve. Blood flow was modeled as pulsatile, laminar, Newtonian, incompressible flow. The structural model accounted for material and geometric nonlinearities and also simulated leaflet coaptation. A body fitted grid was used to subdivide the flow domain into computational finite volume cells. Shell finite elements were used to discretize the leaflet volume. A finite volume computational fluid dynamics code and finite element structure dynamics code were used to solve the flow and structure equations, respectively. The fluid flow and structural equations were coupled using an implicit "influence coefficient" technique. Physiologic ventricular and aortic pressure waveforms were prescribed as the flow boundary conditions. The aortic flow field, valve structural configuration, and leaflet stresses were computed at 2 msec intervals. Model predictions on aortic flow and transient variation in valve orifice area were in close agreement with corresponding experimental in vitro data. These findings suggest that the computer model has potential for being a powerful design tool for bioprosthetic aortic valves.     

Dynamics of Air Flow in Sewer Conduit Headspace

Pressurization in sanitary sewer conduit atmosphere is modeled using computational fluid dynamics techniques. The modeling approach considers both turbulent and laminar flow regimes. The turbulent model takes into consideration the turbulence-driven secondary currents associated with the sewer headspace and hence the Reynolds equations governing the air flow field are closed with an anisotropic closure model which comprises the use of the eddy viscosity concept for the turbulent shear stresses and semiempirical relations for the turbulent normal stresses. The resulting formulations are numerically integrated. The turbulent model outputs are verified with experimental data reported in the literature. Satisfactory agreement is obtained between numerical simulations and experimental data. Mathematical formulas and curves as functions of longitudinal pressure gradient, wastewater velocity, and sewer headspace geometry are developed for the cross-sectional average streamwise velocity.     

Effects of the entrained surface film on the reliability of castings

The tilt pouring and gravity top pouring of an Al-4.5 pct Cu alloy have been studied. A computercontrolled rollover casting wheel was used to perform the tilt pouring. Filling sequences with tranquil or turbulent flow patterns have been visualized using real-time X-ray video radiography and modeled using a computational fluid dynamics (CFD) code. The area of the free surface film entrained into the bulk of liquid metal in different filling conditions has been calculated using a filling sequence free from surface turbulence as a baseline. The tensile properties of the castings have been quantitatively assessed for reliability using a two-parameter Weibull distribution function. The study reveals that the liquid metal flow in the mold filling process can be accurately simulated using a CFD code. In addition, the computed total surface area of the entrained surface film can be used as a criterion to judge the deterioration of reliability. The high Weibull modulus achieved by filling a mold without surface turbulence was reduced by a factor of 2.5 of its original value by entrained surface films. Entrainment of bubbles required surface turbulence, but folded films could be entrained simply by contraction of the free surface, creating excess surface film that necessarily folds inward.     

CFD Predictions and Experimental Comparisons of Pressure Drop Effects of Turning Vanes in 90° Duct Elbows

This paper presents new results for numerical predictions of air flow and pressure distribution in two commonly used elbows: (1) 90° mitered duct elbows with turning vanes having 0.05 m radius, 0.038 m vane spacing and (2) 90° mitered duct elbows without turning vanes, in 0.2×0.2?m (8?in.×8?in.) duct cross section using the STAR-CD computational fluid dynamics (CFD) code. A k-ε turbulence model for high Reynolds number and k-ε Chen model were used for that purpose for comparative purposes. The simulation used 13 different Reynolds numbers chosen between the range of 1×105 and 2×106. To validate the CFD results, the results of two experimental papers using guided vanes were compared with simulated vane runs under the same condition. The first experimental study used a 0.6×0.6?m (24?in.×24?in.) square elbow with 0.05 m radius, 0.038 m vane spacing and air velocities at 2.54 m/s (500 fpm) and 25.4 m/s (5,000 fpm), the second experiment used a 0.81×0.2?m (32?in.×8?in.) rectangular elbow geometry with 0.05 m radius, 0.038 m vane spacing with air velocities from 10.16 m/s (2,000 fpm) to 13.97 m/s (2,750 fpm). For Reynolds numbers (1.00–2.00)×105 the pressure drop difference between vaned and unvaned elbows was found to be 35 Pa as compared to 145 Pa. The simulations also agreed reasonably well with published experimental results. For the 0.6×0.6?m (24?in.×24?in.) square elbow and 0.81×0.2?m (32?in.×8?in.) rectangular elbow with vanes, the difference in pressure drop was 3.9 and 4.1% respectively and indicates that CFD models can be used for predictive purposes in this important HVAC applications area.     

Comparison of Computation Fluid Dynamics Simulation against Tracer Data from a Scale Model and Full-Sized Waste Stabilization Pond

The use of computation fluid dynamics (CFD) for waste stabilization pond design is becoming increasingly common but there is a large gap in the literature with regard to validating CFD pond models against experimental flow data. This paper assesses a CFD model against tracer studies undertaken on a full-sized field pond and then on a 1:5 scale model of the same pond operated under controlled conditions in the laboratory. While the CFD tracer simulation had some discrepancies with the field data, comparison to the laboratory model data was excellent. The issue is, therefore, not in the way the model solves the problem, for example, the choice of turbulence model or differencing scheme, but rather with how accurately the physical conditions in the field are defined. Extensive survey of the sludge layer and transient input of changing flow rates, wind velocities, and temperature could allow closer alignment of CFD simulations to field data. However, in the practical application of CFD where a modification such as baffle installation results in a large change, then a simple pragmatic model, while not exact, can still provide valuable design insight.     

开槽阳极对铝电解气液两相流及气泡分布特性影响的数值模拟

基于计算流体动力学原理,建立了全尺度三阳极铝电解槽内气液两相流三维CFD-PBM耦合计算模型,采用Grace曳力系数模型和Simonin湍流扩散力模型分别计算气液相间曳力和湍流扩散力,研究和讨论了开槽阳极对阳极底掌区域内气液两相流体流动及气泡分布特性的影响。结果表明,电解质流场预测结果与文献测试结果吻合良好;对阳极进行开槽可明显加快气泡的逸出方式,从而改变电解质流场和气体体积分数分布;长度方向开槽可明显降低气体体积分数和减小气泡索特平均直径。     

Computational Fluid Dynamic Modeling of Zinc Slag Fuming Process in Top-Submerged Lance Smelting Furnace

Slag fuming is a reductive treatment process for molten zinciferous slags for extracting zinc in the form of metal vapor by injecting or adding a reductant source such as pulverized coal or lump coal and natural gas. A computational fluid dynamic (CFD) model was developed to study the zinc slag fuming process from imperial smelting furnace (ISF) slag in a top-submerged lance furnace and to investigate the details of fluid flow, reaction kinetics, and heat transfer in the furnace. The model integrates combustion phenomena and chemical reactions with the heat, mass, and momentum interfacial interaction between the phases present in the system. A commercial CFD package AVL Fire 2009.2 (AVL, Graz, Austria) coupled with a number of user-defined subroutines in FORTRAN programming language were used to develop the model. The model is based on three-dimensional (3-D) Eulerian multiphase flow approach, and it predicts the velocity and temperature field of the molten slag bath, generated turbulence, and vortex and plume shape at the lance tip. The model also predicts the mass fractions of slag and gaseous components inside the furnace. The model predicted that the percent of ZnO in the slag bath decreases linearly with time and is consistent broadly with the experimental data. The zinc fuming rate from the slag bath predicted by the model was validated through macrostep validation process against the experimental study of Waladan et al. The model results predicted that the rate of ZnO reduction is controlled by the mass transfer of ZnO from the bulk slag to slag–gas interface and rate of gas-carbon reaction for the specified simulation time studied. Although the model is based on zinc slag fuming, the basic approach could be expanded or applied for the CFD analysis of analogous systems.