Computational fluid dynamics: advancements in technology for modeling iron and steelmaking processes

Computational fluid dynamics (CFD) software technology has formed the basis of many investigations into the behavior and optimization of primary iron and steelmaking processes for the last 25+ years. The objective of this contribution is to review the progress in CFD technologies over the last decade or so and how this can be brought to bear in advancing the process analysis capability of primary ferrous operations. In particular, progress on key challenges such as compute performance, fluid-structure transformation and interaction, and increasingly complex geometries are highlighted.

A non-Newtonian computational fluid dynamics study of the stencil printing process

This paper describes the application of computational fluid dynamics (CFD) to simulate the macroscopic bulk motion of solder paste ahead of a moving squeegee blade in the stencil printing process during the manufacture of electronic components. The successful outcome of the stencil printing process is dependent on the interaction of numerous process parameters. A better understanding of these parameters is required to determine their relation to print quality and improve guidelines for process optimization. Various modelling techniques have arisen to analyse the flow behaviour of solder paste, including macroscopic studies of the whole mass of paste as well as microstructural analyses of the motion of individual solder particles suspended in the carrier fluid. This work builds on the knowledge gained to date from earlier analytical models and CFD investigations by considering the important non-Newtonian rheological properties of solder pastes which have been neglected in previous macroscopic studies. Pressure and velocity distributions are obtained from both Newtonian and non-Newtonian CFD simulations and evaluated against each other as well as existing established analytical models. Significant differences between the results are observed, which demonstrate the importance of modelling non-Newtonian properties for realistic representation of the flow behaviour of solder paste.

SMARTFIRE: an integrated computational fluid dynamics code and expert system for fire field modelling

SMARTFIRE, an open architecture integrated CFD code and knowledge based system attempts to make fire field modeling accessible to non-experts in Computational Fluid Dynamics (CFD) such as fire fighters, architects and fire safety engineers. This is achieved by embedding expert knowledge into CFD software. This enables the 'black-art' associated with the CFD analysis such as selection of solvers, relaxation parameters, convergence criteria, time steps, grid and boundary condition specification to be guided by expert advice from the software. The user is however given the option of overriding these decisions, thus retaining ultimate control. SMARTFIRE also makes use of recent developments in CFD technology such as unstructured meshes and group solvers in order to make the CFD analysis more efficient. This paper describes the incorporation within SMARTFIRE of the expert fire modeling knowledge required for automatic problem setup and mesh generation as well as the concept and use of group solvers for automatic and manual dynamic control of the CFD code.

Utilising computational fluid dynamics (CFD) for the modelling of granular material in large-scale engineering processes

In this paper, the framework is described for the modelling of granular material by employing Computational Fluid Dynamics (CFD). This is achieved through the use and implementation in the continuum theory of constitutive relations, which are derived in a granular dynamics framework and parametrise particle interactions that occur at the micro-scale level. The simulation of a process often met in bulk solids handling industrial plants involving granular matter, (i.e. filling of a flat-bottomed bin with a binary material mixture through pneumatic conveying-emptying of the bin in core flow mode-pneumatic conveying of the material coming out of a the bin) is presented. The results of the presented simulation demonstrate the capability of the numerical model to represent successfully key granular processes (i.e. segregation/degradation), the prediction of which is of great importance in the process engineering industry.

Dynamics of magnetically suspended fluid

Magnetic suspension is a technique for processing pure or reactive materials without contact to walls. This work is concerned with the flow in the rapidly deforming liquid volume, suspended in an AC magnetic field. Intense flow motion due to the induced electromagnetic force distorts dynamically the droplet envelope. The relative positional change between the liquid surface and the surrounding coil means that fluid flow and magnetic field computations need to be closely coupled. The computed results are compared against a physical experiment and nearly spherical analytic solutions. A comparison between the "magetic pressure" approximation and the full electromagnetic force solutions shows fundamental differences; the full electromagnetic force is necessary for accurate results in most practical applications of this technique. The physical reason for the fundamental discrepancy is the difference in the electromagnetic force representation: only the gradient part of the full force is accounted for in the "magnetic pressure" approximation.

AC and DC magnetic levitation: melting, fluid flow and oscillations

The presented numerical modelling for the magnetic levitation involves coupling of the electromagnetic field, liquid shape change, fluid velocities and the temperature field at every time step during the simulation in time evolution. Combination of the AC and DC magnetic fields can be used to achieve high temperature, stable levitation conditions. The oscillation frequency spectra are analysed for droplets levitated in AC and DC magnetic fields at various combinations. An electrically poorly conducting, diamagnetic droplet (e.g. water) can be stably levitated using the dia- and para-magnetic properties of the sample material in a high intensity, gradient DC field.

Investigation into the performance of turbulence models for fluid flow and heat transfer phenomena in electronic applications

Computational Fluid Dynamics (CFD) is gradually becoming a powerful and almost essential tool for the design, development and optimization of engineering applications. However the mathematical modelling of the erratic turbulent motion remains the key issue when tackling such flow phenomena. The reliability of CFD analysis depends heavily on the turbulence model employed together with the wall functions implemented. In order to resolve the abrupt changes in the turbulent energy and other parameters situated at near wall regions a particularly fine mesh is necessary which inevitably increases the computer storage and run-time requirements. Turbulence modelling can be considered to be one of the three key elements in CFD. Precise mathematical theories have evolved for the other two key elements, grid generation and algorithm development. The principal objective of turbulence modelling is to enhance computational procedures of efficient accuracy to reproduce the main structures of three dimensional fluid flows. The flow within an electronic system can be characterized as being in a transitional state due to the low velocities and relatively small dimensions encountered. This paper presents simulated CFD results for an investigation into the predictive capability of turbulence models when considering both fluid flow and heat transfer phenomena. Also a new two-layer hybrid kε / kl turbulence model for electronic application areas will be presented which holds the advantages of being cheap in terms of the computational mesh required and is also economical with regards to run-time.

Thermo-mechanical modelling of power electronics module structures

Power electronic modules distinguish themselves from other modules by their high power operation. These modules are used extensively in high power application markets such as aerospace, automotive, industrial and traction and drives. This paper discusses typical packaging technologies for power electronics modules. It also discusses the latest results from a UK research project investigating the physics-of-failure approach to reliability analysis and predictions for power modules. An integrated design enviroment for incorporating of affects of uncertainty into the design environment was outlined.

Reliability analysis for power electronics modules

This paper discusses the reliability of power electronics modules. The approach taken combines numerical modeling techniques with experimentation and accelerated testing to identify failure modes and mechanisms for the power module structure and most importantly the root cause of a potential failure. The paper details results for two types of failure (i) wire bond fatigue and (ii) substrate delamination. Finite element method modeling techniques have been used to predict the stress distribution within the module structures. A response surface optimisation approach has been employed to enable the optimal design and parameter sensitivity to be determined. The response surface is used by a Monte Carlo method to determine the effects of uncertainty in the design.

Predicting the reliability of power electronic modules

This paper discusses the reliability of an IGBT power electronics module. This work is part of a major UK funded initiative into the design, packaging and reliability of power electronic modules. The predictive methodology combines numerical modeling techniques with experimentation and accelerated testing to identify failure modes and mechanisms for these type of power electronic module structures. The paper details results for solder joint failure substrate solder. Finite element method modeling techniques have been used to predict the stress and strain distribution within the module structures. Together with accelerated life testing, these results have provided a failure model for these joints which has been used to predict reliability of a rail traction application

A prognostic assessment method for power electronics modules

This paper describes a prognostic method which combines the physics of failure models with probability reasoning algorithm. The measured real time data (temperature vs. time) was used as the loading profile for the PoF simulations. The response surface equation of the accumulated plastic strain in the solder interconnect in terms of two variables (average temperature, and temperature amplitude) was constructed. This response surface equation was incorporated into the lifetime model of solder interconnect, and therefore the remaining life time of the solder component under current loading condition was predicted. The predictions from PoF models were also used to calculate the conditional probability table for a Bayesian Network, which was used to take into account of the impacts of the health observations of each product in lifetime prediction. The prognostic prediction in the end was expressed as the probability for the product to survive the expected future usage. As a demonstration, this method was applied to an IGBT power module used for aircraft applications.

Computer simulation of crack propagation in power electronics module solder joints

A numerical modelling method for the analysis of solder joint damage and crack propagation has been described in this paper. The method is based on the disturbed state concept. Under cyclic thermal-mechanical loading conditions, the level of damage that occurs in solder joints is assumed to be a simple monotonic scalar function of the accumulated equivalent plastic strain. The increase of damage leads to crack initiation and propagation. By tracking the evolution of the damage level in solder joints, crack propagation path and rate can be simulated using Finite Element Analysis method. The discussions are focused on issues in the implementation of the method. The technique of speeding up the simulation and the mesh dependency issues are analysed. As an example of the application of this method, crack propagation in solder joints of power electronics modules under cyclic thermal-mechanical loading conditions has been analyzed and the predicted cracked area size after 3000 loading cycles is consistent with experimental results.

Computer simulation of aluminium wirebonds with globtop in power electronics modules

In this paper, computer modelling techniques are used to analyse the effects of globtops on the reliability of aluminium wirebonds in power electronics modules under cyclic thermal-mechanical loading conditions. The sensitivity of the wirehond reliability to the changes of the geometric and the material property parameters of wirebond globtop are evaluated and the optimal combination of the Young's modulus and the coefficient of thermal expansion have been predicted.

Design, modeling and characterization of a microinductor for future DC-DC power converters

Experimental, analytical and simulated data are presented in this article to assess the performance of electrodeposited nickel-iron within a novel solenoid microinductor. A design flowchart highlights the primary design principles when developing a microscale magnetic component for DC-DC power converters. Thermal modeling is used to predict the operational conditions that generate undesirable thermal generation within the component. Operating at 0.5MHz, the microinductor achieves an efficiency and power density of 78% and 7.8 W/cm3, respectively.

Integrated reliability and prognostics prediction methodology for power electronic modules

The article consists of a PowerPoint presentation on integrated reliability and prognostics prediction methodology for power electronic modules. The areas discussed include: power electronics flagship; design for reliability; IGBT module; design for manufacture; power module components; reliability prediction techniques; failure based reliability; etc.