High-quality silicon crystals provide the basis of many industrial technological advances, including computers and telecommunication devices. The increasing size and extremely high quality requirements of silicon wafers have made furnace design and crystal manufacturing a very challenging task. Numerical simulations have become an essential and powerful tool to overcome the difficulties of the experimental approach with a view to understanding the crystal growth process but also to finding an appropriate path to optimize the crystal pulling conditions in industry.</br></br> This thesis deals with the use of alternating and steady transverse magnetic fields in silicon growth from the melt. The use of magnetic fields represents a powerful tool to damp out turbulence and control the melt flow. This technique can also be used to heat the system. We focus on the numerical modeling of (i) induction heating in the Floating Zone process and of (ii) melt convection under the effect of transverse magnetic fields in the Czochralski process. For each of these topics, our work is subdivided in two parts : firstly mathematical modeling, based on asymptotic or Fourier expansions, and secondly numerical implementation and simulation of the considered processes. </br></br> First, a theoretical and numerical model of the alternating magnetic field distribution (as generated by induction heating) has been developed by means of an asymptotic expansion technique. Moreover, a new methodology has been developed to calculate the thermal and mechanical effects of alternating magnetic fields on the liquid conductor flow, leading to accurate expressions for the equivalent magnetic heat flux and surface stresses in the 2D and 3D cases. Second, investigation of the effect of a transverse magnetic field on the melt flow in semi-conductor crystal growth has been performed by the simplified FLET method (“Fourier Limited Expansion Technique”.)

Micro-needle platforms are the core components of many recent drug delivery and gene-editing techniques, which allow for intracellular access, controlled cell membrane stress or mechanical trapping of the nucleus. This dissertation work is devoted to the development of micro-needle platforms that offer customized fabrication and new capabilities for enhanced cell analyses. The highest degree of geometrical flexibility is achieved with 3D printed micro-needles, which enable optimizing the topographical stress environment for cells and cell populations of any size. A fabrication process for 3D-printed micro-needles has been developed as well as a metal coating technique based on standard sputter deposition. This extends the functionalities of the platforms by electrical as well as magnetic features. The micro-needles have been tested on human colon cancer cells (HCT116), showing a high degree of biocompatibility of the platform. Moreover, the capabilities of the 3D-printed micro-needles have been explored for drug delivery via the well-established electroporation technique, by coating the micro-needles with gold. Antibodies and fluorescent dyes have been delivered to HCT116 cells and human embryonic kidney cells with a very high transfection rate up to 90%. In addition, the 3D-printed electroporation platform enables delivery of molecules to suspended cells or adherent cells, with or without electroporation buffer solution, and at ultra-low voltages of 2V. In order to provide a micro-needle platform that exploits existing methods for mass fabrication a custom designed template-based process has been developed. It has been used for the production of gold, iron, nickel and poly-pyrrole micro-needles on silicon and glass substrates. A novel delivery method is introduced that activates the micro-needles by electromagnetic induction, which enables to wirelessly gain intracellular access. The method has been successfully tested on HCT116 cells in culture, where a time-dependent delivery rate has been found. The electromagnetic delivery concept is particularly promising for future in-vivo applications. Finally, the micro-needle platforms developed in this work will provide researchers with new capabilities that will help them to further advance the field of mechanobiology, drug delivery treatments, stem cells research and more. The proposed platforms are capable of applying various stimuli, analyzing cell responses in real time, drug delivery, and they also have the potential to add additional functionalities in the future.

The field of self-healing materials is growing dramatically due to the obvious in- centive of having structural materials with the ability to repair damage. Some polymers have demonstrated the ability to heal from damage autonomously[12, 26], when exposed to heat[1], or when punctured[5, 9]. The goal of this research is to develop a "proof-of-concept" polymer composite that has the ability to heal when exposed to an alternating magnetic field. Several types of magnetic particulate were inspected for use in the production of polymer composite test samples. The types of particulate used in sample production were two supplies of γ-Fe₂O₃, one supply of α-Fe₂O₃, and one supply of Ni-Zn Ferrite. Surlyn 8940 was selected as the bulk polymer due to its self-healing qualities[9]. A method for melt mixing the particulate with the polymer in various volume fractions was developed and an SEM was used to study the dispersion of the particulate. Once the polymer composite samples were made, various tests were conducted to characterize the samples in order to determine what effects the particulate had on the prop- erties of the bulk polymer. These tests included differential scanning calorimetry (DSC), rheology, conductivity, and magnetic response. Once the samples were characterized, tests were performed to study the composite polymers ability to heat and heal. These tests included healing microscopy, induction heating, and tensile testing. From this study, it was found that the addition of particulate to the bulk polymer does alter the properties by increasing viscosity and electrical conductivity. However, the addition of particulate does not change the melt temperature, but allows the magnetic hysteresis loop of each composite sample to be revealed through magnetic testing. Through healing microscopy and tensile testing, the polymer composites were found to heal when heated, but at a higher temperature than the pure bulk polymer samples. Each type of polymer composite also heated to varying degrees through magnetic induction. Due to the ability of the polymer composite to heal and heat, a "proof-of-concept" has been provided for a magnetically healing polymer composite. / Master of Science

With the increasing use of aluminum in naval vessels and the ever-present danger of fires, it is important to have a good understanding of the behavior of aluminum at elevated temperatures. The aluminum samples 5083-H116 and 6061-T651 were examined under a variety of loading conditions and temperatures. Tensile testing was completed on both materials to measure strength properties of elastic modulus, yield strength, and ultimate strength as well as reduction of area from room temperature to 500 deg C taking measurements every 50 deg C. These tests showed how much the material weakened as temperature increases. Low temperatures had a minimal effect on strength while exposure to temperatures between 200 and 300 deg C had the most significant impact. Creep testing was also completed for these materials. These tests were completed at temperatures between 200 and 400 deg C in 50 deg C increments. Stresses for these tests were in the range of 13 to 160MPa for 5083 aluminum and between 13 to 220MPa for 6061 aluminum. These tests showed a significant relationship between stress and temperature and how changes to one can cause a very different resulting behavior. In addition to the creep testing, three creep models were examined as a means of predicting creep behavior. These models included a power law, exponential, and hyperbolic-sine versions and were able to predict creep results with decent accuracy depending on the stress used in the model. / Master of Science

Chemical and allied industries produce significant quantities of chlorinated wastes each year. Thermal treatnent of these chlorinated wastes has a long and controversial history. The most common and contentious method of waste destruction is incineration. Although waste incinerators are designed to provide greater control over the combustion process, toxic products are inevitably formed from incomplete combustion and released in stack gases and other residues. The most notable group belonging to the products of incomplete combustion (PICs) are dioxins and furans. The fact that oxygen is an integral part of the molecular structure of dioxins and furans suggests that the formation of these particular PICs may be reduced or avoided by minimizing or completely excluding oxygen from thermal waste treatment. Pyrolysis using induction heating is a relatively new technology that has shown much promise from the initial work performed by Pillay (2001). This research was an extension of that study, and investigated equipment and process optimization as well as macroscopic modeling of different systems. The objective of this study was to establish the technology of pyrolysis using induction heating as a competitive alternative to existing waste destruction systems. The novel approach of pyrolysing compounds using induction heating was demonstrated by destroying chlorinated aliphatic, aromatic and a mixture of these compounds. These experiments were conducted at atmospheric pressure in a tubular laminar flow reactor (5.2cm I.D) under a thermally transparent argon atmosphere. In this system heat was generated in an embedded graphite tube using induction heating. Thermal degradation occurred through the bombardment of the compounds by the photons emitted from the heated graphite tube. The compounds were pyrolysed at temperatures ranging from 330°C to 1000°C and at mean residence times from 0.47s to 2.47s. In addition to these process variables the effects of reactant concentration and additives were investigated The major species formed from this thermal treatment were solid carbon black and gaseous hydrogen chloride. Destruction efficiencies (DE) of the order of 99.9999% (six nines) and greater were obtained for the different feed mixtures at their respective operating conditions. A minimum DE of six nines adequately satisfies the regulation set by the Environmental Protection Agency (EPA) for successful waste destruction. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2004.

Microfluidic systems are being used in more and more areas and the demand for such systems is growing every day. To meet such high volume market needs, a cheap and rapid method for sealing these microfluidic platforms which is viable for mass manufacture is highly desirable. In this work low frequency induction heating (LFIH) is introduced as the potential basis of a cost-effective, rapid production method for polymer microfluidic device sealing. Thin metal layers or structured metal features are introduced between the device s substrates and heated inductively. The surrounding material melts and forms a bond when cooling. During the bonding process it is important to effectively manage the heat dissipation to prevent distortion of the microfluidic platform. The size of the heat affected zone (HAZ), and the area melted, must be controlled to avoid blockage of the microfluidic channels or altering the channels wall characteristics. The effects of susceptor shape and area, bonding pressure, heating time, etc, on the heating rate have been investigated to provide a basis for process optimisation and design rules. It was found that the maximum temperature is proportional to the square of the susceptor area and that round shaped susceptors heat most efficiently. As a result of the investigations higher bonding pressure was identified as increasing bond strength and allowing the reduction of heating time and thus the reduction of melt zone width. The use of heating pulses instead of continuous heating also reduced the dimensions of melt zones while maintaining good bond strength. The size of the HAZ was found to be negligible. An analytical model, which can be used to predict the heating rate, was derived. In validating the model by numeric models and experiments it was found that it cannot be used to calculate exact temperatures but it does correctly describe the effect of different heating parameters. Over the temperature range needed to bond polymer substrates, cooling effects were found not to have a significant impact on the heating rate. The two susceptor concepts using thin metal layers (metal-plastic bonds) or structured metal features (plastic-plastic bonds) were tested and compared. While the metal-plastic bonds turned out to be too weak to be useful, the bonds formed using structured susceptors showed good strength and high leakage pressure. Based on the knowledge gained during the investigations a microfluidic device was designed. Different samples were manufactured and tested. During the tests minor leaks were observed but it was found that this was mainly due to debris which occurred during laser machining of the channels. It was concluded that induction bonding can be used to seal plastic microfluidic devices. The following guidelines can be drawn up for the design of susceptors and process optimisation: Materials with low resistivity perform better; For very thin susceptors the effect of permeability on the heating rate is negligible; The cross-sectional area of the susceptor should be as large as possible to reduce resistance; The thickness of the susceptor should be of similar dimensions to the penetration depth or smaller to increase homogeneity of heat dissipation; The shape of the susceptor should follow the shape of the inductor coil, or vice-versa, to increase homogeneity of heat dissipation; The susceptor should form a closed circuit; Higher bonding pressure leads to stronger bonds and allows reduced heating times; Pulsed heating performs better than continuous heating in terms of limited melt area and good bond strength. The drawbacks of the technique are explained as well: introducing additional materials leads to additional process steps. Also the structuring and placement of the susceptor was identified to be problematic. In this project the structured susceptor was placed manually but that is not feasible for mass manufacture. To be able to use the technique efficiently a concept of manufacturing the susceptor has to be found to allow precise alignment of complex designs.

On s’intéresse dans ce travail à la convection thermique en présence de champ magnétique, en lien avec les essais Vulcano du CEA de Cadarache. Ces essais ont pour but de reproduire en laboratoire les écoulements générés par un chauffage volumique dues aux matières radioactives issues d’accidents nucléaires. Le chauffage par induction électromagnétique de ces fluides permet de simuler en laboratoire la puissance volumique des désintégrations nucléaires en évitant l’utilisation de matériaux radioactifs. Néanmoins, ce forçage électromagnétique génère un couplage entre l’écoulement fluide et le champ magnétique, par la force de Lorentz d’une part, et d’autre part le chauffage volumique par effet Joule se concentre dans l’épaisseur de peau. De plus, il peut y avoir dans ces essais présence d’une phase dispersée métallique qui risque de perturber le chauffage inductif de la phase continue (oxyde). Il est nécessaire d’étudier comment ces effets d’origine électromagnétique modifient l’écoulement. À plus petite échelle, les phénomènes magnétiques en jeu peuvent être reproduits grâce à des métaux liquides à température ambiante. Lorsqu’un champ magnétique harmonique est appliqué à la frontière d’un métal liquide, l’effet stabilisant de la force de Lorentz sera prépondérant devant l’effet Joule à basses fréquences, alors que l’effet Joule devient significatif à hautes fréquences. On considère alors plusieurs situations canoniques permettant d’analyser l’effet d’un champ magnétique constant DC et alternatif AC sur un écoulement de convection naturelle monophasique, ou en présence d’une phase dispersée très conductrice. Une première partie est consacrée à l’étude expérimentale d’une méthode de vélocimétrie acoustique sur une cellule de convection naturelle en eau. Par comparaison avec des mesures de vitesse par imagerie de particules (PIV) et des simulations numériques directes (DNS), cela a permis de valider la méthode acoustique en vue de futures expériences en métal liquide. Une seconde étude est dédiée à l’analyse numérique de l’instabilité de Rayleigh-Bénard en présence d’un champ magnétique DC vertical. Les taux de croissance sont déterminés par analyse de stabilité linéaire pour des nombres de Hartmann 0 _ Ha _ 100 et des nombres de Rayleigh 103 _ Ra _ 1.5 × 105. Ces prédictions sont confirmées par DNS. En régime stationnaire, l’analyse des DNS a permis de mettre en évidence un effet marqué de la force de Lorentz sur les structures, à travers leur nombre d’onde et leur orientation. La troisième configuration étudiée est le chauffage inductif d’une couche de métal liquide en imposant un champ magnétique harmonique au niveau de la paroi basse pour des nombres de Rayleigh proportionnels à la puissance déposée 1.1×104 _ Ra _ 1.2×105 et pour des épaisseurs de peau inférieures à la moitié de l’épaisseur de liquide. Dans ce cas, les courants induits sont dissipés par effet Joule sur l’épaisseur de peau. La prédiction des taux de croissance requiert l’utilisation de méthodes adaptées car ici le développement de l’instabilité est concomitant à la conduction instationnaire de la chaleur. Malgré la perte de symétrie des équations introduite par le terme source d’effet Joule, l’écoulement présente une symétrie de réflexion apparente, que ce soit en régimes transitoire ou stationnaire. Cela est lié au brassage conséquent par convection naturelle. Enfin une situation modèle de particules métalliques immergées dans un liquide transparent au champ magnétique est étudiée. Ici, l’énergie magnétique est dissipée sous forme thermique dans les particules, qui transmettent toute leur chaleur au fluide. Des mouvements convectifs se mettent alors en place. La convection est décrite par la concentration relative en particules. Selon les valeurs des paramètres, on observe la formation d’amas de particules en réponse au panache qu’elles génèrent. / In this work, we study thermal convection in the presence of magnetic field in connection with the Vulcano tests at CEA Cadarache. These tests aim at reproducing in the laboratory the behavior of fluids that result from a severe nuclear accident, while avoiding the use of radioactive materials. Induction heating is used to mimic in the laboratory the volume power of nuclear disintegrations. However, there is a parasitic coupling between the flow and the magnetic field (Lorentz force) on the one hand, and on the other hand the concentration of Joule dissipation in the skin layer, while it is homogeneous in a real case. Moreover, the presence of a dispersed metallic phase may interfere with the induction heating of the continuous phase (oxide). At smaller scales, the magnetic phenomena at play can be simulated with liquid metals at room temperature. When a magnetic field is applied at the boundary of a liquid metal, the stabilizing role of the Lorentz force will dominate at very low frequencies, whereas the Joule effect will be significant at high frequencies. Here, we consider several generic configurations that allow to analyze the action of DC or AC magnetic fields on natural convection, for a single phase flow or in the presence of a dispersed phase. The first part is devoted to the experimental study of an acoustic velocimetry method in the case of natural convection in water. The comparison of particle imaging velocimetry (PIV) data along with direct numerical simulations (DNS) allowed the validation of the acoustic method. In the future, experiment in liquid metal will be performed. A second part is dedicated to the numerical analysis of the Rayleigh-Bénard instability in the presence of vertical DC magnetic field. Growth-rates are determined by linear stability analysis for Hartmann numbers 0 _ Ha _ 100 et Rayleigh numbers 103 _ Ra _ 1.5×105. These predictions are confirmed by DNS. In the steady regime, DNS showed a strong effect of the Lorentz force on flow structures, through the modulation of the wavenumber and the structures orientation. The third configuration is the induction heating of a liquid metal layer by impressing an AC magnetic field at the bottom, for power Rayleigh numbers 1.1×104 _ Ra _ 1.2×105 and for skin depths lower than half of the liquid thickness. The prediction of the growth-rates requires to use an adapted method to account for the simultaneous development of the transient heat conduction. Although the Joule dissipation source term breaks the mirror symmetry of the governing equations, the flow exhibits an apparent reflectional symmetry, both in the transient and in the stationary regimes. This is a consequence of the mixing induced by the natural convection. Finally, a model situation of metallic particles immersed in a fluid transparent to the magnetic field is studied. Here the magnetic energy is dissipated in thermal form in the particles, which then transfer their heat to the fluid. As a result, buoyant motion then sets in. Depending on the parameters values, we observe the formation of clusters in response to the thermal plume that they generate.

Thesis. 1977. Ph.D.--Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / Ph.D.

Forging operations are widely used for manufacturing processes. Forging process is done hot, warm or cold. All three temperature ranges have advantages and disadvantages. The aim of this study is to combine the advantages of hot and cold forging in a flange forming process with cylindirical workpieces in a single step. The process idea is the partial heating of the workpiece at locations where large deformations occur and to keep the parts of the workpiece cold at regions where high precision forming is required. Firstly, the process idea has been investigated virtually by the finite element method supplying the theoretical verification of the feasibility of the novel process. By this analysis also the process limits have been estimated. All analysis are based on an elastoplastic large strain material law with thermomechanical coupling. The experimental part of the study served to realize the new process idea and to verify the process window. In the experimental study two different materials, three different part geometries and different initial conditions such as temperature field, lubrication etc. have been investigated. The specifimens are heated by induction.

Hot forming is highly utilized in manufacturing of complex shapes. Relatively low flow stresses of materials at elevated temperatures provide ease of manufacturing. On the other side, the current trend is to replace hot forming with cold forming due to the superior mechanical properties and higher dimensional accuracy of the products and less energy consumption. However, cold forming requires high tooling costs and forming loads. In this study, a new process is proposed for production of complex shaped products where the disadvantages of both of the alternatives are tried to be minimized. The basic idea is to control the mode of deformation by heating the specimen locally prior to forming. Electromagnetic induction is used for local heating. Numerical simulations are carried out by finite element method (FEM) for further investigation on the effect of parameters. Thermo-mechanical analysis of heat diffusion and upsetting is supported by electromagnetic analysis of induction heating. The failure modes and operational window of the novel process is established. Conclusions are drawn on the applicability of the process and the effect of process parameters on the efficiency.