This dissertation examines the suitability of Computational Fluid Dynamics (CFD) modelling for the production of realistic flowfields and temperature fields within a series of vortex combustion chambers of differing geometries and operating under various conditions. Initial validation of the CFD predictions was obtained through modelling of a series of isothermal vortex chambers for which a comprehensive set of experimental data was available. It was observed that CFD did indeed produce representative flowfield predictions for chambers of various geometries and operating conditions. A vortex unit used for the incineration of sewage sludge (US Navy Waste Incinerator) was subsequently investigated, and it was shown that due to the high moisture content of the waste material used, temperature profiles obtained with a modified coal combustion model were similar to those obtained with a more straightforward and computationally less expensive spray drier model. Results from both models were similar to experimentally observed conditions. However, comprehensive validation was not possible. In order that full validation could be provided for a CFD model of a vortex combustion unit, a model was developed of a commercial thermal oxidiser used for the incineration of liquid and gaseous wastes. CFD temperature predictions for the BASF Thermal Oxidiser were validated by a series of experimental measurements obtained from the operating unit. In general, it was found that the Reynolds Stress Model for turbulence produced the most representative velocity flowfields, with the less computationally demanding k-e model being applicable only under certain limited circumstances. Furthermore, insufficient grid refinement resulted in significantly distorted velocity profiles.

This thesis investigates the use of CO2 laser radiation to treat concrete surfaces. Specimens were treated with varying laser parameters, and the resultant surfaces were analysed mechanically and chemically. A glass was formed by laser interaction, with underlying decomposition of both the cement paste and aggregate. The application of a cement-based coating prior to processing protects the concrete from excessive temperature rises during treatment. Processing of the coated material resulted in a glazed surface with no decomposition of the concrete substrate. With low energy density, OPC concrete exhibits only surface dehydration. However, when the energy density is increased, a glassy layer, with surrounding and underlying dehydration, is formed. Increasing the spot size results in a change in behaviour when the material is laser treated: several mm of concrete are removed, leaving either rough, bare concrete or a glazed trench. The resulting surface condition is dependent on the laser power. Thermal analysis techniques were used to identify the degradation reactions and the temperatures at which they occur during laser treatment. These are dehydration of the ettringite and ferrite phases at 1149C, dehydration of Ca(OH)2 at 462C, decarbonation of CaCO3 and ejection of material from 8129C onwards and the formation of a fiised glass layer at 1283 `C. The strength of attachment of the glass to the concrete decreases with increasing power or decreasing traverse speed due to the dehydration of the underlying material. The strength also decreases with time after treatment, due to rehydration of CaO. Mechanical failure occurs several mm below the glassy area into the dehydrated substrate, where dehydration of Ca(OH)2 has caused disruption to the structure of the material. The temperature rise in the material was monitored using embedded thermocouples at various depths. A one dimensional theoretical model agrees well with the experimental results over only a limited range of depth and time. A three dimensional finite difference model shows close agreement with experimental results over a range of operating parameters equivalent to those determined experimentally. Operating maps were generated which predict the depths to which the identified reactions occur. II A combination of pozzolanic Portland cement, chamotte, sand and waterglass can be successfully applied to the concrete surface. It acts both as a thermal insulator and provides vitrifiable material for laser treatment. Low power levels drive water out of the coating resulting in dehydration and colour changes, whilst higher power levels result in the formation of a glass on the coating surface. The attachment of the glass shows an area of maximum strength when power levels are below 150 Watts and traverse speeds below 2mm/s. Beyond these parameters the attachment becomes progressively weaker. Thermal analysis of the coating material shows no evidence of Ca(OH)2 dehydration and no decarbonation, resulting in no ejection of material. The underlying concrete is unheated, and therefore undergoes no decomposition reactions. Mechanical failure occurs at the limit of the glassy region rather than several mm below it as with bare concrete. Thus, the weakest point is the interface of the glazed-unglazed regions now that no significant Ca(OH)2 dehydration occurs.

The primary objective of this thesis is to develop a methodology for fast, yet accurate temperature estimation during design space exploration. Power and temperature of modern day systems have become important metrics in addition to performance. Static and dynamic power dissipation leads to an increase in temperature, which creates cooling and packaging issues. Furthermore, the transient thermal profile determines temperature gradients, hotspots and thermal cycles. Traditional solutions rely on cycle-accurate simulations of detailed micro-architectural structures and are slow. The thesis shows that the periodic power estimation is the key bottleneck in such approaches. It also demonstrates an approach (FastSpot) that integrates accurate thermal estimation into existing host-compiled simulations. The developed methodology can incorporate different sampling-based thermal models. It achieves a 32000x increase in simulation throughput for temperature trace generation, while incurring low measurement errors (0.06 K- transient,0.014 K- steady-state) compared to a cycle-accurate reference method. / text

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This dissertation provides several techniques for solving a class of nonconvex optimization problems that arise in the thermal analysis of electronic chip packages. The topic is of interest because in systems containing delicate electronic components both performance and reliability are impacted by thermal behavior. A modeling paradigm, called Compact Thermal Modeling (CTM), has been demonstrated to show promise for accurately estimating steady state thermal behavior without resorting to computationally intensive finite element models or expensive direct experimentation. The CTM is a network model that gives rise to a nonconvex optimization problem. A solution to this nonconvex optimization problem provides a reasonably accurate characterization of the steady state temperature profile the chip will attain under arbitrary boundary conditions, which allows the system designer to model the application of a wide range of thermal design strategies with useful accuracy at reasonable computational cost. This thesis explores several approaches to solving the optimization problem. We present a heuristic technique that is an adaptation of the classical coordinate search method that has been adapted to run efficiently by exploiting the algebraic structure of the problem. Further, the heuristic is able to avoid stalling in poor local optima by using a partitioning scheme that follows from an examination of special structure in the problem's feasible region. We next present several exact approaches using a globally optimal method based on the Reformulation Linearization Technique (RLT). This approach generates and then solves convex relaxations of the original problem, tightening the approximations within a branch and bound framework. We then explore several approaches to improving the performance of the RLT technique by introducing variable substitutions and valid inequalities, which tighten the convex relaxations. Computational results, conclusions, and recommendations for further research are also provided.

The problem solved in this thesis is one of transient linear heat conduction in a two layer, three-dimensional slab subjected to an arbitrary heat flux on one surface, where each layer is thermally orthotropic. The sides and bottom of the slab are either insulated (Bi = 0) or held at a constant temperature (Bi = infinity). The Biot number of the top surface varies from zero to infinity. The solution is developed by decomposing the problem into a number of simpler problems, each of which is solved using eigenfunction expansions. In the vertical direction, the eigenvalue problem is solved using the Krawczyk algorithm, and an orthogonality relationship is found by Vodicka's method.

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