Microchannels and micro pin fins have been employed for almost four decades in the cooling of microelectronic devices and research is still being done in this field to improve the thermal performance of these micro heat sinks. In this research, the constructal design and computational fluid dynamics code was used with a goal-driven optimisation tool to numerically investigate the thermal performance of a novel design of combining microchannels and micro pin fins for microelectronic cooling applications. Existing designs of microchannels were first optimised and thereafter, three to seven rows of micro pin fins were inserted into the microchannels to investigate whether there was further improvement in thermal performance. The microchannels and micro pin fins were both embedded in a highly conductive solid substrate. three-dimensional geometric structure of the combined micro heat sink was optimised to achieve the objective of maximised thermal conductance, which is also minimised thermal resistance under various design conditions. The micro heat sinks investigated in the study were the single microchannel, two-layered microchannels with parallel and counter flow configurations, three-layered microchannels with parallel and counter flow configurations, the single microchannel with circular-, square- and hexagonal-shaped micro pin-fin inserts and the two-layered microchannels with circular-shaped micro pin-fin inserts. A numerical computational fluid dynamics (CFD) package with a goal-driven optimisation tool, which employs the finite-volume method, was used to analyse the fluid flow and heat transfer in the micro heat sinks investigated in this work. The thermal performances of all the micro heat sinks were compared for different application scenarios. Furthermore, the temperature variation on the heated base of the solid substrate was studied for the different micro heat sinks to investigate which of the heat sink designs minimised the temperature rise on the heated base best. This is very important in microelectronic cooling applications because temperature rise affects the reliability of the device. The heat sink design that best maximised thermal conductance and minimised temperature rise on the heated base was chosen as the best for microelectronic cooling. For all the cases considered, fixed volume constraints and manufacturing constraints were applied to ensure real-life applicability. It was concluded that optimal heat sink design for different application scenarios could be obtained speedily when a CFD package which had an optimisation tool was used. / Thesis (PhD)--University of Pretoria, 2016. / Mechanical and Aeronautical Engineering / PhD / Unrestricted

The research conducted at the department of Electrical Engineering of the University of South Florida campus in Tampa only covers the electrical aspect of electric drives. However, the performance of electric machinery is significantly impacted by temperature variation. The literature review shows three main control techniques in use today in electric drives namely, Scalar control, Direct Torque control and Field Oriented control. This thesis presents a temperature rise of rotor bars, stator winding, stator core and stator frame in a running three phase field-oriented controlled induction machine. A literature search shows that none of research has been carried out to investigate a thermal response of a field-oriented controlled induction motor. With this motivation, we were able to implement a lumped parameters thermal model of a three-phase field-oriented IM in MATLAB Simulink, which allows us to determine that rotor bars have the highest temperatures rising to 84 degrees Celsius. This confirms that rotors bars are the hottest part of a running IM as stipulated in literature.

A graphite foam was developed at Oak Ridge National Laboratory (ORNL) by Dr. James Klett and license was granted to POCO Graphite, Inc. to manufacture and market the product as PocoFoam™. Unlike many processes currently used to manufacture carbon foams, this process yields a highly graphitic structure and overcomes many limitations, such as oxidation stabilization, that are routinely encountered in the development of carbon foam materials. The structure, thermal properties, electrical resistivity, isotropy, and density uniformity of PocoFoam™ were evaluated. These properties and characteristics of PocoFoam™ are compared with natural and synthetic graphite in order to show that, albeit similar, it is unique. Thermal diffusivity and thermal conductivity were derived from Fourier's energy equation. It was determined that PocoFoam™ has the equivalent thermal conductivity of metals routinely used as heat sinks and that thermal diffusivity is as much as four times greater than pure copper and pure aluminum. SEM and XRD results indicate that PocoFoam™ has a high degree of crystalline alignment and near theoretical d spacing that is more typical of natural flake graphite than synthetic graphite. PocoFoam™ is anisotropic, indicating an isotropy factor of 0.5, and may yield higher thermal conductivity at cryogenic temperatures than is observed in polycrystalline graphite.

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No description available.

This thesis characterizes the transient thermal response of a 12/16 External Rotor Switched Reluctance Machine (ERSRM) for an E-bike application. A method for calculating coil capacitance based on machine design parameters was introduced and implemented into a standard commercial Lumped Parameter Thermal Network (LPTN). A sizing criterion was proposed for the cuboid number in a physically accurate LPTN coil model design. This sizing criterion considers the change in model size with motor speed or forced convection. The LPTN with a more accurate calculation of capacitance within the coil and a known number of cuboids in the coil was validated with experimental results. An analytical proof was provided that a small number of capacitances is not sufficient to model a typical power-dense coil design. The validated model was used to study the impact of a more accurate capacitance calculation method on motor temperature. Both overload and rated operation were investigated. During overload conditions, it was found that the standard capacitance calculation from commercial software massively underestimated the heating rate and peak temperature of the coil hot spot, even with the same number of cuboids. The capacitance of the rest of the motor was able to be varied and investigated for its effects on cooldown dynamics. It was found that for short-time transients the coil could be assumed to act adiabatically in this operating range. Operating points across the operating envelope for the motor under study were mapped to determine the region where the adiabatic assumption could be made. It was shown that a transition occurred where the adiabatic assumption ceases to be valid. / Thesis / Doctor of Philosophy (PhD) / This thesis deals with the thermal modelling of electric machines for traction applications using lumped parameter thermal modelling. A novel approach is presented for calculating and distributing thermal capacitance in motor coils. A 12/16 External Rotor Switched Reluctance Motor is characterized based on its transient thermal response and the novel methods proposed are validated. The sizing of a coil-based thermal model is discussed and a criterion for physical validity proposed. The validated model is used in a sensitivity analysis of coil and motor capacitances. For severe overload conditions and short periods, a result is obtained showing the coil can be modelled as adiabatic. Finally, a rated load condition is tested, and a transition is suggested between overload conditions and non-overload conditions.

No description available.

Gamma-ray bursts (GRBs) are the most luminous phenomena in the Universe, explosions whoseenergy is generated by supernovae or mergers of dense objects such as neutron stars. The GRBemission is divided into the prompt emission phase characterized by γ-ray radiation and the afterglowof lower energy radiation. The prompt emission phase is still not understood; as of now, there aretwo leading descriptions: the photospheric- and the synchrotron models. The synchrotron model hashad great success in describing GRB spectra, and specifically some of the brightest ones, although notwithout issues such as some observations being at odds with theory. On the other hand, photosphericmodels have had problems too of how to broaden the spectrum in order to explain the observeddata. One explanation for this broadening is that Radiation Mediated Shocks (RMSs) dissipate energybelow the photosphere. In this report, a time resolved spectral analysis of the prompt emission of GRB160625B – a very bright GRB known to produce synchrotron-like emission – is done. Komrad is animplementation of the Kompaneets RMS Approximation (KRA), which is a dissipative photosphericmodel. Komrad is then used to fit a photospheric model to the prompt emission of GRB 160625Bin order to explore whether photospheric models can account for synchrotron-like emission spectra.Great statistical support is found for the photospheric model in comparison to standard GRB fittingfunctions as well as a synchrotron function which is indicative of the photospheric model being able toexplain a synchrotron-like spectra.

The following research investigates the effect that axial cooling channels will have on the performance of the thermal management system of a hypothetical switched reluctance motor. A baseline motor with no axial cooling will be compared to an identical motor with the innovative cooling design implemented. This will allow for a direct comparison of the two designs, with a quantifiable performance increase determined through thermal simulations. The ability of a polymer composite to transfer heat to the axial cooling channel is also explored. A detailed material selection process is discussed with the result being an epoxy polymer composite. The material development of a thermally enhanced polymer composite is then investigated to achieve a maximum thermal conductivity material that can exist within the stator slot to achieve enhanced thermal energy transfer. / Thesis / Master of Applied Science (MASc) / The desire to increase the power density of electric machines is becoming an increasingly popular challenge, especially in the automotive industry. With the advent of electrified powertrains as an alternative solution to conventional internal combustion powered vehicles, the topic of increasing electric motor performance is becoming very attractive area of research. An important aspect of electric motor performance is the way in which the generated thermal energy is managed. Through material development and innovative motor design, there exists the opportunity to cool electric motors through cooling paths flowing axially through the stator. This ‘axial cooling’ design has the opportunity to greatly increase motor cooling by removing thermal energy directly from its main source, the motor windings. The following research is aimed at the thermal design of the axial cooling and the role in which thermally conductive polymer composites play in order to enhance motor cooling.

<p> This thesis focuses on the thermal plasma treatment of non-point source pollutants accumulating in stormwater ponds. Stormwater ponds are constructed as a part of urban non-point source pollution control systems. Pollutants from various sources are collected in the stormwater ponds as sediments. In this work, stormwater sediments were first separated by a filter with an opening of 208μm. The filtered sludge-water was subjected to pulsed arc electrohydraulic discharge (PAED) treatment while the solid part (i.e., wet sludge and dried PAED treated sludge) was subjected to thermal plasma treatment under non-DC transferred and partial transferred operation modes. The results from the PAED sludge-water treatment show that the reduction of TOC in sludge-water was approximately 80% and was greater than 90%, respectively, after 5 minutes and 2 hours of PAED treatment. The accumulated gaseous concentrations of CxHy, CO, C02, S02, H2S and NO emission from sludge-water treatment were 8.2, 3.1, 1.9, 0.32, 0.29 and 0.07 mg/L, respectively, after 2 hours of PAED treatment. The concentrations of volatile elements in sediments such as S, Br, Cl and K decreased approximately 80, 90, 30 and 20% respectively. The solid-phase carbon was observed to be approximately completely removed after treatment. Based on the above results, it can be concluded that PAED successfully degraded organic compounds into C02, CO and CxHy, and converted sulfur and nitrate compounds into S02, HzS and NO. </p> <p> Thermal plasma wet-sludge treatments showed that a reduction of TOC was approximately 52% with argon plasma gas and air flow rates (in the reaction zone) of 24 and 2.4 L/min, respectively. Based on SEM images, wet sludge was melted under partial transferred mode. Thirteen elements with concentration relationships of 0 > Si > Al > Ca > S >Fe> K > Mg > Na > Cu > C > Ti > Cl were quantified by the X-ray energy dispersion technique. The elemental weight percentages of Si, K, Fe and 0 increased with increasing reaction zone air flow rate, while Ca and Cu decreased with increasing air flow rate. Thirty two elements were quantified by Neutron Activation Analyses (NAA) but only 27 elements were above the detection limits. Major elements (concentration> 1000 ppm) with relative concentrations of Ca > Al >Fe> K > Mg > Na > Ti > Cl; minor elements (100 - 1000 ppm) with relative concentrations of Mn > Ba > Sr > Zn; and trace elements(< 100 ppm) with relative concentration were Mo > V > Cr > Br >La> As > Sc > Th> As > Co > Dy > W > Sb > Eu; were determined. Concentrations of Zn, La and Co were enriched 90, 50 and 30% on average respectively, while concentrations of Br, W and As decreased by 80, 50 and 20% on average respectively. The chemical compositions in sludge were quite different after thermal plasma treatment. The average percentages of sand (Si02) and calcite (CaC03) decreased 35 and 10% respectively, while compounds such as KAlSi08, Fe304, NaCl and CaS04 were formed after thermal plasma treatment. Gaseous hydrocarbons, H2S, CO and NO were emitted continuously during the thermal plasma treatment of sludge. Higher reduction of organics and sulfur compounds and suppression of NOx formation were observed in the thermal plasma treatment of wet sludge. The integrated system consisting of PAED sludge-water treatment and thermal plasma wet sludge treatment under partial transferred mode may provide a potential for stormwater pond sediment treatment control. </p> / Thesis / Doctor of Philosophy (PhD)