Fueled by increasing human appetite for high computing performance, semiconductor technology has now marched into the deep sub-micron era. As transistor size keeps shrinking, more and more transistors are integrated into a single chip. This has increased tremendously the power consumption and heat generation of IC chips. The rapidly growing heat dissipation greatly increases the packaging/cooling costs, and adversely affects the performance and reliability of a computing system. In addition, it also reduces the processor's life span and may even crash the entire computing system. Therefore, dynamic thermal management (DTM) is becoming a critical problem in modern computer system design. Extensive theoretical research has been conducted to study the DTM problem. However, most of them are based on theoretically idealized assumptions or simplified models. While these models and assumptions help to greatly simplify a complex problem and make it theoretically manageable, practical computer systems and applications must deal with many practical factors and details beyond these models or assumptions. The goal of our research was to develop a test platform that can be used to validate theoretical results on DTM under well-controlled conditions, to identify the limitations of existing theoretical results, and also to develop new and practical DTM techniques. This dissertation details the background and our research efforts in this endeavor. Specifically, in our research, we first developed a customized test platform based on an Intel desktop. We then tested a number of related theoretical works and examined their limitations under the practical hardware environment. With these limitations in mind, we developed a new reactive thermal management algorithm for single-core computing systems to optimize the throughput under a peak temperature constraint. We further extended our research to a multicore platform and developed an effective proactive DTM technique for throughput maximization on multicore processor based on task migration and dynamic voltage frequency scaling technique. The significance of our research lies in the fact that our research complements the current extensive theoretical research in dealing with increasingly critical thermal problems and enabling the continuous evolution of high performance computing systems.

This study aims to experimentally investigate the spray cooling characteristics for active two-phase cooling of automotive power electronics. Tests are conducted on a small-scale, closed loop spray cooling system featuring a pressure atomized spray nozzle. Two types of refrigerants, HFC-134a (R-134a) and HFO-1234yf, are selected as the working fluids. The test section (heater), made out of oxygen-free copper, has a 1-cm2 plain, smooth surface prepared following a consistent procedure, and would serve as a baseline case. Matching size thick film resistors, attached onto the copper heaters, generate heat and simulate high heat flux power electronics devices. The tests are conducted by controlling the heat flux in increasing steps, and recording the corresponding steady-state temperatures to obtain cooling curves. The working fluid is kept at room temperature level (22oC). Performance comparisons are made based on heat transfer coefficient (HTC) and critical heat flux (CHF) values. Effects of spray characteristics and liquid flow rates on the cooling performance are investigated with the selected coolants. Three types of commercially available nozzles that generate full-cone sprays with fine droplets are utilized in the tests. Effect of liquid flow rate is evaluated varying flow rates at 2, 3, 4 ml/s. The experimental results obtained from this study provide a framework for spray cooling performance with the current and next-generation refrigerants aimed for advanced thermal management of automotive power electronics.

Lighting technologies have evolved over the years to become higher quality, more efficient sources of light. LEDs are poised to become the market standard for general lighting because they are the most power efficient form of lighting and do not contain hazardous materials. Unfortunately, LEDs pose unique problems because advanced thermal management is required to remove the high heat fluxes generated by such relatively small devices. These problems have already been overcome with complex packaging and exotic materials, but high costs are preventing this technology from displacing current lighting technologies. The purpose of this study is to develop a low-cost LED lighting package capable of successfully managing heat. Several designs were created and analyzed based on cost, thermal performance, ease of manufacturing, and reliability. A unique design was created which meet these requirements. This design was eventually assembled as a prototype and initial testing was conducted. This thesis reviews the design process and eventual results of the LED package design.

Tato práce je zaměřena na zlepšení tepelného managementu mikroelektroniky implementací materiálů na bázi uhlíku, přesněji grafitových fólií, do tepelné architektury mikroelektroniky. Práce začíná vysvětlením současných metod chlazení a výzev v oblasti mikroelektroniky. Poté přechází k běžně používaným materiálům - hliníku a mědi a přidává do výběru i uhlíkové alotropie. Ve druhé části tato práce obsahuje několik příkladů použití pyrolytické grafitové fólie v tepelném managementu mikroelektroniky, prokazuje jeho použitelnost a analyzuje přínosy pro šíření tepla, tepelnou vodivost při dodržení elektrické izolace a možné využití ve flexibilní elektronice.

The aim of this diploma thesis is 3D package design study and elaboration of rules for effective thermal and electrical design. There are recommendations and equations for calculating parameters affecting design of modern SOP and SIP packages mentioned in this thesis. Advantages of modern technologies in thermal management of packages are demonstrated in the second part of thesis using ANSYS workbench.

Les convertisseurs électroniques de puissance sont aujourd’hui très largement utilisés dans tous les domaines de la conversion d’énergie. Ils sont des outils désormais incontournables de tout processus de gestion des transferts de l’énergie électriques depuis les puissances les plus faibles (quelques mW) jusqu’à plusieurs dizaines voire centaines de MW. Le domaine de l’électronique de puissance subit actuellement une double mutation liée aux possibilités offertes par les technologies d’intégration d’une part et l’arrivée de nouveaux composants à semi-conducteur de puissance de type grand-Gap d’autre part.Dans cette thèse supportée par l’ANR, nous avons étudié et évalué les potentialités associées à l’intégration de composants de puissance traditionnels (Silicium) et à base de matériaux grands Gap (GaN). Nous avons, pour cela, développé des procédés de fabrication destinés à l’intégration de composants GaN à structure latérale et de composants Silicium à structure verticale. Le contexte applicatif de cette thèse est celui de l’accroissement du niveau d’électrification dans les avions de nouvelle génération.Pour les composants grand Gap de type GaN à structure latérale (basse tension), nous avons proposé un nouveau procédé de report sur substrat céramique (DBC) et nous avons démontré que cette solution permettait d’améliorer considérablement la gestion thermique de ces composants. Sur la base de ces structures, nous avons également présenté et évalué des méthodes de modélisation permettant la conception de ces dispositifs. Cette modélisation, utilisant des méthodes numériques de type éléments finis ou des méthodes analytiques, traite de deux aspects de la conception : la prédétermination du comportement thermique et la prédétermination du comportement électrique et CEM (en ce qui concerne les aspects conduits)Pour les composants à structures verticales (haute tension), nous avons démontré la faisabilité technologique d’une solution alternative aux packagings traditionnels (assemblage sur DBC et connexion par fils de Bonding). Le process proposé permet, par enterrement des puces dans le PCB, de réaliser une interconnexion 3D permettant de réduire les inductances parasites de boucle très largement dues aux inductances parasites des fils de Bonding. Ceci a pu être démontré sur un prototype de convertisseur complet. Ce procédé d’enterrement des puces s’avère donc particulièrement adapté dans le cas de composants à commutation très rapide. / Power Electronic converters are now widely used in all areas of energy conversion. They are tools that cannot be ignored in any process of managing electrical energy transfers from the lowest powers levels (a few mW) to several tens or even hundreds of MW. Power electronics technologies are currently undergoing a double mutation linked to the possibilities offered by integration technologies on the one hand and the arrival of new Wide-Band-Gap power semiconductor components on the other hand.In this thesis supported by the French ANR, we studied and evaluated the potentialities associated with the integration of traditional power components (Silicon) as well as those based on Wide-Band-Gap materials (GaN). We have developed new technological processes for the integration of GaN components with a lateral structure and silicon components with a vertical structure. The application context of this thesis is linked to the problematic of increasing the level of electrification in new generation of aircrafts.For Wide-Band Gap GaN type power devices with a lateral structure (low voltage), we proposed a new method of device-attachment to a metalized ceramic substrate (DBC) and we demonstrated that this solution made it possible to considerably improve the thermal management of these components. On the basis of these structures, we also presented and evaluated modeling methods allowing the design of the whole packaging. This modeling, using numerical tools based on finite element method or analytical equations, deals with two aspects of the design: the predetermination of the thermal behavior and the predetermination of the electrical and electromagnetic behavior (with regard to the conducted aspects)For components with vertical structures (high voltage), we have demonstrated the technological feasibility of an alternative solution to traditional packaging (assembly on a DBC substrate and electrical connection by wire bonding process). The proposed process allows, by embedding the power dies in the PCB, to carry out a 3D interconnection making it possible to reduce the parasitic loop inductances mainly linked to the parasitic inductances of the bondwires. This has been demonstrated on a converter prototype. Embedding power devices is thus particularly suitable in the case of components with very fast switching capabilities.

<div>The United States Environmental Protection Agency (EPA) is charged with pro-tecting human health and the environment. Part of this mission involves regulating heavy-duty trucks that produce particulate matter (PM), unburned hydrocarbons (UHC), carbon dioxide (CO2), and nitrogen oxides (NOx). A byproduct of lean burn combustion in diesel engines is NOx. NOx output limits from commercial vehicles have been reduced significantly from 10 g/hp-hr in 1979 to 0.2 g/hp-hr in 2010. Ad-ditional reductions are expected in the near future.</div><div><br></div><div>One pathway to meet future NOx emissions regulations in a fuel efficient manner is with higher performing exhaust aftertreatment systems through improved engine air handling. As exhaust aftertreatment’s capability to convert harmful NOx into harmless N2 and H2O is a function of temperature, a key performance factor is how quickly does the exhaust aftertreatment system heat up (warm-up), and how well does the system stay at elevated temperatures (stay-warm).</div><div><br></div><div>When the warm-up strategy of iEGR was implemented over the heavy duty federal test procedure (HD-FTP) drive-cycle, it was able to get the SCR above the critical 250◦C peak NOx conversion threshold 100 seconds earlier than the TM baseline. While iEGR consumed 2.1% more fuel than the TM baseline, it reduced predicted tailpipe NOx by 7.9%.</div><div><br></div><div>CDA implemented as a stay-warm strategy over the idle portions of the HD-FTP successfully kept the SCR above the 250◦C threshold for as long as the TM baseline and consumed 3.0% less fuel. Implementing CDA both at idle and from 0 to 3 bar BMEP consumed an additional 0.4% less fuel, for a total fuel consumption reduction of 3.4%.</div><div><br></div><div>A method to predict and avoid compressor surge (which can destroy turbochargers and in fact did so during the HD-FTP experiments) instigated by CDA was devel-oped, as discussed later, and implemented with staged cylinder deactivation to avoid compressor surge.</div><div><br></div><div>The literature does not consider the fidelity of road grade data required to ad-equately predict vehicle fuel consumption and operational behavior. This work ad-dresses this issue for Class 8 trucks by comparing predicted fuel consumption and operation (shifting, engine torque/speed, and braking) of a single Class 8 truck simu-lated with grade data for the same corridor from different sources. The truth baseline road grade (best fidelity available with LiDAR) was obtained previously. This work compares road grade data to the truth baseline from four other typical methods i) utilizing GPS to record horizontal position and vertical elevation, ii) logging the pitch of a cost effective, commercially available IMU, iii) integrating the horizontal and ver-tical velocities of the same IMU, and iv) a commercially available dataset (Comm). Comm grade data (R2=0.992) best matches the LiDAR reference over a 5,432 m stretch of US 231 where high quality LiDAR data was available, followed in quality by the integrated IMU velocity road grade (R2=0.979). Limitations of the Comm dataset are shown, namely missing road grade (decreased point density) for up to 1 km spans on other sections of US 231, as well as for Interstate 69. Vehicle simulations show that both the Comm data (where available and accurate) and integrated IMU road grade data result in fuel consumption predictions within 2.5% of those simulated with the truth reference grade data.</div><div><br></div><div>The simulation framework described in Chapter 6 combines high fidelity vehicle and powertrain models (from Chapter 5) with a novel production-intent platooning controller. This controller commands propulsive engine torque, engine-braking, or friction-braking to a rear vehicle in a two-truck platoon to maintain a desired following distance. Additional unique features of the framework include high fidelity road grade and traffic speed data. A comparison to published experimental platooning results is performed through simulation with the platooning trucks traveling at a constant 28.6 m/s (64 MPH) on flat ground and separated by 11 m (36 ft). Simulations of platooning trucks separated by a 16.7 m (54.8 ft) gap are also performed in steady-state operation, at different speeds and on different grades (flat, uphill, and downhill), to demonstrate how platooning affects fuel consumption and torque demand (propulsive and braking) as speed and grade are varied. For instance, while platooning trucks with the same 16.7 m gap at 28.6 m/s save the same absolute quantity of fuel on a 1% grade as on flat ground (1.00 per-mile, normalized), the trucks consume more fuel overall as grade increases, such that relative savings for the platoon average decrease from 6.90% to 4.94% for flat vs. 1% grade, respectively. Furthermore, both absolute and relative fuel savings improve during platooning as speed increases, due to increase in aerodynamic drag force with speed. There are no fuel savings during the downhill operation, regardless of speed, as the trucks are engine braking to maintain reasonable speeds and thus not consuming fuel. Results for a two-truck platoon are also shown for moderately graded I-74 in Indiana, using traffic speed from INDOT for a typical Friday at 5PM. A 16.7 m (54.8 ft) gap two-truck platoon decreases fuel consumption by 6.18% over the baseline without degradation in trip time (average speed of 28.3 m/s (63.3 MPH)). The same platooning trucks operating on aggressively graded I-69 in Indiana shows a lower platoon-average 3.71% fuel savings over baseline at a slower average speed of 24.5 m/s (54.8 MPH). The impact of speed variation over, and grade difference between, these realistic routes (I-74 & I-69) on two-truck platooning is described in detail.<br></div><div><br></div>

These days, the cooling of new generation electronic servers is a challenge due to the immense heat generated by them. In order to avoid overheating caused by the important rise in temperature appropriate cooling procedures must be used in order to meet the thermal requirement. The current study aims at addressing the issue of overheating in this field, and focuses on the thermal management of electronic devices modelled as a discrete heat sources (mounted in a rectangular cavity) with uniform heat flux applied from the bottom. A review of the literature published regarding the convective heat transfer from heated sources as well as a thorough background on the theory of the cooling of discrete sources by forced convection in rectangular channel is provided in this study. It was showed that the heat transfer performance in channel is strongly influenced by the geometric configurations of heat sources. Therefore, the arrangement and geometric optimisation are the main considerations in the evaluation of thermal performance. Unlike experimental methods that were carried out widely in the past, which provided less cost-effective and more time-consuming means of achieving the same objective, in this study we first explore the possibilities and the advantages of using the CD-adapco's CFD package Star-CCM+ to launch a three dimensional investigation of forced convection heat transfer performance in a channel mounted with equidistant heatgenerating blocks. Numerical results were validated with available experimental data, and showed that the thermal performance of the heat transfer increases with the strength of the flow. The second objective was to maximise the heat transfer density rate to the cooling fluid and to minimise both the average and the maximum temperature in the channel by using the numerical optimisation tool HEEDS/Optimate+. The optimal results showed that better thermal performance was not obtained when the heated sources followed the traditional equidistance arrangement, but was achieved with a specific optimal arrangement under the total length constraint for the first case. Subsequently, for the second case study, on the volume constraints of heat sources, the results proved that optimal configurations that maximise the heat transfer density rate were obtained with a maximum of either the height-to-length ratio or the height-to-width ratio. It was concluded that the heat transfer rate to the cooling fluid increases significantly with the Reynolds number and the optimal results obtained numerically are found to be fairly reliable. / Dissertation (MSc)--University of Pretoria, 2016. / Mechanical and Aeronautical Engineering / MSc / Unrestricted

Los materiales porosos están atrayendo mucha atención tanto en la Academia como en la industria por su amplia gama de aplicaciones y potenciales de desarrollo. Debido a sus superiores propiedades intrínsecas y funcionales, se han incrementado los esfuerzos para desarrollar materiales con diferente estructura, tamaño de poro y distribución, con el fin de satisfacer los requisitos en numerosas áreas de aplicación. Se pueden enunciar como ejemplos la gestión del calor, la biomedicina, la filtración, los procesos de separación, el catalizador o el soporte, el almacenamiento, el control acústico, el tratamiento del agua, entre otros. Sin embargo, una parte considerable de la investigación se ha centrado en materiales con una distribución uniforme del tamaño de los poros. No obstante, los estudios actuales sobre materiales multi-porosos indican que, con un diseño metodológico adecuado, es posible adaptar y controlar la microestructura en función de los fines de la aplicación y dar diferentes funciones a cada nivel de porosidad introduciendo diferentes tamaños de poros en la estructura unimodal. Dado que estos materiales multi-porosos bien diseñados (es decir, con distribución bimodal, trimodal y jerárquica) reducen las limitaciones debidas a la difusión con sus distintos niveles de porosidad, son excepcionalmente preferidos en aplicaciones en las que se requiere contener el flujo de fluidos y una elevada superficie. Aunque la atención en el diseño de estructuras multiporosas ha aumentado en los últimos años, los estudios sobre estos materiales multifuncionales ajustables han sido limitados. Esto se debe a que la relación entre la microestructura y las propiedades funcionales es difícil de comprender y controlar. Así pues, el diseño de materiales multi-porosos sigue siendo una tarea difícil en el mundo científico. Teniendo en cuenta la insuficiencia de estudios sobre la síntesis y caracterización de materiales multi-porosos en la literatura, se necesita especialmente la investigación más profunda y detallada de la influencia de los diferentes tamaños de poros en una misma estructura sobre las propiedades funcionales. De acuerdo con este propósito en esta tesis se sintetizaron materiales con porosidad única y múltiple siguiendo métodos de fabricación tanto novedosos como convencionales. Comparando el rendimiento de los materiales con porosidad simple y múltiple, se investigó la influencia de la microestructura en las propiedades y su relación desde diferentes perspectivas. En conclusión, los objetivos específicos de esta tesis son: i) diseñar dos nuevos enfoques experimentales para fabricar espumas metálicas de celdas-abiertas interconectadas multi-porosas utilizando metodologías conocidas y sus combinaciones. ii) demostrar el efecto de la multi-porosidad en un solo cuerpo sobre las propiedades de las espumas fabricadas y demostrar que superan, junto con los nuevos enfoques, a sus homólogos convencionales. iii) presentar nuevos hallazgos científicos y nuevos enfoques sobre la relación entre las propiedades funcionales y estructurales (porosidad, tamaño y distribución de los poros, etc.) mediante una amplia gama de caracterizaciones. iv) Ofrecer metodologías reproducibles de vanguardia para la síntesis de materiales multi-porosos que puedan aplicarse a diferentes tipos de materiales e inspirar futuros trabajos en la comunidad científica. Este estudio de tesis consta de 6 capítulos. El Capítulo 1 explica brevemente la motivación y los objetivos de la tesis. En este capítulo se expone la información sobre los materiales multi-porosos que se pretenden fabricar y el alcance de la tesis. El Capítulo 2 ofrece una introducción a los materiales multi-porosos y sus métodos de fabricación en perspectiva. Se ha realizado un amplio estudio bibliográfico y desde el pasado hasta el presente se presentan los avances y trabajos recientes realizados en la fabricación de estos materiales. En este capítulo se ha prestado especial atención a la producción de espumas metálicas monomodales, bimodales y jerárquicas mediante métodos de replicación, dealeación, plantillas, sinterización y sus combinaciones. En el Capítulo 3 se explican todas las metodologías, montajes experimentales, materiales, parámetros de funcionamiento y maquinaria/dispositivos seguidos en esta tesis sobre la fabricación y caracterización de materiales y se presenta la información teórica relevante. El Capítulo 4, en primer lugar, resume la literatura necesaria sobre la fabricación de espumas metálicas, la infiltración con el método de replicación, las espumas de aluminio y sus áreas de aplicación, y los métodos de caracterización. También se presenta en este capítulo la extensa revisión de la literatura sobre la relación entre las características microestructurales y las propiedades funcionales de los materiales porosos. Se expone cómo, mediante el método de replicación, se fabricaron espumas de aluminio interconectadas de célula abierta con una distribución monomodal y bimodal del tamaño de los poros. Después de la fabricación, se caracterizaron en detalle las propiedades estructurales (densidad, porosidad, distribución del tamaño de los poros, etc.), el comportamiento del flujo de fluidos (caída de presión, permeabilidad, coeficiente de arrastre, regímenes de flujo, etc.) y el comportamiento térmico (coeficiente de transferencia de calor, conductividad térmica) de las espumas. (coeficiente de transferencia de calor, conductividad térmica) de las espumas. El Capítulo 5 presenta un método novedoso para fabricar espumas de plata con eficacia antibacteriana y distribución jerárquica del tamaño de los poros. Para ello, se ha utilizado la combinación de métodos de templado, replicación y dealeación. Con esta combinación y el diseño adecuado de las metodologías se introdujeron micro-, meso- y macroporos en las estructuras de las espumas. Para comparar las propiedades y el rendimiento de las espumas jerárquicas, se fabricaron espumas de plata con porosidad uniforme mediante el método de replicación y el proceso de sinterización, y espumas de plata con solamente nanoporos mediante el método de dealeación. Se llevaron a cabo estudios de caracterización para todas las espumas fabricadas en el sentido de la distribución del tamaño de los poros, la porosidad, la superficie específica, la eficacia antibacteriana, además de la modelización y la estimación de la superficie específica y la distribución del tamaño de los poros. Además de los pasos de las estrategias experimentales, se presentó una información de fondo detallada sobre los principios rectores de los métodos utilizados en este capítulo. En el Capítulo 6 se evaluaron todos los estudios realizados, se resumieron los resultados y las conclusiones, y se presentaron recomendaciones y estrategias para futuros estudios. / Financial support from the Spanish “Agencia Estatal de Investigación” (AEI) and European Union (FEDER funds) through grant MAT2016-77742-C2-2-P. “Santiago Grisolía” grant (GRISOLIA/2017/187) financed by Generalitat Valenciana.

In this study, CFD simulations of a complete truck are carried out to investigate the effect of altered simulation settings at cold climatic conditions. The aim of this study is to obtain knowledge through CFD simulations performed on a selected driving condition namely at a vehicle speed of 93 kph, an ambient temperature of -20 °C and for an engine operating at 25 % load. Data from measurement carried out in a climatic wind tunnel is available and utilized as boundary conditions for the simulations.The simulations are performed under steady state conditions utilizing the commercial software STAR-CCM+. The first simulation case (reference simulation case) is constructed through java macro-scripts as per the standard VTM settings at Scania. The results from the simulations are compared with the measurement data utilizing temperature validation probes. These probes are located around the engine and measure the air temperature in the underhood engine compartment. The results from the first simulation case show that the temperature of each probe located in front of the engine and above the engine agrees well with the measured probe temperatures. But the temperature of the remaining probes show larger differences with the measured probe temperatures. To investigate the larger differences in probe temperatures, additional simulations are carried out by changing specific simulation settings. For instance, this is achieved by including thermal radiation in the physics continua. Finally, a simulation of engine load of 100 % is carried out and the results from the simulation are compared with the measurement from the same engine load as well as the results from the measurement and simulation of 25 % engine load. The results from all the simulations indicate that additional boundaryconditions and/or different methodologies need to be explored to better replicate the cold climatic conditions in the simulations.