This thesis investigates the potential of wafer-scale integration (WSI) for the implementation of low-cost fine-grain parallel processing computer systems. As WSI is a relatively new subject, there was little work on which to base investigations. Indeed, most WSI architectures existed only as untried and sometimes vague proposals. Accordingly, the research strategy approached this problem by identifying a representative WSI structure and architecture on which to base investigations. An analysis of architectural proposals identified associative memory to be general purpose parallel processing component used in a wide range of WSI architectures. Furthermore, this analysis provided a set of WSI-level design requirements to evaluate the sustainability of different architectures as research vehicles. The WSI-ASP (WASP) device, which has a large associative memory as its main component is shown to meet these requirements and hence was chosen as the research vehicle. Consequently, this thesis addresses WSI potential through an in-depth investigation into the feasibility of implementing a large associative memory for the WASP device that meets the demanding technological constraints of WSI. Overall, the thesis concludes that WSI offers significant potential for the implementation of low-cost fine-grain parallel processing computer systems. However, due to the dual constraints of thermal management and the area required for the power distribution network, power density is a major design constraint in WSI. Indeed, it is shown that WSI power densities need to be an order of magnitude lower than VLSI power densities. The thesis demonstrates that for associative memories at least, VLSI designs are unsuited to implementation in WSI. Rather, it is shown that WSI circuits must be closely matched to the operational environment to assure suitable power densities. These circuits are significantly larger than their VLSI equivalents. Nonetheless, the thesis demonstrates that by concentrating on the most power intensive circuits, it is possible to achieve acceptable power densities with only a modest increase in area overheads.

<p>The aim of my work is to model a segment of a unit cell of a fuel cell stack using numerical methods which is classified as computational fluid dynamics and implementing the work in a commercial computational fluid dynamics package, FLUENT. The focus of my work is to study the thermal distribution within this segment. The results of the work aid in a better understanding of the fuel cell operation in this temperature range. At the time of my investigation experimental results were unavailable for validation and therefore my results are compared to previously published results published. The outcome of the results corresponds to this, where the current flux density increases with the increasing of operating temperature and fixed operating voltage and the temperature variation across the fuel cell at varying operating voltages. It is in the anticipation of determining actual and or unique material input parameters that this work is done and at which point this studies results would contribute to the understanding high temperature PEM fuel cell thermal behaviour, significantly.</p>

Thermal characterization of electronic cabinets is becoming increasingly important, due to growing power dissipation and compact packaging. Usually, multiple length scales of interest and modes of heat transfer are simultaneously present. A steady reduced order thermal modeling framework for electronic cabinets was developed to provide an efficient method to model thermal transport across multiple length scales. This methodology takes advantage of compact modeling at the chip or component level and reduced order modeling at subsystem and cabinet levels. Compact models, which were incorporated into system level simulation, were created for components, and reduced order models (ROMs) were developed using proper orthogonal decomposition (POD) for subsystems and system. An efficient interfacial coupling scheme was developed using the concept of flow network modeling to couple the heat and mass flow rates and pressure at each interface, when interconnecting ROMs together to simulate the entire system. Thermal information was then subsequently extracted from the global modeling and applied to the component model for detailed simulation. A boundary profile-matching scheme for ROM of each subsystem was developed to broaden the applicability of the multi-scale thermal modeling methodology. The output profiles of the subsystem upstream can be transferred to the input profiles of the subsystems downstream by adding necessary flow straightening ducts during the snapshots generation process. A general method to create dynamic multi-layer compact models for components and modules was developed. These dynamic compact models were incorporated into enclosure level simulation. The dynamic reduced order model for the enclosure was developed using POD. The transient multi-scale thermal modeling approach was illustrated through an electronic enclosure with insulated gate bipolar transistor (IGBT) module. The multiscale thermal modeling methodology presented here was validated through experiments conducted on a simulated electronic cabinet and the test vehicle with hybrid cooling technique. The latter incorporated double-sided cooling with hybrid forced air convection, thermoelectric cooling, and micro-channel liquid cooling. The overall multi-scale modeling framework was able to reduced numerical models containing 107 DOF down to around 102, while still retaining an approximation accuracy of around 90% in prediction of chip junction temperature rises, compared to measurements.

Abstract Carbon nanotubes (CNTs) have fascinating mechanical, electrical and thermal properties, all of which significantly depend on structural properties such as nanotube length, number of walls, lattice defect densities, impurities and surface functional groups. A number of different applications of carbon nanotubes have been demonstrated during the past two decades including electrical interconnects, transistors, heating and cooling devices, sensors and various actuators. However, further studies on the structure-dependent properties and innovative handling techniques of these materials are needed in order to explore the limitations of use and to be able fully to exploit the advantageous properties of such one-dimensional sp2 hybridized carbon nanomaterials. In this thesis, random networks of single-wall and multi-walled carbon nanotubes (SWCNTs and MWCNTs, respectively) and aligned films of multi-walled carbon nanotubes are studied in the context of three main application fields: gas sensing, electrical interconnects/electrodes and thermal cooling elements. Analyses of associated material properties and some feasible integration techniques are discussed. Single-wall and multi-walled carbon nanotube films cast from aqueous dispersions are shown to be selective nitric oxide sensing components in Taguchi-type sensor devices, in which films based on SWCNTs outperformed those made of MWCNTs. The thickness dependent electrical conduction mechanism of inkjet-printed SWCNT films is also discussed. Robust aligned MWCNT films are demonstrated as soft electrical contact brushes in DC motors and in other moving electrical contacts. The thermal properties of freestanding aligned MWCNT forests are analyzed and shown to be potential alternatives to copper or aluminium in the thermal management of electrical components. / Tiivistelmä Hiilinanoputkien kiehtovat mekaaniset, sähköiset ja lämmönjohto-ominaisuudet ovat kiinnostaneet tutkijoita suuresti viimeisten kahden vuosikymmenen ajan. Monia erilaisia applikaatioita on demonstroitu tänä aikana: mukaan lukien sähköiset kontaktit, transistori-rakenteet, lämmitys- ja jäähdytyslaitteet, anturirakenteet sekä erilaiset aktuaattori-rakenteet. Tämän väitöskirjan päätavoitteena on tutkia hiilinanoputkien toiminnollisuutta ja käytännöllisyyttä erilaisissa sovelluskohteissa. Tässä työssä käytettävät hiilinanoputkirakenteet ovat joko satunnaisjärjestyksessä olevia nanoputkista koostuvia verkostorakenteita tai yhdensuuntaisia, makroskooppisia hiilinanoputkikalvoja. Nanoputkia tutkitaan kolmessa erityyppisessä sovelluskohteessa: kaasuanturisovelluksessa, sähköisissä kontaktirakenteissa sekä jäähdytyselementteinä. Työssä analysoidaan hiilinanoputkirakenteiden ominaisuuksia eri sovelluskohteissa sekä esitetään joitain käyttökelpoisia tekniikoita hiilinanoputkien integroimiseen olemassa oleviin tekniikoihin. Hiilinanoputkien osoitetaan olevan käyttökelpoisia aktiivisia materiaaleja typpioksidille resistiivisessä kaasuanturirakenteessa. Tulosten perusteella yksiseinämäiset hiilinanoputket ovat moniseinämäisiä herkempiä ja parempia kyseisessä sovelluksessa. Lisäksi tutkitaan ja analysoidaan mustesuihku-tulostettujen yksiseinämäisten hiilinanoputkifilmien sähköisten ominaisuuksien riippuvuutta filmin paksuudesta. Vantterien yhdensuuntaisten moniseinämäisten hiilinanoputkirakenteiden osoitetaan toimivan erinomaisesti pehmeinä sähköisinä kontaktielementteinä liikkuvissa sähköisissä kontakteissa. Vapaasti seisovien yhdensuuntaisten, moniseinämäisten hiilinanoputkirakenteiden lämmönjohto-ominaisuuksien tutkiminen ja analysointi osoittaa, että kyseisiä rakenteita voidaan käyttää tehokkaina jäähdytyselementteinä ja mahdollisesti korvaavana vaihtoehtona alumiinille ja kuparille sähköisten komponenttien lämmönhallinta sovelluksissa.

Magister Scientiae - MSc / The aim of my work is to model a segment of a unit cell of a fuel cell stack using numerical methods which is classified as computational fluid dynamics and implementing the work in a commercial computational fluid dynamics package, FLUENT. The focus of my work is to study the thermal distribution within this segment. The results of the work aid in a better understanding of the fuel cell operation in this temperature range. At the time of my investigation experimental results were unavailable for validation and therefore my results are compared to previously published results published. The outcome of the results corresponds to this, where the current flux density increases with the increasing of operating temperature and fixed operating voltage and the temperature variation across the fuel cell at varying operating voltages. It is in the anticipation of determining actual and or unique material input parameters that this work is done and at which point this studies results would contribute to the understanding high temperature PEM fuel cell thermal behaviour, significantly. / South Africa

Les travaux de cette thèse portent sur le refroidissement descomposants électroniques de puissance par métal liquide. Les efforts se sontconcentrés plus particulièrement autour de deux fonctions : la pompeélectromagnétique servant à mettre le fluide en mouvement et le refroidisseur àminicanaux situé sous la source de dissipation.Le mémoire de thèse se structure en quatre chapitres équivalents. Dans lepremier, l’apport des métaux liquides pour le refroidissement des composantsactifs de puissance est démontré. Dans un deuxième temps, l’étude théorique etexpérimentale d’une pompe électromagnétique à conduction est effectuée. Lesystème de refroidissement est plus particulièrement abordé dans le troisièmechapitre. Enfin, des réflexions sur la mise en oeuvre des refroidisseurs à métauxliquides en électronique de puissance sont discutées dans la dernière partie.Grâce à elles, nous voyons que le champ d’application de ces travaux favorisel'émergence de solutions innovantes pour la gestion thermique des composantsélectronique de puissance. / The work presented in this Phd manuscript deals with cooling powerelectronics devices using an electrical conductive fluid. Two important functionshave been considered: the study and the realization of the electromagnetic pumpwhich circulated the fluid in the cooling loop. The second function was study andrealization of the cooler which evacuated the heat from the electronics device.This document has four chapters: introduction to power electronics coolingsystem with liquid metal, electromagnetic pump study, cooler study, and at lastreflections on realizing liquid metal cooler for power electronics devices. Theresults of this work concern a wide range of applications, especially towards newthermal management solutions of power electronics devices.

In an effort to reduce harmful pollutants emitted by medium and heavy duty diesel engines, stringent emission regulations have been imposed by the Environmental Protection Agency (EPA) and the California Air Resources Board (CARB). Effective aftertreatment thermal management is critical for controlling tail pipe outlevels of NOx and soot, while improved fuel efficiency is also necessary to meet greenhouse gas emissions standards and customer expectations. Engine manufacturers have developed and implemented several engine and non-engine based techniques for emission reduction, a few examples being: exhaust gas recirculation (EGR), use of delayed in-cylinder injections, exhaust throttling, electric heaters and hydrocarbon dosers. This work elaborates the use of variable valve actuation strategies for improved aftertreatment system (ATS) thermal management of a modern medium-duty diesel engine while presenting opportunities for simplification of engine air handling architecture.<div><br></div><div>Experimental results at curb idle demonstrate that exhaust valve profile modulation enables effective ATS warm-up without requiring exhaust manifold pressure (EMP) control. Early exhaust valve opening with internal exhaust gas recirculation (EEVO+iEGR) resulted in 8% lower fuel consumption and reduction in engine out emissions. Late exhaust valve opening with internal EGR in the absence of EMP control was able to reach exhaust temperature of 287^◦C, without a penalty in fuel consumption or emissions compared to conventional thermal management. LEVO combined with EMP control could reach turbine outlet temperature of nearly 460^◦C at curb idle.<br></div><div><br></div><div>LEVO was studied at higher speeds and loads to assess thermal management benefits of LEVO in the absence of EMP control, with an observation that LEVO can maintain desirable thermal management performance up to certain speed/load conditions, and reduction in exhaust flow rate is observed at higher loads due to the inability of LEVO to compensate for loss of boost associated with absence of EMP control.<br></div><div><br></div><div>Cylinder deactivation (CDA) combined with additional valvetrain flexibility results in low emission, fuel-efficient solutions to maintain temperatures of a warmed-up ATS. Late intake valve closing, internal EGR and early exhaust valve opening were studied with both three cylinder and two cylinder operation. Some of these strategies showed additional benefits such as ability to use earlier injections, elimination of external EGR and operation in the absence of exhaust manifold pressure control. Three cylinder operation with LIVC and iEGR is capable of reaching exhaust temperatures in excess of 230^◦C with atleast 9% lower fuel consumption than three cylinder operation without VVA. Three cylinder operation with early exhaust valve opening resulted in exhaust temperature of nearly 340^◦C, suitable for extended idling operation. Two cylinder operation with and without the use of valve train flexibility also resulted in turbine outlet temperature relevant for extended idling (and low load operation), while reducing fuel consumption by 40% compared to the conventional thermal management strategy.<br></div><div><br></div><div>A study comparing the relative merits of internal EGR via reinduction and negative valve overlap (NVO) is presented in order to assess trade-offs between fuel efficient stay-warm operation and engine out emissions. This study develops an understanding of the optimal valve profiles for achieving reinduction/NVO and presents VVA strategies that are not cylinder deactivation based for fuel efficient stay-warm operation. Internal EGR via reinduction is demonstrated to be a more fuel efficient strategy for ATS stay-warm. An analysis of in-cylinder content shows that NOx emissions are more strongly affected by in-cylinder O2 content than by method of internal EGR.<br></div>

No description available.

This work deals with the issue of emissivity and its impact on the heat dissipation.The first part describes the basics of thermal management, the issue of emissivity and its measurement. In the second, experimental part, are dedicated the emissivity values of examined specimens. These values are then used as initial conditions for the thermal simulation. In the last part are compared the measured results and the simulated results and is evaluated the impact of emissivity for the heat dissipation.

The diploma thesis deals with the simulation of heat dissipation for LED Seoul SZ5-P. The heat transfer is discussed first. Further, the issue of thermal management and its design is analyzed. The dependence of LED junction temperature on area of single and double layer printed circuit board is simulated with Ansys Icepak. Additionally, influences of the number and placement of vias on the printed circuit board and aluminum substrate printed circuit board are simulated. Last but not least, the equations describing the dependence of printed circuit board area on desired LED junction temperature are derived. Finally, the values of heat transfer coefficient including convection and radiation are determined for various heat losses and junction temperatures.