Dissertationen zum Thema „Cooling Devices“

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, September, 2020
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 110-111).
Evaporative cooling devices are low-cost, low-energy solutions for post-harvest storage of fruits and vegetables on farmlands. Surface area and porosity are two design parameters that affect the cooling devices' evaporation rate and cooling performance. Both design parameters lack prior systematic testing that methodically varies levels of surface area and material porosity to understand their effects on these devices' cooling performance (e.g. maximum temperature drop, duration of high internal relative humidity, cooling efficiency and total cooling). For fruits and vegetables, storage environments with low temperature and high humidity are critical to reduce deterioration. In this thesis, ridges were cut into the outer wall of pot-in-pot evaporative cooling devices at four different interridge distances to vary total available surface area. Sawdust was added to clay in different ratios to create devices with varying porosity.
A new performance metric of total cooling is also introduced to account for the maximum temperature drop and the total duration of evaporative cooling. The surface area experiments reveal that adding corrugations on the surface introduces competing effects between increased surface area for water evaporation and decreased vapor concentration gradient inside of the corrugations' troughs; consequently, among the devices with corrugations, the amount of total surface area does not always correlate with cooling performance. Between the devices with some surface corrugation and the device without corrugation, the devices with corrugation do consistently achieve greater temperature drops. However, the devices with corrugation are unable to maintain temperature drops and high levels of internal relative humidity for as long as the device without corrugation. The porosity experiments conclude that the greater the porosity in the device's outer vessel, the greater the maximum temperature drop.
This is due to the reduced transport resistance during water and moisture movement to the device's surface. Higher percentages of porosity lead to faster evaporation rates which deplete the amount of water inside the devices quicker and explain why the temperature drops and internal relative humidity of the more porous devices do not last as long as the temperature drops and internal relative humidity of the less porous devices. This thesis investigates two design parameters of cooling devices and shows that increasing surface area and porosity increases maximum temperature drops but decreases both the duration of temperature drops and high internal relative humidity. Between the two design parameters, increasing porosity is the more practical and less burdensome solution to improve the overall performance of evaporative cooling devices for low-resource communities.
by Trang Luu.
S.M.
S.M. Massachusetts Institute of Technology, Department of Mechanical Engineering

A detailed experimental and theoretical investigation of a magneto-optical trap for caesium atoms is presented. Particular emphasis has been placed on achieving high spatial number densities and low temperatures. Optimizing both of these together enables efficient evaporative cooling from a conservative trap, a procedure which has recently led to the first observations of Bose-Einstein condensation in a dilute atomic vapour. The behaviour of a magneto-optical trap is nominally determined by four independent parameters: the detuning and intensity of the light field, the magnetic field gradient and the number of trapped atoms. A model is presented which incorporates previous treatments into a single description of the trap that encompasses a wide range of its behaviour. This model was tested quantitatively by measuring the temperature of the cloud and its spatial distribution as a function of the four parameters. The maximum density was found to be limited both by the reabsorption of photons scattered within the cloud and by a reduction of the confining force at small light shifts. The nonlinear variation with position of the restoring force was found to be significant in limiting the number of atoms confined to a high density. A maximum density in phase space (defined as the number of atoms in a box with sides of dimension one thermal de Broglie wavelength) of (1.5 ± 0.5) x 10^-5 was observed, with a spatial density of 1.5 x 10¹¹ atoms per cm³. Cold collision losses from a caesium magneto-optical trap have been studied with the purpose of assessing their influence on spatial densities. In contrast to previous measurements of similar quantities, these measurements did not require the use of an ultra-low (< 10^-10 Torr) background vapour pressure. The dependence of the cold collision loss coefficient β on the trapping intensity was measured to permit identification of the different cold collision processes. The largest loss rates observed were those due to hyperfine structure-changing collisions, with a coefficient β = (2±1) x 10^-10cm³s^-1. A study is presented of a modified magneto-optical trap in which a fraction of the population is shelved into a hyperfine level that does not interact with the trapping light. In this so-called "dark" magneto-optical trap, improved densities of nearly 10¹²cm^-3 have been previously reported for sodium. The application of the technique to caesium is not straightforward due to the larger excited state hyperfine splittings. A simple theory for caesium is presented and its main predictions verified by measurements of density, number and temperature. A density of nearly 10¹²cm,^-3 was indeed obtained but at a temperature substantially higher than in the conventional magneto-optical trap.

Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Glezer, Ari; Committee Member: Alben, Silas; Committee Member: Joshi, Yogendra; Committee Member: Smith, Marc; Committee Member: Webster, Donald. Part of the SMARTech Electronic Thesis and Dissertation Collection.

A stacked microchannel heat sink was developed to provide efficient cooling for microelectronics devices at a relatively low pressure drop while maintaining chip temperature uniformity. Microfabrication techniques were employed to fabricate the stacked microchannel structure, and experiments were conducted to study its thermal performance. A total thermal resistance of less than 0.1 K/W was demonstrated for both counter flow and parallel flow configurations. The effects of flow direction and interlayer flow rate ratio were investigated. It was found that for the low flow rate range the parallel flow arrangement results in a better overall thermal performance than the counter flow arrangement; whereas, for the large flow rate range, the total thermal resistances for both the counter flow and parallel flow configurations are indistinguishable. On the other hand, the counter flow arrangement provides better temperature uniformity for the entire flow rate range tested. The effects of localized heating on the overall thermal performance were examined by selectively applying electrical power to the heaters. Numerical simulations were conducted to study the conjugate heat transfer inside the stacked microchannels. Negative heat flux conditions were found near the outlets of the microchannels for the counter flow arrangement. This is particularly evident for small flow rates. The numerical results clearly explain why the total thermal resistance for counter flow arrangement is larger than that for the parallel flow at low flow rates. In addition, laminar flow inside the microchannels were characterized using Micro-PIV techniques. Microchannels of different width were fabricated in silicon, the smallest channel measuring 34 mm in width. Measurements were conducted at various channel depths. Measured velocity profiles at these depths were found to be in reasonable agreement with laminar flow theory. Micro-PIV measurement found that the maximum velocity is shifted significantly towards the top of the microchannels due to the sidewall slope, a common issue faced with DRIE etching. Numerical simulations were conducted to investigate the effects of the sidewall slope on the flow and heat transfer. The results show that the effects of large sidewall slope on heat transfer are significant; whereas, the effects on pressure drop are not as pronounced.

Thermoelectric devices are capable of providing both localized active cooling and waste heat power generation. This work will explore the possibility of embedding thermoelectric devices within electronic packaging in order to achieve better system performance. Intel and Nextreme, Inc. have produced thin-film superlattice thermoelectric devices that have above average performance for thermoelectrics and are much thinner than most devices on the market currently. This allows them to be packaged inside of the electronic package where the thermoelectric devices can take advantage of the increased temperatures and decreased thermal lag as compared to the devices being planted on the outside of the package. This work uses the numerical CFD solver FLUENT and the analog electronic circuit simulator SPICE to simulate activity of thermoelectric devices within an electronics package.

With technology scaling, the amount of transistors on a single chip doubles itself every 18 months giving rise to increased power density levels. This has directly lead to a rapid increase of thermal induced issues on a chip and effective methodologies of removing the heat from the system has become the order of the day. Thermoelectric (TE) devices have shown promise for on-demand cooling of ICs. However, the additional energy required for cooling remains a challenge for the successful deployment of these devices. This thesis presents a closed loop control system that dynamically switches a TE module between Peltier and Seebeck modes depending on chip temperature. The autonomous system harvests energy during regular operation and uses the harvested energy to cool during high power operation. The system is demonstrated using a commercial thin-film TE device, an integrated boost regulator and few off chip components. The feasibility of the integration of the TEM and the automated mode switching within the microprocessor package is also evaluated. With continuous usage of thermoelectric modules, it starts to degrade over time due to thermal and mechanical induced stress which in turn reduces the cooling performance over time. Impact of thermal cycling on thermoelectric cooling performance over time is evaluated using the developed full chip package model.

Thesis (M.S.)--University of Missouri-Columbia, 2005.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (December 20, 2006) Includes bibliographical references.

Power electronics is a constantly growing and demanding technical field. Consumer demand and developing technologies have made the improvement of power density a primary emphasis of research for this area. Power semiconductors present some of the major challenges for increasing system level power density due to high loss density and interconnection requirements. Advanced cooling schemes, such as double-sided, forced liquid convection or multi-phase flow, can be implemented with non-wire bond packaging to improve thermal management while maintaining proper electrical performance. Embedded power is one such packaging technology, which provides a compact structure for interface of power semiconductor to fluid flow.

The objective of this work was to identify the potential of implementing embedded power packaging with double-sided forced liquid convection. Physics based, electro-thermal models were first used to predict the improvement in heat transfer of double-sided, forced liquid convection with embedded power packaging over single-sided liquid cooled wire bond based packaging. A liquid module test bed was designed and constructed based on the electro-thermal models, which could be interfaced with high power MOSFET based samples implementing various packaging technologies. Experiments were used to verify the model predictions and identify practical limitations of high flow rate, double-sided liquid cooling with embedded power. An improvement of 45% to 60% in total junction to case thermal resistance is shown for embedded power packaging with double-sided liquid cooling for water flow rates between 0.25 and 4.5 gal/min.
Master of Science

Thesis (MScEng)--University of Stellenbosch, 2008.
ENGLISH ABSTRACT: The performance of a natural draught wet-cooling tower can be improved by reducing the average drop size in the rain zone. In this thesis, the effect of installing different horizontal grids below the fill on drop size in the rain zone is investigated experimentally and theoretically. A specially designed horizontal grid consisting of evenly spaced slats and a grid made from expanded metal sheeting are tested. Drop size distribution measurements are taken below different cooling tower fills to determine the respective Sauter mean drop sizes and also below different configurations of splash grids to determine the reduction in drop size. Drop break-up through a grid of horizontally placed slats is modelled and compared to measured data to determine the optimum configuration in terms of spacing between the grid and fill, slat width and slat spacing. A cross flow rain zone is modelled under different air and water flow combinations with CFD for two distributions that represent the rain with and without splash grids and the results are compared. The Merkel transfer characteristic for all the flow conditions using both distributions are determined using a Lagrangian, Merkel, Poppe and e- NTU method in order to quantify the increase in rain zone Merkel number. Pressure drop over the cross flow rain zone is also determined and compared for the two distributions under considerations.
AFRIKAANSE OPSOMMING: Die verkoelingsvermoë van ‘n reënsone van ‘n natuurlike trek nat koeltoring kan verbeter word deur die verkleining van die gemiddelde druppelgrootte. In hierdie tesis word die effek wat horisontale roosters op die druppelgrootte het, wanneer dit onder die pakking geïnstalleer is, eksperimenteel en teoreties ondersoek. ‘n Spesiaal ontwerpte rooster bestaande uit horisontaal gepakte latte en ‘n gerolde metaal rooster word onderskeidelik vir hierdie doel gebruik. Druppelgrootte metings word geneem onder verskillende koeltoring pakkingsmateriaal om die Sauter gemiddelde diameter te bepaal, asook onder die verskillende rooster opstellings om die verkleinde druppelgrootte te bepaal wat die rooster veroorsaak. Druppelopbreking deur ‘n laag horisontaal gepakte latte word gemodelleer en vergelyk met gemete data om sodoende die beste kombinasie tussen die afstand onder die pakkingsmateriaal, latwydte en latspasiëring te bepaal. ‘n Kruisvloei reënsone word gemodelleer met CFD onder verkillende lug- en watervoeikombinasies vir twee druppelverdelings wat die reënsone met en sonder roosters verteenwoordig. Die Merkel oordragskoëffisiënt vir die twee verdelings word bereken en vergelyk deur van ‘n Lagrange- , Merkel- , Poppe- en e-NTU metode gebruik te maak om sodoende die verbetering in reënsone Merkelgetal te kwantifiseer. Drukvalle oor die reënsone word ook bereken en vergelyk vir die twee verdelings wat beskou is.

Degut a la fi de l’escalament de Dennard, la potència i la densitat de potència requerides pel funcionament dels xips comencen a augmentar. Si aquesta tendència continués en augment, el consum d’energia seria prohibitiu tant per criteris d’eficiència com per a la gestió tèrmica. Per tal de complir els criteris d’eficiència i gestió tèrmica, la millora dels xips es va limitar restringint el nombre de nuclis i la seva freqüència de funcionament. Aquesta tendència implica la necessitat d’una solució de refrigeració capaç d’extreure un flux de calor heterogeni d’alta densitat de potència i variant en el temps, a més de reduir el gradient de temperatura que redueix la fiabilitat de l’electrònica. Aquesta tesi es desenvolupa en el marc del projecte Europeu Horitzó 2020 STREAMS (Smart Technologies for eneRgy Efficient Active cooling in advanced Microelectronics Systems), que té com a objectiu desenvolupar un dispositiu capaç de satisfer les necessitats de refrigeració de la microelectrònica. L’objectiu principal d’aquesta tesi és desenvolupar un sistema de refrigeració de cel·les microfluídiques i avaluar el seu impacte en la microelectrònica i en els receptors fotovoltaics de concentració. El dispositiu de refrigeració desenvolupat està format per una matriu de cel·les microfluídiques, cadascuna de les quals és responsable de l’extracció del flux de calor local. El refrigerant es subministra a les cel·les de forma paral·lela mitjançant canals de subministrament i de recollida connectats als col·lectors. Per tant, cada cel·la té l’entrada de refrigerant fred independentment de la seva localització. La calor és extreta per cada cel·la, la qual pot contenir microcanals que milloren la transferència de calor i vàlvules autoadaptatives capaces d’ajustar el cabal a les seves necessitats de refrigeració. En l’etapa de disseny, la cel·la microfluidica MC6T és dissenyada i avaluada numèricament en un escenari de càrrega de calor no uniforme i variable en el temps, reduint el cabal en un 42.5 % i la caiguda de pressió en un 81.0 % comparat amb un dispositiu de microcanals sotmès a les mateixes condicions. La combinació de la reducció de cabal i la caiguda de pressió suposa una disminució de la potència mitjana de bombeig en un 89.1 % comparat amb un dispositiu de microcanals. Tanmateix també es millora la uniformitat de temperatura gràcies a l’ús de les vàlvules microfluídiques. Altrament, s’avalua numèricament l’impacte d’aquest nou dispositiu de refrigeració sobre els receptors fotovoltaics de concentració solar (CPV) de matriu densa. Segons la configuració elèctrica dels receptors i de la no uniformitat del perfil d’irradiació, l’increment de potència pot arribar a un 9.7 % comparat amb el mateix receptor CPV refrigerat amb microcanals. Un cop validat numèricament el concepte i després de la identificació i resolució dels reptes inherents al procediment de microfabricació dels dispositius autoadaptatius de refrigeració, es fabriquen els dispositius dissenyats per tal d’avaluar experimentalment el rendiment del sistema de cel·les microfluídiques, amb vàlvules autoadaptatives i sense. A més a més, s’aplica un algoritme de control que adapta el cabal total del dispositiu a les necessitats d’extracció d’aquest. Si es compara el nou disseny amb un dispositiu de microcanals convencionals amb cabal constant, la matriu de cel·les microfluidiques sense vàlvules redueix la potència de bombeig en un 83.7 % i presenta una millora del 10.8 % en uniformitat de temperatura. Tot i això, la matriu de cel·les amb vàlvules autoadaptatives redueix la potència de bombeig en un 74.7 %, al mateix temps que també millora la uniformitat de temperatura en un 31.7 %. Altrament, quan s’aplica l’algoritme de control de cabal al dispositiu de microcanals, la potència de bombeig requerida pels dispositius de cel·les microfluídiques amb vàlvules autoadaptatives i sense és, respectivament, del 15.5 % i del 45.6 % en comparació amb microcanals. En aquestes condicions, la uniformitat de temperatura de les cel·les microfluídiques sense vàlvula és semblant a la dels microcanals amb cabal controlat, però el dispositiu de cel·les amb vàlvules millora la uniformitat de temperatura en un 23.9 %.
Con el fin del escalamiento de Dennard, la potencia y la densidad de potencia requeridas por chip empiezan a aumentar. Si esta tendencia continuara, el consumo de energía sería prohibitivo tanto por criterios de eficiencia como para la gestión térmica. Para cumplir los criterios de eficiencia y gestión térmica la mejora de los chips se limitó restringiendo el número de núcleos y su frecuencia de funcionamiento. Esta tendencia implica la necesidad de una solución de refrigeración capaz de extraer un flujo de calor heterogéneo de alta densidad de potencia y variando en el tiempo, además de reducir el gradiente de temperatura que reduce la fiabilidad de la electrónica. Esta tesis se desarrolla en el marco del proyecto europeo Horizonte 2020 STREAMS (Smart Technologies for eneRgy Efficient Active cooling in advanced Microelectronics Systems), que tiene como objetivo desarrollar un dispositivo de refrigeración capaz de satisfacer las necesidades de refrigeración en la microelectrónica. El objetivo principal de esta tesis es desarrollar un sistema de refrigeración de celdas microfluídicas y evaluar su impacto en microelectrónica y en receptores fotovoltaicos de concentración. El dispositivo de refrigeración está formado por una matriz de celdas microfluídicas, cada una de las cuales es responsable de la extracción del flujo de calor local. El refrigerante se suministra a las celdas paralelamente mediante canales de suministro y recogida conectados a los colectores. Por lo tanto, cada celda tiene la entrada de refrigerante frío independientemente de su localización. El calor es extraído por cada celda la cual puede contener microcanales para mejorar la transferencia de calor y válvulas autoadaptativas capaces de adaptar el caudal de cada celda a sus necesidades de refrigeración. En la etapa de diseño, la celda microfluídica MC6T es diseñada y evaluada numéricamente en un escenario de carga de calor no uniforme y variable en el tiempo, reduciendo el caudal un 42.5 % y la caída de presión un 81.0 % comparado con un dispositivo de microcanales sometido a las mismas condiciones. La combinación de la reducción de caudal y caída de presión supone una reducción de la media de potencia de bombeo de un 89.1 % en comparación con microcanales, mientras se mejora la uniformidad de temperatura gracias al uso de las válvulas microfluídicas. En otro caso, se evalúa numéricamente el impacto de este nuevo dispositivo de refrigeración sobre los receptores fotovoltaicos de concentración solar (CPV) en matriz densa. Según la configuración eléctrica de los receptores y de la no uniformidad del perfil de irradiación, el incremento de potencia puede llegar a un 9.7 %, comparado con el mismo receptor CPV refrigerado con microcanales. Una vez validado numéricamente el concepto y tras la identificación y resolución de retos inherentes al procedimiento de microfabricación de los dispositivos autoadaptativos de refrigeración, se fabrican los dispositivos diseñados para evaluar experimentalmente el rendimiento del sistema de celdas microfluídicas, con y sin válvulas autoadaptativas. Además, se aplica un algoritmo de control que adapta el caudal total del dispositivo a las necesidades de extracción del dispositivo. Comparando con microcanales convencionales con caudal constante, la matriz de celdas microfluídicas sin válvulas reduce la potencia de bombeo en un 83.7 % y presenta una mejora del 10.8 % en uniformidad de temperatura. Sin embargo, la matriz de celdas con válvulas autoadaptativas reducen la potencia de bombeo en un 74.7 %, al tiempo que también mejora la uniformidad de temperatura en un 31.7 %. De lo contrario, cuando se aplica el algoritmo de control de caudal también al dispositivo de microcanalas, la potencia de bombeo requerida por los dispositivos de celdas microfluídicas con y sin válvulas autoadaptativas es, respectivamente, el 15.5 % y el 45.6 % comparado con microcanales. En estas condiciones, la uniformidad de temperatura de las celdas microfluídicas sin válvula es similar a la de los microcanales con caudal controlado, pero el dispositivo de celdas con válvulas mejora la uniformidad de temperatura en un 23.9%.
With the end of Dennard scaling, the power and the power density required by chips start to increase. If this trend were to continue, the microelectronics power consumption needed to satisfy efficiency requirements and for thermal management would be prohibitive. To meet the efficiency and thermal management requirements, the chip improvement is limited by restricting the number of cores and their operation frequency. This trend implies the need for a cooling solution that is able to extract the non-uniform and time-dependent high power density heat flux and reduce the temperature non-uniformity, which reduces the electronic reliability. This thesis is developed in the framework of the Horizon 2020 Project STREAMS (Smart Technologies for eneRgy Efficient Active cooling in advanced Microelectronics Systems), which aims to develop a cooling device that is able to satisfy the microelectronics cooling needs. The main objective of this thesis is to design a microfluidic cell cooling system and assess its impact on the microelectronics and concentrating photovoltaic receivers. The cooling device is formed by an array of microfluidic cells, each one responsible for removing the local heat flux. Coolant flow is fed in parallel to the cells by interdigitated cold and warm flow channels connected to manifolds. Each cell therefore has a cold inlet flow, irrespective of its location. Heat is removed by the flow through each cell, which can contain microchannels to enhance the heat transfer and self-adaptive valves capable of tailoring the flow rate of each cell to its cooling needs. In the design stage, the MC6T microfluidic cell is designed and numerically assessed under a non-uniform and time-dependent heat load scenario, reducing the flow rate by 42.5 % and the pressure drop by 81.0 % with respect to the microchannel cooling device under the same boundary conditions. The combination of both low flow rates and pressure drops implies an average pumping power reduction of 89.1 % in comparison to microchannels, while the temperature uniformity is improved by the use of the self-adaptive microfluidic valves. The impact of this novel cooling solution on the performance of dense array CPV receivers is numerically assessed. Depending on the electrical configuration and the non-uniformity of the illumination profile, the increase in power generation of the dense array CPV receiver can reach up to 9.7 %, compared with the same CPV receiver cooled by microchannels. Once the concept is validated numerically, and after identifying and resolving the challenges inherent in the microfabrication procedure of self-adaptive cooling devices, selected designs are fabricated in order to assess experimentally the performance of the self-adaptive microfluidic cell cooling device, with and without self-adaptive valves. A control algorithm tailors the total flow rate to the heat extraction needs. Compared to conventional microchannels with fixed flow rates, the microfluidic cell array without valves improves the pumping power by 83.7 % and improves a 10.8 % in terms of temperature uniformity. However, the array of microfluidic cells with self-adaptive valves reduces the pumping power by 74.7 %, while the temperature non-uniformity is reduced by 31.7 %. When applying the flow rate control algorithm to the microchannels, the pumping power needs of the array of microfluidic cells with and without self-adaptive valves are, respectively, 15.5 % and 45.6 %, compared to microchannels. In these conditions, the temperature uniformity of the microfluidic cell without self-adaptive valves presents a similar behaviour as the flow rate controlled microchannels, however the microfluidic cell with self-adaptive valves improves the temperature uniformity a 23.9 %.

The main objectives of this dissertation is to investigate the prospects of embedded thermoelectric devices integrated in a chip package and to develop a design methodology aimed at taking advantage of the on-chip on-demand cooling capabilities of the thermoelectric devices. First a simulation framework is established and validated against experimental results, which helps to study the cooling capabilities of embedded thermoelectric coolers (TEC) in both a transient and steady state. The potential for up to 15°C of total cooling has been shown. The thermal simulation framework allows for rapid assessment of TEC and system level thermal performance. Next, the thesis develops a co-simulation environment that is capable of simulating the thermal and electrical domain and couples them to design intelligent TEC controllers. These controllers are implemented on chip and can leverage the transient cooling capability of the device. The controllers are simulated within the co-simulation environment and their potential to control high power chip events are thoroughly investigated. The system level overheads are considered and discussions on implementation techniques are presented. The co-simulation framework is also extended to allow for simulation of real predictive technology microprocessor cores and their workloads. Finally the thesis implements a fully on-chip autonomous energy system that takes advantage of the TEC in its reverse energy harvesting mode and uses the same device to harvest energy and use the energy to power the on-chip cooling circuit. This increases the overall energy efficiency of the cooler and verifies the TEC control methods.

In recent years, the SiC power semiconductor has emerged as an attractive alternative that pushes the limitations of junction temperature, power rating, and switching frequency of Si devices. These advanced properties will lead converters to higher power density. However, the reliability of the SiC semiconductor is still under investigation, and at the same time, the standard Si device packages do not meet the requirement of high temperature operation. In order to take full advantage of SiC semiconductor devices, high density, high temperature device packaging needs to be developed. In this dissertation, a high temperature wirebond package for multi-chip phase-leg power module using SiC devices was designed, developed, fabricated and tested. The details of the material selection and thermo-mechanical reliability evaluation are described. High temperature power test shows that the presented package can perform well at the high junction temperature. In order to increase the power density, reduce the parasitic parameters, and enhance the electrical, thermo-mechanical performance over wirebond packages, planar package is utilized to better take advantages of SiC device. This dissertation proposed a novel package, in which the interconnections can be formed on small dimensional pads and enclosed pads that may baffle the regular solder based connection in other planar packages. Electrical and thermo-mechanical tests of the prototype module demonstrate the functionality and reliability of the presented planar packaging methodology. In this dissertation, together with the design example, the manual module layout design and automatic module layout design process are also presented. Furthermore, a systematic optimal design process and parametric study of the heatsink-fan cooling system by applying the analytical model is described. This dissertation also established a systematic testing procedure which can rapidly detect defects and reduce the risk in high temperature packaging testing. Finally, a wirebond module and a planar module are designed for 175 ºC junction temperature and 250 ºC junction temperatures. All the key concepts and ideas developed in this work are implemented in the prototype module development and then verified by the experimental results.
Ph. D.

In this study, forced cooling of heat sinks mounted on CPU&rsquo
s was investigated. Heat sink effectiveness, effect of turbulence models, effect of radiation heat transfer and different heat sink geometries were numerically analyzed by commercially available computational fluid dynamics softwares Icepak and Fluent. The numerical results were compared with the experimental data and they were in good agreement. Conjugate heat transfer is simulated for all the electronic cards and packages by solving Navier-Stokes equations. Grid independent, well converged and well posed models were run and the results were compared. The best heat sink geometry is selected and it is modified in order to have lower maximum temperature distribution in the heat sink.

Internal combustion engines are the most commonly used engines in the automotive world. However, these engines lack an overheating prevention system against cooling system failures when they exceed their normal operating temperature. Less experienced drivers (users) usually do not notice overheating until the engine stops, generating economic expenses in engine repairs. As such, this paper describes the design and construction of an electromechanical device to prevent engine overheating. This device is installed in a vehicle and operates independently from the electronic control unit (ECU); it records the coolant temperature and controls air admission to the engine of the vehicle in which it is installed. In addition, a new Arduino-based card will receive signals from a temperature sensor as input and process them according to its programming. Then, it will send signal outputs to the actuators: A servomotor, monitor, LED display, and buzzer. To control the intake flow, a butterfly valve is used with the servomotor. This valve partially or totally restricts the engine airflow, based on the temperature programmed for the Arduino, thus protecting the engine from overheating.

This thesis employs computational and experimental methods to explore hotspot cooling and high heat flux removal from a 3-D stacked chip using thermoelectric and microfluidic devices. Stacked chips are expected to improve microelectronics performance, but present severe thermal management challenges. The thesis provides an assessment of both thermoelectric and microfluidic technologies and provides guidance for their implementation in the 3-D stacked chips. A detailed 3-D thermal model of a stacked electronic package with two dies and four ultrathin integrated TECs is developed to investigate the efficacy of TECs in hotspot cooling for 3-D technology. The numerical analysis suggests that TECs can be used for on demand cooling of hotspots in 3-D stacked chip architecture. A strong vertical coupling is observed between the top and bottom TECs and it is found that the bottom TECs can detrimentally heat the top hotspots. As a result, TECs need to be carefully placed inside the package to avoid such undesired heating. Thermal contact resistances between dies, inside the TEC module, and between the TEC and heat spreader are shown to significantly affect TEC performance. TECs are most effective for cooling localized hotspots, but microchannels are advantageous for cooling large background heat fluxes. In the present work, the results of heat transfer and pressure drop experiments in the microchannels with water as the working fluid are presented and compared to the previous microchannel experiments and CFD simulations. Heat removal rates of greater than 100 W/cm2 are demonstrated with these microchannels, with a pressure drop of 75 kPa or less. A novel empirical correlation modeling method is proposed, which uses finite element modeling to model conduction in the channel walls and substrate, coupled with an empirical correlation to determine the convection coefficient. This empirical correlation modeling method is compared to resistor network and CFD modeling. The proposed modeling method produced more accurate results than resistor network modeling, while solving 60% faster than a conjugate heat transfer model using CFD. The results of this work demonstrate that microchannels have the ability to remove high heat fluxes from microelectronic packages using water as a working fluid. Additionally, TECs can locally cool hotspots, but must be carefully placed to avoid undesired heating. Future work should focus on overcoming practical challenges including fabrication, cost, and reliability which are preventing these technologies from being fully leveraged.

Thesis (MSc)-- Stellenbosch University, 2013.
ENGLISH ABSTRACT: A Magneto Optical Trap (MOT) is a configuration formed by three orthogonal pairs of counterpropagating circularly polarized laser beams and a magnetic field gradient. A MOT is used to cool, capture and trap large numbers of atoms in vacuum at very low temperature in K range. In this thesis the development of an experimental setup for realising a MOT of 87Rb atoms is presented. The atomic structure of Rb and the theoretical background of laser cooling and magneto optical trapping was reviewed. The influence of rubidium background pressure in the vacuum system, the laser beam size and the power and frequency on the number of the trapped atoms were studied in literature. The trapping and repumping lasers were characterised experimentally. Six circularly polarised trapping beams with equal power were formed and properly aligned to intersect at the center of the trapping cell. Two optical setups were designed and exploited to investigate and optimise the trapping beam polarisation. The repumping laser beam was successfully aligned and colinearly combined into all the trapping beams. Three different experimental setups for saturated absorption spectroscopy were developed. Saturated absorption spectra showing the hyperfine structure of both 85Rb and 87Rb isotopes were measured and are discussed. Using two saturated absorption spectroscopy setups, the frequencies of both lasers were successfully locked to the trapping and repumping transitions of 87Rb respectively. A rectangular trapping cell was designed and attached to the vacuum system. A pressure of about 10­¯7 mbar was achieved. The magnetic field coils were characterised and affixed on both sides of the cell in an anti-Helmholtz configuration. Setups for imaging and quantification of the 87Rb atoms in the MOT were designed. Finally, the procedures for demonstrating a MOT are presented. In conclusion, the current status of the project is reported, with recommendations for the future work.
AFRIKAANSE OPSOMMING: ’n Magneto optiese val (Magneto Optical Trap, MOT) is ’n konfigurasie wat gevorm word deur drie ortogonale laserbundelpare, wat elk uit twee sirkelvormig gepolariseerde bundels met teenoorgestelde voortplantingsrigtings bestaan, en ’n magneetveld gradient. ’n MOT word gebruik om ’n groot aantal atome af te koel, te vang en vas te hou in vakuum by ’n baie lae temperatuur in die K bereik. In hierdie tesis word die ontwikkeling van ’n eksperimentele optelling vir die realisering van ’n MOT van 87Rb atome voorgelê. Die atoomstruktuur van Rb en die teoretiese agtergrond van laser afkoeling en ’n magneto optiese val is hersien. Die invloed van die rubidium agtergronddruk in die vakuumstelsel, die grootte van die laserbundels en die laser drywing en frekwensie op die aantal gevangde atome is bestudeer uit die literatuur. Die MOT-laser en die optiese pomplaser is eksperimenteel gekarakteriseer. Ses sirkelvormig gepolariseerde MOT-laserbundels met gelyke drywings is gevorm en behoorlik belyn om in die middel van die MOT-sel te kruis. Twee optiese opstellings is ontwerp en gebruik om die polarisasie van die MOT-laserbundels te ondersoek en te optimeer. Die optiese pomplaserbundel is suksesvol belyn en ko-liniêr ekombineer met al die MOT-laserbundels. Drie verskillende eksperimentele opstellings vir versadigde absorpsie spektroskopie is ontwikkel. Versadigde absorpsie spektra wat die hiperfyn struktuur van beide die 85Rb en 87Rb isotope toon is gemeet en bespreek. Deur twee versadigde absorpsie spektroskopie opstellings te gebruik is die frekwensies van beide lasers suksesvol gestabiliseer op die MOT- en optiese pomp-oorgange van 87Rb onderskeidelik. ’n Reghoekige MOT-sel is ontwerp en aangesluit by die vakuumstelsel. ’n Druk van ongeveer 10­¯7 mbar is bereik. Die magneetveld spoele is gekarakteriseer en weerskante van die sel gemonteer in ’n anti-Helmholtz konfigurasie. Ten einde word die prosedures vir die demonstrasie van ’n MOT voorgelê. In die gevolgtrekking word daar verslag gedoen oor die status van die projek, met aanbevelings vir toekomstige werk.

This thesis is concerned with the guiding of cold atoms using optical forces, which is of great importance in the field of atom optics. Atomic beams can be used for precision sensor equipment, building nano-scale structures, construction of quantum computers and to further the understanding of the properties of atoms. Atoms are guided along light beams using the dipole force; there are two regimes under which this force works. Typically red-detuned guides are used (atoms are attracted towards the light) such guides, however, require large detuning and high powers. In this thesis we investigate the use of blue-detuned (atoms are repelled from the light) hollow light beams of moderate power (a few hundred mW) and confine atoms in the dark centre of the beams. Several magneto-optical traps (MOTs) have been constructed to exploit different guiding geometries. Hollow beams have been generated using a variety of methods; in particular the use of a computer controlled spatial light modulator (SLM) has provided great versatility and simplicity to the experimental arrangements. First, experiments were performed with a low-velocity intense source (LVIS) of atoms. A co-linear LG beam significantly enhances the observed flux, however, considerable difficulties are encountered loading atoms into oblique guides. Imaging a hole in the walls of the light tube was used to improve the loading efficiency. Second, guiding a free-falling atom cloud is performed using a non-diffracting Bessel beam. It is found that while the potential of the Bessel beam is steeper than equivalent LG beams the power distribution across the beam severely limits its usefulness. The next study investigated higher-order LG guide beams generated with an SLM. High order modes have a narrower profile so confine the atoms with less interaction with the guide beam, leading to a more natural guide (as opposed to a pushing force). Finally the SLM was used to create non-trivial beam shapes for beam splitters and interferometers.

L’objectif de cette étude est d’améliorer les performances des transformateurs piézoélectriques en terme de courant de sortie et de puissance pour des applications d’alimentation DC/DC, grâce à la gestion de l’échauffement. Le courant de sortie des transformateurs piézoélectriques, et donc la puissance transmise, sont directement liés à la vitesse de vibration qui pour des valeurs élevées engendre des pertes et une forte élévation de température. Cette élévation excessive de la température a comme conséquence le changement des caractéristiques du transformateur et plus particulièrement la diminution du facteur de qualité Q. Ainsi cela entraine une limite structurelle de la puissance transmise du transformateur. Une solution pour augmenter le courant de sortie est l’utilisation d’un redresseur doubleur de courant, qui grâce à 2 inductances permet, à courant de charge donné, de diminuer la vitesse de vibration du transformateur, mais ne permet pas de régler le problème d’échauffement du transformateur. Dans cette thèse nous proposons des moyens d’évacuation de la chaleur ainsi que le choix de l’environnement dans lequel le transformateur devra fonctionner. L’influence de différents systèmes de refroidissement d’un convertisseur DC/DC à base transformateur piézoélectrique est étudiée. L’étude thermique du transformateur piézoélectrique multicouche polarisé en épaisseur et ayant des électrodes circulaires met en évidence un comportement non linéaire. Une plaque vibrante piézoélectrique est d’abord envisagée pour créer un flux d’air qui augmente l’évacuation de chaleur par convection, puis un module de refroidissement utilisant l’effet thermoélectrique. Les mesures montrent que la première solution est plus avantageuse car elle améliore sensiblement les performances du transformateur pour un coût énergétique très faible. Une étude thermique par éléments finis complète cette étude, montrant que l’approche par schéma électrique est pertinente. La puissance que peut délivrer le transformateur sur une charge optimale est encore augmentée. Enfin, ce travail montre qu’en combinant les dispositifs de refroidissement tout en respectant la condition de température inférieure à 55°C, le rendement du convertisseur reste raisonnable (70%) et la puissance disponible peut doubler dans le meilleur des cas
The objective of this study was to increase the output current and power in a piezoelectric transformer (PT) based DC/DC converter by adding a cooling system. It is known that the output current of PT is limited by temperature build-up because of losses especially when driving at high vibration velocity. Excessive temperature rise will decrease the quality factor Q of piezoelectric component during the operational process. Simultaneously the vibration energy cannot be increased even if under higher excitation voltage. Although connecting different inductive circuits at the PT secondary terminal can increase the output current, the root cause of temperature build-up problem is not solved.This dissertation presents the heat transfer technology to deal with the temperature build-up problem. With the heat transfer technology, the threshold vibration velocity of PT can be increased and thus the output current and output power (almost three times).Furthermore, a comparison between heat transfer technology and current-doubler rectifier applied to the piezoelectric transformer based DC/DC converter was also studied. The advantages and disadvantages of the proposed technique were investigated. A theoretical-phenomenological model was developed to explain the relationship between the losses and the temperature rise. It will be shown that the vibration velocity as well as the heat generation increases the losses. In our design, the maximum output current capacity can increase 100% when the operating condition of PT temperature is kept below 55°C. The study comprises of a theoretical part and experimental proof-of-concept demonstration of the proposed design method

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CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Com a rápida evolução da tecnologia, os dispositivos eletrônicos tornaram-se compactos e com o alto poder de processamento, aumentando a geração de calor. Mas devido à baixa eficiência de ventiladores e dissipadores utilizados atualmente, há a necessidade de desenvolver novas formas de resfriamento. O uso de jatos sintéticos no resfriamento de dispositivos eletrônicos ainda é incipiente. Estudos monstram que este método pode ser uma alternativa eficaz. Assim, neste trabalho foi desenvolvido um estudo experimental com jatos sintéticos onde foram analisadas diferentes configurações de jatos com orifício retangular. Um alto-falante foi utilizado como diafragma e excitado através de um gerador de sinais senoidais para produzir o jato. A frequência de ressonância era desconhecida e foi necessário analisá-la antes de iniciar o experimento. O sistema foi montado em um suporte móvel para que fosse possível variar a posição vertical do gerador de jatos. Foram analisadas as dimensões do orifício para diferentes diâmetros hidráulicos (4 – 8 mm) e razões de aspecto (2 – 4), como também a profundidade da cavidade (2 – 8 mm). Também se analisou a transferência de calor através do impacto de jatos sobre uma placa aquecida. Dentre os estudos, verificaram-se outros parâmetros como o número de Reynolds e o número de Strouhal a fim de calcular a frequência mais adequada para a produção de vórtices. Os resultados demonstraram que para orifícios retangulares, as configurações com diâmetro hidráulico maior e razão de aspecto menor, são as melhores opções para resfriamento dos dispositivos eletrônicos.
With the rapid evolution of technology, electronics have become more compact and with higher processing power, increasing heat generation. Thus, there is a need to develop new forms of cooling, due to the low efficiency of cooling fans and heatsinks used currently. Using synthetic jets for cooling electronic device is still incipient but studies show that this method is an effective alternative. Thus, this work was developed an experimental study with synthetic jets where different configurations were tested with rectangular orifice. A loudspeaker was used as diaphragm and it was excited by a sinusoidal signal generator to produce the jet. The previously unknown ressonant frequency was determined experimentaly as part of this study. The system was mounted on a vertical traverse to allow changes in the vertical position of the synthetic jet generator. Orifice dimensions were analyzed covering variations in hydraulic diameter (4-8 mm) and aspect ratio (2-4), as well as the depth of the cavity (2-8 mm). Also the heat transfer was examined through the jet impingement on a hot plate. Other parameters such as Reynolds and Strouhal number were also examined in order to calculate the best frequency for jet performance. Results show that for rectangular orifice, geometries with larger hydraulic diameter and aspect ratio smaller are the best options for electronic cooling devices.

The thesis deals with the design and creation of a system for recording and reporting error states of cooling devices on the principle of a compressor heat pump. An important element of the concept of the entire monitoring system is a built-in platform based on the ESP32 microcontroller for evaluating data measured by sensors. Another key element is the communication module, which sends measured data via GPRS in the form of MQTT messages to the service web application. The application receives, evaluates and records measured data. Subsequently are measured data and evaluated error states presented to the user in the form of tables and interactive graphs.

Thesis (Ph. D.)--University of Oregon, 2008.
Typescript. Includes vita and abstract. Includes bibliographical references (leaves 114-119). Also available online in Scholars' Bank; and in ProQuest, free to University of Oregon users.

A wearable cooling system was developed in this study for use in elevated temperature environments by military, fire-fighting, chemical-response, and other hazardous duty personnel. Such a system is expected to reduce heat-related stresses, increasing productivity and allowable mission duration, reduce fatigue, and lead to a safer working environment. The cooling system consists of an engine-driven vapor-compression system assembled in a backpack configuration, coupled with a cooling garment containing refrigerant lines worn in close proximity to the skin. A 2.0 L fuel tank in the backpack powers a small-scale engine that runs a compressor modified from the original air compression application to the refrigerant compression application here. A centrifugal clutch and reduction gear train system was designed and fabricated to couple the engine output to the refrigerant compressor and heat rejection fan. The overall cooling system, including the wearable evaporator, had a total mass of 5.31 kg (11.7 lb) and measured 0.318 נ0.273 נ0.152 m (12.5 נ10.75 נ6 inches). Testing was conducted in a controlled environment to determine system performance over a wide range of expected ambient temperatures (37.7-47.5㩬 evaporator refrigerant temperatures (22.2-26.1㩬 and engine speeds (10,500-13,300 RPM). Heat removal rates of up to 300 W, which is the cooling rate established in the literature as being required for maintaining comfort at an activity level comparable to calisthenics or moderate exercise, were demonstrated at a nominal ambient temperature of 43.3㠨110橮 Modeling the fuel as 88 percent methanol (LHV ~ 1.992ױ07 J/kg) and 12 percent oil, the system consumed 1750 W at an average fuel mass flow rate of 0.316 kg/hr to provide a nominal cooling rate of 178 W for 5.7 hrs between refueling.

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O escoamento bifásico de gás-líquido é encontrado em muitos circuitos fechados que utilizam circulação natural para fins de resfriamento. O fenômeno da circulação natural é importante nos recentes projetos de centrais nucleares para a remoção de calor. O circuito de circulação natural (Circuito de Circulação Natural - CCN), instalado no Instituto de Pesquisas Energéticas e Nucleares, IPEN / CNEN, é um circuito experimento concebido para fornecer dados termo-hidráulicos relacionados com escoamento monofásico ou bifásico em condições de circulação natural. A estimativa de transferência de calor tem sido melhorada com base em modelos que requerem uma previsão precisa de transições de padrão de escoamento. Este trabalho apresenta testes experimentais desenvolvidos no CCN para a visualização dos fenômenos de instabilidade em ciclos de circulação natural básica e classificar os padrões de escoamento bifásico associados aos transientes e instabilidades estáticas de escoamento. As imagens são comparadas e agrupadas utilizando mapas auto-organizáveis de Kohonen (SOM), aplicados em diferentes características da imagem digital. Coeficientes da Transformada Discreta de Cossenos de Quadro Completo (FFDCT) foram utilizados como entrada para a tarefa de classificação, levando a bons resultados. Os protótipos de FFDCT obtidos podem ser associados a cada padrão de escoamento possibilitando uma melhor compreensão da instabilidade observada. Uma metodologia sistemática foi utilizada para verificar a robustez do método.
Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

Continued development of highly compact and powerful electronic components has led to the need for a simple and effective method for controlling the thermal characteristics of these devices. One proposed method for thermal control involves the use of a micro heat pipe system containing a working fluid with physical properties having been speciffcally selected such that the heat pipes, as a whole, vary in effective thermal conductance, thereby providing a level of temperature regulation. To further explore this possibility, a design scenario with appropriate constraints was established and a model developed to solve for the effective thermal conductance of individual heat pipes as a function of evaporator-end temperature. From the results of this analysis, several working fluids were identified and selected from a list over thirteen hundred that were initially analyzed. Next, a thermal circuit model was developed that translated the individual heat pipe operating characteristics into the system as a whole to determine the system level effects. It was found that none of the prospective fluids could completely satisfy the established design requirements to regulate the device temperature over the entire range of operating conditions. This failure to fully satisfy design requirements was due, in large part, to the highly constrained nature of problem definition. Several fluids, however, did provide for an improved level of thermal control when compared to the unmodified design. Suggestions for improvements that may lead to enhanced levels of thermal control are offered as well as areas that are in need of further research.

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.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 60-63).
We investigated the experimental performance of a nanoporous membrane for ultra-high heat flux dissipation from high performance integrated circuits. The biporous evaporation device utilizes thermally-connected, mechanically-supported, high capillarity membranes that maximize thin film evaporation and high permeability liquid supply channels that allow for lower viscous pressure losses. The 600 nm thick membrane was fabricated on a silicon on insulator (SOI) wafer, fusion-bonded to a separate wafer with larger liquid channels. Spreading effects and overall device performance arising from non-uniform heating and evaporation of methanol was captured experimentally. Heat fluxes up to 412 W/cm2, over an area of O.4x 5 mm, and with a temperature rise of 24.1 K from the heated substrate to ambient vapor, were obtained. These results are in good agreement with a high-fidelity, coupled fluid convection and solid conduction compact model, which was necessitated by computational feasibility, which incorporates non-equilibrium and sub-continuum effects at the liquid-vapor interface. This work provides a proof-of-concept demonstration of our biporous evaporation device. Simulations from the validated model, at optimized operating conditions and with improved working fluids, predict heat dissipation in excess of 1 kW/cm2 with a device temperature rise below 30 K, for this scalable cooling approach.
by Jay D. Sircar.
S.M.

A high electric field RFQ device was developed and tested to investigate the design requirements needed for such a device to effectively cool and confine ions in gaseous environments. Segmented cylindrical quadrants placed 1mm apart were used to create axially confining fields similar to present trapping systems. High Q air-cored resonating coils were designed to drive the RFQ device at 4.76 MHz and place up to 5.4 kV between adjacent electrodes in vacuum. By removing the transformer cores from the resonating circuit and using a 1 kW RF amplifier it was found that up to 15 kV of RF potential could be achieved across adjacent quadrants at helium pressures of up to 80 Pa.
The main limiting factor associated to the device's function was found to be the power losses in the transformer coupling the resonant circuit to the RF amplifier. These results show that with a proper RF power supply RFQ confinement of ions severaI hundred times stronger than in present devices is indeed possible.

L'électronique de puissance est en pleine mutation matérielle, technologique et conceptuelle. Cette évolution bouscule l'approche traditionnelle de la conception et de la fabrication des convertisseurs statiques avec pour objectif de proposer des solutions plus performantes, plus fiables et plus compactes et tout cela dans un contexte technico économique de plus en plus exigeant. Cette thèse analyse et expérimente un concept innovant de terminaisons en tension verticales ouvrant la voie vers l'intégration en 3D des composants de puissance mais également l'intégration, au sein même de la zone active d'un échangeur thermique. En s'appuyant sur la technique de réalisation des tranchées profondes issue de la micro électronique, ce document présente une approche permettant la co-intégration de plusieurs composants de puissance indépendants partageant la même électrode et le même substrat en face arrière. L'autre volet de ce travail de thèse est focalisé sur le concept DRIM Cooler (Drift Region Integrated Microchannel Cooler), un réseau de microcanaux perpendiculaires au plan de jonction du composant de puissance permettant son refroidissement direct. Les analyses numériques sont complétées par de nombreuses réalisations, caractérisations et mises en œuvre des approches précitées.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 44-46).
Heat dissipation is a limiting factor in the performance of integrated circuits, power electronics and laser diodes. State-of-the-art solutions typically use air-cooled heat sinks, which have limited performance owing to the use of air. One of the promising approaches to address these thermal management needs is liquid vapor phase-change. In this thesis, we present a study into the design and modeling of a cooling device based on thin film evaporation from a nanoporous membrane supported on microchannels. The concept utilizes the capillary pressure generated by the small pores to drive the liquid flow and largely reduces the viscous loss due to the thinness of the membrane. The interfacial transport has been re-investigated where we use the moment method to solve the Boltzmann Transport Equation. The pore-level transport has been modeled coupling liquid transport, vapor transport and the interfacial balance. The interfacial transport inside the pore also serves as a boundary condition for the device-level model. The heat transfer and pressure drop performance have been modeled and design guidelines are provided for the membrane-based cooling system. The optimized cooling device is able to dissipate 1 kW/cm² heat flux with a temperature rise less than 30 K from the vapor side. Future work will focus on more fundamental understanding of the mass and energy accommodation at the liquid vapor interface.
by Zhengmao Lu.
S.M.

This thesis deals with simulation of cooling of rail during its passing through cooling device which has been designed by the heat transfer and fluid flow laboratory. Inputs of the computational model have been set up to get best possible correspondence between outputs of the computational model and results of experimental measurement. The solution with using of model of austenitic stainless steel is provided in first part of the thesis. The solution with considering model of carbon steel is performed in next part. Using of model of carbon steel allows including evolution of latent heat during phase changing. A fields of residual stress has been calculated for different cooling conditions in the last part of this thesis.

This work investigates three-dimensional power loop layout for application to a SiC based matrix converter, providing a symmetric, low-inductance solution. The thesis presents various layout types to achieve this design target, and details the implementation of a hybrid layout to the matrix converter phase-leg. This layout is more easily achievable with a surface-mount device package, which also offers benefits such as ease in manufacturing, and a compact package. In order to implement a surface-mount device, a PCB thermal management strategy should be utilized. An evaluation of these methods is also presented in the work. The final power loop solution that implements an aluminum nitride inlay is evaluated through simulated parasitic extraction and experimental double pulse tests. The layout achieves small, symmetric loop inductances. Finally, the full power, three-phase matrix converter demonstrates the successful implementation of this power loop layout.
Master of Science
In the United States, 40% primary energy consumption comes from electricity generation, which is the fastest growing form of end-use energy. Industries such as commercial airlines are increasing their use of electric energy, while phasing out the mechanical and pneumatic aircraft components, as they offer better performance and lower cost. Thus, implementation of high efficiency, electrical system can reduce energy consumption, fuel consumption and carbon emissions [1]. As more systems rely on this electric power, the conversion from one level of power (voltage and current) to another, is critical. In the quest to develop high efficiency power converters, wide bandgap semiconductor devices are being turned to. These devices, specifically Silicon Carbide (SiC) devices, offer high temperature and high voltage operation that a traditional Silicon (Si) device cannot. Coupled with fast switching transients, these metal oxide semiconductors field effect transistors (MOSFETs), could provide higher levels of efficiency and power density. This work investigates the benefits of a three-dimensional (3D) printed circuit board (PCB) layout. With this type of layout, a critical parasitic – inductance – can be minimized. As the SiC device can operate at high switching speeds, they incur higher di/dt, and dv/dt slew rates. If trace inductance is not minimal, overshoots and ringing will occur. This can be addressed by stacking PCB traces on top of one another, the induced magnetic field can be reduced. In turn, the system inductance is lowered as well. The reduction of this parameter in the system, reduces the overshoot and ringing. This particular work applies this technique to a 15kW matrix converter. This converter poses a particular design challenge as there are a large number of devices, which can lead to longer, higher inductance PCB traces. The goal of this work is to minimize the parasitic inductance in this converter for high efficiency, high power density operation.

O objetivo deste estudo foi testar um sistema de Polietileno para o transporte de sêmen equino refrigerado por um período de até oito horas. Foram utilizados um total de 87 ejaculados de cinco diferentes garanhões, com idade média de 10 anos, sendo três da raça Puro Sangue de Corrida e dois da raça Pônei Miniatura Brasileiro. Os garanhões foram coletados duas vezes por semana utilizando vagina artificial. Após cada coleta, o sêmen foi avaliado a fresco e diluído na proporção 1+1 (diluente + sêmen) com leite desnatado UHT e dividido em quatro alíquotas de igual volume. No grupo controle (GC) o sêmen foi analisado logo após a diluição (zero hora – 0h). Nos demais grupos o sêmen foi mantido por oito horas (8h) em três diferentes sistemas de transporte: Equitainer® (GE), Botuflex®(GB) e Sistema de Polietileno - Refrigerado (SP) ou Não-Refrigerado (SPN). Foram avaliadas a motilidade total, vigor, a integridade de membrana plasmática (CFDA/PI), funcionalidade de membrana plasmática (HOST) e morfologia espermática. No SP não ocorreu diferença estatística em todos os parâmetros avaliados, quando comparado com o GE e o GB (médias da motilidade total = 45,00%, 49,29% e 46,40%; médias do vigor = 2,04, 2,18 e 2,01; médias do CFDA/PI = 71,12%, 73,29%, 71,32; médias do HOST = 39,70%, 41,21% e 39,76%; e médias da morfologia = 80,50%, 82,29% e 81,28%, valores respectivos de cada parâmetro para SP, GE e GB), enquanto o SPN apresentou valores médios inferiores ao GE para todos os parâmetros avaliados (médias da motilidade total = 50,65% e 62,60%; médias do vigor espermático = 1,78 e 2,43; médias do CFDA/PI = 72,56% e 78,30%; médias do HOST = 43,56% e 48,87%; médias da morfologia = 77,17% e 84,82%, respectivamente para SPN e GE). Com base nos dados podemos concluir que o SP foi igual ou não diferiu dos demais sistemas estudados, já o SPN se apresentou inferior aos demais sistemas estudados neste experimento. Portanto, o uso do SP é indicado para o transporte de sêmen refrigerado por oito horas, quando comparado aos demais sistemas estudados neste trabalho.
The aim of this study was to test a polyethylene system to ship equine cooled semen. A total of 87 ejaculates from five different stallions with known fertility, mean age 10 years, were used, being three Thoroughbred and two Miniature Pony horse. The stallions were collected twice a week using an artificial vagina. After each collection the semen was diluted 1+1 (diluent+semen) with UHT skim milk and divided into four aliquots of equal volume, yielding a total of four groups. In the control group (CG) the semen was analyzed immediately after dilution (zero hour - 0h). In the other groups semen was stored for eight hours (8h) in three different transport systems: Equitainer® (EG), Botuflex® (BG) and Polyethylene System - Cooled (PS) or Non-Cooled (NPS). The total motility, vigor, plasma membrane integrity (CFDA/PI), plasma membrane functionality (HOST) and sperm morphology were evaluated. In PS did not occur a statistical difference in all parameters compared with EG and BG (averages of total motility = 45.00%, 49.29% and 46.40%, the average effect = 2.04, 2 18 and 2.01; averages CFDA / PI = 71.12%, 73.29%, 71.32; averages HOST = 39.70%, 41.21% and 39.76%, and the average of morphology = 80.50%, 82.29% and 81.28%, respective values of each parameter to PS, EG and BG), while the NPS showed lower mean values than the EG to all parameters (total motility averages = 50,65% and 62,60%, sperm vigor averages = 1,78 and 2,43; CFDA / PI averages = 72,56% and 78,30%; HOST averages = 43,56% and 48,87 %, morphology averages = 77.17% and 84.82%, respectively for NPS and EG). Based on the results we can conclude that the PS was equal or did not differ from the other systems studied, the NPS already performed lower than the other systems studied in this experiment. Therefore, the use of the SP is indicated for the transport of cooled semen for eight hours as compared to other systems studied in this work.

Thesis (M.S.)--University of Cincinnati, 2009.
Advisors: Dr. Michael Kazmierczak PhD (Committee Chair), Dr. Milind A. Jog PhD (Committee Member), Dr. Sang Y. Son PhD (Committee Member). Title from electronic thesis title page (viewed April 26, 2009). Includes abstract. Keywords: Peltier cooling; developing internal turbulent forced convection; heat pump and coefficient-of-performance. Includes bibliographical references.

Thesis (M.S.)--University of Cincinnati, 2008.
Advisor: Dr. Michael Kazmierczak PhD (Advisor), Dr. Milind A. Jog PhD (Committee Member), Dr. Sang Y. Son PhD (Committee Member), Title from electronic thesis title page (viewed Feb. 9, 2009). Includes abstract. Keywords: Peltier cooling; developing turbulent flow; internal forced convection; discrete heat flux. Includes bibliographical references.

This thesis is concerned with the influence of nanoscale boundaries and interfaces upon the electronic processes that occur within the inorganic semiconductors. Inorganic semiconductor nanowires and their blends with semiconducting polymers have been investigated using state-of-the-art ultrafast optical techniques to provide information on the sub-picosecond to nanosecond photoexcitation dynamics in these systems. Chapters 1 and 2 introduce the theory and background behind the work and present a literature review of previous work utilising nanowires in hybrid organic photovoltaic devices, revealing the performances to date. The experimental methods used during the thesis are detailed in Chapter 3. Chapter 4 describes the crucial roles of surface passivation on the ultrafast dynamics of exciton formation in gallium arsenide (GaAs) nanowires. By passivating the surface states of nanowires, exciton formation via the bimolecular conversion of electron-hole plasma can observed over few hundred picoseconds, in-contrast to the fast carrier trapping in 10 ps observed in the uncoated nanowires. Chapter 5 presents a novel method to passivate the surface-states of GaAs nanowires using semiconducting polymer. The carrier lifetime in the nanowires can be strongly enhanced when the ionization potential of the overcoated semiconducting polymer is smaller than the work function of the nanowires and the surface native oxide layers of nanowires are removed. Finally, Chapter 6 shows that the carrier cooling in the type-II wurtzite-zincblend InP nanowires is reduced by order-of magnitude during the spatial charge-transfer across the type-II heterojunction. The works decribed in this thesis reveals the crucial role of surface-states and bulk defects on the carrier dynamics of semiconductor nanowires. In-addition, a novel approach to passivate the surface defect states of nanowires using semiconducting polymers was developed.

Une cellule thermophotovoltaïque (TPV) convertit l’énergie de photons émis par des corps chauds en énergie électrique. Lorsque la distance séparant deux corps rayonnants devient inférieure à la longueur d’onde caractéristique du rayonnement thermique (~10 µm à température ambiante, ~2,3 µm vers 1000°C), le transfert de chaleur radiatif peut s’accroître de plusieurs ordres de grandeur grâce à la contribution des ondes évanescentes. Cette propriété a un intérêt pour la récupération d’énergie en promettant une augmentation de la puissance électrique générée par une cellule TPV lorsqu’elle est placée en champ proche d’un émetteur thermique radiatif. Dans le but de vérifier cette prédiction, cette thèse a consisté à développer un banc expérimental de mesures TPV en champ proche. Le dispositif est basé sur un montage de microscopie thermique avec actuateurs piézo-électriques (SThM). L’émetteur est une sphère micrométrique de graphite attachée sur un levier SThM chauffé de manière thermorésistive jusqu’à 1200 K et la cellule TPV en antimoniure d’indium (InSb), qui ne peut fonctionner au-delà de 100 K, est placée sur le doigt froid d’un cryostat. Le flux radiatif en champ proche transféré par l’émetteur peut être mesuré indépendamment de la puissance électrique générée par la cellule. La preuve expérimentale de l’accroissement de la densité de puissance électrique générée en champ proche, par rapport à la prédiction de la théorie macroscopique du rayonnement, a été apportée avec un facteur jusqu’à 6. L’étude de différents paramètres a permis d’atteindre des puissances TPV de 7.5 kW.m-2 et des rendements de conversion mesurés de ~20 %. Des expériences de transfert radiatif en champ proche dans diverses configurations (matériaux, géométries, températures) ont également été menées. La puissance radiative transférée en champ proche suit des lois de puissance très différentes de celles du champ lointain. Ces résultats démontrent expérimentalement l’intérêt applicatif des effets de champ proche pour le rayonnement thermique
Thermophotovoltaic (TPV) cells convert the energy of photons emitted by hot bodies into electrical energy. When the distance between two radiating bodies becomes smaller than the characteristic wavelength of thermal radiation (~ 10 µm at room temperature and ~ 2.3 µm near 1000 °C), radiative heat transfer can be enhanced by several orders of magnitude due to the contribution of evanescent waves. This property has an interest for energy harvesting because it should increase the electrical power generated by a TPV cell located in the near field of a radiative thermal emitter. With the aim of confirming this prediction, this thesis consisted in the development of an experimental setup for performing near-field TPV measurements. The setup is based on a scanning thermal microscopy (SThM) design involving piezoelectric actuators. The emitter is a microsphere made of graphite and glued on a SThM cantilever heated by Joule effect up to 1200 K and the TPV cell made of indium antimonide (InSb), which cannot operate above 100 K, is placed on the cold finger of a cryostat. Near-field radiative heat flux transferred from the emitter is measured independently from the electrical power generated by the cell. A study of different parameters provided the experimental proof of the near-field enhancement of the electrical power density generated in the near field by a factor up to 6 compared with the prediction based on the macroscale theory of thermal radiation. Output electrical power densities reach 7.5 kW.m-2 and conversion efficiencies ~20 %. In addition, near-field radiative heat transfer experiments were performed in various configurations (materials, geometries and temperatures). The near-field radiative power follows power laws different from those of the far field. These results highlight the interest of near-field effects on radiative heat transfer for applications