No description available.

Nucleation is a stochastic process, most accurately represented by a probability distribution. Obtaining sufficient data to define this probability distribution is a laborious process. Here, we describe a novel instrument capable of the automated determination of hydrate nucleation probability under non-equilibrium conditions for a range of natural gas mixtures at pressures up to 10MPa. The instrument is based on the automated lag time apparatus (ALTA) which was developed to study the stochastic nature of nucleation in ambient pressure systems [1].We demonstrate that the probability distribution represents a robust and reproducible tool for the quantitative evaluation of hydrate formation risk under pseudo-realistic pressure conditions.

The research performed in this work investigated evaporative spray cooling systems using water near a 45 degree bends in gas turbine exhaust piping systems. Both experimental data and numerical data were generated with the goal of evaluating the ability of Fluent 6.3.26 to predict the performance of these systems for the purpose of design using only modest computational resources. Three cases were investigated in this research: single phase exhaust flow with no water injection, injecting water before the bend and injecting water after the bend. Various probes were used to measure dry bulb temperature, total pressure and water mass flux of the two phase flow at the exit of the pipe. Seven hole probes and pitot static probes were used to measure single phase flow properties. Numerical simulations were performed using mass flow boundary conditions which were generated from experimental results. A turbulence model was selected for the simulations based on comparisons of single phase simulations with experimental data and convergence ability. Using Fluent’s discrete phase model, different wall boundary conditions for the discrete phase were used in order to find the model which would best match the evaporation rates of the experimental data. Mass flux values through the exit plane of the pipe were found to be the most reliable of all the two phase data collected. Results from numerical simulations revealed the shortcomings of the available discrete phase wall boundary conditions to accurately predict the interaction of the liquid phase with the wall. Experimental results for both cases showed extensive areas of the wall which had liquid film layers running down the length of the pipe. Simulations resulted in particles either failing to impact the wall and create a liquid film, or creating a liquid film which was much smaller than the film present in experimental results. This led to 8% and 15% discrepancy in evaporation amounts between numerical and experimental results for water injection upstream and downstream of the bend respectively. Under-prediction of areas wetted with a wall film in the simulations also led to gross over predictions of wall temperature in numerical results. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2014-01-02 11:02:00.955

Technological developments in the area of high power LED light sources have enabled their utilization in general illumination applications. Along with this advancement comes the need for progressive thermal management strategies in order to ensure device performance and reliability. Minimizing an LED's junction temperature is done by minimizing the total system's thermal resistance. For actively cooled systems, this may essentially be achieved by simultaneously engineering the conduction through the heat sink and creating a well-designed flow pattern over suitable convective surface area. While such systems are routinely used in cooling microelectronics, their use in LED lighting systems encounter additional constraints which must be accounted for in the design of the cooling system. These are typically driven by the size, shape, and building codes involved with the lighting industry, and thus influence the design of drop-in replacement LED fixtures. Employing LED systems for customary down-lighting applications may require shrouded radial fin heat sinks to increase the heat transfer while reducing the space requirement for active cooling. Most lighting is already in some form of housing, and the ability to concurrently optimize these housings for thermal and optical performance could accelerate the widespread implementation of cost-efficient, environmentally-friendly solid-state lighting. In response, this research investigated the use of conical, cylindrical, square, and pyramidal shrouds with pin/radial fin heat sink designs for the thermal management of high power LED sources. Numerical simulations using FLUENT were executed in order to account for details of the air flow, pressure drop, and pumping power, as well as the heat transfer and temperature distributions throughout the system. The LEDs were modeled as a distributed heat source of 25 - 75 W on a central portion of the various heat sinks. Combinations of device junction temperature and pumping power were used to assess the performance of shrouded heat sink designs for their use in air-cooled, down-lighting LED fixtures.

Thesis (Master)--İzmir Institute Of Technology, İzmir, 2005. / Keywords: Artificial neural networks, fuzzy logic, modeling, cooling load, prediction. Includes bibliographical references (leaves. 44-45).

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Efficient face milling of titanium alloys provides a global challenge. Difficult-to-cut super alloys such as Ti-6Al-4V is considered the “workhorse” material for aerospace components. During the machining of aerospace components, 80% – 90% of the material is removed. This requirement drives the innovation for machines and tooling to become more efficient, while driving down costs. In South Africa, this requirement is no different. Due to the historic practice of exporting valuable minerals such as Ilmenite, leucoxene and rutile, South Africa does not enjoy many of financial benefits of producing value added titanium alloy products. The Titanium Centre of Competence (TiCoC) is aimed at creating a South African titanium manufacturing industry by the year 2020. More specifically, the roughing of Ti-6Al-4V aerospace components has been identified as an area for improvement. The thermal conductivity of Ti-6Al-4V is significantly lower than that of other “workhorse” metals such as steel or aluminium. Therefore, heat rapidly builds up in the tool tip during high speed machining resulting in shortened tool life and increased machining costs. Hence the ongoing developments in the field of cooling methods for high speed machining. The latest development in high pressure cooling (HPC) is split tools that deliver coolant into the cutting interface via flat nozzles in the rake face of the insert. Although it has been released recently and limited to a single supplier, this cooling method is commercially available, yet little is known about its performance or application conditions. The operational characteristics of split tools are studied by answering set research questions. A dynamometer was used to measure the tangential cutting forces during 11 cutting experiments that follow a three-factor factorial design at two levels and with three centre points. A second-order model for predicting the tangential cutting force during face milling of Ti-6Al-4V with split tools was fit to the data at 95% confidence level. A predictive cutting force model was developed in terms of the cutting parameters: (1) Axial depth of cut (ADOC), (2) feed per tooth and, (3) cutting speed. The effect of cutting parameters on cutting force including their interactions are investigated. Data for chip evacuation, surface finish and tool wear are examined and discussed. Practical work was done at a selected industry partner to determine: (1) impact of an analytical approach to perform process development for aerospace component roughing, (2) determine the feasibility of implementing split tools to an existing process. A substantial time saving in the roughing time of the selected aerospace component was achieved through analytical improvement methods. Furthermore it was found that the split tools were not a suitable replacement for current tooling. It was established that certain critical operational requirements of the split tools are not met by the existing milling machine at the industry partner. / AFRIKAANSE OPSOMMING: Doeltreffende masjinering van titaan allooie bied `n wêreldwye uitdaging. Moeilik-om-te-sny super allooie soos Ti-6Al-4V word as die “werksesel” materiaal vir lugvaart komponente beskou. Gedurende die masjinering van lugvaart komponente word 80% - 90% van die materiaal verwyder. Dit is hiérdie behoefte wat die innovering van masjien -en snygereedskap dryf om dit meer doeltreffend en finansieël vatbaar te maak. Die Suid Arikaanse behoefte vir doeltreffende snygereedskap vir Ti-6Al-4V masjinering stem ooreen met hierdie internationale behoefte. Die geskiedkundige Suid Afrikaanse praktyk om onverwerkte, waardevolle minerale soos Ilmeniet, rutiel en leucoxene uit te voer, kniehalter die land se kans om winste uit verwerkte titaan allooi produkte te geniet. Die “Titanium Centre of Competence” (TiCoC) se mikpunt is om `n Suid Afrikaanse titaanproduk vervaardigingsmark op die been te bring teen 2020. Stellenbosch Universiteit se funksie, binne hierdie strategiese raamwerk, fokus op hoë spoed masjinering van Ti-6Al-4V lugvaart komponente. Die hitte geleidingsvermoë van Ti-6Al-4V is noemenswaardig laer as die van ander “werksesel” materiale soos byvoorbeeld staal of alumium. Om hierdie rede word hitte in die freesbeitelpunt gedurende hoë spoed masjinering opgeberg. Dit verkort gereedskap leeftyd en verhoog masjinerings kostes. Daarvandaan deurlopende ontwikkelinge in verkoelingsmetodes vir hoë spoed masjinering. Die mees onlangse ontwikkeling in hoë druk verkoeling is “split tools” wat koelmiddel na die snyoppervlak deur middel van langwerpige gleufies in die hark gesig van die beitelpunt lewer. Hierdie tegnologie is op die mark beskikbaar, maar slegs deur `n enkele verskaffer. Daar is ook geen akademiese publikasies wat oor Ti-6Al-4V masjinering met “split tools” handel nie. Die verrigtings vermoë en toepassings gebied vir die gereedskap is steeds onbekend. 'n Dinamometer is gebruik om die tangensiale snykragte tydens 11 sny eksperimente te meet. Die eksperiment ontwerp is faktoriaal van aard en bevat drie faktore en drie middelpunte oor twee vlakke. `n Kwadratiese model is geskik om die data op 95% vertroue vlak voor te stel en voorspellings mee te maak. Die voorspellingsmodel is ontwikkel in terme van: (1) Diepte van snit, (2) voertempo, en (3) Snyspoed. Die invloed van die drie parameters op die tangentiale snykrag, asook invloed met mekaar word ondersoek. Verdere data in verband met materiaal verwydering, oppervlak afwerking en beitel slytasie word ook bespreek. Praktiese werk is met behulp van `n bedryfsvennoot gedoen om vas te stel: (1) die impak van 'n analitiese benadering en ontwikkelings proses op die uitrof van lugvaart komponente, (2) en om die lewensvatbaarheid van implementering van “split tools“ aan 'n bestaande proses te bepaal. `n Noemenswaardige besparing is sodoende behaal. Dit is verder bevind dat “split tools” nie `n geskikte plaasvervanger vir die huidige snygereedskap is nie. Die rede daarvoor is gedeeltelik omdat die huidige freesmasjien by die bedryfsvennoot nie aan die kritiese operasionele vereistes van die gereedskap vervaardiger voldoen nie.

L’écoulement de refroidissement, qui pénètre par les entrées d’air sous le capot des véhicules automobiles,est étudié à partir de trois approches complémentaires : les approches théorique, expérimentale et numérique. Ces trois approches s’appuient sur une maquette simplifiée à culot droit basée sur le corps de Ahmed et équipée d’un compartiment moteur. Les mesures expérimentales montrent que placer la sortie du compartiment moteur au culot de la maquette est plus favorable à une faible traînée de refroidissement qu’une sortie placée au niveau du soubassement. La contribution de la traînée de refroidissement dans la traînée totale peut ainsi varier de 2% à 24%. Les simulations numériques donnent elles accès au débit de refroidissement. Pour les configurations étudiées, les sorties au culot sont là encore les plus favorables puisqu’elles fournissent les débits les plus importants à travers le milieu poreux modélisant un échangeur aérothermique. Par ailleurs, la mise en place d’étanchéités de part et d’autre de l’échangeur améliore significativement le débit de refroidissement où une augmentation d’environ 45% est obtenue. La mise en place d’un modèle analytique permet de relier la traînée et le débit de refroidissement à partir d’une analogie entre les circuits électriques et les écoulements fluides. Il est alors possible de prévoir le sens d’évolution du débit de refroidissement, donc de la performance des échangeurs aérothermiques, à partir d’une modification géométrique interne au compartiment moteur. / The cooling airflow, which flows through the underhood of motor vehicles from the inlet sections, is studied by means of three complementary approaches: the theoretical, experimental and numerical approaches. The three approaches use a simplified geometry with a blunt rear end, based on the Ahmed body, and equipped with an engine compartment. The experimental measurements show that locating the outlet section of the engine compartment at the base of the geometry favors low cooling drag values compared to an outlet section located in the underbody. The variation of the cooling drag contribution in the total drag is between2% and 24%, as a function of the location of the outlet. As for the numerical simulations, they provide the cooling flow rates. For the studied configurations, rear end outlets are again the most favorable since they provide the highest flow rates through the porous media that simulates a heat exchanger. Besides, the implementation of sealing above and below the porous media significantly increases the cooling flow rate by45%. An analytical model, based on the analogy between electrical circuits and fluid flows, connects the aerodynamic drag with the cooling flow rate. It is then possible to predict the evolution trend of the cooling flow rate, hence the heat exchangers efficiency, from a geometrical modification inside the engine compartment.

xi, 125 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / This dissertation presents experimental and theoretical studies of radiation pressure cooling in silica optomechanical microresonators where whispering gallery modes (WGMs) are coupled to thermal mechanical vibrations. In an optomechanical system, circulating optical fields couple to mechanical vibrations via radiation pressure, inducing Stokes and anti-Stokes scattering of photons. In analogy to laser cooling of trapped ions, the mechanical motion can in principle be cooled to its ground state via the anti-Stokes process in the resolved-sideband limit, in which the cavity photon lifetime far exceeds the mechanical oscillation period. Our optomechanical system is a slightly deformed silica microsphere (with a diameter 25-30 μm ), featuring extremely high Q -factors for both optical ( Q o ∼ 10 8 ) and mechanical ( Q m ∼ 10 4 ) systems. Exploiting the unique property of directional evanescent escape in the deformed resonator, we have developed a free-space configuration for the excitation of WGMs and for the interferometric detection of mechanical displacement, for which the part of input laser that is not coupled into the microsphere serves as a local oscillator. Measurement sensitivity better than 5 × 10 -18 m /[Special characters omitted.] has been achieved. The three optically active mechanical modes observed in the displacement power spectrum are well described by finite element analysis. Both radiation pressure cooling and parametric instabilities have been observed in our experiments. The dependence of the mechanical resonator frequency and linewidth on the detuning as well as the intensity of the input laser show excellent agreement with theoretical calculations with no adjustable parameters. The free-space excitation technique has enabled us to combine resolved sideband cooling with cryogenic cooling. At a cryogenic temperature of 1.4 K, the sideband cooling leads to an effective temperature as low as 210 m K for a 110 MHz mechanical oscillator, corresponding to an average phonon occupation of 37, which is one of the three lowest phonon occupations achieved thus far for optomechanical systems. The cooling process is limited by ultrasonic attenuation in fused silica, which should diminish when bath temperature is further lowered, with a 3 He cryostat, to a few hundred millikelvin. Our experimental studies thus indicate that we are tantalizingly close to realizing the ground-state cooling for the exploration of quantum effects in an otherwise macroscopic mechanical system. / Committee in charge: Michael Raymer, Chairperson, Physics; Jens Noeckel, Member, Physics; Hailin Wang, Member, Physics; Paul Csonka, Member, Physics; Jeffrey Cina, Outside Member, Chemistry

Made available in DSpace on 2014-10-09T12:53:58Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:27Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

O Brasil possui a maior parte de suas terras em clima tropical. Sendo a cobertura o elemento construtivo mais exposto à radiação solar direta, toma-se um desafio aos pesquisadores e projetistas, atenuar as temperaturas nas coberturas das edificações e contribuir para o uso racional de energia. O objetivo desta pesquisa é monitorar o desempenho térmico de coberturas de fibrocimento em_ células-teste na cidade de Campinas, SP, com aplicação de técnicas passivas de resmamento. Utilizaram-se quatro células-teste: uma célula-teste de referência, e outras três com os sistemas: evaporativo, radiante e reflexivo, respectivamente, e monitoramento das temperaturas superficiais internas das telhas (TT' s) e temperaturas do ar dos áticos (T AA' s), no período de 21 de janeiro a 9 de fevereiro de 2006. Para o sistema de resmamento evaporativo foram utilizados ciclos de aspersão com diferentes intervalos no período todo. Entre as técnicas monitoradas, o melhor comportamento térmico foi verificado no 2° período (de 26 a 30/jan com aspersão contínua) na temperatura da superficie interna da telha do sistema evaporativo (TTevap = 23,2°C) apresentando um decréscimo de 1,3°C em relação a célulateste de referência e um acréscimo de 0,1 °C em relação as médias da temperatura do ar para o período. Nas médias da temperatura do ar dos áticos, o 2° período apresentou os menores valores para os sistemas: reflexivo (TAArefl =23,4°C) e evaporativo (TAAevap = 23,5°C), apresentando uma atenuação de 0,5°C e 0,4°C em relação a célula de referência respectivamente, além de uma elevação de 0,3°C em relação as médias da temperatura do ar externo. Os resultados, analisados através de tratamento estatístico, demonstram a viabilidade do uso do sistema evaporativo em condições climáticas de elevada umidade relativa do ar, contribuindo para atenuar os efeitos das hostilidades climáticas em coberturas das edificações._________________________________________________________________________________________ ABSTRACT: In Brazil, the tropical climate is predominant in most of regions. Roofing is the building component with the highest exposition to direct solar radiation. The challenge for researchers and designers is to achieve cornfort in the built environrnent and to contribute to energy saving, proposing roofing systems with good thermal insulation, and consequently lesser internal surface temperatures. The objective of this research is to monitor the thermal behavior of fiber-cement roofing and to present a discussion about the results obtained in cell-tests in the city of Campinas, SP, through passive cooling techniques. Four cell-tests were used: one cell-test was adopted as reference, and the other three were analyzed with evaporative, radiative and reflective systems, respectively. The evaporative system was tested with different aspersion cycles through spraying systems and intervals. The monitored parameters were the internal surface temperatures of the roofing tiles (TT s) and attic air temperatures (TAA's) in the period of January 21st to February 9th of2006. Among the monitored passive techniques, the best thermal behavior was observed in the 2nd period (iTom January 26th to 30th, corresponding to continue spraying), related to the internal surface temperature with the evaporative system (TTevap = 23,2°C). A reduction of 1,3°C was observed, as compared to the reference test-cell and and an increase of 0,1 °C in comparison with the average air temperature. In relation to the average of attic air temperature, the 2nd period presented the lowest temperature for reflexive system (T AArefl = 23,4°C) and evaporative system (TAAevap = 23,5°C); a reduction of 0,5°C and 0,4°C in relation of the reference test-cell respectively was observed; also, it showed an increase of 0,3°C as compared with air temperature. The results presented through statistical analyses demonstrated that the use of the evaporative system in climatic conditions with high relative humidity is viable, contributing, therefore, to attenuate the effects of climatic hostilities in the roofing buildings.