The aftertreatment techniques introduced to follow the emission legislations require a constant improvement process to comply with the gradually more stringent demands. SCR is the system used nowadays to deal with NOx emissions in most heavy-duty vehicles. An aqueous-urea solution, AdBlue, is sprayed into the evaporation unit, where urea should decompose to ammonia, the reducing agent. This is a critical step because the NH3 amount available heavily affects the final nitrous oxides reduction to nitrogen. Moreover the urea decomposition’s sides reactions are likely to occur, forming deposits that increase the pressure drop and in a certain time period could even foul the system. The evaporation module used in the silencer for Scania trucks equipped with V8 engines consists of a pipe in pipe configuration made in stainless steel 1.4509, where the exhaust gases flow heating up the inner pipe finned on its outer surface. The AdBlue is sprayed on the inner pipe’s inner surface, creating a wall film and cooling down the tube. The production of the evaporation pipe however involves a costly manufacturing process, being made of 144 flanges laser welded on a 0.355 m length, for a total of more than 52 m of welding. The goal of this thesis is to analyse the heat transfer from the exhaust gases to the pipe and how to improve it, in order to achieve a lower temperature drop on the pipe due to the AdBlue dosing, reducing at the same time the risk of building up deposits. The application of different materials for the evaporation unit is also considered. Furthermore many manufacturing processes are evaluated as a cost-effective alternative to the current one. Although the operating points have a wide range of variation, the analysis is focused on the worst conditions for urea evaporation which are low mass flow and low flow temperature. Stainless steel is the best trade-off between cost, thermal conductivity and corrosion resistance but the much higher conductivity of copper alloys would justify the investigation of a copper evaporation pipe coated with stainless steel. Different designs of the heat flanges are assessed, first with correlations and FEA and then through a CFD analysis, where 62 different solutions are compared. The fins height results to be the most influencing parameter, requiring an increment from 7.5 mm to 11 mm to improve the heat transfer performances of the evaporation unit. The gap between each fin is also important, leading to a flanges quantity reduction suggestion. With the current fin design and half of the number of flanges, 11 mm high, the performances would improve by almost 40% (at 800 kg/h and 300℃). Furthermore both the Abstract pipe thickness and thermal conductivity are affecting the temperature drop, with different weight depending on the design and the operating point. It is however always advantageous to use a thicker wall and a material with a higher thermal conductivity. Lastly the tests performed on the specifically developed test rig show a good accordance with the simulations in comparing different materials but are not suitable to compare finned designs. / Avgasefterbehandlingssystem har utvecklats för att reducera utsläppen ifrån lastbilar, och det är ett lagkrav att en lastbil ska ha ett efterbehandlingssystem. Lagkraven för avgasemissioner skärps gradvis, vilket resulterar i att efterbehandlingssystemet ständigt måste förbättras och utvecklas för att möta de nya lagkraven. I de flesta heavy-duty-lastbilar som säljs på Euro 6 marknader är ett SCR-system installerat ihop med ljuddämparen för att hantera NOx-utsläppen. En vätska kallad AdBlue, det vill säga Urea, sprayas in i efterbehandlingssystemet där det förångas. Urea är en vätska baserad på bl.a. urinämne som utsöndras till ammoniak, vilket sedan fungerar som reduceringsmedel. Ett viktigt steg i reduktionsprocessen av kväveoxiden är när ammoniak reagerar med NOx och omvandlas till kväve och vatten. Det är mängden ammoniak som bestämmer det slutliga resultatet av kväveoxidreduktionen. Om urean inte är tillräckligt uppblandad med avgaserna bildas avlagringar utmed flödeskanalen. Detta ökar tryckfallet, vilket i sin tur leder till ökad bränsleförbrukning, avlagringarna kan över tid även skada efterbehandlingssystemet. Förångningsmodulen som används i Scanias ljuddämpare (kallad large), utvecklad för V8-motorer, består av en rör-i-rör konfiguration. Rören tillverkas i rostfritt stål 1.4509 och när AdBlue sprayas på insidan av innerröret bildas en film av urea som förångas när den möter rörets varma väggyta. För att uppnå en varm förångningsyta leds en delmängd av avgaserna om på utsidan av innerröret för att bibehålla hög temperatur på röret och undvika nedkylning av urean. Förångningsrörets nuvarande design består av 144 utvändiga värmeflänsar (med längden 0,355 m) som lasersvetsas fast på röret. Designen medför en dyr och komplicerad tillverkningsprocess. Den totala längden svets uppgår till 52 m. Syftet med examensarbetet är att analysera och förbättra värmeöverföringen från avgaserna till röret för largeljuddämparen. En förbättrad värmeöverföring skulle leda till att temperaturfallet som uppkommer på grund av AdBlue-doseringen blir lägre. Ett lägre temperaturfall skulle då leda till en minskad risk för avlagringar. I studien undersöks olika material och tillverkningsmetoder för att eventuellt reducera tillverkningskostnaden av förångningsenheten med bibehållen eller förbättrad prestanda. Driftfallen har ett brett spektrum där mängden energi (överförd värme) varierar och studien är inriktad på de värsta förhållandena för urea-utsöndring, dvs. ett lågt massflöde och låga flödestemperaturer. Rostfritt stål har bra korrosionsbeständighet och tämligen bra värmeledningsförmåga i kombination med ett rimligt pris. Kopparlegeringar har en mycket högre värmeledningsförmåga än rostfritt stål, vilket motiverar en undersökning av förångringsrör tillverkade i kopparlegering belagda med rostfritt stål. I studien undersöks olika utformning av värmeflänsar, både genom FEA och CFD-analyser, där 62 olika utformningar har tagits fram och jämförs. Flänsarnas höjd visade sig vara den parametern som påverkar temperaturfallet mest. En ökning från 7,5 mm till 11 mm av flänstoppens höjd gav en kraftig förbättring av förångningsenhetens värmeöverföringsförmåga. En annan viktig faktor visade sig vara avståndet mellan flänsarna. Med dagens flänsutformning, men med en utökad höjd till 11 mm, skulle man uppnå en förbättrad prestanda med nästan 40 % (vid 300℃ och 800 kg/h) om man dessutom minskade antalet flänsar med hälften. Beroende på design och driftspunkt är rörtjockleken och materialets värmeledningsförmåga andra faktorer som påverkar temperaturfallet. Det är dock oftast fördelaktigt med en tjockare rörvägg och ett material med högre värmeledningsförmåga. Flera prototyper med olika utformning har testats fysiskt i en specialtillverkad testrigg. Slutresultatet påvisade en bra korrelation med simuleringarna vid jämförelse av olika materialval, men det fysiska testet hade svårare att hantera geometrisk utformning på flänsarna.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Due to increasing power demands and decreasing component size, thermal management has become the bottleneck for many power electronic applications. The aerospace industry has focused on reducing weight, operating temperature, and pumping power of power converters since these will limit an aircrafts' range and load carrying capacity. This paper outlines a tool created in MATLAB to automate the cold plate design process for DC-DC converters (or similar applications). The tool incorporates a genetic algorithm to fi nd the optimal aligned or staggered pin fi n confi guration that maintains the devices below their critical junction temperature while reducing the system's overall weight and pressure drop. Utilizing this MATLAB design tool, a cold plate was designed, manufactured, and tested. The convection coefficient calculated within MATLAB (via empirical correlations) was veri fed using simplifi ed CFD simulations within 5% of each other. The same CFD setup, boundary condition types, and methodology are then applied for the full-sized prototype cold plate simulations. These simulations were then validated using the experimental results. For all cases, the percentage error between the simulated convection coefficient values (CFD) and the experimental results was less than 12%. The experiments' measured surface temperature and pressure drop errors were less than 8% of the predicted CFD results. Therefore, the MATLAB tool and its correlations/calculations could be veri fied (via CFD) and validated (experimentally) based on good agreement between the CFD and the experimental results. This three-pronged approach (analytical calculations, CFD simulations, and experimental validation) is an effective and robust method to solve heat transfer problems. Overall, with the framework outlined in this thesis, a complete cold plate design can now be completed in weeks instead of months. This streamlined approach will save companies signifi cant time and money in the design and simulation phases, making this tool a valuable addition to the current literature available. / Thesis / Master of Applied Science (MASc)

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The effects of greenhouse gases have seen a significant rise in recent years due to the use of fossil fuels like gasoline and diesel. Conversion of the energy stored in these fossil fuels to mechanical work is an extremely inefficient process which results in a high amount of energy rejected in the form of waste heat. Thermoelectric materials are able to harness this waste heat energy and convert it to electrical power. Thermoelectric devices work on the principle of the Seebeck effect, which states that if two junctions of dissimilar materials are at different temperatures, an electrical potential is developed across them. Even though these devices have small efficiencies, they are still an extremely effective way of converting low grade waste heat to usable electrical power. These devices have the added advantage of having no moving parts (solid state) which contributes to a long life of the device without needing much maintenance. The performance of thermoelectric generators is dependent on a non-dimensional figure of merit, ZT. Extensive research, both past and ongoing, is focused on improving the thermoelectric generator's (TEG's) performance by improving this figure of merit, ZT, by way of controlling the material properties. This research is usually incremental and the high performance materials developed can be cost prohibitive. The focus of this study has been to improve the performance of thermoelectric generator by way of improving the heat transfer from the exhaust gases to the TEG and also the heat transfer from TEG to the coolant. Apart from the figure of merit ZT, the performance of the TEG is also a function of the temperature difference across it, By improving the heat transfer between the TEG and the working fluid, a higher temperature gradient can be achieved across it, resulting in higher heat flux and improved efficiency from the system. This area has been largely neglected as a source of improvement in past research and has immense potential to be a low cost performance enhancer in such systems. Improvements made through this avenue, also have the advantage of being applicable regardless of the material in the system. Thus these high performance heat exchangers can be coupled with high performance materials to supplement the gains made by improved figure of merits. The heat exchanger designs developed and studied in this work have taken into account several considerations, like pressure drop, varying engine speeds, location of the system along the fuel path, system stability etc. A comprehensive treatment is presented here which includes 3D conjugate heat transfer modeling with RANS based turbulence models on such a system. Various heat transfer enhancement features are implemented in the system and studied numerically as well as experimentally. The entire system is also studied experimentally in a scaled down setup which provided data for validation of numerical studies. With the help of measured and calculated data like temperature, ZT etc, predictions are also presented about key metrics of system performance. / Ph. D.

The heat transfer characteristics through arrays of pin fins were studied for the further development of internal cooling methods for turbine airfoils. Low aspect ratio pin fin arrays were tested through a range of Reynolds numbers between 5000 and 30,000 to determine the effects of pin spacing as well as aspect ratio on pin and endwall heat transfer. Experiments were also conducted to determine the independent effects of pin spacing and aspect ratio on arrays with different flow incidence angles. The pin Nusselt numbers showed almost no dependence on pin spacing or flow incidence angle. Using an infrared thermogaphy technique, spatially-resolved Nusselt numbers were measured along the endwalls of each array. The endwall results showed that streamwise spacing had a larger effect than spanwise spacing on array-averaged Nusselt numbers. Endwall heat transfer patterns showed that arrays with flow incidence angles experienced less wake interaction between pins than arrays with perpendicular flow, which caused a slight decrease in heat transfer in arrays with flow incidence angles. The effect of flow incidence angle on array-average Nusselt number was greater at tighter pin spacings. Even though the pin Nusselt number was independent of pin spacing, the ratio of pin-to-endwall Nusselt number was dependent on flow conditions as well as pin spacing. The pin aspect ratio had little effect on the array-average Nusselt number for arrays with perpendicular flow; however, the effect of flow incidence angle on array-average Nusselt number increased as aspect ratio decreased. / Master of Science

The performance of many engineering devices from power electronics to gas turbines is limited by thermal management. Pin fins are commonly used to augment heat transfer by increasing surface area and increasing turbulence. The present research is focused on but not limited to internal cooling of turbine airfoils using pin fins. Although the pin fins are not limited to a single shape, circular cross-sections are most common. The present study examines heat transfer from a single row of circular pin fins with the row oriented perpendicular to the flow. The configurations studied have spanwise spacing to pin diameter ratios of two, four, and eight. Low aspect ratio pin fins were studied whereby the channel height to pin diameter was unity. The experiments are carried out for a Reynolds number range of 5000 to 30,000. Heat transfer measurements are taken on both the pin and on the endwall covering several pin diameters upstream and downstream of the pin row. The results show that the heat transfer augmentation relative to open channel flow is highest for the smallest spanwise spacing for the lowest Reynolds number flows. The results also indicate that the pin fin heat transfer is higher than on the endwall. / Master of Science

Made available in DSpace on 2016-04-28T18:24:17Z (GMT). No. of bitstreams: 1 Jorge Onodera.pdf: 1478594 bytes, checksum: 004cbdbe062b1abdde69d20b7c37f168 (MD5) Previous issue date: 2010-05-25 / Secretaria da Educação do Estado de São Paulo / This research study took place in a Business Unit, a division of an American multinational company in de area of power systems located in the city of Guarulhos. This study aimed to carry out a Needs Analysis in ten departments of the Business Unit and to identify the working tasks performed by the employees in the target situation and the tasks that offer difficulties executing the job. The theoretical approach underpinning this study is based on the ESP approach to Language Teaching. For Teaching English for Business Purposes (EBP) this study was based on Ellis & Johnson (1994), Dudley-Evans & St John (1998); for Needs Analysis it was based on Hutchinson & Waters (1987), Strevens (1988), Brindley (1989), Berwick (1989), Robinson (1991), Dudley-Evans and St John (1998) and Long (2005). Data were obtained in the ten departments by using questionnaires and interviews. This research is in the qualitative paradigm and the methodology used was case study, oriented by Yin (2005), Stake (1988), Chizotti (2006) and Johnson (1992). The community focus of this study was the employees of a Business Unit division of an American Multinational that use the English Language to perform tasks. The target situation needs and also the language learning needs were identified. The results of this study identified relevant information about the main genres used in the company. Employees of the multinational company use the English Language mainly to: read and write e-mail, answer phone calls, participate in conference calls, write and make presentations. Data demonstrated difficulties in performing tasks like answering the telephone, participating in conference call, reading and writing presentations and the skill that causes problems while performing the tasks are listening-speaking; i.e. oral interactional skills. The results of this research may be used to generate syllabuses that can be used to supply the company general needs and also each specific department needs / Esta pesquisa foi realizada em uma empresa multinacional de grande porte da área de sistema de energias situada na cidade de Guarulhos e teve como objetivos fazer a análise de necessidades do uso de Língua Inglesa junto aos diversos departamentos dessa instituição e identificar tanto as tarefas que os funcionários desempenham utilizando essa língua nas diversas situações de trabalho, quanto as tarefas que oferecem dificuldades em sua execução. Utilizei como aporte teórico a Abordagem Instrumental com foco no Ensino de Inglês para Fins de Negócios (EBP) de Ellis e Johnson (1994), Dudley-Evans e St John (1998), baseando-me, no que se refere especificamente à análise de necessidades, em Hutchinson e Waters (1987), Strevens (1988), Brindley (1989), Berwick (1989), Robinson (1991), Dudley-Evans e St John (1998) e Long (2005). Esta pesquisa se insere no paradigma qualitativo e desenvolveu um estudo de caso, orientado segundo Yin (2005), Stake (1988), Chizotti (2006) e Johnson (1992), Foi realizada no âmbito de uma comunidade específica funcionários de uma empresa multinacional que utilizam a Língua Inglesa para executar tarefas em contexto profissional. Os dados deste estudo foram obtidos junto aos dez departamentos de uma unidade de negócios da empresa multinacional por meio de questionários e entrevistas. Foram mapeados todos os departamentos em que a Língua Inglesa é imprescindível na execução das tarefas e foram definidas as necessidades das situações-alvo, assim como as necessidades de aprendizagem dos funcionários. Nos resultados desta pesquisa foram identificadas informações relevantes acerca dos principais gêneros utilizados nesse contexto empresarial. Os funcionários que trabalham nessa empresa multinacional utilizam a Língua Inglesa principalmente para: ler e escrever e-mail, atender telefonemas, participar de conference calls, redigir e fazer apresentações. Os dados demonstraram também que as principais dificuldades são: atender telefonemas e participar de conference calls e a principal habilidade que oferece dificuldades ao executar as tarefas é a de falar-ouvir. O resultado do mapeamento de tarefas poderá ser utilizado como base para um syllabus de cursos que poderá atender tanto às necessidades dos departamentos de uma forma mais geral, quanto às de cada departamento isoladamente

Grid fins (lattice fins) are used as a lifting and control surface for highly manoeuvrable missiles. Grid fins also find their applications for air-launched submunitions. The main advantages are its low hinge moment requirement and good high angle of attack performance characteristics. Two dimensional analysis has been carried out using linear and shock-expansion theo- ries. The results indicate that above certain depth-to-height ratio, (called critical depth-to-height ratio,) the local normal force becomes negative due to shock reflection from the opposite side. Hence, depth (chord) for grid fin cell should not exceed a critical value. A prediction method has been developed for the estimation of aerodynamic character- istics of grid fin-body combinations at supersonic Mach numbers based on shock-expansion theory. Body upwash theory has been used for the effect of body; method of images has been used for carry-over forces onto the body. Empirical relation has been used for the modelling of separated body vortices and their effect on the leeward side fins. The method has been validated with experimental results for three configurations. The comparison is good for individual fin characteristics as well as overall characteristics for all the cases at higher supersonic Mach numbers. For lower supersonic Mach numbers at higher angles of attack, the prediction deviates from experiment. The reason for the deviation is due to shock detachment and shock reflection from opposite side, which is not modelled in the present method. Vortex lattice method has been used for prediction of linear aerodynamic character- istics of grid-fins at subsonic Mach numbers. Empirical relation based on trends from available experimental data has been used for the non-linear effect. The method has been validated with experimental results for several configurations without and with control surface deflections. The predicted aerodynamic characteristics compare well with experimental results for all the cases and the difference is within 15%. Based on the subsonic and supersonic analytical methods, a prediction code for the aerodynamic analysis of configuration with grid fins has been developed. Flow field computations inside isolated cells have been carried out using CFD code, PARAS-3D. Effects of depth-to-height ratio, web thickness, web leading edge angle and cell width-to-height ratio have been studied. Increase in thickness reduces the critical depth and increases the normal force. This increment in normal force is due to shock wave formation at the expansion side and its interaction with the opposite side. Effect of cell cross sectional shape has been studied using inviscid computation over isolated cells. Square, right triangular, equilateral triangular and hexagonal cross sections have been considered for this study. The normal force for square cell at zero roll is higher compared to 45 deg roll (diamond shape). Triangular cells show large variation in normal force with roll orientation due to large variation in projected area with roll angle. To compare the characteristics of different cross sectional cells, the normal force is normalised with respect to total internal web area. The comparison shows that the hexagonal cell gives maximum normal force and right triangular cell gives the minimum. Packaging efficiency of different cross sections is analysed by normalising the normal force with frontal area. The results show that triangular cells are preferred for packaging efficiency. Viscous flow computations over complete configuration have been carried out using FLUENT. GAMBIT has been used for geometry definition and grid generation. Hexahedral finite volumes are used to generate the grids including the nose region. Flow computations have been carried out at supersonic Mach numbers. To reduce the compu- tational time, Flow computations upto 0.5 calibre ahead of grid fin have been carried out with body-alone configuration. Flow over the fin-body section has been computed sep- arately taking the inlet pressure condition from the body-alone computed results. This procedure has reduced the grid size to around 1/5th and the computations converged faster due to imposition of converged solution at the pressure inlet. The computed results on the body show that the Flow separation occurs on the lee- ward side of the body and formation of separated vortices. The comparison of pressure distribution on the body with experiment is good. Flow computations over the fin-body section have been carried out at different Mach numbers and angles of attack. The computed normal force coefficient on the horizontal fin compares well with experimental data. Computations with fin deflection of -15 deg have also been carried out and the computed results are within 10% of the experimental data. Flow computations over another grid fin configuration have been carried out at dif- ferent roll angles. The comparison of individual fin force and overall normal force and pitching moment coefficients with experiment is good. The comparison demonstrates the capability of prediction methods as well as CFD in analysing aerodynamic performance of grid fin configurations.