Uma família de esquemas upwind denominada FUS-RF (Family of Upwind Scheme via Rational Functions), que é derivada via funções racionais e dependentes de parâmetros, é proposta para o cálculo de soluções aproximadas de equações de conservação. A fim de ilustrar a capacidade dos novos esquemas, vários resultados computacionais para sistemas hiperbólicos de leis de conservação são apresentados. Esses testes mostram a inflluência dos parâmetros escolidos sobre a qualidade dos resultados numéricos. Fazendo o uso de alguns testes de padrões, comparação dos novos limitadores de fluxo correspondentes com o esquema bem estabelecido van Albada e esquema atual EPUS (Eight-degree Polynomial Upwind Scheme) é também realizada. Os testes numéricos realizados em transporte de escalares e problemas de dinâmica dos gases confirmam que alguns esquemas da família FUS-RF são não oscilatórios e fornecem resultados confiáveis quando perfis descontínuos são transportados. Um esquema particular dessa nova família de esquemas upwind é então selecionado e utilizado para resolver escoamentos complexos com superfícies livres móveis / A family of upwind schemes named as FUS-RF (Family of Upwind Scheme via Rational Functions), which is derived via rational functions and dependent of parameters, is proposed for computing approximated solutions of conservation equations. In order to illustrate the capability of the new schemes, several computational results for system of hyperbolic conservation laws are presented. These results clarify the influence of the chosen parameters on the quality of the numerical calculations. Using some standard test cases, comparison of the new corresponding limiters with the well established van Albada and the recently introduced EPUS (Eight-degree Polynomial Upwind Scheme) limiters is also done. Numerical tests on both scalar and gas dynamics problems confirm that some schemes of the FUS-RF family are non-oscillatory and yield sharp results when solving profiles with discontinuities. A particular upwind scheme of this new family is then slected and used for solving complex incompressible moving free surface flows

A presente pesquisa trata de um estudo experimental da transferência de calor e da perda de carga de fluidos refrigerantes puros e suas misturas em mudança de fase convectiva no interior de tubos lisos e aqueles dotados de ranhuras internas. Para tanto, foi desenvolvido um equipamento experimental cujo componente básico é composto por um tubo horizontal, aquecido por intermédio de uma resistência elétrica do tipo fita, aderida à superfície externa do tubo. As condições de ensaio variaram numa ampla faixa, permitindo cobrir as condições verificadas na maioria das instalações frigoríficas. Os resultados experimentais foram agrupados em duas faixas de velocidades mássicas: elevadas (G > ou = 200 kg/s.m2), onde prepondera o padrão anular de escoamento, e reduzidas (G < 200 kg/s.m2), predominando o padrão estratificado. Os principais parâmetros que afetam o coeficiente de transferência de calor, tais como, velocidade mássica, fluxo de calor, tipo de refrigerante, temperatura de evaporação e diâmetro do tubo foram analisados. O desempenho termo-hidráulico, relativo ao efeito combinado da transferência de calor e da perda de carga dos tubos ranhurados, foi sensivelmente superior quando comparados aos tubos lisos. A análise dos resultados experimentais permitiu a proposição de correlações para a perda da carga, avaliada através do multiplicador bifásico, &#966L, e para coeficiente de transferência de calor, em tubos lisos e ranhurados. As correlações propostas se mostraram adequadas para aplicações práticas, proporcionando desvios reduzidos em relação aos resultados experimentais. Destacam-se as correlações obtidas para o multiplicador bifásico para tubos microaletados e para o coeficiente de transferência de calor para vazões reduzidas em tubos lisos. Diversos registros fotográficos dos principais padrões de escoamento foram levantados, tendo sido importante na análise e entendimento da mudança de fase. / Present research deals with an experimental study of the heat transfer and pressure drop of pure and mixtures of refrigerants undergoing convective boiling inside horizontal smooth and microfin tubes. An experimental apparatus has been developed and constructed whose main component is a horizontal tube electrically heated. Experimental results have been grouped into two mass velocity ranges: the one corresponding to mass velocities lower than 200 kg/s.m2, where the stratified flow pattern is dominant, and that for mass velocities higher than 200 kg/s.m2, where typically the annular flow pattern can be found. Effects over the heat transfer coefficient of physical parameters such as mass velocity, heat flux, diameter, saturation temperature, and refrigerant have been investigated and analyzed. It has been found out that the thermo-hydraulic performance of microfin tubes is better than that of the smooth ones. Empirical correlations have been proposed for both the two-phase flow multiplier and the heat transfer coefficient for different ranges of operating conditions as well as for smooth and microfin tubes. Results from the proposed correlations can be deemed adequate for practical applications given the limited dispersion obtained with respect to their experimental counterpart. Noteworthy are the results obtained from correlations for both the two phase flow multiplier for microfin tubes and the heat transfer coefficient for the lower range of mass velocities in smooth tubes. Finally, worth mentioning is the photographic essay developed in present research involving the flow patterns that occur under convective boiling of refrigerants in horizontal tubes.

This research comprises an experimental and theoretical study on convective boiling inside tubes containing twisted-tape inserts. The demand for more compact and efficient thermal systems, in which the heat exchangers plays an important role, has led to the development and use of various heat transfer enhancement techniques. Among them twisted-tape insert as a swirl flow device is one of the most used. Twisted-tape inserts have been used for over more than one century ago as a technique of heat transfer enhancement applied to heat exchangers. However, the heat transfer augmentation comes together with pressure drop increment, impacting the pumping power and, consequently, the system efficiency. Moreover, until now it is not clear, the operational conditions under which the heat transfer coefficient augmentation by the use of twisted-tape inserts overcomes pressure drop penalty. In the present study, initially, extensive investigations of the literature concerning convective boiling inside plain tubes with and without twisted-tape inserts were performed. This literature review covers pressure drop, heat transfer coefficient and the leading frictional pressure drop gradient and heat transfer coefficient predictive methods during convective boiling inside tubes with and without twisted-tape inserts. Then, pressure drop and heat transfer coefficient results acquired in the present study were obtained in an experimental apparatus of 12.7 and 15.9 mm ID tubes during flow boiling of R134a for twisted-tape ratios of 3, 4, 9, 14 and tubes without inserts, mass velocities ranging from 75 to 200 kg/m2 s, saturation temperatures of 5 and 15°C and heat fluxes of 5 and 10 kW/m2. The experimental results were parametrically analyzed and compared against the predictive methods from literature. An analysis of the enhancement of the heat transfer coefficient and the pressure drop penalty is presented. Heat transfer coefficient increments up to 45% keeping the same pumping power and pressure drop penalty of about 35% were obtained by using twisted-tape relative to tubes without inserts. Additionally, through comparison of the present study experimental results with the predictive methods from the literature for heat transfer coefficient during two-phase flow inside tube containing twisted-tape inserts, it was verified that non of these methods predict satisfactory well the experimental results. However, a new method was develop for predicting the heat transfer coefficient during flow boiling inside tubes containing twisted-tape inserts based on the experimental results obtained in the present study. The predictive method takes into account the physical picture of the swirl flow phenomenon by including swirl flow effects promoted by the twisted-tape inserts. The proposed method predicts satisfactorily well the data obtained in the present study, predicting 89.1% of the experimental data within an error band of ± 30% and absolute mean deviation of 15.7%. / A presente pesquisa trata-se de um estudo teórico e experimental sobre a ebulição convectiva no interior de tubos com fitas retorcidas. A crescente demanda por sistemas térmicos mais compactos e eficientes, nos quais os trocadores de calor apresentam elevada relevância, tem motivado o desenvolvimento de inúmeras técnicas de intensificação de troca de calor, sendo que a utilização de fitas retorcidas é uma das técnicas mais adotadas. Fitas retorcidas são utilizadas como técnicas de intensificação de troca de calor há mais de um século. Entretanto o incremento da transferência de calor é acompanhado do aumento da perda de pressão, que por sua vez implica em aumento da potência de bombeamento, e consequentemente afeta a eficiência global do sistema. Adicionalmente, até os dias de hoje não há consenso sobre as condições operacionais em que o ganho com o incremento do coeficiente de transferência de calor é superior à perda devido ao aumento da perda de pressão. Neste estudo, inicialmente foi realizada uma extensa revisão da literatura sobre a ebulição convectiva no interior de tubos com e sem fitas retorcidas. Esta revisão aborda aspectos relacionados à perda de pressão e ao coeficiente de transferência de calor, juntamente com os métodos de previsão destes parâmetros. Foram realizados experimentos para determinação experimental de perda de pressão e coeficiente de transferência de calor, em aparato experimental contando com tubos horizontais com diâmetros internos iguais a 12,7 e 15,9 mm, para escoamento bifásico de R134a, razões de retorcimento iguais a 3, 4, 9, 14 e tubo sem fita, velocidades mássicas entre 75 e 200 kg/m²s, temperaturas de saturação iguais a 5 e 15°C, e fluxo de calor iguais a 5 e 10 kW/m². Os resultados experimentais foram analisados e comparados com estimativas segundo métodos disponíveis na literatura. Uma análise do aumento do coeficiente de transferência de calor e da perda de pressão friccional é apresentada. Foram verificados incrementos do coeficiente de transferência de calor de até 45% para a mesma potência de bombeamento, e aumento de perda de pressão de aproximadamente 35% para tubos com fitas retorcidas em relação aos tubos sem fita. Adicionalmente, através da comparação dos resultados experimentais com os métodos de previsão para coeficiente de transferência de calor, foi verificado que nenhuma metodologia apresentava previsões satisfatórias dos resultados. Portanto um novo método para previsão do coeficiente de transferência de calor durante ebulição convectiva no interior de tubos com fitas retorcidas foi desenvolvido com base nos resultados experimentais obtidos durante o presente estudo. O método proposto é função de parâmetros geométricos e do escoamento, e também de parâmetros físicos do escoamento rotacional induzido pela fita. A metodologia desenvolvida apresenta previsões satisfatórias dos resultados experimentais, prevendo 89,1% dos resultados experimentais com erro inferior a ± 30% e erro médio absoluto igual a 15,7%.

Submitted by Maria Beatriz Vieira (mbeatriz.vieira@gmail.com) on 2017-05-12T16:01:36Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) dissertacao_gabriela_lameu_moreira.pdf: 48934124 bytes, checksum: 7e62f6ed70d4fb9e308cbc0b8671374f (MD5) / Approved for entry into archive by Aline Batista (alinehb.ufpel@gmail.com) on 2017-05-12T21:23:26Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) dissertacao_gabriela_lameu_moreira.pdf: 48934124 bytes, checksum: 7e62f6ed70d4fb9e308cbc0b8671374f (MD5) / Made available in DSpace on 2017-05-12T21:23:26Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) dissertacao_gabriela_lameu_moreira.pdf: 48934124 bytes, checksum: 7e62f6ed70d4fb9e308cbc0b8671374f (MD5) Previous issue date: 2015-02-12 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Este trabalho teve como objetivo principal analisar uma Linha de Instabilidade (LI) e um Complexo Convectivo de Mesoescala (CCM) e as condições atmosféricas que conduziram à sua formação, desenvolvimento e geração de descargas elétricas atmosféricas. Estes sistemas ocorreram entre os dias 17 e 19 de outubro de 2007, na região Sudeste do Brasil. A análise dos casos de estudo foi feita em quatro períodos: pré-formação, ocorrência da LI, período de transição e ocorrência do CCM. Para a obtenção dos resultados, a base de dados foi composta por dados de descargas atmosféricas e dados simulados, obtidos com o modelo WRF. As simulações com o modelo WRF foram feitas com três grades aninhadas, de resoluções horizontais de 36, 12 e 4km, que permitiram extrair os campos meteorológicos à grande escala, mesoescala e microescala, respectivamente, bem como o cálculo e análises de alguns parâmetros meteorológicos. Os dados de descargas atmosféricas foram obtidos pela RINDAT (Rede Integrada Nacional de Detecção de Descargas Atmosféricas), que foram sobrepostas às imagens de satélite e aos campos meteorológicos. Dentre os resultados obtidos, observou-se que a região onde os sistemas se formaram e desenvolveram estava propícia para a ocorrência de tempestades, apresentando grande umidade, confluência de ventos, índices de instabilidades com valores que atestavam o potencial de desenvolvimento de tempestades. As condições de grande escala associadas à ocorrência da LI e do CCM apresentaram diferenças e semelhanças, mas em ambos os casos, a atividade elétrica máxima esteve associada ao período mais favorável ao desenvolvimento de correntes ascendentes intensas. / This study had as main objective to analyze a Squall Lines (SL) and a Mesoscale Convective Complex (MCC) and the weather conditions that conducted to its formation, development and generation of lightning. These systems occurred between 17 and 19 October 2007, in Southeastern Brazil. The analysis of the case studies was done in four periods: pre-initiation, occurrence of SL, transition period and occurrence of MCC. To obtain the results, the database consisted of data lightning and simulated data, obtained using the WRF model. The simulations with the WRF model were made with three nested grids with horizontal resolutions of 36, 12 and 4 km, which allowed extracting the meteorological fields to large-scale, mesoscale and microscale, respectively, and an evaluation and analysis of some meteorological parameters. The lightning data were obtained by RINDAT (Rede Integrada Nacional de Detecção de Descargas Atmosféricas), which were superimposed on satellite images and meteorological fields. Among the results, it was observed that the region where the systems were formed and developed was favorable to the occurrence of storms, with high humidity, confluence of winds, instability indices with values that attested to the potential development of storms. The large-scale conditions for the occurrence of SL and MCC showed differences and similarities, but in both cases the maximum electrical activity was associated with more favorable period for the development of intense updrafts.

We consider both a long-wave model and a first-order weighted-residual integral boundary layer (WIBL) model in the investigation of thin film flow down a topographical incline whilst under the effects of a normal electric field. The liquid is assumed to be a perfect dielectric, although is trivially extended to the case of a perfect conductor. The perfect dielectric case with no topography includes a simple modified electric Weber number which incorporates the relative electrical permittivity constant into itself. Linear stability analysis is carried out for both models, and critical Reynolds numbers which depend on the electric Weber number and the capillary number are produced. Regions of stability, convective instability and absolute instability are then determined for both models in terms of our electric Weber number and Reynolds number parameters in the case of no topography. Time-dependent simulations are produced to corroborate the aforementioned regions and investigate the effect of normal electric field strength in addition to sinusoidal and rectangular topographical amplitude on our system for various domain sizes. For the time-dependent simulations we find strong agreement with the linear stability analysis, and the results suggest that the inclusion of a normal electric field may have some stabilising properties in the long-wave model which are absent in the case of a flat wall, for which the electric field is always linearly destabilising. This stabilising effect is not observed for the same parameters in the WIBL model with a sinusoidal wall, although a similar effect is noticed in the WIBL model with a rectangular wall. We also investigate the simultaneous effect of domain size, wall amplitude and electric field strength on the critical Reynolds numbers for both models, and find that increasing the electric field strength can make large-amplitude sinusoidal topography stabilising rather than destabilising for the long-wave model. Continuation curves of steady solutions and bifurcation diagrams are also produced, and comparisons between the two models are made for various parameter values, which show excellent agreement with the literature. Subharmonic branches and time-periodic solutions are additionally included, similarly showing very good agreement with the literature.

<p>Su&scaron;enje dunje kao voćne vrste u praksi nije uobičajeno, zbog povi&scaron;ene vrijednosti<br />tvrdoće i čvrstoće. Prethodna istraživanja su&scaron;enja dunje, pokazala su da se osmotskim<br />su&scaron;enjem u okviru kombinovane tehnologije su&scaron;enja dobijaju povoljnije mehaničke<br />osobine su&scaron;enih proizvoda. Na osnovu plana obavljeni su eksperimenti osmotskog i<br />konvektivnog su&scaron;enja dunje u obliku četvrtina. Eksperiment osmotskog su&scaron;enja je<br />obavljen kao trofaktorni, gdje su uticajni faktori: temperatura rastvora, koncentracija<br />rastvora i vrijeme trajanja su&scaron;enja. TakoĎe, eksperiment konvektivnog su&scaron;enja je obavljen<br />kao trofaktorni, a uticajni faktori su: primjenjeni predtretman, temperature vazduha za<br />su&scaron;enje i brzina strujanja vazduha ispred sloja.<br />Na osnovu rezultata mjerenja eksperimenta osmotskog su&scaron;enja, zaključeno je da sa<br />porastom temperature i koncentracije rastvora postiže se veća brzina su&scaron;enja, &scaron;to se i<br />očekivalo. Disperzionom analizom osmotskog su&scaron;enja je ispitan uticaj faktora na brzinu<br />su&scaron;enja i zapreminsko skupljanje četvrtina dunje. Sa statističkom vjerovatnoćom od 99%<br />je dokazano da postoji uticaj svih faktora na brzinu su&scaron;enja uzoraka. Dokazano je sa<br />statističkom vjerovatnoćom od 99% da vrijeme trajanja osmotskog su&scaron;enja ima uticaj na<br />zapreminsko skupljanje četvrtina dunje, dok uticajni faktori temperatura i koncentracija<br />rastvora imaju uticaj sa statističkom vjerovatnoćom od 95%.<br />Analizom rezultata mjerenja veličina tokom eksperimenta konvektivnog su&scaron;enja<br />evidentno je da se sa vi&scaron;om temperaturom vazduha postiže brže sniženje vlažnosti<br />četvrtina dunje. Povećanjem vremena trajanja osmotskog predtretmana, smanjuje se<br />brzina konvektivnog su&scaron;enja. UtvrĎeno je da kori&scaron;ćenje osmotskog predtretmana sa<br />vi&scaron;om temperaturom rastvora i većom koncentracijom rastvora dovodi do smanjenja<br />brzine konvektivnog su&scaron;enja. Na osnovu disperzione analize konvektivnog su&scaron;enja sa<br />statističkom vjerovatnoćom od 99% dokazano je da postoje uticaji predtretmana i<br />temperature vazduha na brzinu su&scaron;enja i zapreminsko skupljanje četvrtina dunje. Uticaj<br />faktora brzine vazduha ispred sloja materijala nije dokazan disperzionom analizom, ali je<br />na osnovu kinetički krivih evidentan uticaj ovog faktora na brzinu su&scaron;enja, pri vi&scaron;im<br />vlažnostima materijala i vi&scaron;oj temperaturi konvektivnog su&scaron;enja. Najvjerovatniji razlog<br />ovakvih rezultata disperzione analize su male vrijednosti brzine vazduha za su&scaron;enje,<br />odnosno njihova mala razlika vrijednosti (0,5 m/s).<br />Kinetika prenosa mase tokom kombinovane tehnologije su&scaron;enja dunje u formi<br />četvrtine je matematički opisana, modelovanjem kinetike osmotskog su&scaron;enja i kinetike<br />konvektivnog su&scaron;enja. U okviru kinetike osmotskog su&scaron;enja četvrtina dunje, obavljeno je<br />matematičko modelovanje promjene vlažnosti u odnosu na suvu bazu i modelovanja<br />zapreminskog skupljanja. Za kinetiku konvektivnog su&scaron;enja četvrtina dunje, obavljeno je<br />matematičko modelovanje promjene vlažnosti u odnosu na suvu bazu tokom vremena<br />konvektivnog su&scaron;enja. Za svaku veličinu koja se modeluje usvojeno po tri matematička<br />modela, a modeli su pro&scaron;ireni uticajnim faktorima u bezdimenzionom obliku. Izvedeni<br />modeli su imali dobro slaganje sa eksperimentalnim rezultatima, &scaron;to pokazuju visoke<br />vrijednosti koeficijente korelacije. Primjena svih modela je jednostavna, gdje je uz pomoć<br />standardnih računara moguće brzo izračunavanje svih modelovanih veličina.<br />Primjenom osmotskog predtretmana u kombinovanoj tehnologiji su&scaron;enja dunje,<br />dobijaju se neke pozitivne osobine su&scaron;enog proizvoda. Smanjenje zapremine je manje<br />izraženo, nego primjenom samo konvektivnog su&scaron;enja. Vlažnost u voćnom tkivu je<br />ravnomjernije rasporeĎena i manje je presu&scaron;ivanje spoljnjih slojeva voćnog tkiva.<br />Stvaraju se manji unutra&scaron;nji naponi izmeĎu slojeva tkiva, uslijed čega nastaju manje<br />deformacije oblika. U povr&scaron;inskom sloju voćnog tkiva postoje adsorpcione veze vlage,<br />rastvorka i suve materije, a ove veze utiču na povećanje vrijednosti vlažnosti pri kojima<br />se osu&scaron;eni proizvod bezbjedno skladi&scaron;ti.</p> / <p>Drying of the quince as a fruit species is not common in practice due to its increased hardness<br />and firmness. Previous researches on quince drying have indicated that osmotic drying, within<br />the combined drying technology, enables favourable mechanical properties of dried products.<br />Planned experiments of the osmotic and convective drying of quince quarters were conducted.<br />The osmotic drying experiment was based on three significant experimental factors: the<br />temperature of osmotic solution, the concentration of osmotic solution, and the duration of<br />osmotic drying. The convective drying experiment was also based on three experimental<br />factors entailing the applied pretreatment, the temperature of drying air and the velocity of<br />drying air in front of material layers.<br />The measurement results obtained during the osmotic drying experiment indicate that an<br />increase in the temperature and the concentration of osmotic solution accelerates the drying<br />process, as expected. A dispersion analysis of the osmotic drying indicated the effects of<br />experimental factors on the drying speed and the volume shrinkage of quince quarters. With a<br />statistical probability of 99%, it was proven that all factors influence the speed of drying.<br />Moreover, with a statistical probability of 99%, it was proven that the duration of osmotic<br />drying influences the volume shrinkage of quince quarters, whereas the significant factors such<br />as the temperature and the concentration of osmotic solution exert influence with a statistical<br />probability of 95%.<br />The analysis of measurement results obtained during the convective drying experiment shows<br />that an increase in the air temperature accelerates a decrease in the moisture content of quince<br />quarters. An increase in the duration of osmotic pretreatment decelerates the convective drying<br />process. It was determined that the application of the osmotic pretreatment with higher<br />solution temperature and concentration decelerates the convective drying. On the basis of a<br />dispersion analysis of the convective drying with a statistical probability of 99%, it was proven<br />that the pretreatment and the air temperature affect the speed of drying and the volume<br />shrinkage of quince quarters. The effects of the air velocity in front of the material layer was<br />not determined by means of the dispersion analysis, nevertheless kinetic curves indicate the<br />influence of this factor on the drying speed, especially in the instance of higher moisture<br />content of the material and higher temperature of the convective drying. The most probable<br />causes of such dispersion analysis results are low values of the drying air velocity, i.e. a slight<br />difference in the values (0.5 m/s).<br />The kinetics of mass transfer during the combined drying of quince quarters was<br />mathematically described by means of the modelling of the kinetics of osmotic drying and the<br />kinetics of convective drying. The kinetics of osmotic drying of quince quarters was expressed<br />via the mathematical modelling of moisture content change in relation to dry basis and the<br />modelling of volume shrinkage. The kinetics of convective drying of quince quarters was<br />expressed via the mathematical modelling of moisture content change in relation to dry basis<br />during the convective drying. Three mathematical models were established for every modelled<br />value, and the models were extended by significant non-dimensional experimental factors. The<br />developed models had a good fit with the experimental results, which was indicated by the<br />high values of the correlation coefficient. The application of all models is simple and standard<br />personal computers can be used for rapid calculations of modelled values.<br />The application of the osmotic pretreatment in the combined quince drying enables<br />favourable properties of dried products. Volume shrinkage is slighter in comparison with the<br />convective quince drying. The moisture content in the fruit tissue is more evenly distributed<br />and the dehydration of the outer layers of the fruit tissue is lower. The tension between the<br />layers of the tissue is reduced thus reducing the shape defects. Within the surface layers of fruit<br />tissues, the adsorption bonds of moisture, solute and dry matter are formed. These bonds<br />increase the moisture content value, which enables the safe storage of dry products.</p>

Cette thèse porte sur la caractérisation expérimentale et la simulation numérique d’une configurationde jet rond en impact peu rencontrée dans la littérature : un jet chauffé issu d’une conduitepleinement développée à un haut nombre de Reynolds (ReD = 60 000) impacte normalement uneparoi située à trois diamètres en aval. Le premier volet de ce travail est dédié à la génération d’unebase de donnée expérimentale à l’aide de plusieurs moyens de mesure, avec pour objectif de caractériserà la fois la dynamique et la thermique de l’écoulement. Les techniques complémentaires devélocimétrie laser à franges (LDV) et vélocimétrie par image de particules (S-PIV) ont été mises àprofit pour la caractérisation du champ de vitesse et du tenseur de Reynolds tandis que les champsde température moyenne et fluctuante ont été mesurés à l’aide d’un fil froid. Enfin, les échangesthermiques au niveau de la paroi ont été obtenus par la méthode inverse de thermographie en facearrière (ThEFA). En plus de fournir une base de donnée très complète nécessaire à la validation dessimulations numériques, ces mesures ont également permis de mettre en évidence l’organisation àgrande échelle de l’écoulement, avec la présence de grandes structures tourbillonnaires dont la fréquencede passage correspond au mode colonne du jet libre et qui s’approchent de la paroi d’impactaux alentours du second maximum observé dans la distribution des échanges pariétaux. Le secondvolet concerne les simulations numériques visant à reproduire la configuration expérimentale. Deuxapproches ont été évaluées : l’approche RANS pour quantifier la pertinence des modèles utilisés parles industriels et l’approche LES, plus coûteuse, mais donnant accès aux propriétés instationnaireset tridimensionnelles de l’écoulement. Les simulations RANS ont montré que les modèles reconnuscomme les plus performants pour ce type de configuration sont incapables de prévoir correctementle niveau des échanges pariétaux. Ils sont, en revanche, bien reproduits par la simulation LES. Lesdonnées obtenues ont été mises à profit pour mieux comprendre les mécanismes liés à l’apparitiondu second maximum. Cette analyse a mis en avant le rôle des « points chauds ». Seuls certains d’entreeux ont pu être reliés à la présence de régions « décollées » tandis que la majorité est associée à desstructures allongées dans la direction de l’écoulement. / This thesis is dedicated to the experimental characterisation and the numerical simulations ofa round impinging jet configuration seldom dealt with in the literature : a heated jet issues from apipe fully developed pipe at a high Reynolds number (ReD = 60 000) and normally impinges a platelocated three diameters downstream. The first part of this work is directed towards the generationof an experimental database by means of several measurement techniques in order to characteriseboth the dynamical and thermal flow features. The complementary techniques of laser Doppler velocimetry(LDV) and particle image velocimetry (S-PIV) allowed for the velocity and Reynolds tensorfield characterisation. The mean and fluctuating temperature fields were measured through cold-wirethermometry. Finally, the plate heat transfer distribution was obtained through the inverse methodof « rear face thermography » (ThEFA). The gathered data not only provided a comprehensive databasenecessary to validate numerical simulations but also permitted to highlight the large-scale floworganisation, with the presence of large vortices shedding at the free jet preferred mode and closelyapproaching the plate in the vicinity of the secondary peak observed in the heat transfer distribution.The second part of this thesis focuses on the numerical simulations aiming at reproducing the experimentalconfiguration. Two approaches were evaluated : the RANS approach in order to quantifythe relevance of industrial turbulence models and the Large-Eddy Simulation, more expensive, butproviding the 3D unsteady flow features. The RANS simulations showed that the models recognisedas the most efficient for this kind of configuration are unable to correctly predict the heat transferlevels. They are, on the other hand, well reproduced by the LES. The generated data allowed for betterunderstanding of the mechanisms leading to the secondary peak. This analysis highlighted theprominent role of the "hot spots", where only some of them can be related to « separated » regions,while the majority are associated with streamwise elongated structures.

Em decorrência ao grande crescimento e evolução dos processos de usinagem e a demanda para adequação ambiental, novos fluidos de corte tem sido aplicados. Uma comprovação de sua eficiência em refrigerar a peça, e a ferramenta melhorando a produtividade do processo ainda é necessária. O presente trabalho propõe o estudo e o desenvolvimento de um sistema para avaliar a eficácia de fluidos de corte em operações de usinagem. Inicia-se com uma abordagem matemática da modelagem do processo de dissipação de calor em operações de usinagem. Em seguida prossegue-se com uma investigação de diferentes maneiras de solução do modelo proposto. Experimentos práticos foram realizados no laboratório de Otimização de Processos de Fabricação - OPF. A partir dos dados obtidos foi realizada uma análise assintótica das equações diferencias parciais que governam o modelo. Finalizando, o modelo selecionado foi aplicado no fresamento do aço AISI 4340 endurecido usinado sob alta velocidade. / Due to the rapid growth and development of machining processes there has been a demand for environmental sustainability and news cutting fluids have been applied. A reliable assessment of their efficiency in cooling the workpiece, tools and improving productivity is still a requirement. The present thesis presents a theoretical study and a proposal of a system to assess the effectiveness of cutting fluids applied to machining operation. It begins using a mathematical approach to model the heat propagation during machining operations. Then, it continues with an investigation into different ways to solve the proposed theorical model. Machining experiments using realistic cutting operations were also conducted at the Laboratory for Optimization of Manufacturing Processes - OPF. From the experimental data, was carried out an asymptotic analysis of partial differential equations, which govern the mathematical model. Finally, the selected model will be applied to a milling operation using High Speed Machining (HSM) technique on hardened steel AISI 4340.

La première partie de cette thèse se concentre sur la modélisation unidimensionnelle de la zone à contre-gradient pour les couches limites convectives. La méthode développée consiste à prendre en compte les moments d'ordre trois dans un modèle à l'ordre 1.5. La seconde partie concerne la modélisation de couches limites neutres. Afin d'initialiser et de valider des simulations LES, une série d'expériences en veine hydraulique a été réalisée. Outre l'estimation des quantités moyennes et turbulentes, les mesures obtenues par vélocimétrie par imagerie de particules ont permis de paramétrer la longueur de mélange.

Cette thèse sinscrit dans une dynamique de recherche qui a vu le jour assez récemment dans le domaine du séchage des boues de station dépuration. Conscientes des problèmes de gestion que va entraîner laugmentation des quantités de boue produites suite à lapplication de la législation européenne, différentes équipes de recherche se sont lancées dans létude du séchage des boues. Considérant que lépandage agricole et la valorisation énergétique demeureront les principales filières délimination pour les boues, le séchage constitue, dans les deux cas, une étape essentielle après la déshydratation mécanique. Lambition de ce travail est de contribuer à améliorer les connaissances dans le domaine du séchage convectif des boues et à mieux appréhender les changements de texture qui surviennent au cours du séchage à laide de la microtomograhie à rayons X. Le chapitre I décrit le contexte général dans lequel se situe le travail, cest-à-dire lépuration des eaux usées et la production de boues qui en résulte. La place du séchage dans les différentes filières de valorisation, compte tenu des exigences de la législation européenne, est présentée. Ensuite, un état des connaissances dans le domaine du séchage des boues ainsi quune présentation des technologies de séchage actuellement mises en oeuvre sont effectués. Ce chapitre met en évidence que létat divisé de la matière se situe au cur du travail et pose les objectifs majeurs de la présente étude. Le chapitre II est consacré à la définition des notions essentielles à létude du séchage. Le concept disotherme de sorption à leau est présenté avant de passer en revue les différents types deau que lon trouve dans les boues. Les modes de transport deau pendant le séchage sont ensuite rappelés. La suite du chapitre se concentre sur la manière dont les données de séchage sont exploitées et reprend, brièvement, les progrès effectués en modélisation de la cinétique. La fin du chapitre décrit le retrait qui constitue un phénomène indissociable du séchage des matériaux déformables dont font partie les boues. Lensemble des dispositifs expérimentaux et des méthodes utilisés au long de ce travail sont décrits dans le chapitre III. Les principaux dispositifs expérimentaux sont la cellule de filtration sous pression, le système dextrusion des échantillons, le microsécheur convectif et le microtomographe à rayons X. Les méthodes décrites concernent la caractérisation des boues, la déshydratation des boues, le filtrage des courbes de séchage, lexploitation des coupes tomographiques par analyse dimages et la manière de rassembler les informations issues du séchage et de la microtomographie. Le chapitre IV est consacré au développement dune procédure de conditionnement et de déshydratation permettant dobtenir une boue déshydratée dont la siccité est la plus élevée et la plus reproductible possible. La mise au point de cette procédure permet deffectuer cette étude sur des boues réelles. Les boues sont prélevées après létape dépaississement dans deux stations dépuration gérées par lAIDE, à Retinne et à Embourg. Les gâteaux de boue obtenus sont ensuite caractérisés : les propriétés rhéologiques sont déterminées ainsi que le taux deau liée par lintermédiaire des isothermes de désorption à leau. Des essais de séchage sur des échantillons extrudés à partir du gâteau de filtration montrent que les conditions opératoires de conditionnement et de déshydratation des boues nont pas dinfluence significative sur la cinétique. La procédure de production déchantillons mise au point (conditionnement-filtration-extrusion) est utilisée dans toute la suite du travail. Tout au long du chapitre V, linfluence de trois variables opératoires (la température, la vitesse superficielle et lhumidité absolue de lair) sur le retrait, la cinétique de séchage, la fissuration et le développement de profils dhumidité au cours du séchage dextrudats de chacune des deux boues est étudiée. Pour ce faire, les données issues du microsécheur et du microtomographe sont exploitées conjointement. Une analyse multi-zones permet de relier différents phénomènes observés se produisant de manière simultanée. Le développement de résistances intragranulaires au transfert, lapparition de gradients dhumidité à la paroi et le phénomène de fissuration sont en effet liés. Le chapitre VI aborde une caractérisation plus détaillée de la texture des échantillons, principalement dans leur état séché. À cet effet, des techniques telles la microscopie électronique à balayage, la mesure des isothermes dadsorption-désorption dazote et la porosimétrie au mercure sont utilisées en plus de la microtomographie. Le travail se termine par une conclusion rassemblant lensemble des résultats et par lénoncé de perspectives qui pourraient constituer une suite intéressante à cette étude. This thesis comes within a recent research dynamic in the field of sludge drying, according to European requirements concerning urban wastewater treatment and landfilling of biodegradable materials. Considering landspreading and utilization for energy purposes as the two major issues to eliminate sludges, drying constitutes, in both cases, an essential step after mechanical dewatering. Despite obvious economic, industrial and environmental interests, rather few studies have been devoted to wastewater sludge drying till lately. This work aims to improve the knowledge in the field of sludge drying and to better apprehend the textural changes that occur during drying by using X-ray microtomography. A first part of the work is dedicated to the development of a method allowing the production of sludge samples with a reproducible dryness, in order to realize the study on real sludges. Sludges are collected after secondary settling and thickening in two domestic wastewater treatment plants near university. Conditioning and mechanical dewatering are realized in the laboratory. Filtration cakes are characterized by different techniques : rheology, sorption isotherms, Rheological measurements indicate that, for a same sludge, elastic and viscous modulus only depends on the cake dryness. Drying experiments performed on individual cylindrical extrudates obtained from the cake show that operating conditions used for conditioning (polyelectrolyte dose) and dewatering (filtration pressure drop) have no significant influence on drying kinetics. The next part of the work shows that X-ray microtomography, despite this technique is still few used in chemical engineering, is a choice tool to follow the textural changes of individual samples submitted to convective drying. Contrary to methods traditionally or newly used (caliper, volume displacement methods, NMR,), X-ray microtomography is a non destructive, accurate and easy to use technique. The analysis of the images obtained by microtomography allows quantifying the shrinkage of the sample, the cracks and the moisture gradients at the sample wall at successive drying levels. The study of the influence of three operating variables (temperature, superficial velocity and absolute humidity of air) on the shrinkage, the development of cracks and moisture gradients is performed in a convective microdryer specially designed in the laboratory. Extragranular heat and mass transfer coefficients, intragranular diffusion coefficient and the water evaporation capacity are estimated from experimental data. A multi-zone analysis proposes to relate the different phenomena observed. Moisture gradients are induced by internal diffusional limitations and cause mechanical stresses. Cracks appear when mechanical stress exceeds the breakage level. Results show clearly that the crack extent depends on the value of the moisture gradients. The last part of the work deals with a detailed textural characterization of the dried samples. Several characterization techniques (scanning electron microscopy, mercury porosimetry, analysis of N2 adsorption-desorption isotherms, X-ray microtomography) show that the two sludges considered in the study present very different final textures. 3D images and binary images of cross sections indicate, among others, that the cracks developed during drying have different shapes and configurations. Morphological analysis of these cracks gives some ideas about the way cracks develop and brings to the fore a relation between texture and drying kinetics. Although the presence of cracks is not of the highest importance for the final quality of dried sludges, the methodology developed in this thesis can be applied to a large variety of other soft materials (food, ceramics,) for which crack formation has to be avoided because it impairs the final quality of the dried material. In the future, a fully coupled thermo-hydro-mechanical model will be implemented in a Finite Element code to quantify the evolution of the stress tensor versus the drying level especially at the onset of cracks formation. Results obtained in this thesis will allow validating the model.