The purpose of this thesis is to reveal production mechanisms of lubrication films between non-conformal surfaces in situations, when is not possible to designate lubrication regime as fully flooded elastohydrodynamic contact. Under certain conditions of lubrication volume, rolling speeds, temperatures, lubrication properties or loads could lubrication film decrease under values determined by fully flooded formulas. This regime is designated as starvation at it includes risk of increased wear. In this thesis the methodology and the new simulator of starving contact are described. Obtained film thickness results are compared with existing numerical models.

This thesis deals with the experimental study of the formation of the lubricating film used for sintered metal parts impregnated with oil. The thickness of the lubricating film in a line contact is measured by the method of optical interferometry of thin lubricating films. In this thesis, the effects of various operating parameters on the formation of the lubricating film are described. The usage of impregnated lubricant leads to insufficient supply of lubricant to the contact. Individual results are significantly influenced by the degree of flooding of the contact area.

ectroscopic reflectometry is measurement technique that enables the study of the thickness and refractive index of thin layers. This thesis deals with its use for the study of lubrication films within EHD contact and verifies a new approach suggested in recent publications. It is focused on the development of an optical arrangement and mathematical model for the lubrication film thickness measurement within the entire EHD contact. This technique brings the possibility to study the pressure distribution within the contact area through the evaluation of changes in lubricant refractive index.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第19475号 / 理博第4135号 / 新制||理||1595(附属図書館) / 32511 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)講師 市川 正敏, 教授 佐々 真一, 教授 山本 潤 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

This work specifically aims to provide a fundamental framework, with some experimental validation, for understanding droplet emulsion dynamics in a microfluidic channel with an applied electric field. Electrification of fluids can result in several different modes of electrohydrodynamics (EHD). Several studies to date have provided theoretical, experimental, and numerical results for stationary droplet deformations and some flowing droplet configurations, but none have reported a method by which droplets of different diameters can be separated, binned and routed through the use of electric fields. It is therefore the goal of this work to fill that void and report a comprehensive understanding of how the electric field can affect flowing droplet dynamics. This work deals with two primary models used in electrohydrodynamics: the leaky dielectric model and the perfect dielectric model. The perfect dielectric model assumes that fluids with low conductivities do not react to any effects from the small amount of free charge they contain, and can be assumed as dielectrics, or electrical insulators. The leaky dielectric model suggests that even though the free charge is minimal in fluids with low conductivities, it is still is enough to affect droplet deformations. Finite element numerical results of stationary droplet deformations, implemented using the level set method, compare well both qualitatively (prolate/oblate and vortex directions), and quantitatively with results published by other researchers. Errors of less than 7.5% are found when comparing three-dimensional (3D) numerical results of this study to results predicted by the 3D leaky dielectric model, for a stationary high conductivity drop suspended in a slightly lower conductivity suspending medium. Droplet formations in a T-junction with no applied electric field are adequately predicted numerically using the level set finite element technique, as demonstrated by other researchers and verified in this study. For 3D models, droplet size is within 6%, and droplet production frequency is within 2.4% of experimental values found in the microfluidic Tjunction device. In order to reduce computational complexity, a larger scale model was solved first iii to obtain electrical potential distributions localized at the channel walls for the electrode placement configurations. Droplet deceleration and pinning is demonstrated, both experimentally and numerically, by applying steep gradients of electrical potential to the microchannel walls. As droplets flow over these electrical potential “steps,” they are pinned to the channel walls if the resulting electric forces are large enough to overcome the hydrodynamic forces. A balance between four dimensionless force ratios, the electric Euler number (Eue – ratio of inertial to electric forces), Mason number (M a – ratio of viscous to electric forces), electric pressure (P s – ratio of upstream pressure forces to electric forces), and the electric capillary number (Cae – ratio of electric to capillary forces) are used to quantify the magnitudes of each of these forces required to pin a droplet, and is consistent with a cubic dependency on the drop diameter. For larger drop diameters, effects of hydrodynamic forces become more prominent, and for smaller droplets, a greater electric forces is required due to the proximity of the droplet boundary with reference to the electrified channel wall. Droplet deceleration and pinning can be exploited to route droplets into different branches of a microfluidic T-junction. In addition, using steep electrical potential gradients placed strategically along a microchannel, droplets can even be passively binned by size into separate branches of the microfluidic device. These characteristics have been identified and demonstrated in this work.

Electrohydrodynamics in convective boiling heat exchangers has been studied since the early 1990’s and has been shown to result in a large variation in the average performance enhancement of these systems. The behaviour of EHD assisted convective boiling heat exchangers, is still largely unpredictable owing to a number of conflicting parameters which are rarely kept constant in empirical studies, i.e. flow pattern and heat flux. In this thesis, it is hypothesised that by reducing the number of confounding variables in the experimental test conditions, and understanding the behaviour of EHD in convective boiling systems from a flow pattern dependent point of view, this can allow for the development of flow pattern dependent experimental correlations & numerical models to develop a methodology for performance prediction, control strategies and system integration for an EHD assisted convective boiling heat exchange device. A 30 cm long, smooth, concentric, annular test section is used to analyse the effect of EHD on convective boiling performance under constant flow pattern, constant, low heat flux, and negligible free charge conditions. Saturated boiling conditions for flow-rates between 60 kg/m2s and 180 kg/m2s and thermodynamic quality range of 0.25 - 0.55 were tested. Heat transfer enhancement ranged from 0.95 to 2.3 fold and pressure drop penalty varied from 1.4-3 fold over these test conditions. The local EHD behaviour was found to be more consistent along the axial length of the test section compared to empirical data in the literature, which uses much longer test section lengths, where flow pattern can vary. An experimental database of EHD convective boiling data for horizontal annular electrode geometries was compiled to be used for analysis purposes. The performance of the heat exchanger in both free-field and high voltage conditions could be explained by looking at the flow patterns in each case. Electrostatic modelling was used to determine electric field strength distributions and interfacial stress due to the dielectrophoretic and electrostriction forces on the liquid vapour interface, which induce liquid extraction based flow pattern re-distribution in two phase dielectric flows. A fully coupled 2D, adiabatic numerical model for the effect of the electric body force on two phase flow pattern distribution was developed. Charge was neglected in this model. Two different models for the interface migration were used and compared; a moving mesh (MM) interface tracking model and a volume of fluid (VOF) interface tracking mode. Both were verified against published experimental data. For the liquid extraction verification case, the VOF model suffers interface stretching up to 300% resulting in a 42% slower extraction time and underestimated forces. However, it is useful to use the VOF model when simulating complex flow patterns which are subject to topological changes like bubble detachment or droplet coalescence as these cannot be simulated with the moving mesh model. The moving mesh model can be used to determine the error in forces and phase velocities when using the VOF model. A methodology for generating two-phase EHD flow pattern maps was developed by incorporating the electric Froude number into each of the flow pattern transition equations. A semi-analytical model was developed to determine the maximum interfacial stress due to EHD for stratified flows to reduce the requirement of numerical modeling, and thus the flow pattern map generation methodology is fully equation based. Although transition equations developed by multiple researchers were used and compared, it is recommended that the Steiner transitions equations be used for EHD two-phase flow pattern mapping, until more fundamental experimental data can be gathered to modify the semi-empirical transition equations used in more state-of-the-art maps. EHD was found to significantly affect the “stratified-stratified wavy (SSW)” and “stratified wavy – intermittent/annular (SWIA)” transitions for concentric horizontal geometries, with minimal effect on the transition to dryout and no effect on the “intermittent dispersed bubbly (IB)” transition. The EHD flow pattern maps were generated and compared against data from the present study and a database of experimental EHD convective boiling studies. The regions where maximum enhancement were seen in the literature correlate well with those regions predicted by the maps. Performance correlations for the EHD convective boiling heat transfer and pressure drop were developed. They are based on the free-field Kandlikar correlation [1] for two-phase heat transfer and the Chisholm-Laird [2] correlations for two-phase pressure drop, respectively. The EHD flow pattern map is used to determine what the flow pattern for a given applied voltage will be, and flow pattern based enhancement linear multipliers are then used to determine the EHD performance above the free-field case. EHD is a form of active enhancement, i.e. it requires power. Thus, it would be used in systems that require performance control or regulation, in addition to some niche applications like space where it can be used instead of gravity. A method for EHD controller design was established and an EHD control algorithm was designed and implemented on the test section for the flow pattern and applied waveforms that were determined to be optimal to maximize enhancement in this geometry. System identification was performed empirically to determine the transfer function between EHD voltage and heat load to be controlled for. This resulted in a 1st order plus dead-time model to which proportional-integral controller constants were tuned. Two controllers were developed; a PID control system and a Smith model predictive control system and these were compared based on their ability to regulate the output quality of the heat exchanger when subject to dynamic heat loading. Regulation was achieved for a dynamic heat load within ±25% bound from the designed steady state load. These controllers operate on one flow pattern as the test section is 30 cm long. Flow pattern dependent controller design would be required for a full length convective boiling heat exchanger. / Thesis / Doctor of Philosophy (PhD) / Control of boiling heat transfer using electric fields is hard to predict. This thesis presents a set a design guidelines based on how the electric field enhances the flow pattern.

Ce travail présente les résultats de recherches sur le contrôle d'écoulement dans les liquides diélectriques. L'objectif est d'étudier les potentialités du contrôle d'écoulement au moyen d'actionneurs ElectroHydroDynamiques. La 1re partie de cette thèse est notamment consacrée à l'étude bibliographique générale du contrôle d'écoulement et des techniques disponibles pour la mesure de vitesse de fluide. La méthode PIV est choisie pour caractériser l'écoulement de panache chargé. Cependant la présence d'un champ électrique intense dans un liquide diélectrique remet potentiellement en question l'hypothèse selon laquelle les traceurs suivent fidèlement les mouvements du liquide. Des études théorique et expérimentale permettent de préciser les conditions d'un traceur idéal et de choisir le meilleur type d'ensemencement pour l'huile de silicone. La 2nde partie de ce travail est consacrée à l'étude du contrôle d'écoulement sur un profil d'aile NACA0015 à ultra-bas Reynolds (Re < 5000). Une étude bibliographique présente les stratégies de contrôle d'écoulement autour de profil d'aile ainsi que les types d'actionneurs EHD appliqués aux liquides diélectriques. L'écoulement naturel en champ de vitesse moyen puis instationnaire est caractérisé et comparé à l'écoulement contrôlé. Le calcul de la force à partir d'un bilan de quantité de mouvement (Navier-Stokes), permet d'estimer les efforts hydrodynamiques appliqués par le fluide sur le profil immergé. Des polaires de portance et de traînée sont obtenues et permettent de quantifier l'efficacité de l'actionneur EHD. Enfin, les mécanismes de contrôle sont précisés et mettent en lumière les potentiels et les limites de l'actionneur. / This work presents results of research on flow control in a dielectric liquid. The aim is to demonstrate our ability to control flow by means of ElectroHydroDynamic actuation. The first part of this PhD thesis is dedicated to a general overview of flow control and the methods available for measuring fluid velocity. The PIV method is selected to charaterize the flow of a charged plume. However, the presence of a high electric field in the dielectric liquid might bring into question the validity of using PIV, which is based on the fact that tracers accurately follow fluid movement. Theoretical and experimental studies were performed to find the proper conditions for using an ideal tracer that guarantees the accuracy of velocity measurements. This part enables us to choose the best seeding particle in silicone oil. The second part of this work is devoted to the study of flow control on a NACA0015 wing profile at ultra-low Reynolds numbers (Re < 5000). A bibliographic study presents strategies of flow control around wing profiles and in addition deals with different EHD actuators for dielectric liquids. Mean velocity fields and unsteady velocity fields of baseline flow are characterized and compared to controlled flow. The calculation of force based on the conservation of momentum (Navier-Stokes equations) enables us to estimate the hydrodynamic stresses applied by the fluid to the immersed profile. Lift and drag polarities are obtained to quantify the efficiency of the EHD actuator. Finally, the mechanisms of control are clarified and highlight the potential and limits of the EHD actuator for flow control applications.

La température et la pression sont deux paramètres particulièrement importants pour l’optimisation des performances du régime de lubrification élastohydrodynamique (EHL). A ce jour, différentes méthodes expérimentales ont été développées, avec plus ou moins du succès, pour la mesure de ces deux paramètres. Ce travail présente, en continuité de ces approches, des investigations visant à développer une nouvelle technique in situ permettant de mesurer localement ces deux grandeurs dans les contacts élastohydrodynamiques (EHD). Cette technique exploite la sensibilité en photoluminescence (PL) des boîtes quantiques (ou en anglais « quantum dots (QDs)) de CdSe/CdS/ZnS aux variations de température et de pression. A cet égard, des calibrations ont été réalisées afin d’évaluer la sensibilité de ces QDs aux deux paramètres. De plus, la versatilité de ces QDs comme nanosondes a été examinée en testant deux lubrifiants différents : le squalane et un mélange de squalane et de cyclopentane. Des mesures ont été également effectuées sous conditions dynamiques afin d’étudier (i) l’influence de la présence des QDs sur la rhéologie du lubrifiant et (ii) l’influence du taux de cisaillement sur la PL des QDs. Bien que ces différents tests aient prouvé le potentiel des QDs de CdSe/CdS/ZnS, ils ont révélé l’existence d’autres paramètres qui peuvent, tout comme la température et la pression, en modifier la réponse. L’étude a été menée afin d’approfondir la compréhension des mécanismes responsables de tels effets. Plus important encore, une méthodologie a été définie pour minimiser ces effets indésirables, et pour in fine, permettre l’usage de ces QDs en tant que nanosondes fiables. / Temperature and pressure are two relevant parameters for the optimization of lubrication performance in the elastohydrodynamic lubrication (EHL) regime. To date, various experimental methods have been developed to measure these two parameters with more or less success. In a continuation of these efforts, some investigations are presented in the current work in view of developing a new in situ technique allowing for local measurements of these two parameters throughout elastohydrodynamic (EHD) contacts. This technique exploits the photoluminescence (PL) sensitivity of CdSe/CdS/ZnS quantum dots (QDs) to changes in temperature and pressure. In this respect, calibrations have been carried out in order to establish the sensitivity of these QDs to the two parameters. Moreover, the versatility of these QDs for sensing applications have been examined by testing two different lubricants, namely squalane and a mixture of squalane and cyclopentane. Some measurements were also conducted under dynamic conditions, in order to study (i) the influence of the QDs presence on the lubricant rheology and (ii) the influence of shear rate on the PL of QDs. Although these different tests demonstrated the potential of CdSe/CdS/ZnS QDs, they revealed the existence of other parameters that affect, in addition to temperature and pressure, their response. A comprehensive study was thus conducted in order to elucidate the mechanisms behind these findings. More importantly, a methodology was defined in order to minimize these undesired influences and, in fine, enable these QDs to be used as reliable nanosensors.

Les systèmes diphasiques à pompage capillaire sont couramment utilisés pour contrôler la température de l'électronique embarquée. Ces systèmes sont fiables et performants, mais ils présentent certaines limites associées essentiellement à la vaporisation dans le milieu poreux (limite capillaire, limite d'ébullition). Une façon d'étendre leurs performances en termes de longueur de transport de la chaleur et d'intensification des transferts serait de les coupler avec un système mécaniquement actif. Un des moyens pour réaliser cela est d'utiliser les forces électro-hydro-dynamiques (EHD) se développant dans le fluide lorsqu'on applique un champ électrique. Les travaux proposés sont une contribution à la compréhension de l'interaction entre une interface liquide-vapeur et un champ électrique afin de déterminer quels sont les mécanismes qui dans ces conditions contrôlent le pompage et le transfert de chaleur. La première partie se focalise sur l'étude expérimentale d'une interface liquide-vapeur sous un champ électrique avec ou sans flux de chaleur dans une configuration très académique (deux électrodes planes et verticales) tout en étant proche de ce qui se passe dans une cannelure de caloducs par exemple. L'objectif est d'observer, de quantifier et d'analyser les effets (forces, structures, instabilités) se développant sur l'interface. Une analyse a ensuite été menée à partir de modèles 1D et 2D. Nous avons ainsi pu vérifier que parmi l'ensemble des forces s'exerçant sur l'interface, la force diélectrophorétique est celle qui contrôle sa position et sa forme avec ou sans vaporisation. On a montré cependant qu'il existait des effets de couplage avec la conduction électrique dans le liquide pouvant sensiblement agir sur la courbure de l'interface. Enfin, les résultats en vaporisation ont confirmé que le champ électrique, en donnant des moyens de contrôle de la position et de la structure de l'interface de vaporisation, peut être effectivement mis à profit pour une intensification des transferts de chaleur proches d'une paroi chauffée. Dans un dernier volet, les travaux se sont concentrés sur la mise en mouvement d'un liquide diélectrique en mettant à profit le régime de conduction. Une étude expérimentale permettant d'étudier l'influence des différents paramètres (géométrie des électrodes, distance inter électrodes, nombre de modules) a été réalisée dans les fluides HFE-7000 et HFE-7100. Les résultats ont montré une faible reproductibilité des performances de la pompe pour ces fluides suggérant une forte sensibilité des phénomènes à l'état de surface des électrodes et aux régimes parasites d'injection de charge. / Two-phase systems based on the capillary pumping are widely used for electronics cooling. These systems are reliable and efficient, but the maximum heat load is given by the porous medium characteristics (pore size and conductivity) and the fluid properties. The use of an additional source of energy to actively control the heat transport and the heat transfers is a way to extend the performance. Electro-hydrodynamic forces (EHD) could fulfill this objective. This work proposed a contribution to the understanding of the interaction between a liquid-vapor interface and an electric field in order to determine which mechanisms control the pumping and heat transfer. The first part focused on the experimental study of a liquid-vapor interface under an electric field with or without heat flux in a very academic configuration while being close to the operating conditions of the vaporization in a groove of a heat pipe for example. The objective was to observe, quantify and analyze the effects (forces, structures, instabilities) developing on the interface. On top of that, analysis based on 1D and 2D models were made. We found that the dielectrophoretic force mainly controlled the position and the shape of the interface with or without vaporization. However, some effects of coupling with the electrical conduction in the liquid were proved to substantially modify the interface curvature. Finally, the results confirmed that the electric field can effectively be used to the heat transfer enhancement close to a heated wall. In a final section, the work is related to the pumping of a dielectric liquid based on the conduction regime. An experimental study was carried out in HFE-7000 and HFE-7100 fluids to investigate the role of different parameters (electrode geometry, inter-electrode distance, number of modules). For these fluids, the repeatability of results was not satisfactorily suggesting a high sensitivity of the phenomena according to the surface state of the electrodes and parasitic charge injection.

La maladie épizootique hémorragique (EHD) est une arbovirose inscrite sur la liste de l'OIE (organisation mondiale de la santé), qui affecte aussi bien les ruminants sauvages (essentiellement les cervidés) que les ruminants domestiques (les bovins) par la morsure de petits moucherons hématophages, les Culicoïdes (Diptera: Ceratopogonidae). Au début du 21ème siècle, cette maladie a émergé au Maghreb et au Moyen Orient (Turquie, Israël et Jordanie), générant de lourdes pertes économiques pour les éleveurs.L'émergence inattendue de l'EHDV en Tunisie en 2006, simultanément avec l’observation de foyers d'EHDV-6 au Maroc et en Algérie, a suscité une vive inquiétude dans le monde agricole tunisien, qui avait déjà eu à faire face à la survenue d’épizooties d'autres orbivirus : la peste équine africaine en 1960 et de la fièvre catarrhale ovine en 1999 donnant l’exemple qu'une maladie, réputée exotique, puisse émerger et devenir endémique (cas pour la fièvre catarrhale ovine).Ce projet a donc été réalisé pour améliorer les connaissances sur le virus de l’EHDV responsable de l'infection en Tunisie, en 2006, qui entrainait l’apparition de signes cliniques semblables à ceux du BTV.Dans un premier temps, nous avons disposé d'un échantillonnage de différents prélèvements de bovins, Culicoïdes de type imicola collectés en 2006 et conservés à la sérothéque de l'IRVT. Nous y avons donc recherché le génome de l’EHDV par RT-PCR afin de le caractériser et d'isoler le virus. Les résultats ont démontré que l'EHDV-6 était bien le sérotype qui circulait en Tunisie en 2006. Cette partie du travail a fait l'objet d'une publication dans Acta Veterinaria Hungarica.Le deuxième travail exposé s'est intéressé à la recherche d'une présence éventuelle de l’EHDV-6 en Tunisie avant et après l'épidémie de 2006 dans deux espèces animales : les bovins et les dromadaires. Pour cela, nous avons recherché les anticorps ou le génome viral à partir de prélèvements de terrain réalisés de 2000 à 2014 sur des bovins et des dromadaires. A l'issue de cette étude, nous avons détecté une possible circulation à très bas bruit de l'EHDV-6 chez les bovins. Les résultats obtenus sont discutés et ont fait l'objet d'une publication en cours de publication dans le journal Véterinaria Italiana.Concernant l’étude réalisée chez le dromadaire, espèce sensible au BTV, nous voulions évaluer son rôle de réservoir potentiel pour le virus de l’EHD. L’ensemble des résultats sérologiques et virologiques de notre étude nous indique que cette espèce ne semble pas jouer un rôle dans l’épidémiologie de l’EHD.Enfin, parallèlement à ces recherches sur le virus de l’EHD, nous avons mené une enquête sur la présence du virus de la Bluetongue à partir des échantillons de dromadaires et de bovins tunisiens. Les résultats ont été discutés. L'ensemble de ces études contribue à une meilleure connaissance de l'EHDV-6 présent en Tunisie, et permet de rendre compte des espèces potentiellement réservoirs. Certains travaux présentés pourraient être poursuivis pour évaluer le rôle du dromadaire comme réservoir d’Orbivirus et mieux déterminer les espèces de l'inventaire faunique des Culicoïdes impliquées dans la transmission des Orbivirus. / The epizootic hemorrhagic disease (EHD) is an arthropod-borne virus that is on the OIE’s list (World Animal Health Organisation, formerly Office international des épizooties), this disease is mainly transmitted to wild (mainly deer) as well as domestic (primarily cattle) ruminants, by the bites of minute size midges, the culicoides (Diptera: Ceratopogonidae) also known as biting midges. In the beginning of the 21st century, EHD was emerged in Maghreb (North Africa) and in the Middle East (Turkey, Israel, Jordan), causing severe losses for the farmers and ranchers.The unexpected emergency of EHDV in Tunisia in 2006, simultaneously with the observation of EHDV-6 cases in Morocco and Algeria, has aroused great concern in the Tunisian agricultural sector, which had already to face the occurrence of other animal diseases orbivirus: African horse sickness in 1966 and bluetongue in 1999 giving examples of the possibility that deemed exotic disease could emerge and become endemic (case bluetongue).This project was carried out to raise the knowledge on the EHDV virus causing the infection in Tunisia in 2006, which led to the appearance of clinical signs similar to those of BTV.First, we prepared a sampling of various samples of cattle, Culicoides type imicola collected in 2006 and stored at the serum bank of IRVT. So, we searched therefore the genome of the EHDV by RT-PCR in order to characterize and isolate the virus. Results showed that EHDV-6 was actually the serotype circulating in Tunisia in 2006. This part of the job was published in Acta Veterinaria Hungarica.The second working paper concerned the potential presence of the EHDV-6 in Tunisia before and after the epidemic of 2006 in two animal species: cattle and camels. For this we looked for antibodies or viral genome from field samples collected from 2000 to 2014 cattle and camels. Following this study, we detected a possible circulation of EHDV-6 at a very low level of intensity among the cattle. The found results were discussed and made the subject of a publication to be in the newspaper Veterinaria iItaliana.Regarding the study on the dromedary species sensitive to BTV, we wanted to examine its potential role as a reservoir species for EHD virus. All serological and virological results of our study indicate that this species does not seem to play a role in the epidemiology of EHD.Finally, alongside these researches on EHD virus, we have investigated the presence of Bluetongue Virus in Tunisian samples from camels and cattle. The results were discussed.All these studies contribute to a better knowledge of EHDV-6 present in Tunisia and allows taking into account some species that are potentially reservoir. Some presented researches could be pursued to assess the role of the camel as a reservoir for Orbivirus and better identify species of the faunal inventory of Culicoides involved in transmission of orbivirus.