<p>A droplet subjected to external aerodynamic disturbances disintegrates into smaller droplets and is known as secondary atomization. Droplet breakup has been studied for low Ohnesorge (<b><i>Oh < </i></b>0.1) numbers and good agreement has been seen amongst researchers. However, when it comes to cases with high the <b><i>Oh</i></b> number, i.e. atomization where the influence of viscosity is significant, very little data is available in the literature and poor agreement is seen amongst researchers. </p> <p> </p> <p>This thesis presents a complete analysis of the modes of deformation and breakup exhibited by a droplet subjected to continuous air flow. New modes of breakup have been introduced and an intermediate case with no droplet fragmentation has been discovered. Further, results are presented for droplet size-velocity distributions. In addition, Digital in-line holography (DIH) was utilized to quantify the size-velocity pdfs using a hybrid algorithm. Finally, particle image velocimetry (PIV) was employed to characterize the air flow in the unique cases where drops exhibited no breakup and cases with multiple bag formation. </p> <p> </p> <p>A droplet subjected to external aerodynamic disturbances disintegrates into smaller droplets and is known as secondary atomization. Secondary breakup finds relevance is almost every industry that utilizes sprays for their application. </p> <p> </p>

Cette thèse s’inscrit dans le cadre du développement de nouveaux matériaux composites multifonctionnels, permettant de remplacer l’aluminium en tant qu’élément constituant le packaging de l’électronique embarquée dans les avions, afin de rendre ces derniers plus légers. L’association d’un polymère mécaniquement résistant avec des nano-charges conductrices est une alternative prometteuse. Cette thèse concerne l’étude du procédé de Dépôt Chimique à partir d’une phase Vapeur (CVD) en lit fluidisé pour déposer des métaux conducteurs, tels que le fer et le cuivre, à la surface de nanotubes de carbone multi-parois (MWCNTs) produits industriellement (Arkema Graphistrength®C100), enchevêtrés en pelotes poreuses de 388 μm de diamètre. Tout d’abord, afin d’augmenter la réactivité de surface des nanotubes, un procédé d’oxydation en lit fluidisé a été étudié à température ambiante, à partir de plusieurs mélanges gazeux à base d’ozone. Les diverses analyses réalisées (MET, spectroscopie IR, XPS,..) montrent que des groupements chimiques de type hydroxyl, acide carboxylique, éther, … sont greffés de façon uniforme sur toute la surface externe des MWCNTs et que leurs parois externes sont aussi gravées de façon modérée et localisée. Au final, il apparait que les défauts créés et les fonctions oxygénées greffées ont permis d’accroitre le nombre de sites de nucléation sur la surface des nanotubes et donc la masse de métal déposé. Le dépôt de fer à partir de ferrocène Fe(C5H5)2 a été étudié à haute température (entre 400 et 650°C), sous différentes ambiances gazeuses (azote, hydrogène, air, vapeur d’eau). Les analyses réalisées (MEB-FEG, DRX, MET, ICP-MS, ...) montrent un dépôt uniforme du bord jusqu’au coeur des pelotes, de nanoparticules à base de carbure de fer Fe3C prisonnières de l’enchevêtrement des nanotubes. La présence d’hydrogène a permis de minimiser la formation parasite de nano-objets (tubes et fibres). Le dépôt de cuivre à partir d’acétylacétonate de cuivre (II) Cu(C5H7O2)2 a été étudié entre 250 et 280°C sous hydrogène. Les caractérisations réalisées indiquent que des nanoparticules de Cu pur ont été déposées sur l’ensemble des parois externes des MWCNTs, du bord au coeur des pelotes. L’ensemble des résultats obtenus démontre que le procédé de CVD en lit fluidisé est capable de déposer de façon uniforme des métaux à la surface de nanotubes de carbone enchevêtrés en pelotes poreuses, pour des conditions opératoires spécifiquement choisies. / This Ph.D project is part of the development of new composite multi-functional materials allowing replacing aluminum in the on-board electronic packaging of airplanes, to make them lighter. The combination of a polymer mechanically resistant with conductive nano-fillers is a promising alternative. The thesis concerns the study of the Fluidized Bed Chemical Vapor Deposition (CVD) process of conductive metals, such as iron and copper, on the surface of industrial multi-walled carbon nanotubes (MWCNTs, Arkema Graphistrength®C100) tangled in porous balls of 388 μm in diameter. First, in order to increase the surface reactivity of nanotubes, an oxidation process in fluidized bed has been studied at room temperature, from several gaseous mixtures containing ozone. The various analyses (TEM, IR spectroscopy, XPS, …) show that hydroxyl, carboxylic acid, ether, … chemical bonds are grafted uniformly on all the outer surface of MWCNTs and that their outer walls are locally and moderately etched. At the end, it appears that the created defects and the oxygen containing bonds have allowed to increase the number of nucleation sites on the nanotubes surface and then the weight of the deposited metal. The iron deposit from ferrocene Fe(C5H5)2 has been studied at high temperature (between 400 and 650°C) under different gaseous atmospheres (nitrogen, hydrogen, air, water vapor). The analyses (FEG SEM, XRD, TEM, ICP-MS, ...) show a uniform deposit from the outer part to the center of the balls, of nanoparticles containing iron carbide Fe3C. The presence of hydrogen has allowed minimizing the parasitic formation of nano-objects (tubes and fibers). The copper deposition from copper (II) acetylacetonate Cu(C5H7O2)2 has been studied at 250-280°C under hydrogen. The characterizations indicate that nanoparticles of pure copper have been deposited on all the MWCNT outer walls, from the outer part to the center of the balls. The whole results obtained prove that the Fluidized Bed CVD process is able to deposit uniformly metals on the outer surface of MWCNTs tangled in porous balls, for specifically chosen operating conditions.

<p>Hydraulic systems have many applications in the construction, transportation, and manufacturing sectors. Recent design trends involve systems with higher working pressures and more compact systems, which are advantageous because of power density increase. However, these trends imply higher forces and larger vibration amplitudes while having lesser mass and damping, leading to higher noise levels. Meanwhile, hydraulic machinery started prospecting new applications with tighter noise regulations, a trend which was also pushed by the electrification tendency in several fields of transportation and agriculture. One method to attain noise mitigation is passive-noise canceling techniques have the advantage of not introducing energy to the system. This approach arranges pressure ripple waves in a destructive pattern by projecting a hydraulic circuit's geometry, configuration, and features.</p> <p> </p> <p>This dissertation aims to predict fluid-borne noise sources and investigate passive noise-canceling solutions for multiple operations conditions targeting to impact many hydraulic systems and a broad range of operating conditions. Primarily a coupled system model strategy that includes a one-dimensional line finite element model is developed. The line model predicts pressure wave generation and propagation. The model features versatility since parameters like line diameter and material can be discretized node by node. Simulations are compared to measured data in a realistic novel hydraulic hybrid transmission for validation. </p> <p> </p> <p>Subsequently, an extensive numerical investigation is performed by setting fixed parameters along the hydraulic lines' length and comparing several isolated geometric properties in simulation. The developed line model is also used to study the influence of line features such as diameter and extent of the conduit. Cost-effective and simple passive solution solutions such as Quincke tubes (parallel lines), expansion chambers, and closed branches are selected and investigated on simulation. Four target pressure ripples are chosen as indicators for summarizing passive line elements behavior. The frequency-domain behavior of the pressure ripple peaks regarding the line's length is identified and isolated in simulation at the 50-5000Hz frequency spectrum. An experiment test rig is designed to implement these solutions and the experiments show three developed passive elements as practical and effective solutions for reducing fluid borne noise sources. The selected designs yielded noise source attenuation over most of the frequency spectrum measured with piezoelectric pressure variation sensors and accelerometers in different positions in the hydraulic circuit. Sound pressure measurements detected reductions over 3dB in the best cases. </p> <p> </p> <p>Also, a passive interference approach based on the principle of secondary source flow ripple cancellation was conceptualized, modeled, and implemented in a tandem axial-piston unit. The strategy consists of setting the phase between the two synchronous units to accomplish destructive interference in targeted unit harmonics. Two indexing strategies are investigated first analytically and then on simulation. One of the indexing strategies was implemented in a pre-existent commercial axial-piston tandem unit. Experiment results confirmed effectiveness for the first and third unit’s harmonics, where reductions over 15dB on pressure ripple were measured.</p> <p> </p> <p>Finally, a fluid-structure interaction based on the poison coupling principle is developed using the method of characteristics. Transfer functions of the pipeline accelerations versus the pressure ripples on lines calculated on simulation and later obtained experimentally to highlight ta critical vibration band from 2000Hz to 3000Hz with high acceleration response.</p> <p> </p><br>

<div>For centuries, fluid flows (hydrodynamics) and electromagnetic phenomena have interested scientists and laypeople alike. The earliest recording of the intersection of these two ideas, electro-hydrodynamics, was reported four centuries ago by William Gilbert who observed that static electricity generated from rubbed amber could ``attract" water. Today electrohydrodynamic phenomena are the underlying mechanisms driving the production of nano-fibers through electro-spinning, printing circuitry, and electrospraying, which John Fenn used in his Nobel prize winning work on electrospray ionization mass spectrometry. In all of these applications, a strong electric field is used to deform a liquid-gas interface (free surface) into a sharp conical tip. Unable to sustain these large interfacial stresses, a thin jet of fluid emerges from the tip of the cone and may subsequently break into a stream of smaller droplets. This tip-streaming phenomenon demands fundamental understanding of three canonical problems in fluid mechanics: electrified cones (Taylor cones), jets, and droplets. </div><div>In this thesis, the electrohydrodynamics of free surface flows are examined through both analytical and numerical treatment of the Cauchy momentum equations augmented with Maxwell's equations. Linear oscillations and stability of (inviscid) conducting charged droplets are examined in the presence of a solid ring shaped constraint. Here the constraint gives rise to an additional mode of oscillation---absent in the analysis of a free (unconstrained) droplet. Interestingly, the amount of charge necessary for instability, the Rayleigh charge limit, is unaltered by the constraint, but the mode of oscillation associated with instability changes. While all of the aforementioned applications involve electrified liquid-gas interfaces, recent experiments reveal a previously unknown type of streaming can occur for droplets suspended in another fluid. In these experiments, the suspending fluid is more conductive and an external electric field drives the intially spherical drop to adopt an oblate shape. Based on the viscosity ratio between the drop and suspending fluid, two different types of instability were observed: (i) if the drop is more viscous, then the drop forms a dimple at its poles and ruptures though its center, a phenomenon that is now referred to as dimpling, and (ii) if the suspending fluid is more viscous, then the drop adopts a lens-like shape and emits a sheet from its equator that subsequently breaks into a stream of rings and then tiny droplets, a phenomenon that is now called equatorial streaming. The physics of these two instabilities are far beyond the applicability of linear theory, requiring careful numerical analysis. Here steady-state governing equations are solved using the Galerkin finite element method (GFEM) to reveal the exact nature of these two instabilities and their dependence on the viscosity ratio. The fate of these drops once they succumb to instability is then analyzed by fully transient simulations.</div><div> Lastly, in a growing number of applications, the working fluid is non-Newtonian, and may even contain suspended solid particles. When non-Newtonian rheology is attributable to the presence of polymer, the dynamics is analyzed by means of a DEVSS-TG/SUPGFEM algorithm that is developed for simulating viscoelastic free surface </div><div>flows. When complex fluid rheology is due to the presence of suspended solid spherical particles, both early-time (linear) and asymptotic dynamics are uncovered by coupling the motion of the particles and Newtonian fluid implicitly in a GFEM fluid-structure interaction (FSI) algorithm. These novel algorithms are used to analyze the pinch-off dynamics of liquid jets and drops.</div>

Considérant l'effet des parois sur la croissance des bulles, nous avons récemment utilisé des plaques ondulées comme cloisons dans des lits minces fluidisés gaz-solide à multi-compartiments. Des analyses approfondies de la dynamique des bulles et du transfert de chaleur paroi-lit dans des lits fluidisés à cloisons planes (FWBFB) ou ondulées (CWBFB) ont été effectuées pour une variété de déclinaisons pariétales et des conditions d'opération couvrant une large gamme d'angles d'ondulation (θ = 120 °, 90 °), de distances moyennes inter-paroi (C), de hauteurs initiales de repos du lit et des rapports de vitesses superficielles du gaz aux vitesses minimales de barbotage, Ug/Umb. Il a été observé que le débit de gaz nécessaire pour amorcer le barbotage était plus faible dans le cas du CWBFB. Par ailleurs, un réseau de zones cou (distance minimale) et hanche (distance maximale) du CWBFB a également favorisé la rupture des bulles, une haute fréquence des bulles, une faible vitesse de montée des bulles et donc tous convergeant vers une meilleure distribution de gaz. Le CWBFB a offert un fonctionnement de fluidisation gaz-solide stable, une faible hauteur de désengagement de transport (HDT) comparé à FWBFB. CWBFB offert significanlty supérieur coefficient de transfert de mur-à-lit chaleur comapred à FWBFB. Des simulations complètes de type mécanique des fluides numériques (CFD) transitoires Euler-Euler 3-D ont également été menées, ce qui a permis de mieux comprendre les effets de parois ondulées sur l'augmentation de la force de traînée sur les particules dans des zones à hautes pressions convergentes-divergentes des parois ondulées. Ceux-ci ont indiqué des changements notables dans le régime de fluidisation en remplaçant les parois planes par des parois ondulées et ont en outre révélé que les zones cou étaient responsables de la création des instabilités comparativement aux zones hanche. La moyenne dans le temps des contours de la fraction volumique simulée de gaz a corroboré avec les résultats expérimentaux que le CWBFB a offert la meilleure distribution de gaz par rapport à FWBFB. Les profils axiaux de la moyenne dans le temps de la fraction volumique solide simulée ont montré que CWBFB réduit de façon nette la HDT. / With the endeavor of approaching an ideal allothermal gasifier, recently our group proposed a reactor concept of allothermal cyclic multi-compartment bubbling fluidized beds for biomass gasification with steam. The concept consisted of multiple intercalated parallelepipedic slim gasification and combustion compartments to enhance unit heat integration and thermal efficiency while preventing contact between flue gas and syngas to generate a N2-free high-quality biosyngas. However, the efficiency of contacting between gas and particles in bubbling fluidized beds is dictated to a large extent by the bubble dynamics which impacts mixing, heat and mass transfers. Literature showed that the decrease in clearance between flat walls for slim fluidization enclosures or in diameter for cylindrical vessels would make fluidized beds very sensitive to wall effects and prone to operate in slug flow regime. Since the occurrence of slugging in multi-compartment slim beds could reduce their thermal and chemical efficiency, the objective of current work was to devise suitable strategies in treating the incipient bubbles to suppress the slugging behavior of bed. By considering the effect of walls on bubble growth, we recently employed corrugated plates as separating walls in slim multi-compartment gas solid fluidized beds. Thorough analyses of bubble dynamics and wall-to-bed heat transfer in flat- (FWBFB) and corrugated- (CWBFB) wall bubbling fluidized beds were performed for a variety of wall declinations and operating conditions covering a range of corrugation angles (θ=120o, 90o), average inter-wall clearances (C), initial rest bed heights (Hi) and ratios of gas superficial velocity to minimum bubbling velocity, Ug/Umb. It was observed that gas flowrate required to achieve the incipient bubbling condition was lower in case of CWBFB. A network of neck (minimum clearance) and hip (maximum clearance) locations in CWBFB also promoted bubbles breakup, higher bubble frequency, lower bubble rise velocity and thus all converging into a better gas distribution. CWBFB offered stable gas-solid fluidization operation and lower transport disengagement height as compared to FWBFB. During the experimental work, digital image analysis technique and fast response heat flux probes were employed to study the effects of operating and geometrical parameters on bubble dynamics and wall-to-bed heat transfer. Two artificial neural network correlations valid both for FWBFB and CWBFB were recommended for the estimation of bubble frequency and size (equivalent diameter). Full 3-D transient Euler-Euler CFD simulations with kinetic theory of granular flow were also carried out which helped shaping an understanding of the effects of corrugated walls on increasing the drag force on particles in the converging-diverging high-pressure zones in corrugated walls. The dynamic fluctuations in the simulated solid phase volume fraction, granular temperature and granular pressure were monitored to determine their standard deviations. These revealed notable shifts in the fluidization regime by replacing flat walls with corrugated walls and further revealed that necks were responsible for inception of instabilities as compared to hips. Time averaged contours of simulated gas volume fraction corroborated with experimental findings that CWBFB offered better gas distribution as compared to FWBFB. Axial profiles of simulated time averaged solid volume fraction and granular temperature showed that CWBFB significantly reduced the transport disengagement height as compared to FWBFB.

Laboratory tests were undertaken to establish the formative mechanism for steps and pools in steep mountain streams. They indicated that the formation of steps and pools is associated with high intensity, low return interval events and the processes of armouring/paving and antidune formation. Lower than formative discharges give the structures their step-pool appearance, and under such discharges they are extremely stable. Step-pool streams may be modelled by a succession of artificial steps or weirs. Wooden steps were placed in a laboratory channel for this purpose, and clear water flow, clear water scour, and sediment transport tests undertaken for a range of discharges and channel slopes. Three distinct flow regimes were observed for the clear water flow and clear water scour tests. They were stable tumbling flow, unstable tumbling flow, and shooting flow. Sediment transport complicated the regimes from low transport rates. Unstable tumbling flow (clear water flow) at a low slope was shown to be caused by the breaking of standing waves at a theoretical maximum of 0.142. For higher slopes (and including clear water scour tests), unstable tumbling flow was shown to be associated with the physical system geometry preventing the submerged hydraulic jump from developing fully. However, unstable tumbling flow was also caused at lower discharges by sediment waves which were a feature of some test runs with sediment transport. Even so, unstable tumbling flow is likely to occur under field conditions only rarely. With clear water scour, the scour dimensions corresponded to the ultimate static limit. That is, no sediment remains suspended by jet action as occurs for the dynamic limit of scour. For clear water flow and clear water scour, resistance to flow may be predicted by logarithmic equations. Resistance to flow with sediment transport correlated strongly with the average scour hole size. A sudden increase in average (and maximum) velocities indicated that with sediment transport, the erosive ability of a step-pool system may increase sharply as pools become drowned by sediment. For a given discharge, increasing the sediment transport rate beyond this drowning led to net deposition, but no real increase in average velocity. With sediment transport, sediment waves and water waves occurred (independently) despite steady inputs of both water and sediment. This behaviour parallels reports of sediment movement as waves in mountain streams. This tendency toward non-uniformity of water and sediment motion suggests that such behaviour may be explicable in terms of recent advances in nonlinear thermodynamics.

Cette thèse s’inscrit dans le cadre du développement d’un combustible nucléaire faiblement enrichi pour les réacteurs de recherche, constitué de particules d’uranium-molybdène mélangées à une matrice d’aluminium. Dans certaines conditions sous irradiations, les particules d’U(Mo) interagissent avec la matrice d’aluminium, provoquant un gonflement rédhibitoire de la plaque combustible. Pour inhiber ce phénomène, une solution consiste à déposer, à la surface des particules d’U(Mo), une fine couche de silicium, pour créer un effet barrière. Cette thèse a concerné l’étude du procédé de dépôt chimique à partir d’une phase vapeur (CVD) en lit fluidisé à partir de silane pour déposer le silicium sur la poudre d’U(Mo), qui a une densité exceptionnelle de 17,5. Pour atteindre cet objectif, deux axes d’études ont été traités au cours de la thèse : l’étude et l’optimisation de la mise en fluidisation d’une poudre aussi dense, puis celles du procédé de dépôt de silicium. Pour le premier axe, une campagne d’essais a été réalisée sur poudre simulante de tungstène dans différentes colonnes de fluidisation en verre et en acier avec des diamètres internes compris entre 2 et 5 cm, à température ambiante et à haute température (650°C), proche de celle des dépôts. Cette campagne a permis d’identifier des phénomènes d’effets de bord au sein du lit fluidisé, pouvant conduire à des dépôts hétérogènes ou à des prises en masse. Des dimensions de colonnes de fluidisation et des conditions opératoires permettant une fluidisation satisfaisante de la poudre ont pu être identifiées, ouvrant la voie à l’étude du dépôt de silicium. Plusieurs campagnes d’essais de dépôt sur poudre simulante, puis sur poudre U(Mo), ont ensuite été menées dans le cadre du second axe d’étude. L’influence de la température du lit, de la fraction molaire d’entrée en silane dilué dans l’argon, et du débit total de fluidisation, a été étudiée pour différents diamètres de réacteur et pour diverses masses de poudre. Des analyses de caractérisation morphologique et structurale (MEB, DRX...) ont révélé un dépôt de silicium uniforme sur toute la poudre et autour de chaque grain, majoritairement cristallisé et dont l’épaisseur atteint les objectifs visés. Des recommandations précises ont ainsi pu être émises pour optimiser les caractéristiques du dépôt de silicium sur la poudre combustible U(Mo) par le procédé de CVD en lit fluidisé. / This thesis is part of the development of low-enriched nuclear fuel, for the Materials Test Reactors (MTRs), constituted of uranium-molybdenum particles mixed with an aluminum matrix. Under certain conditions under irradiations, the U(Mo) particles interact with the aluminum matrix, causing unacceptable swelling of the fuel plate. To inhibit this phenomenon, one solution consists in depositing on the surface of the U(Mo) particles, a thin silicon layer to create a barrier effect. This thesis has concerned the study of the fluidized bed chemical vapor deposition (CVD) process to deposit silicon from silane, on the U(Mo) powder, which has an exceptional density of 17,500 kg/m3. To achieve this goal, two axes were treated during the thesis: the study and the optimization of the fluidization of a so dense powder, and then those of the silicon deposition process. For the first axis, a series of tests was performed on a surrogate tungsten powder in different columns made of glass and made of steel with internal diameters ranging from 2 to 5 cm, at room temperature and at high temperature (650°C) close to that of the deposits. These experiments helped to identify wall effects phenomena within the fluidized bed, which can lead to heterogeneous deposits or particles agglomeration. Some dimensions of the fluidization columns and operating conditions allowing a satisfactory fluidization of the powder were identified, paving the way for the study of silicon deposition. Several campaigns of deposition experiments on the surrogate powder and then on the U(Mo) powder were carried out in the second axis of the study. The influence of the bed temperature, the inlet molar fraction of silane diluted in argon, and the total gas flow of fluidization, was examined for different diameters of reactor and for various masses of powder. Morphological and structural characterization analyses (SEM, XRD…) revealed a uniform silicon deposition on all the powder and around each particle, mostly crystallized and whose thickness reached the objectives. Specific recommendations were proposed to optimize the characteristics of the silicon deposit on the U(Mo) powder by the fluidized bed CVD process.

Ce travail de thèse a pour objet l’étude numérique et expérimentale de la déstabilisation de milieux granulaires immergés par fluidisation. Cette instabilité hydromécanique est un mécanisme précurseur de l’érosion régressive, processus de dégradation au coeur de la problématique de l’érosion interne des ouvrages hydrauliques en terre. La compréhension de ces mécanismes d’érosion nécessite une description rigoureuse du couplage et de l’interaction entre le fluide et les particules de sol. A cette fin, un modèle 2D a été utilisé en couplant deux méthodes particulaires, la méthode des éléments discrets (DEM) pour modéliser le comportement mécanique de la phase solide et la méthode Lattice Boltzmann (LBM) pour la phase fluide. Des expériences servant de validation à cette simulation numérique 2D ont également été réalisées en s’appuyant sur une technique de visualisation interne d’un empilement granulaire combinant l’ajustement d’indice de réfraction des deux phases et la fluorescence induite par plan laser. / The subject of this thesis is the numerical analysis and experimental investigation of the destabilization of submerged granular media caused by fluidization. This hydromechanical instability is one of the mechanisms that may trigger the regressive erosion, which is one of the main degradation phenomena driving the internal erosion of earthen hydraulic constructions. Such erosion mechanisms can only be understood through a rigorous description of the coupling and interaction between the eroding fluid and the soil particles. For this purpose, a 2D model has been used coupling two different numerical techniques, namely the discrete element method (DEM) for modelling the mechanical behaviour of the solid phase and the Lattice Boltzmann method (LBM) for the fluid phase. The experimental validation of this numerical 2D simulation has been carried out using two optical techniques for the internal visualization of a granular sample, namely the adjustment of the refraction index of the two phases and the laser-induced fluorescence.

Microorganisms and drops are ubiquitous in nature: while drops can be found in sneezes, ink-jet printers, oceans etc, microorganisms are present in our stomach, intestine, soil, oceans etc. In most situations they are present in complex conditions: drop spreading on a rigid or soft substrate, drop covered with impurities that act as surfactants, marine microbe approaching a surfactant laden drop in density stratified oceanic waters in the event of an oil spill etc. In this thesis, we extract the physics underlying the influence of two such complicated effects (surfactant redistribution and density-stratification) on the motion of drops and swimming microorganisms when they are in isolation or in the vicinity of each other. This thesis is relevant in understanding the bioremediation of oil spill by marine microbes.<div><br></div><div>We divide this thesis into two themes. In the first theme, we analyze the motion of motile microorganisms near a surfactant-laden interface in homogeneous fluids. We begin by calculating the translational and angular velocities of a swimming microorganism outside a surfactant-laden drop by assuming the surfactant is insoluble, incompressible, and non-diffusing, as such system is relevant in the context of bioremediation of oil spill. We then study the motion of swimming microorganism lying inside a surfactant-laden drop by assuming the surfactant is insoluble, compressible, and has large surface diffusivity. This system is ideal for exploring the nonlinearities associated with the surfactant transport phenomena and is relevant in the context of targeted drug delivery systems wherein one uses synthetic swimmers to transport the drops containing drug. We then analyze the motion of a swimming organism in a liquid film covered with surfactant without making any assumptions about the surfactant and this system is relevant in the case of free-standing films containing swimming organisms as well as in the initial stages of the biofilm formation. In the second theme, we consider a density-stratified background fluid without any surfactants. In this theme, we examine separately a towed drop and a swimming microorganism, and find the drag acting on the drop, drop deformation, and the drift volume induced by the drop as well as the motility of the swimming microorganism.</div>

<div>A microheater and resistance temperature detector (RTD) are designed and fabricated for various applications. First, a hierarchical manifold microchannel heatsink with an integrated microheater and RTDs is demonstrated. Microfluidic cooling within the embedded heat sink improves heat dissipation, with two-phase operation offering the potential for dissipation of very high heat fluxes while maintaining moderate chip temperatures. To enable multi-chip stacking and other heterogeneous packaging approaches, it is important to densely integrate all fluid flow paths into the device. Therefore, the details of heatsink layouts and fabrication processes are introduced. Characterization of two-phase cooling as well as reliability of the microheater/RTDs are discussed. In addition, another application of microheater for mining particle detection using interdigitated capacitive sensor. While current personal monitoring devices are optimized for monitoring microscale particles, a higher resolution technique is required to detect sub-micron and nanoscale particulate matters (PM) due to smaller volume and mass of the particles. The detection capability of the capacitive sensor for sub-micron and nanoparticles are presented, and an incorporated microheater improved stable capacitive sensor reading under air flow and various humidity. </div><div>This paper also introduces the characterization of nanomaterials such as metallic nanowires (NWs) and single layer graphene. First, the copper nanowire (CuNW)/graphene hybrid networks for transparent conductors (TC) is investigated. Though indium tin oxide (ITO) has been widely used, demands for the next generation of TC is increasing due to a limited supply of indium. Thus, the optical and electrical properties of CuNW/graphene hybrid network are compared with other transparent conductive materials including ITO. Secondly, silver nanowire (AgNW) growth technique using electrodeposition is introduced. A vertically aligned branched AgNW arrays is made using a porous anodic alumina template and the optical properties of the structure are discussed.</div><div><br></div>