La microfluidique à goutte a connu un essor remarquable ces dix dernières années. Pourtant, la dynamique de ces objets reste largement inexplorée et incomprise. En effet, une question aussi fondamentale que de prédire la vitesse d'une goutte poussée par une phase porteuse à vitesse imposée, est restée jusqu’à ce jour, sans réponse. Comprendre la dynamique d'une goutte suppose de caractériser les dissipations visqueuses (friction) au sein de la goutte et dans le film de lubrification. Ces dissipations visqueuses sont étroitement liées à la forme et aux propriétés physico-chimiques de l'interface séparant l'intérieur de la goutte de la phase externe. Ce manuscrit présente une caractérisation de la dynamique d’une goutte 2D en cellule de Hele-Shaw en exploitant la double mesure du film de lubrification par microscopie interférentielle et de la vitesse de la goutte. Dans un premier temps, nous étudions expérimentalement la forme adoptée par l'interface en fonction de la viscosité de la goutte et de la concentration en tensioactifs. La comparaison des topographies expérimentales mesurées avec des modèles théoriques déjà existants et un nouveau développé dans ce manuscrit, révèle que l'utilisation d'une approche purement hydrodynamique (sans effet Marangoni) pour déterminer la topographie théorique n'est en mesure de reproduire la topographie expérimentale que lorsque le système ne présente pas de tensioactif ou bien lorsque la viscosité de la goutte est suffisamment importante pour prendre le pas sur d'éventuels effets Marangoni à l'interface. Dans les autres cas, la forment de l'interface évolue en fonction de la contrainte de Marangoni qui peut s'exercer localement ou globalement à l'interface. Dans un deuxième temps, l’établissement d’un modèle théorique pour la vitesse de la goutte, basé sur la modélisation des topographies de films expérimentales mesurées, permet de retrouver quantitativement, et sans paramètre d'ajustement, les vitesses de goutte mesurées expérimentalement. / Droplet microfluidics is a growing field of research. However, the dynamics of these objects remain misunderstood. Indeed, a question as fundamental as predicting the droplet velocity while pushed by an external fluid at a given velocity is still not answered. Understanding the dynamics of a droplet requires to characterize the viscous dissipation mechanisms (friction) within the droplet and in the lubrication film. This dissipation is related to the shape and to the physicochemical properties of the interface separating the inner phase of the droplet from the outer phase. This thesis presents a characterization of the dynamics of 2D droplets in a Hele-Shaw cell, by taking advantage of the double measurement of the lubrication film by interference microscopy and of the droplet velocity. Firstly, we study experimentally the influence of the droplet viscosity and surfactant concentration on the shape of the interface. The comparison between the topographies measured experimentally with the theoretical models already existing and the new one developed in this thesis, reveals that the use of a purely hydrodynamical approach in order to derive the theoretical topography only allows to recover the experimental topography if the system is surfactant free or if the droplet viscosity is high enough to overcome the Marangoni effect at the interface. In the other cases, the shape of the interface depends on the Marangoni stress exerted either locally or globally at the interface of the droplet. In a second part, the derivation of a theoretical model for the droplet velocity, based on the modeling of the lubrication film topographies measured experimentally, allows to recover quantitatively, and without any fitting parameter, the experimental data on droplet velocities.

<p>Engine development is now driven by cost, performance, governmental regulations and customer demands. Several of the requirements have tribological associations. Tribological improvements which consist in lowering friction and improving wear resistance in engines, will play a major role to increase reliability and life cycle.</p><p>The components studied here are parts of the valvetrain mechanism of heavy-duty Diesel engines. The injection cam is one of the most problematic parts of the camshaft, as it is subjected to high pressures from the fuel injector. Lubrication is of significant importance in the prevention of cam failure caused by wear. However, the satisfactory lubrication of the cam and roller contact has proved to be one of the most difficult tribological design challenges to take up.</p><p>For a lubricated contact, the degree of separation between surfaces has a very strong influence on the type and amount of wear. This degree of separation is termed as specific film thickness ; its value provides a measure of the severity of asperities interaction in the lubricated contact. In this report, attention is drawn on the evaluation of oil film thickness in the cam-roller contact, in order to predict regimes of lubrication and thus to identify the probable wear zones of the injection cam. Then, confrontation with experimental results is performed(observation of worn cam surfaces). Future work to achieve is to discover the influence of the different parameters on oil film thickness, by performing a multivariate analysis. The next step will focus on modelling the wear of injection cams, and finally establishing quantified correlations between wear and specific film thickness.</p>

Particulate emissions from diesel engines have been a key issue for diesel engine developers in recent decades. Their work has succeeded in reducing the exhaust particles from the combustion of fuel, which has led to increasing interest in the contribution of particulates from lubrication oil. When discussing oil-related particulate emissions, hydrocarbon particles are customarily referred to. This thesis uses a broader definition, in which oil-related particulate emissions are modelled not only by the hydrocarbons, but also include the ash, carbons, and sulphate oil particulate emissions. The model developed in the project uses input data as oil consumption and oil ash content combined with tuning parameters, such as the oil ash transfer rate (ash emissions divided by oil consumption and oil ash content). Controlled engine tests have been performed to verify assumptions and fill knowledge gaps. The model can be applied to a variety of diesel engines, although the tuning factors might have to be reset. For example, introducing diesel particulate filters would dramatically reduce the oil ash emissions, since oil ash would accumulate in the filter. Oil consumption has played a central role in the present research. The modelling results indicate that special attention should be paid to oil consumption under running conditions with a low in-cylinder temperature, since the oil survival rate is high there. Under low-load and motoring conditions, hydrocarbons proved to be the main contributor to oil-related particulate emissions. At high engine load, oil ash emissions were the largest contributor to oil-related particulate emissions. / QC 20101103

Thin liquid films driven by surface tension gradients are studied in diverse applications, including the spreading of a droplet and fluid flow in the lung. The nonlinear partial differential equations that govern thin films are difficult to solve analytically, and must be approached through numerical simulations. We describe the development of a numerical solver designed to solve a variety of thin film problems in two dimensions. Validation of the solver includes grid refinement studies and comparison to previous results for thin film problems. In addition, we apply the solver to a model of surfactant spreading and make comparisons with theoretical and experimental results.

Wear of the polyethylene (PE) bearing surface and wear particle-induced osteolysis (bone resorption) can lead to failure of modular total knee replacements and make expensive revision surgery necessary. Gamma-in-air sterilization of the PE insert and having a modular tibial component are both risk factors for excessive backside wear that contribute to osteolysis and implant failure. The overall wear (backside and topside) of modular total knee replacements has been subjected to considerable research in order to avoid such implant failure. The investigations reported in the present thesis evaluated both the clinical and in vitro wear performance of modular total knee replacements. The clinical investigations included damage assessment of retrieved PE inserts. A semi-quantitative grading method was developed and used to assess backside surface damage on 52 PE inserts retrieved from contemporary total knee replacement surgeries. Statistical analyses, such as univariate and multiple linear regression analysis, were performed to identify factors that influence backside damage including implant design features and patient characteristics. The damage features on the retrieved tibial PE inserts were also assessed with surface characterization techniques, such as scanning electron microscopy, energy dispersive X-ray analysis, and surface profilometry. To reduce surface damage and thus wear, PE inserts should be either gas-plasma or ethylene-oxide sterilized, used with polished tibial trays and held in place with a partial-peripheral locking mechanism. Synovial fluid samples were aspirated from a total of twenty patients and some basic biochemical analyses were performed. The total protein concentration, protein constituent fractions, the level of osmolality, and trace element concentrations were measured and compared with the same characteristics of four serum lubricants that were frequently used in simulator wear testing to mimic synovial fluid. In vitro investigations were conducted to explore the effects of some major constituents of the serum lubricants on the wear rate using a knee simulator apparatus. Increased protein constituent degradation led to increased wear. Such findings suggested that a protein layer acted as a boundary lubricant to protect the PE surfaces of knee implants. The protein constituent fractions of alpha calf serum (ACS) were similar to those measured for synovial fluid. These ACS lubricants were used in further wear studies in which hyaluronic acid (HA) and phosphate buffer solution (PBS) were successively added. The PBS was used in place of the distilled water to generate a serum lubricant with a clinically relevant level of osmolality. The thermal stability of the ACS lubricants and synovial fluid were measured. The thermal stability of the ACS lubricant that contained HA and PBS was about the same as that of human synovial fluid. The simulator wear rate of PE was significantly influenced by both HA and PBS. In further investigations, sodium azide, which has been used to inhibit microbial growth in simulator wear testing, was shown to be highly ineffective. Microbial contamination was recognized and the organism responsible was identified using standard microbiological methods. The use of an antibiotic-antimycotic mixture as the microbial inhibitor in the ACS + PBS + HA lubricant created a sterile environment and thus very clinically relevant environment for wear testing. The content of this thesis represents a comprehensive data collection on retrieval analysis and lubricant-specific knee simulator wear testing of modular total knee replacements. A more clinically relevant lubricant composition for simulator wear testing was proposed (U.S. patent Serial number 60/899,894; pending since February 9th, 2007) that improved upon the current guideline from the International Standards Organization for knee simulator wear testing. The present thesis should serve as a guide for the surgeon, researcher and the implant manufacturer to evaluate retrieved implant components and to select lubricant additives for wear testing that closely mimics the in vivo wear conditions.

Wind energy accounts for 9.1% of the total energy capacity in Europe. Recent studies have raised critical questions regarding the dependability of current wind turbines. The statistical data reveals that gear box is the most critical component reducing dependability caused by increased failure rate, downtime, and high repair cost (J. Ribrant and L. Bertling, 2007). Gear box failures in wind farms reveal a staggering 19.4 % of downtime of operation (J. Ribrant and L. Bertling, 2007). A significant reduction in the failure rate has been observed in the recent years, but downtime of operation and high repair investment still remains a bottleneck. Wear is the most critical failure mode and a number of theories have been proposed in order to understand the system behavior of wear mechanism. The empirical and historical incident data shows that the lubrication system has the largest share of contribution of gearbox failures and wear rate. On other hand, a number of commercial lubrication system have developed to cope with wear mechanism, however, these systems have different capabilities and characteristics and needed to be assessed in a new life cycle perspective. The purpose of the thesis is to analyze the influence of lubrication system on the current problem of wear in Wind Turbine Gearbox and improve the existing lubrication system architecture. The research methodology adopted is System Engineering approach with architecture assessment tools. The expected result of the thesis is effective and efficient wind turbine gearbox lubrication system architecture and an efficient contractual process between lubrication system provider and purchaser.

Wear of the polyethylene (PE) bearing surface and wear particle-induced osteolysis (bone resorption) can lead to failure of modular total knee replacements and make expensive revision surgery necessary. Gamma-in-air sterilization of the PE insert and having a modular tibial component are both risk factors for excessive backside wear that contribute to osteolysis and implant failure. The overall wear (backside and topside) of modular total knee replacements has been subjected to considerable research in order to avoid such implant failure. The investigations reported in the present thesis evaluated both the clinical and in vitro wear performance of modular total knee replacements. The clinical investigations included damage assessment of retrieved PE inserts. A semi-quantitative grading method was developed and used to assess backside surface damage on 52 PE inserts retrieved from contemporary total knee replacement surgeries. Statistical analyses, such as univariate and multiple linear regression analysis, were performed to identify factors that influence backside damage including implant design features and patient characteristics. The damage features on the retrieved tibial PE inserts were also assessed with surface characterization techniques, such as scanning electron microscopy, energy dispersive X-ray analysis, and surface profilometry. To reduce surface damage and thus wear, PE inserts should be either gas-plasma or ethylene-oxide sterilized, used with polished tibial trays and held in place with a partial-peripheral locking mechanism. Synovial fluid samples were aspirated from a total of twenty patients and some basic biochemical analyses were performed. The total protein concentration, protein constituent fractions, the level of osmolality, and trace element concentrations were measured and compared with the same characteristics of four serum lubricants that were frequently used in simulator wear testing to mimic synovial fluid. In vitro investigations were conducted to explore the effects of some major constituents of the serum lubricants on the wear rate using a knee simulator apparatus. Increased protein constituent degradation led to increased wear. Such findings suggested that a protein layer acted as a boundary lubricant to protect the PE surfaces of knee implants. The protein constituent fractions of alpha calf serum (ACS) were similar to those measured for synovial fluid. These ACS lubricants were used in further wear studies in which hyaluronic acid (HA) and phosphate buffer solution (PBS) were successively added. The PBS was used in place of the distilled water to generate a serum lubricant with a clinically relevant level of osmolality. The thermal stability of the ACS lubricants and synovial fluid were measured. The thermal stability of the ACS lubricant that contained HA and PBS was about the same as that of human synovial fluid. The simulator wear rate of PE was significantly influenced by both HA and PBS. In further investigations, sodium azide, which has been used to inhibit microbial growth in simulator wear testing, was shown to be highly ineffective. Microbial contamination was recognized and the organism responsible was identified using standard microbiological methods. The use of an antibiotic-antimycotic mixture as the microbial inhibitor in the ACS + PBS + HA lubricant created a sterile environment and thus very clinically relevant environment for wear testing. The content of this thesis represents a comprehensive data collection on retrieval analysis and lubricant-specific knee simulator wear testing of modular total knee replacements. A more clinically relevant lubricant composition for simulator wear testing was proposed (U.S. patent Serial number 60/899,894; pending since February 9th, 2007) that improved upon the current guideline from the International Standards Organization for knee simulator wear testing. The present thesis should serve as a guide for the surgeon, researcher and the implant manufacturer to evaluate retrieved implant components and to select lubricant additives for wear testing that closely mimics the in vivo wear conditions.

An elastohydrodynamic analysis of a rotary lip seal is performed numerically, incorporating both the fluid mechanics of the lubricating film and the elastic deformation of the lip, by solving the Reynolds equation with flow factors. Asperities on the lip surface dominate the behavior of the flow field in the lubricating film and the elastic deformation of the lip. Since previous analyses treated those asperities deterministically, they required very large computation times. The present approach is much less computationally intensive because the asperities are treated statistically. Since cavitation and asperity orientation play important roles, these are taken into account in the computation of the flow factors. An asperity distortion analysis is introduced to obtain a more realistic model of the complex variations in the asperity distribution on the surface of the seal. Results of the analysis show how the operating parameters of the seal and the characteristics of the asperities affect such seal characteristics as the thickness of the lubricating film, reverse pumping rate, power dissipation and load carrying capacity.

A theory of the sub-ambient fluid pressure phenomenon observed during the wet sliding of a disk on a polymeric pad is presented. Two-dimensional fluid pressure mapping using membrane pressure sensors reveals a large, asymmetrical sub-ambient pressure region occupying about 70 percent of the disk-pad contact area. At the same time, a small positive pressure region exists near the trailing edge of the disk. This phenomenon is believed to be present during chemical mechanical polishing (CMP) and can contribute to the contact pressure, affecting the material removal rate and removal uniformity. Depending on the load and pad speed, the real contact pressure can be more than 2 times the nominal contact pressure due to the applied load. Tilt measurements of the disk carried out by a capacitive sensing technique indicate that the disk is tilted towards the leading edge and pad center when the pad is rotating. In addition, wafer bow is found to be less than 2 m and wafer tilt with respect to the wafer carrier is 5 to 7 m in the CMP configuration. A two-dimensional mixed-lubrication model based on the Reynolds equation is developed and solved using a finite differencing scheme. The pad is modeled as two layers: a top asperity layer described by the Greenwood and Williamson equation, and the bulk pad as linearly elastic. The orientation of the disk is determined by balancing the fluid and solid forces acting on it and solving using a modified Newtons method. It is found that the tilt of the disk and the pad topography play important roles in the distribution of fluid pressure through affecting the film thickness distribution. For a pad with severe topography, minimum and maximum fluid pressures of -90 kPa and +51 kPa respectively are detected. The model is able to recreate the experimental pressure maps. A material removal rate model based on mechanical abrasion and statistics has also been developed. Comparisons of model predictions and silicon oxide polishing results show agreement.

A droplet may be prevented from wetting a solid surface by the existence of a lubricating film of air, driven by theromcapillary convection, between liquid and solid surfaces. The noncontact nature and the load-carrying capability of a nonwetting droplet lead to potential engineering applications, e.g., low-friction bearings. The present research consists of two thrusts. The first is aimed at quantifying nonwetting-system failures (film and pinning) triggered by application of a mechanical load, gaining insights to failure mechanisms. Experimental results show that film failure occurs over a wide range of droplet volumes when the temperature difference between the droplet and the plate, the driving potential of the free-surface motion, is small. Interferometric observations reveal flow instability just prior to film failure, with the growth of a nonaxisymmetric disturbance on a free surface (m = 1). Pinning failure becomes more prevalent as the temperature difference is increased, stabilizing the film flow. As part of the present investigation, a system was devised, allowing an oscillating free-surface to be reconstructed from a series of interferograms. The dynamic responses of the free surface reveal mode coupling, with harmonics of the input frequency excited through nonlinearity. The second thrust of the research succeeded in levitating and translating a droplet using the mechanism of permanent nonwetting. In this scheme, the droplet is heated by a CO2 laser and is placed above a cooled glass surface in order to drive the lubricating film that supports the weight of the drop. Furthermore, the position of the droplet can be controlled by moving the heating location, which leads to an asymmetry of the flow fields, driving air from the cooler-end of the droplet and propelling it towards the heat source. These demonstrations suggest the techniques potential use as a liquid-delivery scheme in a Lab-On-a-Chip system. Modeling is carried out to estimate propulsive forces on the droplet and to explain oscillatory behavior observed when excessive heating is applied on the drop. The concept to sandwich a droplet between two plates, a necessary configuration for levitating smaller droplets (less than mm-scale), is also discussed.