A half-zone experimental set-up was used to study the effects of various liquid bridge and helium flow parameters on the onset of thermocapillary convection in silicone oil liquid bridges. Experiments confirmed that helium flow has a stabilizing effect, with the effect increasing with helium velocity. Furthermore, helium flow in the same direction as surface flow due to Marangoni convection had a more stabilizing effect than countercurrent flow. It was established that increasing helium temperature has a mixed effect, producing a less stable bridge at low helium flow rates, but a more stable flow pattern at higher helium flow rates. Finally, it was confirmed that decreasing the cold disk temperature results in a decrease in critical temperature difference.

A half-zone experimental set-up was used to study the effects of various liquid bridge and helium flow parameters on the onset of thermocapillary convection in silicone oil liquid bridges. Experiments confirmed that helium flow has a stabilizing effect, with the effect increasing with helium velocity. Furthermore, helium flow in the same direction as surface flow due to Marangoni convection had a more stabilizing effect than countercurrent flow. It was established that increasing helium temperature has a mixed effect, producing a less stable bridge at low helium flow rates, but a more stable flow pattern at higher helium flow rates. Finally, it was confirmed that decreasing the cold disk temperature results in a decrease in critical temperature difference.

Fluid dispensing is a method by which fluid materials are delivered to the targeted boards in a controlled manner and has been extensively applied in various packaging processes in the electronics assembly industry. In these processes, the flow rate of the fluid dispensed and/or the fluid amount transferred onto a board are two important performance indexes. Due to the involvement of the compressibility and non-Newtonian behaviour of the fluid being dispensed, modeling the fluid dispensing process has proven to be a challenging task. This thesis presents a study on the modeling of the positive displacement dispensing process, in which the linear displacement of a piston is used to dispense fluid. Also, this thesis presents an evaluation of different designs of the fluid dispensing system based on the axiomatic design principles. <p>At first, the characterization of the flow behaviour of fluids used in the electronic packaging industry is addressed. Based on the previous experiments conducted in the authors lab, a 3-parameter Carreau model for the fluid Hysol FP4451 is derived for use in the present study. Then, taking into account fluid compressibility and flow behaviour, a model is developed to represent the dynamics of the flow rate of the fluid dispensed. The resulting model suggests that the dynamics of the flow rate in the positive displacement dispensing process is equivalent to that of a second order system. Based on the model developed, the influences of the fluid compressibility and the process parameters such as the dispensing time and needle temperature are investigated by simulations. <p>In the positive dispensing process, it is noticed that the fluid amount dispensed out of needle is different from the fluid amount finally transferred to the board, if the fluid amount dispensed is very small. This difference is considered one major problem affecting dispensing performance. In order to determine the fluid amount transferred to the board, a 3-step method is developed in the present study, based on existing theories of liquid bridges and Laplaces equation. Simulations are conducted based on the developed method to study the influence of surface tension and initial fluid amount on the final fluid amount transferred onto the board. <p> Finally, this thesis presents a new approach to evaluate and compare different designs of the fluid dispensing system, namely air-pressure, rotary-crew, and positive- displacement. In this approach, the axiomatic design principles, i.e., the Independence Axiom and the Information Axiom, are employed. This approach can be used not only to evaluate existing dispensing systems, but also to design new dispensing systems.

Fluid dispensing is a method by which fluid materials are delivered to the targeted boards in a controlled manner and has been extensively applied in various packaging processes in the electronics assembly industry. In these processes, the flow rate of the fluid dispensed and/or the fluid amount transferred onto a board are two important performance indexes. Due to the involvement of the compressibility and non-Newtonian behaviour of the fluid being dispensed, modeling the fluid dispensing process has proven to be a challenging task. This thesis presents a study on the modeling of the positive displacement dispensing process, in which the linear displacement of a piston is used to dispense fluid. Also, this thesis presents an evaluation of different designs of the fluid dispensing system based on the axiomatic design principles. <p>At first, the characterization of the flow behaviour of fluids used in the electronic packaging industry is addressed. Based on the previous experiments conducted in the authors lab, a 3-parameter Carreau model for the fluid Hysol FP4451 is derived for use in the present study. Then, taking into account fluid compressibility and flow behaviour, a model is developed to represent the dynamics of the flow rate of the fluid dispensed. The resulting model suggests that the dynamics of the flow rate in the positive displacement dispensing process is equivalent to that of a second order system. Based on the model developed, the influences of the fluid compressibility and the process parameters such as the dispensing time and needle temperature are investigated by simulations. <p>In the positive dispensing process, it is noticed that the fluid amount dispensed out of needle is different from the fluid amount finally transferred to the board, if the fluid amount dispensed is very small. This difference is considered one major problem affecting dispensing performance. In order to determine the fluid amount transferred to the board, a 3-step method is developed in the present study, based on existing theories of liquid bridges and Laplaces equation. Simulations are conducted based on the developed method to study the influence of surface tension and initial fluid amount on the final fluid amount transferred onto the board. <p> Finally, this thesis presents a new approach to evaluate and compare different designs of the fluid dispensing system, namely air-pressure, rotary-crew, and positive- displacement. In this approach, the axiomatic design principles, i.e., the Independence Axiom and the Information Axiom, are employed. This approach can be used not only to evaluate existing dispensing systems, but also to design new dispensing systems.

The trend towards miniaturization requires to handle even smaller micro-components: they must be picked, placed with high accuracy, and then released. This highly challenging process should take into account two aspects: the yield of successful placements and the minimized risk of damaging the manipulated micrometer-sized objects due to contact forces. Despite the advantages of the latest gripping technologies, including low complexity, high accuracy, and high reliability, the component is subjected to high contact forces that could damage it. As a consequence, there is a need of developing new and innovative ways to manipulate micro-sized components with respect to the requirements mentioned above. Gripping based on capillary bridges is a promising technique to handle components at the micrometric scale. This technique offers many advantages: flexibility and reliability, self-centering effect, the capability of grasping small and delicate components in a wide range of shapes and materials thanks to the “bumper” effect of the mediated liquid bridge. Nevertheless, the liquid residue on the component after breaking up the bridge is undesirable. As a consequence, there is a need to design a capillary gripping system that can retain all the liquid after the breakup of the bridge. Understanding the formation, the stretching, and the liquid distribution after the breakup of the liquid bridge is mandatory. In this thesis and in the first place, we studied the rupture of a liquid bridge confined between different geometries of the gripper and the substrate: plane/plane, cone/plane, and cavity/plane. We developed, based on the resolution of the Young-Laplace equation, an operational quasi-static criterion to predict the rupture gap of the bridge. We also investigated the effect of the geometry on the liquid distribution after the breakup. Optimal geometries are found to retain up to 90$%$ of the liquid after the breakup of the bridge. In the second place, we investigated the secretion dispensing in green dock beetles ( extit{Gastrophysa viridula}). Their ability to walk upside-down on any kind of surfaces rely on mediated secretion between their hairy pad and the surface they walk on. We studied the mechanism of the secretion dispensing from the source where it is produced to the contact zone. Experimental setups have been designed, with advancing 3D printing and micro-fabrication techniques. Models have been developed, discussed, and compared to experimental data. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

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The vocal folds are a complex self-oscillating biological system. In the current research, an equation was developed to model viscous adhesion forces that occur when the collision of the vocal folds results in the formation of a liquid bridge. The adhesion equation was validated using experimental data, and simplified to a one-dimensional approximation with an included correction factor that adjusted the predicted pressure in situations where the one-dimensional approximation was invalid. A non-oscillating vocal fold model with a modeled liquid bridge was used to study stress resulting from viscous adhesion. The vertical normal stress magnitude ranged from about 80 to 1700 Pa. This was shown to be of the same order of magnitude as the stress due to collision of the vocal folds. Also the stress resulted in large normal strains that occurred at small distances below the surface of the vocal folds consistent with lesion development. Therefore, it was determined that the viscous adhesion may be a contributor to damage of the vocal folds that leads to the development of benign lesions, such as vocal nodules. This conclusion was further validated by adding the adhesion equation in a self-oscillating vocal fold model. The influence of adhesion on the dynamics of the model was significant. The frequency of vibration was reduced by nearly 2.5% for the case of adhesion with a mucus viscosity of 0.01 Pa-s. Also adhesion induced positive tensile stress that resulted in normal strain distributions similar to those seen in the non-oscillating cases. These results also indicated that liquid mediated viscous adhesion may be a contributor to the development of benign lesions (nodules). However, further research is needed to validate these conclusions.

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Dernière étape avant l'atomisation d'un volume de liquide, les ligaments sont présents dans de nombreuses applications industrielles, de même que dans le monde qui nous entoure ; leur dynamique demeure mal comprise. L'étirement, qui permet de leur donner naissance, affecte leur évolution et la manière dont ils se fragmentent (ou non). Pour quantifier l'effet de ce dernier, nous avons choisi d'étudier des configurations modèles dans lesquelles plusieurs paramètres peuvent être bien contrôlés. Une configuration de type pont liquide permet notamment de contrôler l'étirement via le déplacement de l'un des supports solides (mors). Lorsque l'étirement imposé est modéré, il est possible de prévoir analytiquement la déviation entre la forme dynamique et la forme d'équilibre correspondante, quelle que soit la loi de déplacement du mors. Cette prédiction montre en particulier qu'un pont liquide étiré peut s'épaissir appréciablement en son centre, suggérant un retardement de la rupture. Elle montre également que l'étirement axial est réparti de manière très inhomogène. Lorsque l'étirement est suffisamment vigoureux, les résultats expérimentaux montrent que le détachement capillaire du ligament peut être significativement hâté. Le temps de rupture est relié à la masse emportée par le mors en mouvement et dépend du protocole d'étirement. Les résultats suggèrent également la possibilité d'obtenir des ligaments démesurément longs et fins sans l'intervention d'effets visqueux. / Liquid ligaments represent the last step before atomization of a liquid volume, and are encountered in a variety of industrial applications, as well as the world around us; yet, there is much to learn about their dynamics and breakup. Stretching is an essential ingredient of ligaments formation, and affect their subsequent dynamics as well as the way they break (or not). In order to quantify its action, we choose model configurations where parameters can be controlled. Liquid bridges, in particular, provide a way to impose stretching by moving one of the solid rod supporting the bridge. When stretching is not too strong, it is possible to predict analytically the shift between the dynamical shape of the bridge and the corresponding static shape, for any given rod displacement. Particularly, this prediction show that the central section of a stretched liquid bridge tend to be thicker, which could delay breakup. It also show that the axial elongation rate is far from being uniform. When stretching is vigorous, experimental results show that the ligament initial breakup can be considerably sped up. Breakup time shows to be linked to the mass taken away by the moving rod and depend on stretching protocol. Finally, results suggest that it is possible to generate infinitely long ligaments without the mediation of viscous effects.