Étude théorique des spectres optiques des ions Pr3+ dans AlLaO 3

The absorption and fluorescence spectra of praseodymium ion in AlLaO 3 have been interpreted by use of crystal field theory on the fundamental configuration 4f2 of an ion in a C3v site symmetry. The parametric method has been used and the hamiltonian of the system has been completely treated. The complexity of the experimental spectra and the small number of lines which can be assigned a priori with certainty have made necessary a study by successive approximations, which allowed the precise calculation of the levels of the ion as a function of 13 parameters and the assignment of all electronic lines of the system. The means square error obtained on 42 experimental levels is ± 23 cm-1, which indicates that the theoretical precision for the entire configuration is 1 ‰.Les spectres d'absorption et de fluorescence de l'ion praséodyme dans l'aluminate de lanthane ont été interprétés dans l'approximation du champ cristallin, en considérant un ion de configuration fondamentale 4f2 placé dans un site de symétrie C3v . La méthode paramétrique a été utilisée avec traitement complet de l'hamiltonien du système. La complexité des spectres expérimentaux et le petit nombre de raies attribuées a priori avec certitude ont imposé la nécessité d'une étude très progressive qui a permis le calcul précis des niveaux de l'ion en fonction de 13 paramètres et l'attribution de l'ensemble des raies électroniques du spectre. L'écart quadratique moyen obtenu sur 42 niveaux expérimentaux est de ± 23 cm -1, ce qui signifie que la précision théorique sur l'ensemble de la configuration est 1 ‰

Friction and Temperature Reduction in a Mechanical Face Seal by a Surface Texturing: Comparison between TEHD Simulations and Experiments

International audienceMechanical face seals are used to avoid fluid leakage from pressurized zones to the environment in many rotating machineries. The initial research into the lubrication mechanism of these components was initiated several decades ago and numerous studies, both theoretical and experimental, have been carried out on the subject. Surface texturing has been of growing interest in recent years, but only a few studies have been devoted to textured mechanical face seals. Thus, the aim of the present work is to provide experimental, as well as theoretical, results with a comparison of smooth and textured seals. The temperatures of the seals are measured by means of infrared thermography. A 50% reduction in friction for the whole speed range and a reduction in the temperature rise of the sealing interface, attaining 40% at the highest speed values, are reported. Because it is not possible to measure the film thickness experimentally, a numerical thermoelastohydrodynamic model is used, taking into account the seal face deformations. A comparison between the experimental and theoretical temperatures allows the model to be validated. It is shown that, as expected, the film thickness increases with speed as a result of the pressure generated in the dimples. However, after a threshold, it starts to decrease because of the detrimental effect of thermal deformation. These results show that fluid solid coupling must be considered when designing the surface texture for a mechanical seal

Influence of the real dimple shape on the performance of a textured mechanical seal

International audienceSurface texturing the friction faces of a mechanical seal reduces friction as well as leakage and wear, where dimples machined on the surface enhance the formation of a full lubricating film in the seal interface. Numerical simulation is used to determine the optimal surface texturing for the investigated operating conditions of the seal. The geometry of the dimples introduced in the model assume a perfect shape, but machining causes the dimple shapes to be imperfect in terms of the roughness in the dimples, absence of sharp angles, deformed boundaries, and so on. The effect of the real geometry must be considered to confirm that surface texturing will provide the desired results. In the present work, surface texturing is performed using low-temperature plasma coupled with a thermo-chemical surface treatment on stainless steel sealing rings. The real dimple shapes are analysed and considered within the hydrodynamic lubrication model. The influence of different types of defects is studied. It is shown that there is a limit above which surface imperfections dispel the texture's positive effects. Controlling the dimple shapes is important when performing surface texturing