Prediction des fuites gazeuses et des fuites liquides dans les joints d'etancheite micro et nano-poreux

The gasket is the central element of any pressurized mechanical assembly. A bad choice or simply a misuse of a gasket can cause unacceptable leakage or seepage of contaminants that can potentially be dangerous to humans and the environment.;The objective of this research work is to predict gas leaks and liquid leaks through gaskets used in bolted joints. After studying the nature of fluid flow through gaskets considered as porous media, our attention was essentially focused on the prediction of leaks in a gasketed joint with several fluids, based on a known behavior with a reference fluid (helium). An experimental test rig was developed to study the flow regime due to the porosity change of the gasket as a result of mechanical and thermal loads. The scientific contributions presented in this report are divided into three parts. The first part of the study aims to propose an analytical model that predicts the leakage of various gases based on leakage measurements of a reference gas from which the porosity parameters of the gasket are deduced. Based on the analytical model and leakage measurements, the number and size of the leak paths are determined. Boundary conditions necessary to establish a model based on a slip flow regime of the first order theory have been adopted to exploit the analytical model. Tests are also performed using a test rig that accurately reproduces the real leakage behavior of a bolted flange joint assembly that runs under Labview programing.;The studies related to the prediction of leakage through porous gaskets have been limited to the use of gases as a fluid media. In the second part, emphasis will be put towards the prediction of leakage using liquids as a fluid media. The elaborated analytical model is based on the experimental measurements of micro-gas flows and the characterization of the internal structure. The analytical model for leakage predictions is based on the theory of Navier- Stokes equations. The development of a technique to measure leak rates down to 10-6 ml/s in the case of liquids was necessary to achieve this part of the study.;In the last part of this study, the challenge was to extend and validate the applicability of the theoretical model based on a slip flow regime to the prediction of gas leakage through the gaskets at high temperature. The change of fluid viscosity and the porosity parameters due to gasket deformation caused by temperature are some of the parameters to consider in the prediction. The same approach used to identify the internal structure of the gasket developed in the first part of this study was used. Preliminary tests were performed in order to gain a better understanding of the different processes involved in liquid leak measurements including the adaptation of the developed instrument.;The perfect control of the whole chain of instrumentation ensures the quality of the measurement results. Therefore, for each part of the study, a particular testing methodology was adopted in order to achieve successful tests. The experimental approach has allowed on the one hand the validation of the theoretical results and on the other hand the development of a small liquid leak measuring device.;The resulting model has allowed a more detailed analysis to characterize the tightness behavior of a gasket as a function of a differential pressure, temperature and gasket stress, while considering the internal structure of the gasket as a system of straight capillary or a set of annular layers.