Étude expérimentale des écoulements eau-air à haut taux de vide dans les faisceaux de tubes

摘要

Two-phase flows are very frequent in the industry, especially in the petroleum industry and in the nuclear industry. In steam generators of nuclear plants, water is heated so that at the top of the generator an important fraction of the water flows as gas. In this upper part a two phase flow transverse to the tube bundle takes place.;Fluids exert significant forces on the tubes in this area, and that is why we want to study this specific geometry. For this we must gather information on the flow conditions associated to the different two-phase flow patterns, which can be bubbly, intermittent, or annular. This requires that we characterize first those flow patterns. Many studies have been done to determine the nature of the flows, but most of them were carried out for internal flows in cylindrical tubes and not for transverse external flows typical of flow inside a steam generator.;We undertook an experimental campaign for a transverse flow in a tube bundle representative of the flow in a steam generator. We were particularly interested with flow patterns that contain high gas fraction. This kind of flow are particularly not well known and they are potentially responsible for damages. Using pressure and void fraction measurements, we characterized the flow patterns and their corresponding flow rates. We obtained a more complete flow pattern map than those presented in the literature, thanks to a new methodology.;We then focused on the flow pattern for which significant pressure fluctuations are noticeable. For this pattern, important damages are expected on the tubes of the steam generator. We showed that two types of pressure fluctuations occur at different frequencies. We characterized dependencies of these fluctuations in term of fluid velocities, location in the experimental setup, mean pressure, as well the geometry of the exit.;Thanks to a new methodology, this study brought a new understanding on causes of destructive forces in the steam generators of nuclear power plants.