Two-phase flow pattern identification in a tube bundle based on void fraction and pressure measurements, with emphasis on churn flow

Abstract Two-phase flow are frequently encountered in the industry. In particular, in steam generators of nuclear plants, water is heated so that at the top of the generator an important fraction of water flows as vapor. In this upper part, a rising co-current two phase flow transverse to the tube bundle takes place. Fluids exert significant forces on the tubes in this area which highly depend on the two-phase flow pattern. Thus, as a prerequisite, it is essential to gather information on the flow conditions associated with the different two-phase flow patterns, which can be bubbly, intermittent, or annular. Then we must analyze the potentially dangerous flow patterns. This paper presents an experimental campaign aimed at characterizing those flow patterns for a rising co-current transverse flow in a tube bundle representative of the geometry in a steam generator. A new methodology based on the understanding of key contributions to vertical two-phase flow pattern maps in tube bundles is proposed that leads to a more complete flow pattern map. Finally, the paper focuses on the churn flow, which is the flow pattern for which significant pressure fluctuations occur. For this pattern, important damages could be expected on the tubes of a steam generator. Different kinds of pressure fluctuations are observed at different frequencies depending on the flow rates and the location in the test section.