Constitutive laws for interaction of gas bubbles within the liquid flow field – modelling and experimental basis

Constitutive models for the interaction between the gaseous and the liquid phase are needed for application of CFD codes on two-phase flow phenomena as they occur in many scenarios concerning safety analysis of nuclear reactor systems. For the bubble flow and slug flow regime this especially concerns the forces acting on a bubble in the liquid flow field and bubble coalescence and break-up. Vertical pipe flow is an appropriate situation to investigate these effects. This is done experimentally by using new measuring techniques, which allow measurements with a high resolution in space an time. The experimental results show, that besides local effects also the bubble size distribution has an important influence of the development of the flow. A simplified model was developed to test and improve the constitutive laws. To ensure the transferability of the models experiments for vertical pipes with an inner diameter of up to 200 mm are planned, using our new test facility TOPFLOW.