Bubbly flow segregation inside a U-bend pipe: Experimentation and numerical simulation

In this paper experimental and numerical data on the phase distribution of gas–liquid bubbly flows taking place inside a pipe of square cross-section are shown. The focus is on the phase segregation that happens when the mixture goes through a U-bend curve, wherein the bubbly flow is under the action of weak centrifugal fields, from 1g to 7g. A set-up was connected to run these air–water flows at nearly atmospheric pressure: a rather homogeneous upward bubbly flow was generated at the basis of a vertical pipe; at the end of this section a U-turn 180° curve received the uprising bubbly flow turning it into a vertical downward counter-current flow. Along the U-bend curve, the gas bubbles were displaced to the inner curve section caused by the action of centrifugal fields. Phenomena like the wall peaking, happening in vertical upward flows, the core-peaking, taking place in downward flows, and the action of the centrifugal field, setting the phase distribution along the curve, could be measured and modeled. For such, the time-averaged Two-Fluid Model was used.