Fluctuating Phenomena and Flow Control of Bubbly Two-Phase Flow Through Sudden Expansion Pipe

Abstract

The fluctuating flow phenomena on a two-phase flow through a vertical sudden expansion pipe system are investigated experimentally and visually. The effect of the volumetric gas flow rate ratio within the range of bubbly flow is investigated. Simple flow control methods are proposed and tested in comparison with the normal expansion case. The first method applies control by mounting a ring shaped obstacle downstream the expansion, and the second by mounting a step-ring just downstream. These two methods are based on a different control concept. The first is based on splitting the vortex region, thus decreasing its intensity, and the second on decreasing the overall generated vortex region length. In single-phase flow, only one dominant frequency is observed. However, when gas is induced, two dominant peaks appear and a tendency of the second peak to shift to lower frequency values when increasing the volumetric gas fraction is observed. When the flow control methods are applied, the fluctuation frequency is not affected, but the fluctuation amplitude decreases. From pressure distribution measurements under several flow conditions, it was confirmed that when the flow control methods are applied, drag reduction is achieved as well.

Investigation of Bubble Size Effect on Vertical Upward Bubbly Two-Phase Pipe Flow Consisted With an Abrupt Expansion

“…A secondary dominant peak has also been seen in other studies (16)- (17) and has been thought to be due only to the volumetric gas flow rate ratio. From the results presented in this study, however, indicate that these kinds of fluctuation phenomena are influenced not just by α v but also by the bubble size and its generation method.…”