Hydrodynamic structure of a bubbly flow in an annular channel: experimental study by means of PIV/PFBI/PTV

Abstract

In the paper, an experimental investigation of the local structure of a bubbly upward flow in an annular channel was carried out by means of a combination of PIV/PFBI/PTV techniques. PIV was applied to measure velocity distributions and turbulent characteristics in the continuous phase, PFBI approach was applied to visualize bubbles in the flow and evaluate their positions and sizes and the simplest PTV method was employed to determine the bubble velocities. The flow was studied at the Reynolds number of 12,500 and different void fractions β = 0, 1 and 2%. The mean air bubble diameter was estimated to be about 0.8 mm for all β. Bubble concentration was observed to increase near the channel walls. Rising velocity of the gas bubbles was measured in various locations across the annulus duct and it was found that it is substantially higher for the bubbles moving in the central part of the channel. An increase of the void fraction resulted in redistribution of the mean velocity in the flow cross-section and intensification of the turbulent fluctuations up to three times for β= 2%.