Investigation on the Characteristic of Bubbles in Horizontal Channel Flow by Fiber Optic Sensor

Friction drag and characteristic of bubbles in horizontal water channel are investigated at bulk liquid velocity U_m = 1 ∼ 5 m/s (Reynolds number Re_m = 16,000 ∼ 120,000 (based on the channel height)) and mean void fraction α = 0.5, 1, 2 %. Firstly, shear stress sensor is applied to investigate the relation between friction drag with bubbles and bulk liquid velocity. Friction drag in the bubbly flow is larger than it in the single-phase flow at U_m = 1 ∼ 2 m/s. It in the bubbly flow, however, decreases with the mean liquid velocity. Furthermore, it in bubbly flow is smaller than it in the single-phase flow at U_m ≥ 3 m/s. Secondly, fiber optic sensor is applied to investigate the void fraction distribution, bubble diameter distribution and streamwise velocity of bubbles. The peak value of the void fraction decreases with increasing of the bulk liquid velocity at U_m = 2 ∼ 5 m/s. Bubbles exist in only y/δ = 0 ∼ 0.5 at U_m = 1, 2 m/s. The mean bubble velocity increases with the bulk liquid velocity. The mean Sauter diameter decreases with increasing of the bulk liquid velocity. It appears that the high void ratio near the wall causes the increasing of drag and friction drag decreases when bubbles exist in whole of upper half of channel.