Influence of Aspect Ratio and Superficial Gas Velocity on the Evolution of Unsteady Flow Structures and Flow Transitions in a Rectangular Two-Dimensional Bubble Column

In this paper, the flow regimes developed in a centrally aerated two-dimensional (2D) bubble column are studied by means of visual observations and the measurement of wall pressure fluctuations. The combined effect of the aspect ratio ( H / W ) and superficial gas velocity ( U G ) on the hydrodynamics of the bubble column is investigated. Moreover, the time-averaged and time-dependent flow behavior are analyzed together. The results reveal the importance of H / W and U G on the developed flow regimes and the significance of the steadiness or unsteadiness of the flow on the resulting time-averaged flow regimes. A detailed description of the flow patterns based on H / W and U G is presented. As U G is increased, at H / W = 1.25, two pseudo-steady-state flow regimes (characterized by one or two circulation cells) are observed. At H / W = 2.25, only unsteady bubble plumes of decreasing oscillation period are obtained. At H / W = 1.50, 1.75, and 2.00, unsteady flow structures occur, at increasing values of U G .