Gas-liquid Flow in a Rectangular Partially Aerated Bubble Column: Combined Effect of Aspect Ratio and Superficial Gas Velocity

Bubble columns are multiphase equipments used to bring into contact gas and liquid phases. Gas, that constitutes the dispersed phase, is distributed at the bottom of the column and rises as bubbles through the liquid that constitutes the continuous phase. They are frequently used in the industry although the partial knowledge of the fluid dynamics of the gas-liquid flow have hindered a complete control over their design and scale-up. The calculation of the optimum conditions for mass and heat transfer in bubble columns is intimately related to precise identification of the existing flow regimes. Depending on the particular values of the superficial gas velocity (UG), the properties of the phases, the gas distributor design and the column dimensions two different flow regimes can be observed [1-6]: the dispersed bubble and coalesced bubble flow regimes. The coalesced bubble flow regime can be subdivided into the vortical and turbulent flow regimes. In this study, a partially aerated plate is used and the combined effect of UG and the liquid height/width of the column ratio (aspect ratio (H/W)) on the resulting flow regimes is studied. The use of partially aerated plates can generate bubble plumes [4, 5, 7-11] that show an oscillatory movement and create ascending and descending liquid circulation structures. The resulting unsteady flow patterns differ considerably from the time-averaged flow regimes [4, 12]. In this work, the quantitative analysis of the flow regimes is based on the measurements of wall pressure fluctuations while qualitative description of the type of flow is obtained by image analysis. The analysis of existing time-averaged flow patterns for given experimental conditions is based on the representation of the global gas hold-up (εG) versus UG [13] while the study of non-stationary structures is based on the spectral analysis, a method that provides information of the oscillation frequency of the bubble plume [7] as well as of the different physical phenomena taking place in the bubble column [2, 7, 14-17] through the resulting spectra and the mean and characteristic frequencies.