Membrane and Desalination Technologies - TCE Moodle Website

674 K. Mohanty and R. Ghosh
3.2. Two-Phase Flow Patterns
Fig. 16.1. Bubble characteristics chart (after Clift et al. (29)).
In gas–liquid flow the two phases can adopt various geometric configurations, these being
known as flow patterns or flow regimes (32). The common flow patterns for a vertical upward
flow are shown in Fig. 16.2. The various regimes are:
Bubbly flow or bubble flow. Here the gas phase is distributed in discrete bubbles within a
liquid continuum.
Slug (or plug) flow. In this type of flow some of the gas bubbles have nearly the same crosssection
as that of the channel and move along in the characteristic bullet-shaped Taylor
bubbles. The Taylor bubbles are separated by liquid slugs which may or may not contain
smaller spherical gas bubbles.
Churn flow. If the velocity of the two-phase flow mixture flowing in a slug flow in a
channel is increased, the flow becomes unstable resulting in “churning” or oscillatory flow.
Annular flow. In this type of flow the liquid flows in the form of a thin film along the
channel walls, while the gas flows along the centre.
4. GAS-SPARGING INSIDE MEMBRANE MODULES
Different types of membrane modules (e.g. tubular, flat sheet, hollow fibre) are used in
ultrafiltration processes. The effect of gas sparging inside these membrane modules depend
primarily on the dimensions of the flow path and the bubbles. In tubular and hollow-fibre