Characteristics of slug flow in a vertical narrow rectangular channel

•Slug flow characteristics in a vertical narrow rectangular duct were investigated.•Three important phenomena different from the classical slug flow were observed.•The Taylor bubble velocities were measured and compared with the correlations.•The Taylor bubble length, the thickness and velocity of liquid film were measured.•The velocity field in liquid slug and the minimum stable liquid slug were measured.

In the view of modeling slug flow, a detailed understanding of its hydrodynamics is of great importance. Non-intrusive flow visualization using a high speed video camera system is applied to study characteristics of slug flow in a vertical narrow rectangular channel (3.25 × 43 mm2). The characteristics of the Taylor bubble, the liquid film and the liquid slug are studied and compared with the models available in literature. It is shown that the slug flow in the present channel is somehow different from the classical slug flow in medium size channels. The gas and liquid flow rates have significant effects on the Taylor bubble length, the thickness and velocity of liquid film at the bottom of Taylor bubble. For the continuous slug flow, the drift velocity is larger than the terminate velocity of a single Taylor bubble in stagnant liquid; the velocity of Taylor bubble could be well predicted by the Nicklin et al. correlation. The minimum stable liquid slug length is in the range from 9 to 17 hydraulic diameters in fully developed turbulent flow. Correlations for calculating the length of Taylor bubble, the thickness and velocity of liquid film at the bottom of Taylor bubble are proposed by fitting the experimental data, respectively.