Flow patterns and pressure drop in vertical upward air-water two-phase flow

The purpose of the present experimental study is to investigate flow patterns of upward air-water two-phase flow corresponding to pressure drop. The experiments were conducted in an air-water two-phase system, which consisted of a 25 mm diameter, 6 m long perspex tube. The flow regimes were visually observed, if necessary, by means of high-speed camera. To clarify effects of different flow conditions on the pressure gradient, real-time measurements of pressure fluctuation were conducted by the computer acquisition system. In the paper, we first define the flow patterns of each flow. Referring to the definition accepted commonly, in upward cocurrent flow, two-phase flow in the present study is mainly classified into five patterns: (1) bubble flow, (2) slug flow, (3) churn flow, (4) annular flow, (5) wispy-annular flow. The flow patterns observed are described in detail. Next, the diagram is drawn to show the variation of pressure gradient with gas superficial velocity for different liquid volumetric fluxes, and considering the characteristics of pressure gradient the flow transition regions are plotted out. Finally, we propose the flow pattern map based on experimental data. It is found that the flow pattern transitions are closely related to the pressure drop, and that time-average pressure gradient with gas volumetric fluxes can be used to identify the flow patterns. (authors)