Pressure Loss in a Horizontal Two-Phase Slug Flow

The study of air-water, two-phase flows in hydraulic structures such as pressurized flow tunnels, culverts, sewer pipes, junctions, and similar conduits is of great importance for design purposes. Air can be provided by vortices at water intakes, pumping stations, aerators, steep channels, etc. Under certain conditions, air may also be introduced into pressurized intake systems, which may form large bubbles in portions of the pipe. The bubbles may, in turn, cause an unstable slug flow, or other flow patterns, that leads to sever periodic transient pressure. In this paper, an experimental model (a circular and transparent pipeline, 90 mm in ID and 10 m in length) is used to predict pressure loss in a pipeline or tunnel involving resonance and shock waves introduced by a two-phase air-water slug flow. For this purpose, differential pressure transducers were used to measure pressure loss variations in time along the pipeline at different sections and for different air/water flow rates. The experimental results of pressure loss for different hydraulic and geometric properties indicate that Weber number (We), Froude number (Fr), and air concentration $(C)$ are the most important parameters affecting pressure loss. Finally, relations for forecasting pressure loss in these situations are presented as a function of flow characteristics.