The influence of surface tension on air-water flows, J. Hydraulic Engineering

I. W. M. Pothof; A. D. Schuit; and F. H. L. R. Clemens (2013).The influence of surface tension on air-water flows, J. Hydraulic Engineering J. Hydraul. Eng., 139(1), 44–50.
Stricter environmental regulations have led to new wastewater treatment plants and a centralization of existing wastewater treatment plants. Therefore, pressurized wastewater mains have become an indispensable link between the collection systems and the treatment plants. In urban areas in particular, these pipelines include many inverted siphons to cross other infrastructure, like railways, motorways, other pipelines, and buildings. Accumulation of air in downward sloping sections of these wastewater mains reduces the transport capacity significantly. A dominant air transport mechanism is the air-entraining hydraulic jump at the tail of an accumulated air pocket. The novelty of this paper is a systematic investigation of the influence of surface tension on the air discharge in downward sloping pipe sections. Experiments have been performed with clean water, surfactant-added water, and wastewater. The experiments with surfactant-added water confirm that the air discharge increases significantly at lower surface tension. However, the lower surface tension of wastewater does not enhance the air transport in comparison with the air transport in clean water.