Air-Water Two-Phase Flows with Applications to Drainage System

This chapter describes the phenomena of air-water two-phase flows with the particular application to the design of a drainage and vent system. The detailed knowledge of air-water interfacial mechanism, the propagation of transient air pressure and the flow resistance in a drainage system is essential in order to prevent the damage of trap seal, the unfavorable acoustic effect and the foul odors ingress into the habitable space through the interconnected drainage and vent network. For a drainage system with the air admittance valve at the exit vent of the vertical stack, the control of the propagation of the air pressure requires the understanding of the transient air-water two-phase flow phenomena in each component of a drainage system. This chapter starts with the background introduction for a drainage and vent system. Research works investigating the air-water two-phase flows through vertical, horizontal and curved tubes as well as through the tube junctions are subsequently reviewed. An illustrative numerical analysis that examines the transient air-water two-phase flow phenomena in a confluent vessel with multiple joints feeding the stratified air-water flows is presented to demonstrate the CFD treatment for resolving the complex transient air-water two-phase flow phenomena in the typical component of a drainage system.