Hydraulic Investigation of Air in Small Diameter Pipes

摘要

Air trapped in pipes is a serious problem resulting in reduced performance or complete blockage of flow in water systems. The minimum critical velocity needed to clear an air pocket from large diameter pipes has been studied but similar studies for small diameters is lacking. In this study, a series of laboratory tests are performed on 25 and 38 mm diameter pipes with 0°, 5°, 10°, 15°, 20° and 30° downward slopes. The relationship between critical Froude number and slope is determined for each diameter and found to be similar to those for larger diameter pipes. The critical velocity for the 38 mm pipe is found to be larger than that for the 25 mm pipe. The energy equation is used with pressure and flow measurements to estimate the head loss attributed to an air pocket. This value compared closely to the measured vertical height of the air pocket. Lastly, the velocity of an air pocket relative to the mean stream velocity is studied.