Air Entrainment into Water in an Overflow Piping. Air Entrainment into Annular Water Flow in a Vertical Pipe.

An Experimental investigation was carried out on air entrainment into water flowing downward in a vertical pipe. Local flow rates of air and water in a fluid layer of annular water flow, formed on the pipe wall, were measured precisely by using a small tube probe. The distributions of local flow rates in the radial direction of the pipe indicate that the fluid layer consists of a water layer adjacent to the pipe wall and a water-air layer located inside of the water layer. The water-air layer is formed as a result of air entrainment. The amount of entrained air increases with the increase of the axial distance of the pipe and of the total flow rate of water.