The Role of Weir Types in Entrainment of Air Bubbles

Abstract: The dominant aeration mechanism in free overfall jet from a weir is that of air bubbles being carried into the biphasic zone when the jet plunges into the receiving pool. The degree of aeration will depend upon the amount of air entrained. This paper investigates effect of the free overfall jets from sharp-crested weirs, broad-crested weirs, labyrinth weirs, and venturi weirs on the air entrainment. Results pointed that the air entrainment of the weirs changed depending on weir types. At low drop heights, triangular broad-crested weir had the higher values of the air entrainment rate than the other weir types tested and this advantage becomes more pronounced as the angle in triangular broad-crested weir was decreased. However, at high drop heights, the venturi weir was observed to have the greater values of air entrainment rate than the other weir types tested. The air entrainment rate increased as the throat width of the venturi weir was decreased