Experimental investigation of the dissipation rate in a chute aerator flow

Abstract

Although chute aerator flows have been experimentally investigated in several studies, there is a paucity of information on the air–water flow properties such as bubble size distribution, dissipation rate, and bubble breakup frequency. Herein, experiments are conducted to investigate the aforementioned microcosmic characteristics for a wide range of Froude numbers (3.3 < F0 < 7.4) at relatively large Reynolds numbers (5 × 105 < R < 10.4 × 105). Observations indicate the development of bubble variation processes in terms of the range of probability for bubble chord lengths along the chute. The dissipation rate increases from the lower surface to the inner flow in the cavity zone and decreases from the bottom to the upper surface in the impact and equilibrium zones. The critical bubble diameter, dc = (σ/2ρ)3/5ε−2/5, exhibits good agreement with the observed change in power–law scaling of the bubble distribution and exceeds the corresponding mean bubble size. With respect to bubbles exceeding the critical bubble diameter that are subject to fragmentation, they exhibit –5/3 power–law scaling with respect to the diameter, and the breakup frequency increases and reaches a maximum when dab = 1.6dc. However, for bubbles with sizes exceeding 1.6dc, the frequency monotonically decreases relative to the bubble diameter.