Bubble-type gas entrainment into liquid from free surface by vortex

Ikoma, Yusuke*; Koizumi, Yasuo*; Ito, Kei; Ohshima, Hiroyuki

A gas entrainment rate into liquid by a vortex formed on the free surface was examined experimentally. When the flow velocity was low, a single bubble was periodically torn off from the bottom tip of the vortex and the bubble-type gas entrainment was observed. An increase in the flow velocity resulted in the transition from the bubble-type gas entrainment to the vortex-type gas entrainment and the gas entrainment rate considerably increased with the flow velocity. After the vortex tip penetrated into the outlet pipe, the rotation speed of the vortex decayed. As a result of it, the Kelvin-Helmholtz instability wave length got long and the size of the generated bubble became large. Then, the outlet pipe was filled with the large bubbles and the flow state in the outlet pipe turned to the slug/churn flow and a large amount of gas began to be carried out form the test vessel.