Gas entrainment rate from free surface by vortex

Koizumi, Yasuo*; Ote, Naosuke*; Kamide, Hideki ; Ohno, Shuji  ; Ito, Kei

The gas entrainment rate into liquid by the vortex formed on the free surface was examined experimentally. Water, 20 cSt silicone oil and kerosene were used as test fluid in the experiments. When the liquid flow rate was low, small air bubbles were torn off from the vortex tip. The torn-off bubble flow rate was small. The gas entrainment increased drastically with the increase of the liquid flow rate. When the liquid level height in the vessel was low, only the latter type of the gas entrainment was observed. As the liquid level was increased, the former type was observed first and then the entrainment turned to the latter type. The physical properties of the viscosity and the surface tension had some effect on gas entrainment phenomena such as the gas entrainment rate and the initiation of the gas entrainment. The Kelvin-Helmholtz instability seemed to explain the inception of the bubble type and also the vortex type entrainment.