Study on Gas Entrainment Rate Into Liquid From Free Surface by Vortex

The gas entrainment rate into liquid by the vortex formed on the free surface was examined experimentally. Water flowed into a cylindrical vessel from a wall tangentially. Swirl flow was formed in the vessel, and then water left from the bottom outlet of the vessel. The flow state of the entrainment was visually observed by using a high speed video camera. The gas entrainment rate into water was measured. A stable vortex was formed in the test vessel. Whether the bottom of the vortex reached the bottom outlet of the vessel was dependent on the downward velocity of water; the velocity at the bottom outlet. Before the vortex tip reached the bottom of the vessel, bubbles were periodically torn off from the bottom tip of the vortex and the bubble-type gas entrainment was observed. After the bottom of the vortex reached the bottom of the vessel, the gas entrainment turned to the vortex-type gas entrainment. When the gas entrainment turned to the vortex-type gas entrainment, the flow state in the outlet pipe changed from the bubbly flow to the churn flow. After the gas entrainment varied from the bubble-type to the vortex-type, the gas entrainment rate increased drastically. The downward water velocities at the initiation of the bubble-type gas entrainment and at the transition from the bubble-type to the vortex-type gas entrainment became fast as the liquid level in the vessel became deep. The Kelvin-Helmholtz instability did not explain the bubble torn-off from the vortex tip.