Gas entrainment rate from free surface by vortex

自由表面の渦流れによるガス巻込み流量

小泉 安郎*; 大手 直介*; 上出 英樹 ; 大野 修司  ; 伊藤 啓

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

本研究では、自由表面渦によるガス巻込み流量を実験的に計測した。試験流体は、水, 20cStのシリコンオイル,ケロシンである。流量が小さい場合、くぼみ渦先端から小さな気泡が離脱するガス巻込みが観察され、ガス巻込み流量は小さいが、流量の増加とともにガス巻込み形態が変化し、ガス巻込み流量が急増した。液位が小さい場合、後者のガス巻込み形態のみが観察され、液位の増加とともに前者の形態が観察されるようになった。粘性係数や表面張力といった流体物性がガス巻込み現象に与える影響について調査し、また、ガス巻込み開始点についてKelvin-Helmholtz不安定性によるモデル化の検討を行った。

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.