AN INVESTIGATION INTERFACE STABILITY AND ITS RELATION TO GAS INGESTION IN VISCOSEALS

A fundamental study of the stability of a dynamic gas-liquid interface between rotating cylinders is reported. The study was initiated for the purpose of seeking factors which have a significant role in the process of gas ingestion, or gas entrainment, in viscoseals. The simplified model of smooth, cylindrical surfaces was selected for mathematical tractability and to provide a visual study, using a transparent acrylic housing, without the obscurity of the more complex fluid flow resulting from the presence of the grooved surfaces employed in voscoseals. The visual study was supplemented by employing stroboscopic photography and high-speed motion picture photography. A phenomenological mechanism of gas ingestion was established, theoretically and experimentally. It was found that gas entrainment can result from a gas-liquid interface instability caused by a velocity of a portion of the interface toward the more viscous fluid and/or an acceleration of a portion of the interface toward the more dense fluid. Results of the study indicate that surface tension tends to stabilize the interface and prevent or delay gas ingestion. (Author)