A Note on Liquid Velocities Arising during Decompression Degassing in Hypergravity

Liquid degassing takes place in several space processes (cooling and lubrication of hardware, combustion of liquid propellants etc.) during launching and re-orbiting of rockets and workstations. The present work studies the effect of hypergravity acceleration on the two phase flow that is developed during the degassing of a liquid jet. Liquid is initially saturated with dissolved gas at 200 kPa and 400 kPa and is then injected at the bottom of a liquid column having its top open to atmospheric pressure. Due to the sudden decompression inside the column, the liquid jet becomes supersaturated with dissolved gas, thus triggering the formation of degassing bubbles within its volume. The local liquid flow pattern inside the column is tracked by recording the motion of bubbles. Experiments are conducted at 1 g, 2 g and 8 g accelerations, using the Large Diameter Centrifuge (LDC) facility of the Technology Center (ESTEC) of the European Space Agency (ESA). The liquid flow behavior registered at varying hypergavity conditions is quite interesting. For an injection pressure of 200 kPa the liquid velocity magnitude increases with acceleration level possibly because of the inertial shear force. Increasing the injection pressure to 400 kPa, not only the magnitude, but also the direction of liquid velocity varies possibly due to the larger effect of Coriolis force induced by the increased liquid velocities.