An Investigation of Gas Bubble Generation and Measurement in Water and Mercury

The pressure increase attributed to the energy deposition in the liquid metal target of the Spallation Neutron Source results in cavitation and pitting erosion of the target pressure boundary. Introducing compressibility in the form of small gas bubbles will extend the lifetime of the target vessel. The pressure rise caused by the beam energy deposition occurs in one microsecond, which encourages use of bubbles of radius less than 20 microns, such that the bubble response to pressure change is adequately fast. Gas volume fraction near 0.5% is sufficient to accommodate the mercury volumetric expansion and reduce the pressure rise. Bubble production and detection technologies are developed herein to allow control of the bubble diameter and volume fraction in an opaque liquid metal.

This research infers bubble size in the form of a probability density function using dynamic gas delivery pressure and mass flow, and passive acoustic emissions at bubble birth, for a single orifice bubbler. Terminal rise velocities are also measured and used to infer bubble diameter. The gas volume fraction is inferred from the acoustic sound speed using the so-called low frequency Wood’s Limit model for sound speed in a bubbly media.