Gas Bubble Formation in Stagnant and Flowing Mercury

The Oak Ridge National Laboratory’s (ORNL) Spallation Neutron Source (SNS) facility uses a liquid mercury target that flows through a stainless steel containment vessel. As the SNS pulsed beam power level is increased, it is expected that the target vessel lifetime could become limited by cavitation damage erosion (CDE). Bubbles produced in mercury at an upwards-oriented vertical gas injector needle were observed with proton radiography (pRad) at the Los Alamos Neutron Science Center (LANSCE). The comparison of volume-of-fluid (VOF) simulation results to the radiographic images reveals some aspects of success and some deficiencies in predicting these high surface tension, highly buoyant, and non-wetting fluid behavior. Although several gas flows were measured with pRad, this paper focuses on the case with a low gas flow rate of 1.66 mg/min (10 sccm) through the 0.2-mm-outer-diameter injector needle. The acoustic waves emitted due to the detachment of the bubble and during subsequent bubble oscillations were also recorded with a microphone, providing a precise measurement of the bubble sizes. When the mercury is also motivated coaxially, the drag on the bubble forces earlier detachment leading to smaller bubble sizes.