Turbulent Gas Breakup Modeling and Acoustic Void-Fraction Determination Studies in Support of Cavitation Damage Mitigation of the Spallation Neutron Source Target Vessel

Pressure pulses induced by proton beam deposition lead to cavitation and pitting erosion of the SNS target vessel; this damage limits the lifetime of the vessel. Dampening the pressure pulse by adding compressibility to the bulk mercury in the form of microbubbles is a promising technique for damage mitigation. The physics governing gas bubble breakup in turbulent flows is examined leading to mechanistic based scaling models for the gas breakup in a swirling jet type microbubble generator. These models are verified experimentally in an air/water system and compared to a legacy empirical model. Verifying the performance of a microbubble generator in a liquid metal application requires knowledge of both the gas void fraction and the bubble size distribution. Since the sound speed in a bubbly mixture is a strong function of the gas void fraction, a fixed point auto-correlation technique is developed to determine the sound speed in a bubbly mixture. The auto-correlation method is verified in a water solid waveguide.