Speaker
Description
Injection of helium microbubbles at the Oak Ridge National Laboratory (ORNL)-Spallation Neutron Source has proven to be a stress mitigation mechanism that may extend fatigue lifetime of liquid mercury target vessels. The production of bubbles with average diameters of less than 0.150 mm is achieved using highly turbulent swirl flow in a liquid metal facility undergoing high radiation conditions. The design of the bubble injector device includes four swirl bubbler units working together in a counter-rotating fashion. In this work, the commercial Ansys-CFD code was used to predict the bubble size distribution obtained nearby the outlet of the bubble injectors and its evolution through the whole target vessel is tracked down to obtain average bubble size distribution vs distance from the injection site un mercury. Bubble production and bubble interactions are calculated using the interfacial area concentration transport method. The current methodology accounts for bubble interaction mechanism in the form of coalescence due to random collisions driven by turbulence, breakage due to the impact of turbulent eddies and coalescence due to wake entrainment. The results show reasonable agreement with experimental data obtained in previous studies. The current predictions provide complementary information about expected bubble size distribution by location, however current comparisons with experimental data have been limited due to experimental data available. Further details about the assumptions and limitations of the proposed two-phase flow methodology using mercury as the liquid phase and Helium gas as the secondary phase will be discussed. It is expected that validated bubble size distribution predictions serve as an input parameter for the current strain prediction models used at the SNS.
| Themes for the contribution | 4 Target design, analysis, and validation of concepts: |
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