Numerical study on bubble hydrodynamics with flow transition for pool scrubbing

Okagaki, Yuria  ; Shibamoto, Yasuteru ; Abe, Satoshi  

A bubbly flow with a single injection orifice is numerically analyzed for pool scrubbing phenomena using different computational fluid dynamics (CFD) methodologies. The calculation covers the total regime of pool scrubbing from air injection to bubble swarm through the transition region. Such two-phase flow behaviors strongly affect particle removal in a bubble. The experimental bubbles are known to be oblate spherical and exhibit secondary motion, including path instability and shape oscillations. Moreover, bubbles in a swarm are subject to coalescence and breakup. While these may well affect bubble internal heat/mass transfer and particle capture, no established way is available for considering such influences in practical calculations. Pool scrubbing code SPARC-90 uses an oblate spherical bubble model but assumes a steady, rectilinear bubble rise without secondary motion. The 3-D CFD has the potential to capture the bubble interaction in the swarm region in detail. In the present study, the experiment by Abe et al. (Nuclear Engineering and Design 337, 2018) was referred for the calculation, and their data were used to validate if the CFD simulation can predict the flow transition accurately. Two types of solvers based on the volume of fluid (VOF) method and the simple coupled volume of fluid with level set (S-CLSVOF) method are used for the interface capture. The two solvers were validated by comparing with the experimental results. As a result, the void fraction profiles along the vertical central axis were in good agreement with the experimental data, regardless of the solvers, and those along horizontal lines in a central plane slightly improved with the S-CLSVOF method by the more accurate calculation of the surface tension.