<p align="left">Accurate 3 dimensional CFD simulation is of great importance to the flow and heat transfer of flow boiling in the steam generator in nuclear power plant, in which bubbly flow is the main flow pattern. One of the biggest challenges for the CFD simulation is the coalescence and breakup model for bubbles dispersed in the continuous fluid. Recently, several new bubble coalescence and breakup models have been developed combined with the inhomogeneous Multi-Size-Group (MUSIG) model in the Eulerian framework in addition to the standard closure model (Luo and Svendsen (1996), and Prince and Blanch (1990)), which has been widely adopted in the CFD simulations in bubbly flow using the Eulerian method. For example, Liao had developed a comprehensive closure model (2015), in which the mechanisms of turbulence, eddy capture, velocity gradient, body forces and wake have been included in the collision&nbsp;model, and the turbulent fluctuation, velocity gradient in mean flow, turbulent eddies and interphase drag have been included in the breakup mechanisms. However, proper coefficients for the Liao model must be determined to properly address the proportion for various mechanism in the coalescence and breakup models. In this paper, we compared the predictions using the standard closure model and the Liao model (2015) combined with the iMUSIG model for the case of adiabatic upward bubbly flow in vertical pipe, as well as the corresponding experimental results reported by Lucas et al (2008) which were obtained at TOPFLOW test facilities. The simulated working conditions covered the ranges of the superficial gas velocity from 0.0368 m/s to 0.0898 m/s and the superficial water velocity from 0.405 m/s to 1.017 m/s. The influences of the superficial gas and water velocity, as well as various mechanisms on the bubble coalescence and breakup were analyzed based on the bubble size distributions, radial gas holdup, and gas velocity distribution&nbsp;in various heights obtained in the CFD predictions and experiments. Finally, a set of proper coefficients for various mechanisms in the coalescence and breakup models of Liao (2015) was developed for the simulated conditions.</p>

Assessment and Analysis of Various Mechanisms in the Coalescence and Breakup Models for  Upward Bubbly Flow

Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE28/volume/85246

2021 28th International Conference on Nuclear Engineering (ICONE28)

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.