An overall assessment of ABND model for large-scale bubble flows

For increasing the predictability of equipment and improving efficiency of production, there is a high demand to develop a compact and efficient mathematical model capable of modelling the complex bubbly flow structures which frequently occur in large-scale industrial engineering systems. A generalized Average Bubble Number Density (ABND) transport equation model in conjunction with three forms of bubble coalescence and breakage kernels was implemented and incorporated into commercial software ANSYS CFX 11. The main focus of this paper is to assess the overall performance of the ABND model and the three different bubble mechanism kernels under a large-scale gas-liquid bubbly flow system. Based on the high-quality TOPFLOW database for airwater two-phase flows in a large vertical pipe with nominal diameter of 195.3mm, experimental data were strategically selected for model validation. To examine the relative merits and drawbacks of three forms of coalescence and breakage kernels, model predictions of local radial distributions of bubble rise velocity, volume fraction and bubble size were compared against experimental results. The capabilities in predicting the 'core peak' volume fraction profiles and evolution process of bubble rise of different kernels were discussed