NUMERICAL SIMULATION OF ISOTHERMAL GAS-LIQUID BUBBLY FLOW: INFLUENCE OF BUBBLE COALESCENCE AND BREAKUP

ABSTRACT Gas–liquid bubbly flows are commonly encountered in many industrial processes. In many cases, the evolution of bubble size distribution is a crucial factor governing the momentum, heat and mass transfer between phases within the system. In this thesis, numerical investigation of gas-liquid bubbly flows is achieved by coupling a population balance model with the three-dimensional, two-fluid model. With the aim of evaluating the capabilities of the population balance model, a model validation study to assess the MUSIG model in a highly asymmetrical distributed bubbly flow in vertical pipe has been presented. Particularly, the research focus has been centered on detailed numerical investigation of the coalescence and breakup phenomenon by performing extensive numerical investigations for the examination and comparison of different model formulations. Two major contributions has been achieved in this thesis; (1) a modification of the coalescence model of Prince and Blanch (1990) to account for the imbalance between coalescence and breakup phenomenon; and (2) the population balance approach with implementation of the modified model into ANSYS CFX code using CFX Expression Language (CEL). Model predictions were validated against experimental measurements reported by Monros et al., (2013). Three different modifications (cases) have been investigated. Overall, predictions of the three cases were in satisfactory agreement with the experimental data. The transition from “wall peak” to “core peak” gas volume fraction profiles has been successfully captured. Encouraging results clearly demonstrates the applicability of the models for large scale industrial systems. In general, the comparison shows that the model labelled as Case 2 presented the best results in most of the experimental conditions.