Numerical Simulations On Phase Split Phenomenon In Two-Phase Bubbly And Annular Flow In T-junction

T-junction is widely used in the pipeline system in energy, chemical plant, environment engineering fields as a most fundamental component, such as steam transportation system in heavy oil exploitation field, oil-water mixture transportation system in oil-field. Because the T-junction has a natural phase split function for two-phase flow, meaning that the mixture qualities are different at the two exits. This will directly decrease the transportation efficiency. Thus, to make an intensive study with regards to the phase split phenomenon is of great importance.In two-phase pipe flow systems, many flow patterns will appear depending on different inlet flow velocities of the two phases, respectively. Two-phase flow pattern means different configurations of two-phase positions, such as stratified flow, wavy flow, slug flow, annular flow and mist flow. Speaking from physics view, different flow patterns have different two-phase positions and quite different flow characteristics. Numerically speaking, there are no well-recognized models for these flow patterns. Trying to modeling such flows is a challenging topic and it has a solid application background. In practical engineering, it is found that phase split result greatly depends on the inflow two-phase flow pattern. Therefore, in order to accurately model the phase split result in T-junctions. The corresponding in-pipe flow pattern should be modeled first.In the present thesis, the author chooses two most commonly encountered flow: pattern: annular flow and bubbly-froth flow. This study first established two self-standing numerical models to simulate the fully developed gas-liquid annular flow. The first one is based on the user defined scalar (UDS) function of Fluent, and the second one is based on species model. Present models only introduce entrainment and deposition correlations. All the other flow parameters, such as pressure gradient, wall shear stress, and wave parameters are deduced by the models themselves. Compared with the available experimental data in the literature, present proposed model can well described this flow. Author also performed a study on the droplet diameter size distribution in the annular flow using the population balance model. In this research, three pairs of coalescence & breakup kernels are included. Simulation results show that the pair with Lehr’s breakup kernel and Saffman’s coalescence kernel can best capture the behavior of liquid droplet in annular flow. This reveals that the droplet movement is determined by turbulence effects in the gas core. An Euler-Euler two-phase model is established to account for gas-liquid bubbly-froth flow in pipe. In this model, four forces are considered. They are drag force, lift force, turbulent dispersion force and wall force. It is found from the force analysis that drag force will force the gas bubble phase to move in the mainstream direction, lift force will push the bubble phase towards wall, and the wall force will keep the gas bubbles away from the wall surface. The integrated result is a peak in gas void fraction profile at the wall-adjacency. Present model can give reasonable predictions compared with experimental data in the open literature.Based on the numerical simulations of pipe flows, the author extends the flows into T-junction in order to study the phase-split result. The bubbly flow model is directly moved to the T-junction simulations. Due to the lack of numerical model for developing annular flow, the author proposed one for the high-turbulent developing annular flow according to experimental observations. This model is extended to predict the flow in T-junction. Phase split results in regular T-junction imply that, for the flow patterns considered in the present thesis, gas phase prefers to rush into the side arm, while the liquid phase prefers to go out though the run arm. These are identical with experimental data in the literature. From the analysis of two-phase velocity-ration result, we can know that the foundation of phase split is the different inertia of the two phases.Based on numerical simulations for regular T-junctions, present thesis proposes several methods to change the natural phase split phenomenon in T-junctions. The simulation results show that for the structure modifications proposed in this thesis. Facing backward inserted tube can enhance phase-split, and can be used as a compact phase-separator. The 3D/4 height baffle can produce equal split result, and can be utilized as an equal-phase-separator. To achieve these, the corresponding cost is quite considerable pressure loss.