3D CFD analysis of generation of bubbles in a double T-junction mini-channel

Abstract

The subject of two or multi-phase flows has become increasingly powerful and important in a wide variety of engineering systems. The aim of our project is to study the bubble generation of the water-air combination in a T-junction capillary, which will be compared to a double T-junction, under microgravity conditions due to the very different behavior when compared to the one observed in the presence of gravitational forces. To reach our goal, we have prepared all the parameters and framework (geometry, mesh, boundary conditions, etc.) to perform the simulations with the open-source program OpenFOAM. We have also carried out different convergence tests by computing the errors and the standard deviations of the bubble generation frequency, velocity, length, and volume. In addition, we have worked on numerous tests to enhance the bubble generation quality, by trying different boundary conditions such as the contact angle, the wettability, boundary layers in the mesh, etc. For the chapter of results, we ended up using the wettability condition, since it solved the most urgent issue, which is the bubble attachment to the walls. We have also used a boundary layer in the mesh because it decreased the fluctuations of the bubble parameters. One of the most important conclusions is that the combination of the air and water superficial velocities have a great effect on the obtained results and that some boundary conditions can be optimal for some of the used combinations but the opposite for some others. For example, the bubble generation grows irregular with high fluctuations if the gas superficial velocity is higher than the liquid's, but becomes more stable if the velocities are similar or if the liquid is faster. As for the final results, it was deduced that the double T-junction is a more optimal geometry since, for higher liquid superficial velocities, the bubble generation was more stable due to its two vertical water entries symmetry. Lastly, the contact angle condition still needs more research due to vagueness revolving around its numerous tests. Not to forget that, since the double T-junction is a newly introduced geometry in this CFD two-phase flow analysis, it will also need more evaluations to fully be accepted as a better option.