Samenvatting
Bubble columns are a widely encountered reactor type in a variety of industrial chemical processes.Their performance is heavily influenced by hydrodynamic phenomena at different length scales, which has stimulated academic research into a deeper understanding of the governing phenomena.
In this work the central phenomenon is bubble detachment from a needle, which may vary depending on the orifice geometry and physical properties. To this end, Direct Numerical Simulations (DNS) are performed with a combined Local Front Reconstruction Method (LFRM) and Immersed Boundary Method (IBM) approach to resolve fluid-fluid, fluid-solid and fluid-fluid-solid interactions. The coupled approach requires adaptation of several LFRM aspects and incorporation of three-phase contact line dynamics, which are implemented and evaluated throughout this work. All separate elements are combined in a designed simulation procedure that serves as a proof-of-concept for simulating
bubble detachment from a solid needle. All simulations and developments are performed in the inhouse FoxBerry code.
The main modifications to the existing LFRM include an initialization procedure for the interface on solid objects, point flagging depending on the phases they are in contact with, adjusting the interface reconstruction to allow for folding around the contact line, restricting the volume-conservative interface smoothing, and including a new surface tension force method. All elements showed adequate results in the performed unit tests.
The contact angle model was developed for imposing a local contact angle on the interface part close to an arbitrary continuous or discrete solid surface. Its performance was evaluated in detail through a comparison of the simulation results of droplet spreading with analytical and literature results. The method showed outstanding radial symmetry in the spreading, and proved to be extremely robust.
Moreover, an excellent match with the analytical solutions was observed, as the error margin in the equilibrium shape was below 1% for almost all imposed angles. This outcome is also superior to the compared literature models, despite of low grid resolution compared to the methods in literature.
The simulation of bubble growth from a needle only produced partial results without any actual detachment due to issues arising in the interface reconstruction. This highlights the complexity of this aspect and demonstrates the necessity for additional development, especially on more intricate solid geometries. Nevertheless, the initial results appeared promising and are a step closer in the desired direction. Solving the residual issues in the LFRM reconstruction would enable a wide range of possibilities for accurately simulating multiphase fluid dynamics around complex solid objects.
| Datum prijs | jan. 2023 |
|---|---|
| Originele taal | Engels |
| Begeleider | Cristina Garcia Llamas (Afstudeerdocent 1) |