The prediction of the hydrodynamics of immiscible liquid-liquid flow is essential for the accurate design of process intensification technologies using micro capillaries and packed bed systems. It is also very complex mainly because of the shear exerted between the phases and the inertial effects that are present. The aim of this work relies on the computational fluid dynamics (CFD) study of liquid-liquid slug flow in capillaries, offering insight on the effectiveness of monoliths and packed bed reactors in biodiesel production for process optimisation.
The main parameters for modelling slug flow in capillaries were investigated. An attempt to predict the terminal droplet velocity was developed by relating the drag force and the Reynolds number over a single droplet of different sizes dispersed in a continuous flow in a capillary. The results showed a significant effect of the film thickness and droplet length on the Stokes-coefficient suggesting predominance of Stokes flow for the conditions under study. Also, the motion of a droplet in pressure driven horizontal flow was investigated. The numerical predictions revealed a notable influence of the film thickness, slug and drop length on the droplet velocity. Moreover, the study of the interfacial forces in the limits of high and low viscosity ratios was developed using an alternative method to the Volume-of-Fluid method. The velocity and shear profiles across the two-phases were efficiently achieved and visualisations of the internal hydrodynamics structures in the continuous and dispersed phases were compared to similar studies from the literature.
Furthermore, an efficient predictive tool based on slug flow correlations from the literature was developed to calculate the film thickness, droplet velocity and pressure drop in a capillary when the properties of the fluids and the inlet flow rates are known. The results are in good agreement with those predicted by CFD methods and with experimental data found in the literature. This tool can be useful for design purposes of technologies involving two-phase flows in capillaries. Also, it can be helpful for predicting initial conditions and input parameters in CFD models applied for two-phase flow in porous systems.
Finally, the first stage of a pressure drop model for liquid-liquid flow in porous media is proposed based on slug flow correlations. The model includes the influence of interfacial forces and inertial effects in porous media and can be further implemented to predict operating conditions of a packed bed reactor for biodiesel production.
