Multiphase Flow CFD Modeling

Multiphase flow CFD simulations typically employ Eulerian-Eulerian models (Monahan et al., 2005 Pan et al., 2000 Rampure et al., 2003 Sokolichin and 

An Introduction to Bioreactor Hydrodynamics and Gas-Liquid Mass Transfer, First Edition. Enes Kadic and Theodore J. Heindel. 

The main advantage of the Eulerian-Lagrangian formulation comes from the fact that each individual bubble is modeled, allowing consideration of additional effects related to bubble-bubble and bubble-liquid interactions. Mass transfer with and without chemical reaction, bubble coalescence, and redispersion, in principle, can be added directly to an Eulerian-Lagrangian hydrodynamic model. The main disadvantage of the Eulerian-Lagrangian approach is that only a limited number of particles (bubbles) can be tracked, such as when the superficial gas velocity is low (Chen et al., 2005), due to computer limitations. 

The Eulerian-Eulerian method is more popular because memory storage requirements and computer power demand depend on the number of computational cells considered instead of the number of particles. Hence, the Eulerian-Eulerian approach can be applied to cases for low and high superficial gas velocities. The disadvantage of using the Eulerian-Eulerian method is that the bubble-bubble and bubble-liquid interactions cannot be considered as straightforward as the Eulerian-Lagrangian method, and models for these interactions are typically applied. 

The DNS methods are the most detailed they typically advance the gas-liquid interface through the flow field in an Eulerian mesh and do not require empirical constimtive equations. However, the DNS methods are limited to a very small number of particles/bubbles (e.g., typically 10s of bubbles in the flow field) due to computational limitations. Most industrial applications require high superficial gas velocities, and therefore the Eulerian-Eulerian method is preferred (Dudukovic, 2002 Pan et al., 2000) and will be summarized later. 

---