
Advances in computational fluid mechanics have provided the basis for further insight into the dynamics of multiphase flows. Currently there are two approaches for the numerical calculation of multiphase flows: the EulerLagrange approach (discussed below) and the EulerEuler approach (discussed in Section 23.2.1).
The EulerLagrange Approach
The Lagrangian discrete phase model in FLUENT (described in Chapter 22) follows the EulerLagrange approach. The fluid phase is treated as a continuum by solving the timeaveraged NavierStokes equations, while the dispersed phase is solved by tracking a large number of particles, bubbles, or droplets through the calculated flow field. The dispersed phase can exchange momentum, mass, and energy with the fluid phase.
A fundamental assumption made in this model is that the dispersed second phase occupies a low volume fraction, even though high mass loading ( ) is acceptable. The particle or droplet trajectories are computed individually at specified intervals during the fluid phase calculation. This makes the model appropriate for the modeling of spray dryers, coal and liquid fuel combustion, and some particleladen flows, but inappropriate for the modeling of liquidliquid mixtures, fluidized beds, or any application where the volume fraction of the second phase is not negligible.