Multiphase Computational Fluid Dynamics A new tool to aid in scale up of chemical processes
Multiphase flows are ubiquitous in chemical and mineral processing industries and the much broader energy industries. Yet it is the most challenging aspect of engineering. Often the challenge in transforming a bench scale concept to field scale practical device is met through a series of expensive pilot scale experiments to aid in the scale up of the operation. Over the last two decades, we have been exploring the use of Computational Fluid Dynamics to study several chemical and mineral processes such as design of gravity separation vessels, slurry flows in pipelines, erosion problems, tray and packed distillation columns etc. In such studies we use volume averaged equations as the basis of CFD models coupled with experimental validation of such predictions in an effort to develop scale invariant closure models that are needed as part of the volume averaged CFD models. We will discuss several of these examples. This provides the motivation for the next part of the presentation that deals with Direct Numerical Simulation of multiphase flows. On the fundamental side, we have developed finite element based algorithms for direct numerical simulation of multiphase flows. For dispersed rigid particles as in suspension flows, sedimentation etc, we couple the Navier-Stokes equations with the rigid body dynamics in a rigorous fashion to track the particle motion in a fluid. For deformable bubbles/droplets dispersed in another fluid, we also track their motion in an Eulerian grid. Discontinuous basis functions are used to enrich the function space near the fluid/fluid interface. The two classes of algorithms show great promise in attempting direct simulation of multiphase flows with many particles or droplets, from which we can extract statistically meaningful average behavior of suspensions or bubbly flows. This will augment experimental validation of predictions based on volume averaged equations.