(45c) Numerical Simulation of the Transport of Volume Expansion Particles in Fluid Flows

The prediction of the particle transport in gas or liquid flows is often carried out by the application of the Lagrangian approach. There the interaction terms between fluid flow and particles are expressed in terms of a drag coefficient Cd. A large number of studies exist to estimate the drag coefficient. The theoretical and experimental investigations are usually confined to the consideration of limited cases; e.g. spherical particles, simple fluid flow characteristics (Couette flow), unbounded flows, steady state flows, ? In almost all practical applications the fluid flow is limited by boundaries and the fluid flow characteristics are more complex. Therefore the distribution of pressure and flow velocity, and hence the drag, will often differ greatly from the above mentioned ideal cases. The application of the approximations to compute the drag coefficient is limited and an enhancement of the existing models is essential.

In this article another method is presented to compute the particle motion for arbitrarily shaped particles in various geometries. In contrast to the Lagrangian approach, where every particle is considered as mass point without volume expansion, now the particles are considered as rigid bodies with their finite expansions. The determination of the translational and angular velocities of the particles is made by integration of the viscous and pressure forces over every surface element at the particle. The model is linked into the commercial CFD software FLUENT by means of user-defined functions (UDF). Dynamic mesh models in FLUENT are used to model the particle motion in the computational domain. The mesh structure is changing with time due to motion of particle boundaries. This simulation tool is able to calculate detailed information about the complex intersections between particles and fluid flows. The particle-wall collisions can also be simulated in detail what is very important to get accurate knowledge of the deposition in separation processes.

Computational simulations with volume expansion particles require very fine grid elements and also the computational costs are huge. Therefore information from these extensive flow simulations is used to get simplified calculation models for the Lagrangian approach.

This procedure contains a huge potential for numerical calculations of particle loaded flows.