(407f) Simulating Periodically Pulsed Fluidized Beds – Pattern Formation As a Fingerprint for CFD Models

More than a decade ago, experimental measurements on periodically pulsed gas-solid fluidized beds showed the formation of remarkably regular bubble arrays within a relatively broad range of frequencies. The square patterns in shallow 3D beds are reminiscent of similar patterns observed in vibrated granular media. In addition, in deeper, quasi-2D beds, hexagonal bubble arrays are observed, which have no known analogue in vibrated granular systems.

Computational fluid dynamics (CFD) have, up to now, not been able to reproduce these patterns convincingly. We have started a systematic program to compare increasingly sophisticated modelling approaches. The approach that we are currently adopting is the Eulerian/Eulerian two-fluid model, which permits to compare, e.g., various drag and solid-stress closure relations, as well as different numerical methods for solving the equations themselves. Direct numerical simulations (DNS) can be employed to obtain closure relations in more coarse-grained models, as part of a multiscale simulation approach. CFD simulations based also allow us to test the effect of (non-)uniform fluid distribution, and the boundary conditions in quasi-2D and fully 3D systems. Screening for regular patterns upon pulsating the gas flow within a range of conditions similar to those in experiments, serves as a “fingerprint” for successful models.