Title: Extremely fast simulations of heat transfer in fluidized beds,
Abstract: Besides their huge technological importance, fluidized beds have attracted a
large amount of research because they are perfect playgrounds to investigate
highly dynamic particulate flows. Their over-all behavior is determined by
short-lasting particle collisions and the interaction between solid and gas
phase. Modern simulation techniques that combine computational fluid dynamics
(CFD) and discrete element methods (DEM) are capable of describing their
evolution and provide detailed information on what is happening on the particle
scale. However, these approaches are limited by small time steps and large
numerical costs, which inhibits the investigation of slower long-term processes
like heat transfer or chemical conversion.
In a recent study (Lichtenegger and Pirker, 2016), we have introduced
recurrence CFD (rCFD) as a way to decouple fast from slow degrees of freedom in
systems with recurring patterns: A conventional simulation is carried out to
capture such coherent structures. Their re-appearance is characterized with
recurrence plots that allow us to extrapolate their evolution far beyond the
simulated time. On top of these predicted flow fields, any passive or weakly
coupled process can then be investigated at fractions of the original
computational costs.
Here, we present the application of rCFD to heat transfer in a lab-scale
fluidized bed. Initially hot particles are fluidized with cool air and their
temperature evolution is recorded. In comparison to conventional CFD-DEM, we
observe speed-up factors of about two orders of magnitude at very good accuracy
with regard to recent measurements.