Fixed Bed Fluid Flow and Heat Transfer by CFD - 2

he CFD simulations of fluid flow and heat transfer in fixed beds are computationally expensive. This is because the flow is three-dimensional and the complex geometry forces us to use a fairly fine mesh in both the fluid and solid regions. A successful simulation also gives an enormous amount of output data to be post-processed.

For these reasons, we have developed models of representative parts of the bed, such as this 120-degree wall segment shown here with flow pathlines. The results obtained from this segment have been verified by comparison to full bed simulations. We can focus on the near-wall flow behavior around a typical particle.

The periodic nature of the packing resulted in a flow pattern that showed periodic behavior, and as the wall heat flux was influenced greatly by the convective behavior of the fluid it also showed a recurring pattern, as can be seen in this figure. This is a contour map of the heat flux through the wall of the reactor tube. It demonstrates that there can be strong variations in the local wall heat flux, which would lead to similar variations in the local temperatures and reaction rates. These local effects had not been realized until they were shown to exist by the use of CFD. Their evaluation and implications for reactor modeling are part of our on-going work. Further details about this work may be found in a recent publication [Nijemeisland, M. and Dixon, A.G., 2004].