Systematic mesh development for 3D CFD simulation of fixed beds: Contact points study

In the development of meshes for computational fluid dynamics (CFD) simulations of transport in fixed beds of spheres, particle–particle and wall–particle contact points often present difficulties. We give results for drag coefficient (CD) and heat flow (Q) for flow past sphere–sphere and wall–sphere contact points, focusing on higher flow rates typical of industrial steam reformers (500 < Re < 10,000). Global methods, in which all particles in a bed are either shrunk or enlarged uniformly, change bed voidage giving erroneous results for CD. Local methods, in which bridges are inserted or spherical caps are removed only at the points of contact, give much better results for CD. The bridges approach is preferable for heat transfer, as fluid gaps reduce heat transfer too much, and particle overlaps increase it. A set of graphs is presented to allow estimation of the error introduced by the various methods of dealing with contact points.

► CFD rational mesh development for beds of spheres around contact points.
► Flow and heat transfer near particle–particle and particle–wall contact points.
► Comparisons of global (Gaps, Overlaps) and local (Bridges, Caps) modifications.
► Set of graphs presented to estimate error using these methods for different Re.