This interface (
), found under the Reacting Flow in Porous Media multiphysics node (
), on the
Chemical Species Transport branch (
), is used to model reactors filled with catalyst pellets. The interparticle macropores (void between pellets), and the intraparticle micropores (pores inside the pellets) result in a system with bimodal porosity. The
Transport of Diluted Species in Packed Beds interface can be used to study interparticle and intraparticle mass transport, as well as reactions, in detail. Heterogeneous reactions and as volumetric reactions, both in the pore fluid inside the pellets and in the bulk fluid in the bed, can also be studied.
The main feature of the interface is the Packed Bed node which adds the governing equations for the concentrations of all bulk species, and the equations for surface species. It has two subnodes,
Fluid and
Pellets, that in turn are used to define the physical properties corresponding to each phase. The latter node is also used to define volumetric and heterogeneous intraparticle reactions. The
Packed Bed node requires the use of a
Porous Material (described in the
COMSOL Multiphysics Reference Manual) for defining phase-specific properties, and for sharing them among different physics interfaces. A packed bed containing several pellet types can be modeled by adding multiple
Pellets nodes to the
Porous Material.
When this physics interface is added, the following default nodes are also added to the Model Builder —
Packed Bed,
No Flux (the default boundary condition), and
Initial Values. From the
Physics toolbar, add other nodes that implement, for example, boundary conditions, reaction rate expressions, and species sources. Optionally, right-click
Transport of Diluted Species in Packed Beds to select physics features from the context menu.