Packed Bed (Moving Packed Bed)
Use this feature to model a packed bed reactor filled with solid catalytic or reactant pellets. The bed pellets are porous, forming a bimodal porosity in the reactor. In addition to mass transfer and reactions in the fluid between the pellets (interparticle processes), the same processes can also be studied inside the pellets (intraparticle). The pellets are available in each point of the bed domain, and are defined using an extra dimension describing the pellet radius.
The Packed Bed includes two subnodes, Fluid and Pellets, which in turn are used to define the physical properties of the corresponding phase. The latter node is also used to define volumetric reactions, as well as heterogeneous reactions, occurring within the porous pellets.
The Packed Bed node requires a Porous Material (described in the COMSOL Multiphysics Reference Manual) on the domains occupied by the bed. Using the porous material it is possible to model a bed comprised of any number of pellet types by adding multiple pellet nodes.
For information on the equations solved in the pore space and inside the pellets see the section The Packed Bed Feature, in the The Transport of Diluted Species Interface chapter. When using the corresponding feature for concentrated mixtures, see The Packed Bed Feature in the Theory for the Transport of Concentrated Species Interface chapter.
For an application using the Packed Bed feature, see
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A Multiscale 3D Packed Bed Reactor: Application Library path Chemical_Reaction_Engineering_Module/Reactors_with_Porous_Catalysts/packed_bed_reactor_3d
Web link: www.comsol.com/model/a-multiscale-3d-packed-bed-reactor-17019
Domain Selection
From the Selection list, choose the domains with porous material. Note that all domains chosen needs to be occupied by a Porous Material.
Bed Properties
Use the Porosity list to specify the bed porosity, that is the volume fraction not occupied by the pellets. Select From material to use the bed porosity defined by the Porous Material. Select User defined to enter a constant or an expression.
Bed Type
Use the Bed type list to specify the bed type: Packed bed or Moving packed bed. If you choose Moving packed bed, enter the bed velocity in the Bed velocity field.
There are two subnodes for the Packed Bed reactor: Fluid and Pellets. For the Moving packed bed reactor, in addition to the two subnodes, there are other three subnodes: Bed Inlet, Bed Outlet, and Bed Wall.
Moving Packed Bed
The solid bed, comprised of solid catalytic or reactant pellets, moves relative to the reactor. For the mass transport inside the solid pellets, there is an extra convective contribution. For species i, this term can be expressed as
where umb denotes the bed moving velocity, εpe is the pellet porosity, and (1 − εp) is the pellet volume fraction of the bed.
The solid pellet bed is rigid, the moving bed velocity is the same in the reactor.