Right-click a Porous Material node to add a Pellet subnode () to define properties of a pellet phase in the porous medium. The Pellet subnode provides the properties for a certain type of pellets that the solid part of the porous material consists of. A porous material can include pellets of different types. For example, the pellets might be a mix of 30% spherical pellets with a certain diameter, 20% spherical pellets with another diameter, and 50% of a third type of pellet that is cylindrical instead of spherical. Those 100% together form the solid phase in the “pellet bed”.

A Pellet node provides the geometrical properties for pellets and material properties for the solid phase in the pellet, such as density and heat capacity. The material properties for the fluid phase should be defined in a Fluid subnode.

When a Porous Material node is used in the physics, then all pellet types will exist at each point in the geometry. Therefore, the plural form, Pellets as a subnode to the Packed Bed node, used in the Chemical Reaction Engineering Module to model packed bed reactors with catalytic pellets. Also, Pellets as a subnode to the Porous Medium node can be used to model the local temperature field within pellets when using a Heat Transfer in Porous Media interface.

From the Material list, choose the material to represent the pellet: Locally defined (the default), or select any other material that you have added. Click the Go to Material button () to move to the selected material’s node. Click the Add Material from Library button ( to add a material from the Add Material to Pellet window. You can also click the downward arrow next to the button and choose Blank Material to add a new blank material. In both cases, the added material becomes selected in the Material list.

From the Shape list, define the shape of the pellet: Sphere (the default), Cylinder, Flake, or User defined. For Sphere and Cylinder, further specify a Diameter dpe (SI unit: m), where the default value is 1 mm. For Flake, define a Thickness dpe (SI unit: m) in a similar way. For User defined, specify the Pellet surface Ape (SI unit: m2) and Pellet volume Vpe (SI unit: m3).

Also specify a Porosity εpe as a relative number between 0 and 1 (default: 0.1). This is the microscale porosity of the inside of an individual pellet.

If you define a second Pellet subnode, the Pellet Bed Properties section below is not available. Instead, specify a Bed volume fraction, a relative number between 0 and 1. Only the first Pellet subnode can define the pellet bed porosity. For additional Pellet subnodes, you instead specify the volume fraction relative to the other pellet types.

In this section you specify the porosity of the pellet bed. From the Porosity list, choose User defined (the default) or From densities. With User defined, add a value for the porosity εp as a relative number between 0 and 1 (default: 0.26, representing perfectly packed spheres). With From densities, the porosity is defined as 1 − ρb/ρpe, where you define the density of the packed bed, ρb, in the Density field (default: 800 kg/m3).

In this section you specify the properties of the mesh for the extra dimension that each Pellet subnode defines so that both the species concentration and the temperature can be computed locally in the pellet.

For the mesh distribution, choose Linear, Cubic root sequence (the default), or Square root sequence from the Distribution list. Also, specify the Number of elements (default: 6).

Click the Extra Dimension Mesh Preview button () in the Mesh section toolbar to get a plot of the extra dimension mesh in a separate plot window, showing the mesh distribution and direction.

This section is only available if you have selected Locally defined from the Material list in the Pellet Properties section. You can then choose material properties that you want to add for the pellet from the list and then click the Add to Material button () to add those properties to the table in the Material Contents section below.

The table in this section contains the material properties for the pellet material. When the Material in the Pellet Properties section is Locally defined, enter values or expressions for the properties in the Value column. You can also click the Edit button () below the table to enter the property values.