This interface (), found under the Chemical Species Transport branch () > Reacting Flow in Porous Media multiphysics node () >  Packed Bed group node, is used to model reactors filled with initially solid reactant particles. As the reactant particles are consumed by heterogeneous reactions from the outside inward, the solid core shrinks, leaving behind a porous layer around it. Apart from the core consuming reactions, transport and reactions inside the porous reacted layer, as well as transport in the pore space around the particles are studied.

The main feature of the interface is the Pellets which is the subnode to the Packed Bed node. With the Pellet Type parameter being changed from Porous catalyst to Shrinking Core model, the Transport of Diluted Species in Packed Beds interface switches to the Transport of Diluted Species in Packed Beds, Shrinking Core interface. For the Transport of Diluted Species in Packed Beds, Shrinking Core interface, the governing equation for core shrinking is,

where rcore (SI unit: m) denotes the radius of the reactant pellet, Rsolid (SI unit: mol/(m2·s)) heterogeneous reaction rate on the reactant pellet surface, Msolid (SI unit: kg/mol) the molar mass of the solid reactant, and ρpe (SI unit: kg/m3) the reactant pellet density.

With the unreacted solid core decreased in size over time, the reacted porous layer grows thicker. The fluid (often gas) reactant moves from an external fluid through the reacted porous layer to the solid core surface, and the product from the heterogeneous reaction leaves the solid core surface through the reacted porous layer to the external fluid. The mass transport phenomena and possible reactions in the reacted porous layer are modeled in the same way as that in The Transport of Diluted Species in Packed Beds Interface.