Pellet-Fluid Interface

The domain selection inherits all valid domains from its parent feature. For the invalid domains, it shows .

Several Pellet-Fluid Interface nodes can be used to specify different boundary conditions between fluid and pellet out-surface for different domains and pellets.

Pellet

This section is invisible for default Pellet-Fluid Interface node. It is visible for later added Pellet-Fluid Interface nodes.

Select or one of existing pellets for the non-default Pellet-Fluid Interface nodes.

Pellet-fluid interface

The list is selectable for the default Pellet-Fluid Interface node, but it is disabled for non-default Pellet-Fluid Interface nodes because it is supposed that there should be only one type of boundary condition in a packed bed.

There are two options for the coupling of concentration between the pellet internals and the surrounding fluid:

•

, assuming that all resistance to mass transfer to/from the pellet is within the pellet and no resistance to pellet-fluid mass transfer is on the bulk fluid side. The concentration in the fluid will thus be equal to that in the pellet pore just at the pellet surface: cpe,i = ci. This constraint also automatically ensures flux continuity between the internal pellet domain and the free fluid domain through so-called reaction forces in the finite element formulation.

•

: The flux of mass across the pellet-fluid interface into the pellet is possibly rate determined on the bulk fluid side, by film resistance. The resistance is expressed in terms of a film mass transfer coefficient, hDi, such that:

. The option computes the inward surface flux, hDi is the mass transfer coefficient (SI unit: m/s) and is calculated with the default setting from a dimensionless or with mass transfer coefficients.

The (SI unit: m-1) is required to couple the mass transfer between the pellets and the bed fluid. Select either the setting that calculates the specific surface area from the shape information given above, or that is available for explicit surface area specification.

Specify the — (the default), or to set the mass transfer parameters.

•

with selected. Specify one of the models from the list to compute the Sherwood number. There are three models available: , , and . The Frössling equation is the default and probably the most commonly used for packed spheres. All of these are based on the dimensionless Reynolds (Re) and Schmidt (Sc) numbers, which are computed from and . Both of these two parameters are specified in the Fluid node under the Packed Bed feature. They can be taken or choose the alternative. They could also be picked up from Chemistry if the species in the Chemistry are coupled to that of the current Transport of Concentrated Species interface.

•

with selected. Specify the type of — (the default), or to be user defined. Enter the mass transfer coefficients and Sherwood numbers for and , respectively.