Pellet-Fluid Interface
Domain selection
The domain selection inherits all valid domains from its parent feature. For the invalid domains, it shows not applicable.
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 the default Pellet-Fluid Interface node. It is visible for Pellet-Fluid Interface nodes if several Pellet-Fluid Interface nodes are present.
Select All or one of existing pellets for the non-default Pellet-Fluid Interface nodes.
Pellet-fluid interface
The Coupling type 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 Coupling type options for the coupling of concentration between the pellet internals and the surrounding fluid:
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Continuous concentration, 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.
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Film resistance (mass flux): The flux of mass across the pellet-fluid interface into the pellet is assumed to be rate determined on the bulk fluid side, by film resistance. The resistance is expressed in terms of a film mass transfer coefficient, hD,i, such that the inward flux is
For the Active specific surface area (SI unit: m-1) select either the Automatic setting that calculates the specific surface area from the pellet shape, or User defined.
Specify the Mass transfer parameters — Automatic (the default), or User defined to define the film mass transfer coefficient.
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Mass transfer parameters with Automatic selected. Specify one of the models from the Sherwood number expression list to compute the Sherwood number. There are three models available: Frössling, Rosner, and Garner and Keey. 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 Density and Dynamic viscosity. Both of these two properties are specified in the Fluid node under the Packed Bed feature.
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Mass transfer parameters with User defined selected. Specify the type of Parameter — Mass transfer coefficient (the default), or Sherwood number, and enter the selected quantity in the corresponding edit field.