Polymerizaton Model Reference

The process of polymerization is comprised of several chemical reactions, such as initiation, propagation, chain transfer, chain branching, scission, and termination, that involve radicals of different chain lengths.

The Polymerization model in Simcenter STAR-CCM+ simulates free-radical polymerization and uses Method of Moments for size distribution calculations.

Polymerizaton Properties

Secondary Gradients

There are two sources of secondary gradients in Simcenter STAR-CCM+ flow solvers:

• boundary secondary gradients for diffusion
• interior secondary gradients at cell faces

Use this property to control which gradients are included in the solver. On gives both gradients while Off excludes them. Interior Only and Boundaries Only select the corresponding gradients.

Convection

Sets the discretization scheme that Simcenter STAR-CCM+ uses for computing the convection flux on a cell face in appropriate transport equations. More information is given in the related topic for the Convection Term:

• 1st-Order: First-order upwind scheme. This scheme scales the transported quantity by the upstream or downstream mass flowrate depending on flow direction. Only use when a higher-order scheme fails to give convergence, or in order to obtain an initial solution before switching to a higher-order scheme.
• 2nd-Order: Second-order upwind scheme. This scheme introduces linear interpolation of cell values on either side of the upstream or downstream face. Using this scheme can lead to poorer convergence properties, but gives accuracy as good as or better than the first-order scheme.

User Rates

Allows you to add user sources to Polymer Scalars and Polymer Moment equations, in addition to the built-in sources. Activating this property populates the Polymer Scalars and Polymer Moments sub-nodes. See User Rates Sub-Nodes.

Model Controls

Free-Radical Polymer Reactions Properties

• Initiator Efficiency, f: Allows you to specify the efficiency of the initiator of the chain in Eqn. (3796), Eqn. (3798), and Eqn. (3800).
• Chain Transfer to Modifier: Activating this property creates an extra Free-Radical Polymer Reactions sub-node that represents a chain transfer to modifier reaction.
• Chain Transfer to Solvent: Activating this property creates an extra Free-Radical Polymer Reactions sub-node that represents a chain transfer to solvent reaction (Eqn. (3788)).
• Chain Transfer to Polymer: Activating this property creates an extra Free-Radical Polymer Reactions sub-node that represents a chain transfer to polymer reaction (Eqn. (3790)).
• Beta Scission: Activating this property creates an extra Free-Radical Polymer Reactions sub-node that represents a Beta Scission reaction (Eqn. (3791) and Eqn. (3792)).
• Heat of Propagation: Allows you to specify a value for the heat that is released due to propagation reactions.
• Heat of Initiation: Allows you to specify a value for the heat that is released due to initiation reactions.

Free-Radical Polymer Reaction Sub-Nodes

Some of these sub-nodes are available by default while others require activation in the properties of the Free-Radical Polymer Reactions node.

• Initiator Decomposition (I -> 2R')
• Radical Chain Initiation (R' + M -> R1)
• Propagation (Rn + M -> Rn+1)
• Chain Transfer to Monomer (Rn + M -> Pn + R1)
• Disproportionation (Rn + Rm -> Pn + Pm)
• Combination (Rn + Rm -> Pn+m)
• Chain Transfer to Modifier (Rn + X -> Pn + R1)
• Chain Transfer to Polymer (Rn + Pm -> Pn + Rm)
• Beta Scission (Rn + Pm -> Pm + Rp + Pm-p)
• Terminal Double Bond (Rn + Pm -> Rn+m)

See Reacting Flow Nomenclature.

Free-Radical Polymer Reaction Sub-Node Properties

• Method: Allows you to specify the Method as a scalar profile.
• Value: Specifies the value with a text entry. You can also enter an expression, such as 10 * sin(3.14 * $Time), directly. This property is only available when Method is set to Constant.
• Scalar Function: Activates an object selector dialog from which you can choose a field function. This property is only available when Method is set to Field Function.
• Unit System: Allows you to define Units that are appropriate to the reaction:
  • kmol, m, s, K
  • mol, cm, s, K

User Rates Sub-Nodes

When the User Rates property is activated, the following sub-nodes of the Polymer Scalars and Polymer Moments nodes allow you to specify User Rate and User Rate Jacobian source terms directly to the Polymer Scalar and Polymer Moment equations. Each of these sub-nodes functions as a scalar profile.

Polymer Scalars

Initiator, Modifier, Monomer, Radical, and Solvent

Polymer Moments

Dead Moment and Live Moment

Initial Conditions

Available within each continuum or phase for which the Polymerization model is selected.

Polymer Dead Moment, Polymer Live Moment

Respectively, sets concentrations for dead moment (Eqn. (3801), Eqn. (3803), and Eqn. (3805)) and live moment (Eqn. (3795), Eqn. (3797), and Eqn. (3799)). Scalar array profile values.

Polymer Initiator, Polymer Modifier, Polymer Monomer, Polymer Radical, Polymer Solvent

Respectively, sets concentrations for initiator (Eqn. (3783)), modifier, monomer (Eqn. (3786)), radical (Eqn. (3784)), and solvent (Eqn. (3789)). Scalar profile values.

Boundary Settings

Available for boundaries within regions that are associated with a continuum (or phase within that continuum) which uses the Polymerization model.

Polymer Dead Moment, Polymer Live Moment

Respectively, sets concentrations for dead moment (Eqn. (3801), Eqn. (3803), and Eqn. (3805)) and live moment (Eqn. (3795), Eqn. (3797), and Eqn. (3799)). Scalar array profile values.

Polymer Initiator, Polymer Modifier, Polymer Monomer, Polymer Radical, Polymer Solvent

Respectively, sets concentrations for initiator (Eqn. (3783)), modifier, monomer (Eqn. (3786)), radical (Eqn. (3784)), and solvent (Eqn. (3789)). Scalar profile values.

Flow Boundaries

The following boundary types have all of the above-listed physics values available by default.

• Free Stream
• Mass Flow Inlet
• Pressure Outlet
• Stagnation Inlet
• Velocity Inlet

Wall Boundary

Wall Combustion Scalar Option

Wall Combustion Scalar	Corresponding Physics Value Nodes
Zero Flux	None
Specified Value	All of the above-listed physics values

Polymerizaton Solver Properties

Under-Relaxation Factor

In order to promote convergence, this property is used to under-relax changes of the solution during the iterative process. If residuals show solution divergence and do not decrease, reduce the under-relaxation factor for the relevant solvers. The default value is 0.9.

Solver Frozen

When On, the solver does not update any quantity during an iteration. It is Off by default. This is a debugging option that can result in non-recoverable errors and wrong solutions due to missing storage. See Finite Volume Solvers Reference for details.

Reconstruction Frozen

When activated, Simcenter STAR-CCM+ does not update reconstruction gradients with each iteration, but rather uses gradients from the last iteration in which they were updated. Activate Temporary Storage Retained in conjunction with this property. This property is deactivated by default.

Reconstruction Zeroed

When On, the solver sets reconstruction gradients to zero at the next iteration. This action means that face values used for upwinding (Eqn. (905)) and for computing cell gradients (Eqn. (917) and Eqn. (918)) become first-order estimates. This property is Off by default. If you turn this property Off after having it On, the solver recomputes the gradients on the next iteration.

Temporary Storage Retained

When activated, Simcenter STAR-CCM+ retains additional field data that the solver generates during an iteration. The particular data retained depends on the solver, and becomes available as field functions during subsequent iterations. Deactivated by default.

Field Functions