19.3.2. Nucleation Reaction Data

To make certain that all information needed to model particle inception is properly presented by the reaction data, certain rules and syntax for the nucleation reaction must be followed.

Figure 19.5: Syntax for nucleation reaction

<gas_reactants> -> jnuc<core_bulk>+<surface_products>+<gas_products>AnucBnucEnuc
               NUCL

Rules:

  1. Auxiliary keyword NUCL must be used to denote a nucleation reaction.

  2. The reaction must be irreversible. Any possible reverse reaction must be presented as a separate reaction.

  3. Only gas-phase species can appear on the reactant side.

  4. There must be one and only one bulk species on the product side. This bulk species represents the composition of the particle core.

  5. The particle class of the new particle created by the nucleation reaction is given by the stoichiometric coefficient of the bulk species product, that is, .

  6. At least one surface species product has to be specified so surface coverage of the new particle can be properly initialized.

  7. The gas phase product is optional and its purpose is to balance the reaction.

  8. A nuc, B nuc, and E nuc are the Arrhenius rate coefficients. As part of the surface mechanism, their format and default units must be compatible with the defaults or those specified for the reaction in the Surface Kinetics input file.

  9. More than one nucleation reaction is allowed for one dispersed material. These must describe the formation of the same bulk species.

Units:

Rate of progress and species production rates of nucleation reactions are given in [mole/cm3 -sec].

Example:

The nucleation reaction below describes the formation of particles from gas species C16 H10 :

Figure 19.6: Formation of particles from gas species C16H10 

2 C16H10 => 32 C(B) + 20 H(SE) + 28.72 OPEN(SE)  9.0E+09  0.5  0.0
     	NUCL

The new particle core consists of 32 C(B) molecules. About 40% of the new particle surface is initially covered by surface species H(S) and the rest of the surface is covered by another surface species, OPEN(S), which in this case are open sites. No gas-phase product is generated by this nucleation process.