The multiphase reactor supports several types of intra- and inter-phase reactions involving bulk phases. Such reactions are specified in the surface/liquid chemistry-input file. (Note that the gas-phase reactions are provided in the gas-chemistry input file.) Figure 9.1: Image of mechanism input files showing possible reaction types for a Multiphase Reactor model simulation shows an image of gas and surface/liquid-chemistry input files. The species and reaction data in Figure 9.1: Image of mechanism input files showing possible reaction types for a Multiphase Reactor model simulation are strictly for illustration purpose; and to emphasize that rate-constant parameters are not shown. The dummy-input consists of some H2/O2 chemistry. The surface/liquid kinetics file shows two bulk phases named AQUA and CATALYST, respectively. The first phase contains two bulk species while the second contains only one. Note that the bulk phase AQUA is declared as LIQUID (Bulk Data in the Chemkin Input Manual ). Following are the types of reactions that may be specified in the surface/liquid-chemistry input file for usage with the Multiphase Reactor model.
Figure 9.1: Image of mechanism input files showing possible reaction types for a Multiphase Reactor model simulation[2]
Reaction involving all species from the same bulk phase: This is therefore an intra-phase reaction. The rate formulation for such reactions uses volumetric concentrations within the bulk phase, just like the formulation for gas-phase reactions. Reaction-order change keywords may be used.
Reaction involving "direct conversion" from a given bulk phase to another bulk/gas phase: In such a reaction, all the species on the reactant side are in one phase and all species on the product side are in another (different) phase. These are considered as the volumetric-phase-change reactions. Consequently, the rate constant is computed using the volumetric concentration of the reactant phase; irrespective of whether the reaction is reversible or not. That is, the "net" molar-production rates (in units of mol/s) of the all species are obtained by multiplying by the volume of the reactant phase. The temperature used in the rate computation is that of the reactant phase.
VLE-type reaction: This is essentially a special case of reaction type b and the rate calculation is described in Vapor Liquid Equilibrium Model for Phase Change . Note that unlike the general reaction of type b, the VLE-based rate calculation considers the interface area between the two phases.
Reaction involving species from two different phases on the reactant side: The rate constants of such reactions are per interphase-area basis. The reaction can be written as reversible if all species in the product side are in the same phase. If not, then the reaction must be specified as irreversible. Reaction-order-change or sticking-coefficient keywords may be used. The temperature used in calculating the rate is that of the phase of the first species on the reactant side as written in the reaction. The phase of the first species on the reaction line must be a bulk phase; that is, it cannot be gas-phase.
Reactions involving only gas-phase species: This is considered as a special type of reaction in the context of it being specified in the surface-liquid chemistry input file. The reaction rate is, hence, considered to be per area basis. This area is taken to be the total interface area between gas and all bulk phases. The rate expression uses concentrations of gas-phase species and the temperature of the gas. Reaction-order-change or sticking-coefficient keywords may be used.
[2] This file example is only for illustration purposes. To emphasize that, the rate constants are not shown.