Mass density

Volume of the cell

Molecular weight of species

Temperature

Mass fraction of species

Area that forms the interface between the gas bulk and the boundary region within the cell active surface area

Mass flux

Transport multiplier for species

Net in-flow of species from neighboring gas-phase cells

Gas molar production rate

Surface molar production rate

Mass transfer coefficient between the boundary-layer and bulk regions of the cell

Characteristic length scale for mass transfer between the boundary-layer and bulk region of the cell

Schmidt Number

The parameters that control the boundary-layer thickness, area, etc., can be set by calls to the Ansys KINetics API routines. In this way, the calling program can either control such parameters directly or can provide control to end-users through the program's user interface. Below is a mapping of which calls are used to set each parameter, and the corresponding terms in the equations below.

By default, the mass-transfer coefficient, , is calculated based on diffusion coefficients that are computed by Chemkin-based Transport-property routines within the KINetics cell calculations. However, for these calculations to occur, the transport-properties must first be pre-processed by the Ansys KINetics API calls prior to the cell calculation. If the transport-property data has not been preprocessed and is therefore not available at the time of the cell call, an optional power law will be used to estimate the mixture diffusion coefficient () in the mass-transfer coefficient calculation, as follows:

(2–17)

Here, is the mass transfer length scale, is the Schmidt number of the mixture, and the mixture viscosity is computed from the relationship:

(2–18)

where is the viscosity of the mixture at =273.15K. Default values for and are 1.716E-5 kg/m-sec (air @ 273.15K) and 0.7, respectively. If the mass transfer length scale is not provided, KINetics will use the length scale given by

(2–19)

The programmer can override these default values by calling the KINSetParameter with keywords BLTK, VISC0, and SCHMD, as described below.