SPECIFY THE MATERIAL PROPERTIES

Title of keyword sub-block that defines some of the material properties and governing equations of the reactor. Part of the DEFINE A MODEL or CHANGE THE MODEL keyword blocks. Requires END statement to close keyword sub-block.

CONSERVE ENERGY =

Indicates how the gas temperature at a given point should be calculated. NO indicates that the gas temperature is set to that of the largest surface in that particular volume. YES indicates that the gas temperature should be calculated by balancing the energy lost or gained through chemical reaction, convection with adjacent cells, conduction with adjacent cells, and conduction with surfaces. It can be advantageous to first solve the problem with the NO option, then use the solution as an initial guess for another simulation that calculates the gas temperatures. Part of the SPECIFY THE MATERIAL PROPERTIES keyword sub-block.

Example: CONSERVE ENERGY = YES

Units: None

Default: No

DIFFUSION COEFFICIENTS =

Indicates how the diffusion coefficients should be calculated. By default, the MIXTURE-AVERAGED approximations are used. Alternatively, MULTICOMPONENT diffusion coefficients can be obtained. These options are described more fully in the Transport User Manual. Part of the SPECIFY THE MATERIAL PROPERTIES keyword sub-block.

Example: DIFFUSION COEFFICIENTS = MULTICOMPONENT

Units: None

Default: MIXTURE-AVERAGED

INCLUDE THERMAL DIFFUSION =

By default the diffusion velocities depend only on gradients of the species’ mole fractions. If CONSERVE ENERGY = YES, then setting INCLUDE THERMAL DIFFUSION = YES will add a dependence on temperature gradients. This is most significant with mixtures of heavy and light species, for example when hydrogen is a significant component of the gas. This option will have no effect for isothermal cases. Part of the SPECIFY THE MATERIAL PROPERTIES keyword sub-block.

Example: INCLUDE THERMAL DIFFUSION = YES

Units: None

Default: No

INCLUDE KNUDSEN DIFFUSION =

Knudsen diffusion can become important in conditions where distances between surfaces become comparable to the mean free path for gas-gas collisions. As these multi-wafer LPCVD reactors are often run in conditions where this may be true, a treatment of Knudsen diffusion is included when mixture-averaged diffusion coefficients are used. Part of the SPECIFY THE MATERIAL PROPERTIES keyword sub-block.

Example: INCLUDE KNUDSEN DIFFUSION = YES

Units: None

Default: No

SCALE FACTOR FOR REACTION RATES =

Gives a scale factor used for reducing rates of gas-phase and surface reactions. This is useful in getting solutions for difficult chemical reaction mechanisms. A solution obtained with a small scale factor can provide an initial guess for a series of problems where the scale factor is gradually increased to 1.0. A scale factor of zero should not be used because it renders the composition of surfaces indeterminate. Part of the SPECIFY THE MATERIAL PROPERTIES keyword sub-block.

Example:: SCALE FACTOR FOR REACTION RATES = 0.7

Units: None

Default: 1.0