Porous Gas Diffusivity#

Porous Gas Diffusivity = {model_name} <integer> <float_list> [L2/t]

Description / Usage#

This card sets the model for the porous gas diffusivity, or the diffusion coefficient for diffusive species flux in the gas phase of a porous medium. It is applicable to media types POROUS_UNSATURATED and POROUS_TWO_PHASE (see Media Type card).

Definitions of the input options for {model_name} and the <integer> and <float> parameters fro each model are as follows:

CONSTANT <integer> <float1>

the name for the constant diffusivity model.

  • <integer> - phase/component; always set to zero until a multicomponent capability exists

  • <float1> - D, Diffusivity [L2/t]

POROUS <integer> <float1> <float2> <float3> <float4> <float5>

the name for a microstructure dependent porous medium model.

  • <integer> - phase/component; always set to zero until a multicomponent capability exists

  • <float1> - Dvo, binary diffusion coefficient in free space [L2/t]

  • <float2> - τ, tortuosity of the matrix skeleton

  • <float3> - P*gas, reference gas phase pressure

  • <float4> - T0, reference temperature.

  • <float5> - n, exponent on the temperature dependence (see below).

For two-phase or unsaturated flow in a porous medium, the diffusivity calculated by this model is the diffusivity of solvent vapor through the gas phase in the pore-space (see Martinez, 1995).


Porous Gas Diffusivity = POROUS 0 1.e-5 0.5 1.e+6 25.0 3

See the equation below for the diffusivity model that this card represents.

Technical Discussion#

The generalized flux of liquid phase solvent, in both gas and liquid phases, contains a term that accounts for diffusion of the liquid solvent species as gas vapor (see references below). That flux is as follows:


If the media type is POROUS_TWO_PHASE, this expression is divided by


and if in addition it is temperature dependent, this expression is multiplied by



GT-008.2: Porous Media Capabilities/Tutorial for GOMA. User Guidance for Saturated Porous Penetration Problems, August 11, 1999, P. R. Schunk

GT-009.3: GOMA’s Capabilities for Partially Saturated Flow in Porous Media, September 1, 2002, P. R. Schunk

SAND94-0379: “Formulation and Numerical Analysis of Nonisothermal Multiphase Flow in Porous Media”, Sandia Technical Report, Martinez, M. J., 1995

SAND96-2149: Drying in Deformable Partially-Saturated Porous Media: Sol-Gel Coatings, Cairncross, R. A., P. R. Schunk, K. S. Chen, S. S. Prakash, J. Samuel, A. J. Hurd and C. Brinker (September 1996)