************************** **Porous Gas Diffusivity** ************************** :: Porous Gas Diffusivity = {model_name} [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 and parameters fro each model are as follows: +----------------------------+-------------------------------------------------------------------------------------+ |**CONSTANT** |the name for the constant diffusivity model. | | | | | | * - phase/component; always set to zero until a multicomponent capability | | | exists | | | * - D, Diffusivity [L2/t] | +----------------------------+-------------------------------------------------------------------------------------+ |**POROUS** |the name for a microstructure dependent porous medium model. | | | | | | * - phase/component; always set to zero until a multicomponent capability | | | exists | | | * - Dvo, binary diffusion coefficient in free space [L2/t] | | | * - τ, tortuosity of the matrix skeleton | | | * - P*gas, reference gas phase pressure | | | * - T0, reference temperature. | | | * - 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). ------------ **Examples** ------------ :: 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: .. figure:: /figures/418_goma_physics.png :align: center :width: 90% If the media type is **POROUS_TWO_PHASE**, this expression is divided by .. figure:: /figures/419_goma_physics.png :align: center :width: 90% and if in addition it is temperature dependent, this expression is multiplied by .. figure:: /figures/420_goma_physics.png :align: center :width: 90% -------------- **References** -------------- 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)