STOMP

Solute/Fluid Interaction Card Options (GT)

Effective Diffusion Options

Constant Diffusion Model

The constant molecular diffusion option assumes that the effective diffusion coefficient in the porous media is equal to the free-water diffusion coefficient. For most simple aqueous species the free-water diffusion coefficient is about 10-5 cm2/s (10-9 m2/s).   

Symbols

effective diffusion coefficient, m2/s
free water diffusion coefficient, m2/s
Conventional Diffusion Model

In a saturated porous medium, the cross-sectional area available for diffusion in the aqueous phase is reduced by the porosity. In unsaturated porous media there is an additional reduction in cross-sectional area available for diffusion as a result of the reduced volumetric water content.

Symbols

effective diffusion coefficient, m2/s
free water diffusion coefficient, m2/s
aqueous phase tortuosity
actual aqueous liquid saturation
diffusive porosity
Kemper and van Schaik Empirical Diffusion Model

Symbols

effective diffusion coefficient, m2/s
free water diffusion coefficient, m2/s
actual aqueous liquid saturation
diffusive porosity
fitting coefficient
fitting coefficient

Gas/Aqueous Partition Function:

Constant

Symbols

solute concentration in aqueous phase, 1/m3
solute concentration, 1/m3
diffusive porosity
total porosity
actual aqueous liquid saturation
porous media grain density, kg/m3
solute solid-aqueous distribution coefficient, m3 aqu/kg solid
Temperature Dependent

Symbols

solute concentration in aqueous phase, 1/m3
solute concentration, 1/m3
diffusive porosity
total porosity
actual aqueous liquid saturation
porous media grain density, kg/m3
solute solid-aqueous distribution coefficient, m3 aqu/kg solid
Water Vapor Equilibrium

Symbols

solute concentration in aqueous phase, 1/m3
solute concentration, 1/m3
diffusive porosity
total porosity
actual aqueous liquid saturation
porous media grain density, kg/m3
solute solid-aqueous distribution coefficient, m3 aqu/kg solid

Solid/Aqueous Partition Options:

Continuous Solid Wetting

Symbols

solute concentration in aqueous phase, 1/m3
solute concentration, 1/m3
diffusive porosity
total porosity
actual aqueous liquid saturation
porous media grain density, kg/m3
solute solid-aqueous distribution coefficient, m3 aqu/kg solid
Noncontinuous Solid Wetting

Symbols

solute concentration in aqueous phase, 1/m3
solute concentration, 1/m3
diffusive porosity
total porosity
actual aqueous liquid saturation
porous media grain density, kg/m3
solute solid-aqueous distribution coefficient, m3 aqu/kg solid

Reaction Options

No Reaction

No reaction occurs.

Radioactive Decay

Decay or generation of solutes occurs in the STOMP simulator through an Arrhenius type kinetic reaction according to

The decay-rate constant can be related to the radionuclide half-life according to

Production of progeny solutes from parent solutes is computed through an Arrhenius type kinetic reaction according to

The chain decay fraction is a function of the parent-progeny pair, and the subscripts j and k indicate parent and progeny solutes respectively.

Symbols

solute concentration of component i, 1/m3
solute concentration of component j, 1/m3
solute concentration of component k, 1/m3
time, s
radioactive decay constant of component i, 1/s
radioactive decay constant of component j, 1/s
radioactive decay half-life of component i, s
chain decay fraction for radionuclide pair jk
First-Order Reactions

Decay can also be simulated based on first-order and Monod chemical reactions. For first-order reactions, the reaction rate for each chemical reaction is dependent on the molar concentration of the primary reactant. The reaction rate factor is a function of the primary and secondary reactant molar concentrations, equation stoichiometry, reaction half-life, and simulation time step according to the following equations:

Symbols

reaction rate factor
component of reaction rate factor
primary reactant concentration, 1/m3
secondary reactant concentration, 1/m3
moles of primary reactant pr
moles of secondary reactant r
time, s
reaction half-life, s
 

References

Campbell, GS. 1985. Soil Physics with Basic: Transport Models for Soil-Plant Systems. Elsevier Science Publishers, New York, New York.

Kemper, WD and JC van Schaik. 1966. "Diffusion of Salts in Clay-Water Systems," Soil Sci. Soc. Am. J., 30:534-554.

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