# HydroGeoSphere/Porous Medium

## Default porous media transport valuesEdit

By default, all porous media zones (and elements) in the domain will be assigned default porous media transport properties which are listed in Table 5.21. Included here are parameters for modifying the porous medium so that it acts as a double-porosity medium for simulating transport, as described in Section 2.6.1.3 and also for isotopic fractionation, as described in Section 2.6.1.4.

Parameter | Value | Unit |
---|---|---|

Longitudinal dispersivity | 1.0 | m |

Horizontal component of transverse dispersivity | 0.1 | m |

Vertical component of transverse dispersivity | 0.1 | m |

Bulk density | 2031.25 | kg m^{−3} |

Tortuosity | 0.1 | - |

Immobile zone porosity | 0.0 | - |

Immobile zone mass transfer coefficient | 0.0 | s^{−1} |

Reverse fractionation rate | 0.0 | s^{−1} |

Fractionation factor | 0.0 | - |

Mass ratio, solid to water phases | 0.0 | - |

Thermal conductivity of the solids | 3.0 | W m^{−1} K^{−1} |

Specific heat capacity of the solids | 738.0 | J kg−1 K−1 |

Density of the solids | 2650.0 | kg m^{−3} |

The following instructions can be applied to porous media, as discussed in Section 5.8.1, to modify the default transport parameters. For each instruction we will indicate its scope (i.e. `.grok`, `.mprops`). Recall that if an instruction is used in the *prefix*`.grok` file, it will affect the current set of chosen zones, while in a properties (e.g. `.mprops`) file, it will only affect the named material of which it is a part.

## Longitudinal dispersivityEdit

`Scope: .grok .mprops`

**val**Longitudinal dispersivity [L], in Equation 2.97.

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## Transverse dispersivityEdit

`Scope: .grok .mprops`

**val**Horizontal component of the transverse dispersivity [L], in Equation 2.97.

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## Vertical transverse dispersivityEdit

`Scope: .grok .mprops`

**val**Vertical component of the transverse dispersivity [L], in Equation 2.97.

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## TortuosityEdit

`Scope: .grok .mprops`

**val**Tortuosity , in Equation 2.97.

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## Anisotropic tortuosity ratioEdit

`Scope: .grok .mprops`

**y_tortratio**Tortuosity ratio in the*y*-direction. Default value is 1.**z_tortratio**Tortuosity ratio in the*z*-direction. Default value is 1.

By default, tortuosity is isotropic, since the ratio values are set to 1 in both the *y*- and *z*-directions. You may make tortuosity anisotropic by entering a value greater than 0 and less than 1. These values will be used to multiple the tortuosity, in the *y*- and *z*-directions respectively, to obtain the directional values.

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## Bulk densityEdit

`Scope: .grok .mprops`

**val**Bulk density [M L^{−3}], in Equation 2.96. If this instruction is used, the value of the density of solids previously saved for this material is overwritten by the density of solids computed from the bulk density, the density of water and the porosity .

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By default, the porous medium acts a single-porosity medium (i.e. the immobile zone is inactive) because the porosity and mass transfer coefficient are set to zero. In order to activate the double-porosity feature, you can enter non-zero values for these parameters using the following two instructions:

## Immobile zone porosityEdit

`Scope: .grok .mprops`

**val**Immobile zone porosity, in Equations 2.101, 2.135 and 2.136.

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## Immobile zone mass transfer coefficientEdit

`Scope: .grok .mprops`

**val**Immobile zone mass transfer coefficient [T^{−1}], in Equation 2.134.

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## Isotope fractionation data...EndEdit

`Scope: .mprops`

Causes **grok** to begin reading a group of isotope fractionation instructions until it encounters an End instruction.

If no further instructions are issued, the default isotopic fractionation parameter values listed in Table 5.21 will be used.

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The following three instructions can be used to change these values:

## Reverse rateEdit

`Scope: .mprops`

**val**Reverse fractionation rate [L^{−1}], in Equation 2.143.

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## Fractionation factorEdit

`Scope: .mprops`

**val**Fractionation factor, in Equation 2.143.

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## Rock-water mass ratioEdit

`Scope: .mprops`

**val**Isotopic rock-water mass ratio, in Equation 2.102.

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The next four instructions can be used to change the thermal properties of the porous medium:

## Thermal conductivity of solidEdit

`Scope: .grok .mprops`

**val**Temperature invariant thermal conductivity of the solids [W L^{−1}K^{−1}]. The bulk thermal conductivity is computed internally from the volume fractions of the solid and liquid phases.

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## Temperature-dependent thermal conductivity of solidEdit

`Scope: .grok .mprops`

**k_s1**Thermal conductivity [W L^{−1}K^{−1}] at temperature .**t_s1**Temperature [°C] at which the thermal conductivity is equal to .

If that instruction is specified, the thermal conductivity of the solid phase is temperature-dependent. The bulk thermal conductivity is also temperature-dependent and is computed internally from the volume fractions of the solid and liquid phases. It is assumed here that the thermal conductivity of the solids decreases at a constant rate of 1% per 10°C increase in temperature and the relationship between thermal conductivity and temperature is defined with the pair of values .

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## Specific heat capacity of solidEdit

`Scope: .grok .mprops`

**val**Specific heat capacity of the solid phase [J kg^{−1}K^{−1}]. The default value is 730.0 J kg^{−1}K^{−1}.

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Note that the density of the solid phase of the porous medium is now computed automatically from the bulk density and porosity.