# HydroGeoSphere/Dual Continuum

## Default dual-continua transport values

By default, all dual continua zones (and elements) in the domain will be assigned default transport properties which are listed in Table 5.23:

Table 5.23: Default Values for Dual-continua Transport Properties
Parameter Value Unit
Longitudinal dispersivity ${\displaystyle {\alpha }_{ld}}$  1.0 m
Horizontal component of transverse dispersivity ${\displaystyle {\alpha }_{td}}$  0.1 m
Vertical component of transverse dispersivity ${\displaystyle {\alpha }_{td}}$  0.1 m
Bulk density ${\displaystyle {\rho }_{bd}}$  2650.0 kg m−3
Tortuosity ${\displaystyle {\tau }_{d}}$  0.1 -
First-order mass transfer coefficient ${\displaystyle {\alpha }_{s}}$  0.0 s−1

The following instructions can be applied to dual continua, as discussed in Section 5.8.1, to modify the default transport parameters. For each instruction we will indicate its scope (i.e. .grok, .dprops). 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. .dprops) file, it will only affect the named material of which it is a part.

## Longitudinal dispersivity

Scope: .grok .dprops

1. val Longitudinal dispersivity [L], ${\displaystyle {\alpha }_{ld}}$  in Equation 2.105.
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## Transverse dispersivity

Scope: .grok .dprops

1. val Horizontal component of the transverse dispersivity [L], ${\displaystyle {\alpha }_{td}}$  in Equation 2.105.
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## Vertical transverse dispersivity

Scope: .grok .dprops

1. val Vertical component of the transverse dispersivity [L], ${\displaystyle {\alpha }_{td}}$  in Equation 2.105.
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## Tortuosity

Scope: .grok .dprops

1. val Tortuosity , ${\displaystyle {\tau }_{d}}$  in Equation 2.105.
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## Anisotropic tortuosity ratio

Scope: .grok .mprops

1. y_tortratio Tortuosity ratio in the y-direction. Default value is 1.
2. 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 , ${\displaystyle {\tau }_{d}}$  in the y- and z-directions respectively, to obtain the directional values.

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## Bulk density

Scope: .grok .dprops

1. val Bulk density [M L−3], ${\displaystyle {\rho }_{bd}}$  in Equation 2.104.
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## First-order mass exchange

Scope: .dprops

1. val First-order mass transfer coefficient [L−1], ${\displaystyle {\alpha }_{s}}$  in Equations 2.138 and 2.139.
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