Creating and Editing Diffusive Mass Flux Links

In addition to the Definition tab, Cell pathway A transport pathway element that is mathematically equivalent to a finite difference node. Cells are commonly applied to simulate discrete compartments in an environmental system (such as ponds, lakes, shallow soil compartments, or the atmosphere). elements in GoldSim have three additional tabs at the top of their editing dialog: Inflows, Outflows, and Diffusive Fluxes:

The Inflows and Outflows tabs are used to create advective and several special purpose mass flux links.

The Diffusive Fluxes tab is used to create diffusive flux links involving the current pathway.

The DiffusiveFluxes tab is shown below:

To create a new Diffusive Flux (a mass flux link An interconnnection between two transport pathways that defines the rate at which species move between the pathways. from the current pathway to another pathway), do the following:

1. Double-click on a Cell pathway to display the pathway editing dialog.
2. Click on the Diffusive Fluxes tab.
3. Press the Add Flux button. This will bring up a browser An alternative view of a GoldSim model, in which elements are displayed in a tree, and organized either hierarchically, or by type. showing all of the other pathways (or Containers with pathways) in the model.
4. Select the pathway you wish to link to and press OK.
5. GoldSim will then display the dialog for selecting the media Materials (such as water, sand, clay, air) that constitute (are contained within) transport pathways. GoldSim provides two types of elements for defining media: Fluids and Solids. involved in the mass flux link:
   
   
   If you change your mind or have selected the wrong pathway, press the Select... button to change the pathway.
   
   The two fields labeled Fluid in this dialog are drop lists containing all of the fluids in the corresponding pathways. (If the mass flux link involves a Pipe, External or Network pathway A transport pathway element that provides a computationally efficient way to simulate large, complex networks of one-dimensional conduits in order to describe contaminant transport through fractured rock systems., the medium involved in the link must be the Reference Fluid A special type of Fluid element that provides a basis for defining partition coefficients between media for the various species in the model (i.e., the ratio of the species’ concentration in the medium to its concentration in the Reference Fluid at equilibrium)., and this will be the only choice in the list.)
   
   The default Link Type for a Diffusive Flux between Cells is Coupled (and, by definition, it cannot be changed). The default Link Type for a Diffusive Flux to a non-Cell pathway is Normal (and, by definition, it cannot be changed to Coupled).
   
   Select a fluid in each pathway and press OK.
6. You will then be returned to the Diffusive Fluxes tab. Move your cursor to the Properties of Selected Diffusive Flux section and enter the Lengths for the two sides of the link. The value must be non-negative. At least one of the lengths must be non-zero.
7. Select the porous medium on each side of the link. The drop-list will include all solids located in the pathway. You do not have to select a porous medium (the default is "none").
8. Specify the Diffusive Area for the link. This must be non-negative.
9. If you wish to save the mass flux Final Values or Time Histories for the link, select one or both of the checkboxes.
10. Press OK to close the pathways dialog.

Note: If the diffusive flux link involves a non-Cell pathway, the Length and Porous Medium will be grayed out for that side of the connection and set to 0 and none, respectively, since GoldSim assumes that there is no diffusive resistance on the non-Cell side of a diffusive mass flux link.

After a diffusive flux is created, you can always change the properties of the flux (i.e., the lengths, diffusive areas, porous media, and whether or not results are to be saved) by selecting the diffusive flux in the top of the dialog (by clicking on the appropriate row in the List of Diffusive Fluxes) and editing the properties in the lower section of the dialog (Properties of Selected Diffusive Flux).

The Diffusive Fluxes tab only displays the pathway name, and does not indicate where the pathway exists in the model. If, however, you hold your cursor over a pathway in the list, a tool-tip displays the full containment path for the pathway.

Note: Once a Diffusive Flux is created, you cannot change the fluids which are involved. The only way to change the fluids is to delete the Diffusive Flux and recreate it.

A Diffusive Flux is deleted by selecting it in the top of the dialog (by clicking on the appropriate row in the List of Diffusive Fluxes) and pressing the Delete Flux button.

When you create a diffusive mass flux link A mass flux link in which species diffuse between pathways according to a concentration gradient., the link automatically appears in the Diffusive Fluxes tab of both pathways. The properties of the mass flux link can be edited from either location.

Note: The Diffusive Fluxes tab is only available for a non-Cell pathway after a diffusive link has been made to it. Furthermore, the Add Flux button is disabled for non-Cell pathways, preventing you from creating new diffusive flux links (i.e., you can only create new diffusive flux links from Cell pathways).