Flux Links to/from External Pathways

In order to integrate the External pathway A transport pathway element that provides a mechanism by which external program modules for contaminant transport (e.g., analytical, finite elelement, or finite difference models) can be directly integrated into GoldSim. into your pathway network, you create mass flux links to and from the pathway.

The only way to transport mass out of an External pathway is by specifying an advective mass flux link A mass flux link in which a quantity of a medium is specified to flow from one pathway to another, carrying dissolved, sorbed, and/or suspended species with it. to another pathway. Diffusive mass flux links from External pathways (diffusive outfluxes) and special purpose (direct transfer, precipitate removal and treatment) mass flux links from External pathways cannot be created.

Note that the flow rate of the fluid defined in an advective mass flux link An interconnnection between two transport pathways that defines the rate at which species move between the pathways. from a External pathway, if used at all, is only used to determine how mass from a single output vector A one-dimensional array. passed from the External pathway function is apportioned between multiple Outflow flux links

That is, the mass flux link is used only to specify where the mass is to be discharged. The External pathway function itself determines the rate at which mass is discharged to that location.

You can transport mass into an External pathway via an advective mass flux link from any other type of pathway and/or via a diffusive mass flux link A mass flux link in which species diffuse between pathways according to a concentration gradient. from a 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).. Within GoldSim, the concentration and diffusive length on the External pathway side of a diffusive mass flux link are assumed to be zero. Hence, like advective mass flux links, diffusive mass flux links involving External pathways are uni-directional.

Note: When you create an advective mass flux link from an External pathway, GoldSim will assume that 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). is the flowing fluid. Note, however, that because the mass flux link is really only used to determine where mass from the External pathway is to be discharged, conceptually the mass flux link can represent any medium (and any type of transport process) you choose. Because all pathways contain a Reference Fluid, you will be able to create an advective mass flux link from an External pathway to any other pathway in the model. Similarly, you can create an advective mass flux link from any pathway in your model to an External pathway, even if the flux link involves a fluid other than the Reference Fluid. That is, unlike advective flux links between other pathway types, GoldSim does not force both pathways to contain the flowing fluid when the link involves an External pathway.