An associated Cell is intended to represent the behavior of a single
package within a Source. If a Source has multiple packages, GoldSim
automatically scales some of the properties of the Associated Cells in order to
represent that the Cells contain the exposed mass of multiple packages.
The Associated Cell properties that are scaled internally
by GoldSim are as follows:
• the
volume and masses of the media in the Cell;
• the flow
rate for advective mass flux links from the Cell; and
• the
diffusive area for diffusive mass flux links to/from the Cell.
These properties are dynamically multiplied by the number
of failed packages. Hence, at any given time in a simulation, an
Associated Cell actually represents the group of all the packages which have
failed up to that time. In effect, GoldSim accounts for the presence of
multiple packages by simply increasing the size of the Associated Cells.
An implicit assumption of this approach is that at any
given time, all of the exposed mass within a Source is evenly distributed among
the failed packages. In reality, the exposed mass may be concentrated in a
fraction of the failed packages (e.g., those that have failed recently). In
cases where solubility limits are involved, assuming that the exposed mass is
evenly distributed throughout all the failed packages can be conservative with
respect to release rates (i.e., result in an overestimate for the rate of mass
transfer). This is because if mass transfer from a single package is
actually limited by solubility considerations, spreading the same mass over a
number of packages could have the effect of artificially negating this
limitation.
In order to avoid this assumption and more accurately
simulate the mass transfer within a source, it would be necessary to represent
every package using a separate set of Associated Cells. If only a limited
number of packages exist (e.g., 10), this could be accomplished by defining a
separate Source for each package. If the number of packages numbers in the
hundreds or thousands, however, such an approach would quickly become
computationally impractical.
Note: Because properties of Associated Cells are scaled internally with the number of failed packages, you should take great care when creating mass transfer connections in which mass could move into an Associated Cell from outside of the Source. In most cases, such a connection would not make sense physically (since the properties of the Associated Cell receiving the mass only represent the failed packages inside the Source). As a result, typically, it would only be physically meaningful to create mass transfer connections into Sources in which all packages are assumed to fail immediately.
Related Topics…