Understanding Precipitate Removal Mass Flux Links

Precipitate removal mass flux links are used to transport precipitated mass directly from one pathway to another. Mass can precipitate in a Cell if solubility limits have been defined for the species in the fluid within the Cell.

They are defined by specifying a fractional rate at which the precipitated mass is being moved from one pathway to another. Hence, a precipitate removal mass flux is computed as the precipitated mass of the species in the pathway multiplied by a fractional transfer rate:

Precipitate Removal Mass Flux = Precipitated Cell Mass * Transfer Rate

The Transfer Rate has dimensions of inverse time. The Transfer Rate is specified as a scalar. That is, all precipitate species are transferred at the same rate.

In most applications, the Transfer Rate will simply be input either as a large number (such that any precipitated mass is immediately removed) or a function that alternates between 0 and a large number (such that any precipitated mass is periodically removed, and allowed to accumulate between removals).

Note that in most cases, in order to use a Precipitate removal mass flux link you will need to specify a local solubility (a solubility that varies depending where you are in the model).

As an example of how you might apply a precipitate removal mass flux link, consider the following. Suppose that you were simulating a process in which a particular metal was precipitated out of solution within a tank. Once a month, you removed the precipitate from the tank. You could use a precipitate removal transfer flux link to represent the kinetics in this case. You would create a link to a Sink Cell (where the precipitate is collected), and the transfer rate would be increased to a large number once per month (e.g., for 1 day), which would have the effect of "cleaning out" the tank of any precipitate. For the rest of the simulation, the transfer rate would be zero (and precipitate would collect in the tank).