Re: modelling a stirred tank reactor

["David L Parkhurst" <dlpark@xxxxxxxx>]

> Now are there more elegant ways to do it ?

I've included an input file that performs a mixing calculation. I think it
is close to what you want to do if you add the kinetic reaction. In the
setup, solution 3 mixes with solution 1 in a two-cell transport
calculation. It uses two cells because the minimum number of cells in a
column for TRANSPORT is two, but calculations for cell 2 are ignored.

For the transport calculation, there is no flow (flow_direction
diffusion_only) and boundary conditions closed. A single stagnant cell is
defined for each cell of the column; this allows explicit mixing factors to
be defined for each cell. The mixing characteristics of cell 1 are defined
explicitly by MIX 1, in this case .9 of solution 1 remains and .1 of
solution 3 is added at each shift (mix). The composition of solution 3 does
not change. The number of mixes is determined by the number of "shifts" in
the transport calculation. You can run a transport calculation for a number
of shifts, then redefine solution 3, and define another transport
calculation to simulate a change in the feed to the reactor. Adding a
definition for KINETICS 1 (and RATES and appropriate time_step in
TRANSPORT) will include a kinetic reaction for cell 1. Similarly, you can
add EQUILIBRIUM_PHASES 1, SURFACE 1, EXCHANGE 1, or SOLID_SOLUTIONS 1 to
include those processes in the reactor.

The example runs two mixes and the amount of bromide initially present in
cell 1 decreases from 1 to .9 to .81 in the successive shifts in accordance
with the mixing fraction of .9 of the solution remains and no additional Br
is added.

> How can I define a new solution from previously stored parameters OUTSIDE
a
rate function ?

Hopefully you do not have to do this. It is probably possible to use clever
definitions of another stagnant cell to save a solution. It is probably
also possible to define a series of kinetic reactions, each of which adds
back a saved quantity for a single element.

> Can one make a DO LOOP to group a MIX and RATE function

No, I've thought about it, but never got around to coding it.

David


solution 0-4
      Na    1
      Cl    1
end
solution 1-2
      K     1
      Br    1
end
MIX 1
      3     .1
      1     .9
END
KINETICS 1
 ....
TRANSPORT
    -cells                 2
    -shifts                2
    -time_step             1 # seconds
    -flow_direction        diffusion_only
    -boundary_conditions   closed closed
    -stagnant              1  0  0  0
    -print_cells           1
    -punch_cells           1
    -warnings              true
END



David Parkhurst (dlpark@xxxxxxxx)
U.S. Geological Survey
Box 25046, MS 413
Denver Federal Center
Denver, CO 80225

Project web page: https://wwwbrr.cr.usgs.gov/projects/GWC_coupled