Concentrations of solids and exchangers when changing number of cells in column

[peterwadeuk]

Hello,

I am modelling a column which is 2.5 dm long and has an internal diameter of 1.52 dm, with porosity 25%.

I believed I should normalise the column to one litre of pore water, so my conceptual model is a column of area 1.6 dm*dm and length 2.5 dm. This gives me a pore volume of one litre.

The column has 0.74 equivalents of exchanger, in this case per litre of solution.

I also have kinetic reactants plagioclase which is present in 0.25 moles per column, or because I have normalised it, 0.25 moles per litre.

Now, I need to divide my column into five or ten cells so as to conveniently model the flow rate as advective shifts.

My understanding is that PHREEQC will interpret my five cells as each having a litre of pore water associated with it.

So when I define the characteristics of the cells in terms of exchanger and kinetics blocks, do I divide by number of cells or keep the definitions as the original "per litre"?

E.g.

EXCHANGE 1-5
    X       0.74 # eq/dm3_porewater?
    -equilibrate with solution 1

KINETICS 1-5
Plagioclase
    -formula  Ca0.5Na0.5Al1.5Si2.5O8  1
    -m        0.25                                   # moles per LITRE
    -m0       0.25


I will need to interpret the output in SELECTED_OUTPUT in terms of moles of calcium as exchange species.

Please note: If I ask for Plagioclase in SELECTED_OUTPUT as a kinetic entity, then dk_Plagioclase sums correctly, if I have defined Plagioclase per cell:

KINETICS 1-5
Plagioclase
    -formula  Ca0.5Na0.5Al1.5Si2.5O8  1
    -m        0.05                                   # moles per CELL
    -m0       0.05


Thank you,
Peter

[peterwadeuk]

? Perhaps the answer to my question resides in this post:

http://phreeqcusers.org/index.php/topic,694.0/topicseen.html

[dlparkhurst]

I thought I made a post, but must not have pushed the button.

Each cell normally has about a liter of water, so you should define the other reactants as per liter. Increasing cells decreases the length for each cell and the residence time for each cell, but you do not need to scale the amount of water or of reactants.

[peterwadeuk]

Thank you David