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Keywords

TRANSPORT

This keyword data block is used to specify the number of cells and the number of "shifts" for a transport simulation. Transport simulations are one dimensional and model advective "plug flow" only. No dispersion is simulated; however, all chemical processes modeled by PHREEQC may be included in a transport simulation.

Example 

Line 0: TRANSPORT 
Line 1:      -cells 5
Line 2:      -shifts 25
Line 3:      -print 5
Line 4:       -selected_output 5

Explanation

Line 0: TRANSPORT

TRANSPORT is the keyword for the data block.

Line 1: -cells ncell

-cells--Indicates that the number of cells in the transport simulation will be given. Optionally, cells, or -c[ells].

ncell--number of cells in a one dimensional column to be used in the transport simulation. Default 0.

Line 2: -shifts nshift

-shifts--Indicates that the number of shifts or "time steps" in the transport simulation will be given. Optionally, shifts, or -sh[ifts].

nshift--number of times the solution in each cell will be shifted to the next higher numbered cell. Default 0.

Line 3: -print modulus

-print--Results will be written to the output file during transport step numbers that are evenly divisible by modulus. Optionally, -p[rint]. Note the hyphen is required to avoid a conflict with the keyword PRINT.

modulus--Printing to the output file will occur after every modulus transport steps. Default 1.

Line 4: -selected_output modulus

-selected_output--Results will be written to the selected-output file during transport step numbers that are evenly divisible by modulus. Optionally, -se[lected_output]. Note the hyphen is required to avoid a conflict with the keyword SELECTED_OUTPUT.

modulus--Printing to the selected-output file will occur after every modulus transport steps. Default 1.

Notes

The transport capabilities of PHREEQC are derived from a more complete formulation of 1-dimensional, advective, dispersive transport presented by Appelo and Postma (1993). In this example a column of five cells (ncell) is modeled and 5 pore volumes of filling solution are moved through the column (nshift/ncell is 5). Most of the information for transport calculations must be entered with other keywords. Transport assumes that solutions with numbers 0 through ncell have been defined using SOLUTION input or SAVE. These solutions represent the infilling solution (solution 0) and the initial solution in each cell (1 through ncell). Pure-phase assemblages may be defined with EQUILIBRIUM_PHASES or SAVE, with the number of the assemblage corresponding to the cell number. Likewise, an exchange assemblage, a surface assemblage, and a gas phase can be defined for each cell through EXCHANGE, SURFACE, GAS_PHASE, or SAVE keywords, with the identifying number corresponding to the cell number. Note that ranges of numbers can be used to define multiple solutions, exchange assemblages, surface assemblages, or gas phases simultaneously and that SAVE allows a range of numbers to be used. REACTION can also be used to define a stoichiometric reaction that applies to each cell at each time step, with the reaction number corresponding to the cell number. This capability is not very useful because it represents only zero-order kinetics. Better definition of kinetic reactions is obviously needed. The MIX keyword can be used in transport modeling to define simplistic dispersion or lateral inflow to the column. At each shift, solution ncell-1 is moved to cell ncell, any stoichiometric reaction or mixing for cell ncell is added, and the solution is equilibrated with the contents of cell ncell; solution ncell-2 is moved to cell ncell-1, reaction or mixing for cell ncell-1 is added, and equilibrated with the contents of cell ncell-1; and so on until solution 0 is moved to cell 1. The moles of pure phases and the compositions of the exchange assemblage, surface assemblage, and gas phase in each cell are updated with each shift.

By default, the composition of the solution, pure-phase assemblage, exchange assemblage, surface assemblage, and gas phase are printed for each cell for each shift. Use of -print will limit the amount of data written to the output file. In the example, results are written to the output file after each integer pore volume has passed through the column. Data written to the output file can be further limited with the keyword PRINT (see -reset false). If SELECTED_OUTPUT has been defined (recommended), then each cell and each shift will produce an additional line in the selected-output file. Use of -selected_output will limit the frequency that data are written to the selected-output file. The setting for -print does not affect the selected-output file.

The capabilities provided with the TRANSPORT keyword are not intended to be a complete formulation of chemical reaction in flowing conditions. It is, however, sufficient to make initial investigations, and by comparison to other programs it is computationally fast. For many systems with limited data, the kinds of calculations available with TRANSPORT are adequate and appropriate.

Example problems

The keyword TRANSPORT is used in example problems 9 and 10.

Related keywords

EXCHANGE, GAS_PHASE, MIX, PRINT, EQUILIBRIUM_PHASES, REACTION, REACTION_TEMPERATURE, SAVE, SELECTED_OUTPUT, SOLUTION, and SURFACE.

Example
Explanation
Notes
Example problems
Related keywords
User's Guide to PHREEQC - 07 MAY 96
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