Processes > Reactive transport modelling

Regarding the effect of RM_SetUnitsKinetics

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adityain2003:
Hello Everyone,

I am working with a variably saturated flow model linked with PhreeqcRM

I have doubt about the effect of RM_SetUnitsKinetics. I am providing the initial concentration of some species, while passing some though set_concentration and get_concentrations, and performing kinetics with the species. How does the RM_SetUnitsKinetics with argument of 0,1 and 2 influences the moles of reactants in a cell?

dlparkhurst:
SetUnitsKinetics only affects the initial moles of the kinetic reactants when InitialKinetics2Module is called. The value has no effect during time stepping, and does not affect the concentrations of aqueous species, only the initial moles of kinetic reactants.

SetUnitsSolution does determine the units that are used in converting the species concentrations from the transport model to the moles used in PhreeqcRM in SSetConcentrations, and in the reverse calculation GetConcentrations. All other SetUnits... methods only affect the initial conditions.

adityain2003:
Thank you, Parkhurst, for your reply.

I also want to ask that which equation does Phreeqc uses to compute new concentrations based on the moles transferred in a kinetic reactions. Say, 'm' moles are produced of species A, how is the new concentration computed?

dlparkhurst:
If your rate equation has


--- Code: ---100 SAVE mol

--- End code ---

and the formula is


--- Code: ----formula Doc -1 CH2O 1

--- End code ---

If mol is positive, then the moles of Doc in solution is decreased by mol; C, H, and O moles in solution are increased by mol, 2*mol, and mol, respectively; and the moles of the kinetic reactant (M or KIN("name")) are decreased by mol.

If mol is negative, then Doc is increased; C, H, and O are decreased; and M is increased.

Note that the changes are in moles, not concentration. The change in molality would be mol times coefficients divided the mass of water currently in the calculation (mass of water is given by the Basic Function TOT("water")).

adityain2003:
Thank you!

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