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Posted: Mon Dec 03, 2007 12:40 pm
by Alessandro
Dear all,
I am very new to STANMOD/CXTFIT, and trying to understand how to use it. I am a bit confused by the output format when using the deterministic non-equilibrium CDE.
Particularly, I do not understand the meaning of the variables C1 and C2. According to the manual, these are the concentrations for the equilibrium and non-equilibrium sites (page 17 of the manual). How are these concentrations related to the fluid concentration at the sampling location?
Also, I would expect the value of C1 to be 0 when I set f=0 (non-equilibrium sites only). This is not the case (see e.g. case 1, example 7.6a). Could you please give me some hints on this?


Posted: Mon Dec 03, 2007 4:37 pm
by Jirka

Here is a quick answer (I'm sure Nobou will give you a more detailed answer later):

C1 is the concentration in the equilibrium phase. This means this is the concentration in liquid (mobile) phase (not on equilibrium sorption sites).

C2 is the concentration in the nonequilibrium phase. This means this is the concentration either in the immobile liquid phase or on the kinetic sorption sites.

For the dimensional forms of both C1 and C2 concentration consult the manual.


Posted: Thu Dec 06, 2007 12:45 am
by ntoride

Thanks, Jirka, for your prompt reply.

>Also, I would expect the value of C1 to be 0 when I set f=0
>(non-equilibrium sites only).

As defined in Table 3.1 of the manual, C2 = s_k/(Kd c_o) for the one-site model assuming f=0. C2 is the adsorbed concentration of the kinetic site and C1 is the concentration of the solution phase for the chemical nonequilibrium model. Please note that we use the same nondimensionless equations for physical and chemical nonequilibrium transport. For detailed information, please refer to

van Genuchten, M. Th., and R. J. Wagenet, Two-site/two-region models for pesticide transport and degradation: theoretical development and analytical solutions, Soil Sci. Soc. Am. J., 53, 1303-1310, 1989

Please also note that the difference between the flux concentration for effluent and the resident the concentration:

Parker, J.C., and M. Th. van Genuchten, Flux-averaged and volume-averaged concentrations in continuum approaches to solute transport, Water Resour. Res., 20, 866-872, 1984a.

If any further questions, please do not hesitate to ask me.


Posted: Tue Dec 11, 2007 8:37 am
by Alessandro
Dear Jirka, dear Nobuo,
thanks for the very prompt reply. There is still something I don't understand, but I am reading the references suggested.
In case I'll need more details, I'll post again on the forum.

Thanks a lot!
All the best