CXTFIT - Conc mode and Type of BC

A discussion forum for STANMOD users. STudio of ANalytical MODels is a software package for evaluating solute transport in porous media using analytical solutions of the convection-dispersion solute transport equation.

Post Reply
Posts: 2
Joined: Mon Apr 07, 2008 8:52 am

CXTFIT - Conc mode and Type of BC

Post by Kelvin » Mon Apr 07, 2008 8:59 am

I am new to the program and I want to estimate the transport parameters (D, V, R) from my laboratory column tests.

My laboratory test setup were as follow:

The 60 mm-long 36 mm-diameters columns were packed with various materials. The objective was to evaluate metal attenuation of the different testing materials and packing conditions. Columns were operated from bottom to top using pump (known flow rate). Background solution (without metal) was first introduced to the columns to saturate the samples. After a few pore volumn, the background solution was switched to the metal solution. The metal solution (100 mg/L lead) was then fed into the columns. Samples were
taken periodically at the top of the column to determine the metal
concentration with respect with time. Relative concentration (C/Co) and the number of pore volume were plotted to obtain breakthrough curves.

Here are my input file for CXTFIT:

(1) Type of Problem: Inverse problem
(2) Type of model: Deterministic Equil CDE (homo. and equil. assumed)
(3) Input and Output data code: time and positional are dimenisonal
(4) Time and space units: cm, mins, mg/L
(5) Concentration mode: *I am not sure on this one*
Even after reading the mannual, I am not sure what is a first/third type inlet, and total/resident/flux avg. I am currently using "Res. conc. 3rd type inlet, Cr"
(6) I put "no constraint" on parameters estimation and "no est. for total mass" (not sure on this one)
(7) Type of BC: *I am not sure on this one* - I started the pump (hence the introduction of the metal solution) and stoped when I done
(8) Type of IC: *I am not sure on this one* - Initially the columns
contain zero metal
(9) Production is zero.
(10) Data structure input code: I put "fixed depth" for BTC
(11) position of the BTC: i put "6" (for 6 cm column)

Basically I dont get any reasonable results. Can any of you tell me whats wrong?

Thank you very much for your time!


Posts: 2
Joined: Mon Apr 07, 2008 8:52 am

Post by Kelvin » Wed Apr 09, 2008 8:07 am

Anyone here can help or know where I can get the answer?

Many thanks.


Posts: 74
Joined: Fri May 21, 2004 12:50 pm
Location: Japan

Post by ntoride » Wed Apr 09, 2008 9:08 am


Sorry for my slow response. You cannot estimate v, D,and R at the same time. If you know v and theta, you can estimate D and R. Or you can estimate v and D for nonreactive solute (R=1).

(5) Flux-averaged concentration is generally used for effluent (manual p.5-6). The tird-type inlet condition is generally preferred unless v is very small and diffusion is dominant at the surface (van Genuchten and Parker, 1994).
(6) Probably step input in your case.

You also need to give reasonable initial parameter values.

If you cannot solve the problem, please send me your project folder with a cxt file (project name.cxt). I will have a look at the project.


Nobuo Toride ntoride at

Post Reply