Running 2 NGCs

Hi Everyone,


I'm new at using TMVOC. I'm trying to run 2 NCGs (Air and CO2).

It's a simple model. Just a model of atmosphere (gas only - with NCGs air and CO2) and soil (water only). the condition is just about 20-25 degC, 1 atm.

But unfortunately it says:

 +++++++++   XX(M) = 0.100000E+06 0.000000E+00 0.000000E+00 0.250000E+02

Can anyone check what's missing? 



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  • Hi Aryo,

    Globally replace 0.999686 with 0.999685 in your INCON block and it will run. Even though the sum of the two mass fractions you specified added up to exactly 1.0 (assuming you don't want any water vapor in your system), it may numerically be slightly above 1.0. Also note that you count CO2 twice: once in air, and once as a separate component (not that TOUGH2 knows about the composition of the pseudo-component "air").

    Hope this helps.


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  • Stefan,

    It's still not working.

    the problem seems appear since the first element (001).  The initial condition in soil (1st element), I put water only, with mole fraction of air =0 and co2 also 0 (assuming there is no air or co2 in soil).

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  • Aryo,

    I did get the issue in the first element as well, but it is a follow-up error from the single-phase gas elements. You may also try to set MOP(21)=6 in case this is related to the accuracy of the solver.

    Since I cannot reproduce Aryo's issue, can anybody else look at it? Thanks.


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  • I've try run some case with this model..

    1 NCG (air only), it seems OK


    1 NCG (CO2 only), it says:

     $$$ 1 ---> 4 $$$ WAT. EVOLVES AT ELEMENT *  7 1*  $$$   PS =  0.10000E+06  PSAT=  0.23366E+04
     $$$ 1 ---> 4 $$$ WAT. EVOLVES AT ELEMENT *  7 2*  $$$   PS =  0.99969E+05  PSAT=  0.23366E+04
     (Element 701, etc is the 1st element in initial condition with gas only)


    what's wrong with this CO2 input?

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  • Aryo,

    The phase index you chose indicates you want to specify single-phase gas conditions for elements >701. The second primary variable for that case is the CO2 mole fraction in the gas phase (see TMVOC manual, Table 3). A CO2 mole fraction of 3.14E-4 is not a thermodynamically correct state for the given pressure and temperature, because for 20 C, the vapor partial pressure is very small (2337 Pa), i.e., the total gas pressure (1 bar) is (much) higher than the sum of the vapor and CO2 partial pressures, which is the reason why TMVOC suggest you wanted to specify single-phase aqueous conditions.

    The primary variables you specified would work for single-phase liquid conditions (where the second primary variable is the CO2 mole fraction in the liquid phase) or two-phase gas-aqueous conditions (where the second primary variable would be aqueous saturation) - both of these states are inconsistent with the phase index of 1 you specified.

    A valid CO2 mole fraction (if CO2 is the only NCG) for single-phase gas conditions has to be close to 1, and at the minimum 1 minus the maximum vapor mole fraction, which corresponds to 100% relative humidity for the given temperature. 

    I hope this helps resolve this and your previous issue.

    Good luck.


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