[riteshnw]

Hi guys...
I want to model fire with the mass fractions of oxygen and nitrogen.
I can add the mass fraction of oxygen by default and the row for mass fraction of nitrogen is not available.
To add the nitrogen row, I have to add air and I can put the nitrogen mass fraction as well.
But, when I start the simulation, the error comes up saying that "Error at Node 27: Species air not in thermo database"
Can someone please help or suggest me something?
Thank you.

Best regards,
Ritesh

[Jegan]

Hi,

Nitrogen is the bulk species(last_species), so it will not appear in species tab but it will consider the rest of the mass fraction.for example if you give 0.21 for oxygen then that bulk species will consider 0.79(i.e,the rest mass fraction).

[Khan_CFD]

Originally Posted by riteshnw

Hi guys...
I want to model fire with the mass fractions of oxygen and nitrogen.
I can add the mass fraction of oxygen by default and the row for mass fraction of nitrogen is not available.
To add the nitrogen row, I have to add air and I can put the nitrogen mass fraction as well.
But, when I start the simulation, the error comes up saying that "Error at Node 27: Species air not in thermo database"
Can someone please help or suggest me something?
Thank you.

Best regards,
Ritesh

You may select oxygen and nitrogen as two fluids in materials section. as N2 is having highest mass fraction in air, order the selection such that N2 is last fluid selected. That means select O2 first and then N2. N2 should appear last in the list. See help section for material selection by clicking help tab on material selection window. You will have option to give composition only for N-1 species. The last species composition is calculated by Fluent as 1-(sum of remaining all mass fractions). Selecting highest mass fraction species at the last will minimize numerical error while solution.

Best wishes...