Species Mass fraction in Fluent
 

hello users,
need some help regarding specifying mass fraction of species in fluent

I have two inlets.. one from which only air enters...
and the other from which CO enters (g/s)...

For the air inlet I do not specify any mass fraction... (all species fraction 0)
for the CO inlet I specify CO mass fraction as 1.

Is this approach correct?

In the Fluent solver i have opted for species transport of air-co mixture template.
No reactions.

Kindly help,
Prashant

Dear All,

I have a similar question. I am trying to use CFD fluent for coal combustion where coal is carried by either CO2 or N2. I could use CO2 as a carrier gas from the species mass fractions. However, I can't find N2 in the species list.
It will be highly appreciated if anyone can suggest that how to add N2 in the species list.

Cheers,
Manab

if you go to Mixture Species/ Selected species , N2 will be at the end of your selected species list. It means that while you are setting your mass fractions, N2 will be selected automatically. For example;

If you chose mass fraction of O2 to 0.23, N2 will be 0.77 automatically or if you chose 0.5, N2 will be 0.5.

Could you explain more? or show a picture of your geometry?

dear a_cucen,
I managed to solve my problem. I wanted to model the CO dispersion due to on-road traffic emission.
I modelled road as a mass flow inlet emitting CO (kg/s). I used to specify CO mass fraction as 1 for this inlet.
The other inlet varied depending on the direction of the ambient wind. NO CO mass fraction was specified.
Using this approach I got very high CO concentration (about 600-700ppm).

However, when switched to a volumetric source (defining a small zone above the road where CO is emitted), I got acceptable CO concentrations (1-4 ppm) which compared well with actual measured concentrations.

If anyone can explain why I did not get results by the first approach, I'd be grateful.

Regards,
Prashant

HI,

Can any one please mention what is the conversion factor used for getting the results in ppm. we are considering 1 ppm = 10^4 of mass fraction (which we are getting in Ansys).

Please tell this is correct or not and will it be changing depending on gas.

Thanks in advance,
Mahesh