Learning Forum

[Carly]

Hey
I want to convert from mass fraction of a species into PPM in a UDF or custom field function. I saw many define it as mass fraction x 10^6 while others define it as mass fraction x density of mixture x 10^6 / density of species. Would you please let me know which one is correct or if there is another way. Thanks

[Amine Ben Hadj Ali]

You need to stick to one of the definitions from the literature: ppm mole or ppm weight or ppm volume or..... All definitions are correct you need to select one which fits your needs. You have to make that decision!

[Dino]

If volume: PPM = mass fraction * density_mix * 10^6 / density_species

If weight: PPM = mass fraction * 10^6

If mole: PPM = mass fraction * 10^6 * MW_mix / MW_species

In UDF: you can access the mass fraction via C_YI(c, t, i) where i is the species index. C_R(c, t) for the density of the mixture. I did not need to call the molecular weight (MW) before so I am not sure how to access it through the UDF. Hope this helps. 

 

 

[jacklien]

I suggest to use ppm to percent calculatornn

[AK AK]

i have a concentration 40,000 ppm of CO2 in cabin of volume 3.4 m^3 ,how to convert to mass or mole fracti

on??

[Rob]

I find Google/Wiki/books to be very good for this sort of thing. 

[AK AK]

how to define these initial conditions in  ansys ??

shall i add source term  in cell zone condition?

 

[Rob]

Initial conditions are set in the Initialisation step. You may find you need to review which of Standard or Hybrid is best suited, but also check Patch. We may want to let the solver calculate some values from a boundary but then pre-set something else (species or phase) via patch. 

A source term is the equivalent to a boundary condition and so will govern how the solution progresses/ends.