Mass Fraction to PPM

  • Last Post 14 August 2018
Carly posted this 14 August 2018


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

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abenhadj posted this 14 August 2018

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!

Best regards, Amine

Dino posted this 14 August 2018

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.