The influence of humidity on the mass fraction of other AIR components #13500
mst-parkhachev
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Yes, the INFTY inputs are for dry air (no moisture). The adjustment is just done by simple algebra. If you had 1 kg of dry air being 0.77 kg of N2 and 0.23 kg of O2 and your humidity was a 2 % mass fraction, then that would mean you now have 0.77 kg N2, 0.23 kg O2, and x kg of H2O where x satisfies x/(1+x) = 0.02. Once you know x you can renormalize everthing back to 1, i.e., N2 becomes 0.77/(1+x). The default species mixutures are defined in read.f90 in SETUP_PREDEFINED_SMIX. |
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Thank You for detailed answer, Dr. Jason! |
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Dear colleagues!
I could not find a detailed description in the manual of how exactly the HUMIDITY parameter affects the mass fraction of other air components at the beginning of the calculation.
I found the following comment by dr_jfloyd
https://groups.google.com/g/fds-smv/c/liYnTJCVEWA/m/dH_oWwh4AQAJ
Air in FDS by default consists of four components: oxygen, carbon dioxide, nitrogen and water vapor. Is it true that Y_O2_INFTY and Y_CO2_INFTY parameters are used to calculate the mass fractions of oxygen, carbon dioxide and nitrogen assuming that there is no water vapor at all? Is it true that their mass fractions are then proportionally reduced to account for the presence of water according to the HUMIDTY parameter?
Could you also provide a link to the FDS code where this calculation is made?
I found the functions WATER_VAPOR_MASS_FRACTION(HUMIDITY,TEMP,PZONE) and RELATIVE_HUMIDITY(Y_H2O,TEMP,PZONE), but they do not answer my question.
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