enthalpy exact calculation
enthalpy exact calculation
(OP)
Hello to all!
I have a question regarding enthalpy calculation... I am trying to do some exergy analysis and I need to have exact enthalpy values... which values for cp,air cp,wv and r (h=cp,a*T+w(r+cp,wv*T)) do I need to use to get exact enthalpy values for moist air (compared to ashrae tables)? using suggested approximate values cp,air=1,006 co,wv=1,86 and r=2501 i get slightly different results than values in ashrae table - error is +/- 0,1 but this can result in a significant error in exergy efficiency in some cases (exergy efficiency larger than 1). I ruled out other possible causes for this...
i tried to get polinomal equations for dry and saturated air enthalpy (form ashrae table) but i do not get good results with excel.. because i need to calculate a lot of different cases, calculating moist air enthalpy 'by hand' from ashrae tables would take A LOT of time...
i hope i was cleat what i need to do :)
thanks!
I have a question regarding enthalpy calculation... I am trying to do some exergy analysis and I need to have exact enthalpy values... which values for cp,air cp,wv and r (h=cp,a*T+w(r+cp,wv*T)) do I need to use to get exact enthalpy values for moist air (compared to ashrae tables)? using suggested approximate values cp,air=1,006 co,wv=1,86 and r=2501 i get slightly different results than values in ashrae table - error is +/- 0,1 but this can result in a significant error in exergy efficiency in some cases (exergy efficiency larger than 1). I ruled out other possible causes for this...
i tried to get polinomal equations for dry and saturated air enthalpy (form ashrae table) but i do not get good results with excel.. because i need to calculate a lot of different cases, calculating moist air enthalpy 'by hand' from ashrae tables would take A LOT of time...
i hope i was cleat what i need to do :)
thanks!





RE: enthalpy exact calculation
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RE: enthalpy exact calculation
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RE: enthalpy exact calculation
http://thermodynamik.hs-zigr.de/fpc/index.php
It should be based on the Hyland Wexler formulation of thermodynamic properties of humid air adopted by ASHRAE.
RE: enthalpy exact calculation
RE: enthalpy exact calculation
I am not sure I understand what your problem is.
There are many good polynomial expressions (and non polynomial) for the Enthalpy (vapor state) for, separately
nitrogen, oxigen, water, and rare gaz if you wish
You do a two step process
1) determine the composition (H2O content, ....)
2) calculate enthalpy from compnents and temperature
If you could provide an exemple, with your calculations, that would help check
RE: enthalpy exact calculation