Volume or Weight ratio in modelling Air?

immortality · August 16, 2013, 09:40

in the constant folder I have set Air coefficients for JANAF thermoType from averaging air components.but have a doubt,I have set coefficients according to 75% N2 and 25% O2 as my adviser proposed,but I want to be more accurate,
is averaging based on weights more precise or based on volumes?
in what extent its important?is it necessary to change the approximate coefficients?
http://www.engineeringtoolbox.com/ai...ion-d_212.html

wyldckat · August 31, 2013, 12:32

Hi Ehsan,

Do you mind providing more information? Namely how did you exactly define those values of 75% vs 25%?

Best regards,
Bruno

immortality · August 31, 2013, 14:39

Hi Bruno
I have multiplyed the JANAF coefficients(7 numbers) of nitrogen to .75 and for oxygen have multiplied them to .25 and then added them together,isn't it correct? the answers look fine but I want to know is this numbers accurate enough?

wyldckat · August 31, 2013, 14:50

Hi Ehsan,

OK, still not enough information. So I ask in more detail:

How exactly did you do the math?
- No need to specify all of the coefficient values, "a0, a1" and so on is enough.
And what results did you get?
And in comparison with the values used in the dictionary file, what values were you using before and are using now?

Best regards,
Bruno

August 16, 2013, 09:40	Volume or Weight ratio in modelling Air?	#1
immortality Senior Member Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,208 Rep Power: 26	in the constant folder I have set Air coefficients for JANAF thermoType from averaging air components.but have a doubt,I have set coefficients according to 75% N2 and 25% O2 as my adviser proposed,but I want to be more accurate, is averaging based on weights more precise or based on volumes? in what extent its important?is it necessary to change the approximate coefficients? http://www.engineeringtoolbox.com/ai...ion-d_212.html __________________ Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King. To Be or Not To Be,Thats the Question! The Only Stupid Question Is the One that Goes Unasked.

August 31, 2013, 12:32		#2
wyldckat Retired Super Moderator Bruno Santos Join Date: Mar 2009 Location: Lisbon, Portugal Posts: 10,975 Blog Entries: 45 Rep Power: 128	Hi Ehsan, Do you mind providing more information? Namely how did you exactly define those values of 75% vs 25%? Best regards, Bruno __________________ OpenFOAM: FAQ \| Getting started Forum: How to get help, to post code/output and forum guide Read this before sending me PM

August 31, 2013, 14:39		#3
immortality Senior Member Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,208 Rep Power: 26	Hi Bruno I have multiplyed the JANAF coefficients(7 numbers) of nitrogen to .75 and for oxygen have multiplied them to .25 and then added them together,isn't it correct? the answers look fine but I want to know is this numbers accurate enough? __________________ Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King. To Be or Not To Be,Thats the Question! The Only Stupid Question Is the One that Goes Unasked.

August 31, 2013, 14:50		#4
wyldckat Retired Super Moderator Bruno Santos Join Date: Mar 2009 Location: Lisbon, Portugal Posts: 10,975 Blog Entries: 45 Rep Power: 128	Hi Ehsan, OK, still not enough information. So I ask in more detail: How exactly did you do the math? No need to specify all of the coefficient values, "a0, a1" and so on is enough. And what results did you get? And in comparison with the values used in the dictionary file, what values were you using before and are using now? Best regards, Bruno __________________ OpenFOAM: FAQ \| Getting started Forum: How to get help, to post code/output and forum guide Read this before sending me PM

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