# How to calculate Enthalpy in j/mol.kg in ansys ?

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 November 22, 2018, 09:13 How to calculate Enthalpy in j/mol.kg in ansys ? #1 New Member   Join Date: Nov 2018 Posts: 5 Rep Power: 7 Hi I have some confusion about how ansys calculates enthalpy in j/mol.kg I have seen many answers that says just multiply enthalpy of a material by the its molecular weight but that simply does not make sense for me because : enthalpy is in j/kg and molecular weight is in kg/mol so the resultant dimension would be j/mol not j/mol.kg as required by ansys? may be this naive question but I am new to ansys and fluid mechanics in general and my background is mainly in computer engineering Thanks

 November 26, 2018, 13:14 #2 Senior Member   Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,712 Rep Power: 66 Enthalpy is indeed J/kg or J/mol. I think you are confusing J/kgmol as being kg*mol. A kgmol is not kg*mol but a type of mol. Chinmaynair likes this.

 November 28, 2018, 10:16 #3 New Member   Join Date: Nov 2018 Posts: 5 Rep Power: 7 so if for example, the enthalpy is 2000 j/mol, how to convert it to j/kgmol?

 November 29, 2018, 10:43 #4 Senior Member   Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,712 Rep Power: 66 Believe it or not, 2000 J/mol is 2000 000 J/kgmol or 2000 kJ/kgmol

 December 19, 2019, 06:35 #5 New Member   Tamil Nadu Join Date: Dec 2019 Posts: 11 Rep Power: 6 Hi Actually standard state of enthalpy of CO2 is -393.5 kJ/mol but in fluent the database value of CO2 is -3.935324e+08 J/kg mol. How this is possible??? whether the unit is correct as mentioned before? BibLi likes this.

 May 14, 2020, 10:01 #6 New Member   Vidushi Join Date: Sep 2018 Location: Cape Town Posts: 20 Rep Power: 7 kgmol is not kg*mol. It is like a kilo mol. So 1kgmol = 1000 mol.

May 20, 2020, 04:35
#7
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Marco Bernagozzi
Join Date: Jul 2019
Location: Brighton, UK
Posts: 3
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Quote:
 Originally Posted by Sowmiya Hi Actually standard state of enthalpy of CO2 is -393.5 kJ/mol but in fluent the database value of CO2 is -3.935324e+08 J/kg mol. How this is possible??? whether the unit is correct as mentioned before?
Hi Sowmiya,

that is correct. In fact you need to multiply by a factor 1000 to go from kJ to J. Moreover, you need to divide by a factor 1000 to go from mol to kmol (let's remember that the lowercase letter 'k' means 'kilo' which is, I think, ancient Greek for 'a thousand'). Thus, being that at the denominator, you need to multiply everything by 1000.
So, 3 digits because of kJ + 3 digits because of kmol + 2 digits for scientific notation and there you go you have your e+08.
Hope it helps,
Marco

 August 7, 2023, 05:56 #8 New Member   Laurens Join Date: Sep 2018 Location: the Netherlands Posts: 20 Rep Power: 7 I'm still confused as to why Fluent adds 'kg' to indicate 1e3 instead if just 'k'. Haven't seen this anywhere but here.