Learning Forum

[Shiyao]

Hi. I found the unit of activation energy of reactions is marked as J/kgmol, which looks strange since it is usually J/kmol or J/mol, and there seems to be no reason for a mass unit to appear in it. A previous post said it equals J/kmol, while another one mentioned it is J/mol.

I believe this has confused many, but I cannot find any answer reasonable enough. 

When I was trying to investigate this, I found the default unit for universal gas constant is J⋅K⁻¹⋅kg⁻¹⋅mol⁻¹, which seems associated with the issue. The constant is commonly known as 8.314 J⋅K⁻¹⋅mol⁻¹, or specific gas constants with a unit of J⋅K⁻¹⋅kg⁻¹, but I have not heard about the usage of J⋅K⁻¹⋅kg⁻¹⋅mol⁻¹. 

May I ask if any one has an idea about why the mass unit kg appears in both universal gas constant and activation energy in Fluent? 

[DrAmine]

That is kgmol or kilo moles nothing to do with "kg".

[Rob]

Yes, it's an American unit from the "good old days" of Fluent when we first added species. kgmol is kmol and there has been a request in to change it for well over 20 years.... 

[Shiyao]

Thanks, mates! Hope this confusing term could be changed soon.