[Weiqiang Liu]

Hi all,
I need to define mass diffusion coefficients with UDF. However, I am very confused about the unit of molar mass fluent uses.
I put two equations below one is how fluent calculate binary diffusion coefficients and the other is how knudsen diffusion coefficient is calculated.

I checked the unit in fluent user guide and found that they use kg/kmol as molar mass unit. However I found the unit of molar mass in the second equation is kg/mol. I am wondering what is exactly the unit of molar mass fluent solver passes to UDF?
Best regards
weiqiang