Relative Humidity isn't a field function in Star CCM+ unfortunately, we have to create a function ourselves, this is actually pretty tough although they do have mole and mass fractions in the program already. If you send me an email I can give you the equations I use to put into a macro to create the field function, I would suggest asking your support person how to implement it. Also it needs some adjustment for temperature so be careful.

I have put in a request that they include it in their field functions and hope that soon they will.

Dr. A.?Marston, Ph.D. LEED? AP