Where to define the reference fluid temperature?

Hi,In the COSMOSFloworks Online help ,the Heat transfercoefficient (W/(m2·K)) h = q/(Tw-Tf), where q is thecalculated heat flux from a wall to fluid, Tw is the calculatedwall temperature, Tf is the reference fluid temperature specifiedby user.
Where to define the Tf?
Thanks

SolidworksFlow Simulation