operating temp. mterials prop.??
 

Hi CFD users,
I am working on heat transfer from a pipe embedded in a porous medium superimposed with a fluid layer.
I am confused with what operating temperature to put. I am using the boussinesq approximation, and was wondering if I put the operating temperature as the temperature which I defined the fluid properties at? or is the operating temperature, the lowest temperature in the system?
Any reply will help!