Assigning Inlet/Outlet Duct Conditions in Mechanica

[EDOUBLE]

I am attempting to model a thermal solution for a heat sink/chip attachment. The heat sink fins will isolated in an aluminum duct. A fan pulls in outside air at the inlet of the duct across the fins to an exit/exhaust where there is no fan.



I am having some trouble determining how to assign boundry conditions to simulate this.



Does anyone have any suggestions? I would greatly appreciate it.



Thank you