The thermal conductivity must be defined when heat transfer is active. You will need to define thermal conductivity when you are modeling energy and viscous flow.
FLUENT provides several options for definition of the thermal conductivity:
Each of these input options and the governing physical models are detailed in this section. User-defined functions (UDFs) are described in the separate UDF Manual.
In all cases, you will define the Thermal Conductivity in the Materials panel (Figure 8.5.1).
Thermal conductivity is defined in units of W/m-K in SI units or BTU/hr-ft- R in British units.