A solid conductor described by surface impedance with different convection/radiation conditions depending on the surface should be defined. More precisely, it is necessary to establish different convection coefficients in the surfaces cooled by forced convection (usually through water) and those cooled by air natural convection.
There are two different methods to do so, depending on the complexity of the solid conductor geometry.
1-Define two different solid conductors: For simple geometries, it is the most straightforward and simple method.
The solid conductor described by surface impedance is divided in two or more different volumetric regions and the desired surface impedances, including different convection and/or radiation coefficients, are assigned to each of them.
The new surfaces created between these new solid conductors will not be considered as thermal exchange surfaces, since they are situated within the solid conductor.
2-Use a spatial quantity depending on surface regions
It is preferably to use this method when the considered geometry is too complex and it is not convenient or possible to divide the solid conductor in different parts.
The list of steps that should be done are:
Create a face region for each different heating exchange condition desired for the solid conductor.
Assign the desired solid conductor surfaces to each face region.
Define a new tabulated spatial quantity associated to each face region.
Finally, the new spatial quantities are used to define the surface convection/radiation variations.