Heat conduction between a solid and the surrounding air
 

Hello,
I want to analyze the temperature distribution of a metallic rack.
On one side of the rack is a heat source. I managed to model that. My Problem is the modelling of the heat conduction to the surrounding air. As this Experiment is under 0g there is no convection (insignificantly small) but conduction.
I am not sure if there is a function for conduction such as there is one for convection or do I have to design for example a big block arround the rack and set air as the material?
Thanks for any help!