comsol 5 2D cable heat-transfer problem
 

Hello,
i am working on my diploma thesis in which I must simulate a 2D cable and get the temperature charts in various cases such as emission (radiation) from the cable to ambient and radiation from ambient (sun) to the cable. And I am stuck due to some (simple for you) problems:
1) i chose the "heat in transfer in solids" model and added "diffuse surface". I chose the outer surface of the cable as the diffuse surface boundary and selected a surface emissivity (0.8). When I compute at a stationary study the results are wrong. They are -600 K at both the surface and the inner of the cable. When I try a time depended study the results are ok. Do you have any idea how to solve that? or why does this happen?
2) how do you simulate radiation from an external source (sun) to the cable in 2d? I tried the "heat transfer with surface to surface radiation module but it didn't work.
I am sorry for my English and for the long questions!

Thank you in advance for you help!