Calculate the effective thermal conductivity

Hi,
im very new in Comsol and its my first post here, so if you need more information for saving my problem just let me know.

I want to calculate the effective thermal conductivity of a tank containing insulation materials. The tank should be heated below and I want to determine the temperature at the top and bottom. With this information, I could then calculate the effective thermal conductivity of the complete tanks.

Now i created my geometry and filled the tank first with air.
But my simulation does not work. I think its due to the physics settings. Because im not sure if i did it right. In the most posts here there is written something about the heat flux. But if i dont know how to set it up.

I've attached my Comsol-file

I hope you can help me.

Greetings
Kevin