Heat Transfer between Cylinders in Vacuum (HELP)
 

Hello everyone, I need some assistance with trying to model heat transfer via thermal radiation between 2 concentric cylinders in a vacuum chamber. The heat energy is being produced by a cartridge heater fit inside of the inner cylinder. (Pictures of setup are attached for reference)

The operating conditions will vary from 200C to 500C. The pressures will vary from less than 10 torr to atmospheric pressure.

I need to figure out how to simulate a "vacuum environment" in the software, how to measure the time it will take for the outer cylinder to reach the varying temperatures (max being 500C), and the temperature the pressure vessel will be at after that "heat up time".

I know the basics of ANYS Fluent and have messed around with different boundary conditions (I'll attach my current process in an image) but my analysis never comes back with anything helpful.

Any help will be GREATLY appreciated.