Discussion Forum

I am modelling a cryostat where the internal cavity is cooled to 4K with thermally-isolated radiation shields to isolate from room temperature. Everything within is held under vacuum. Hence, I am using the surface-to-surface radiation module.

The only heat source is the outer surface at room temperature, and hence I would expect each layer to radiatively cool inwards, and a steady-state temperature to step down across each shield until 4 K (fixed temperature) in the inner-most cavity. The shields are also actively cooled.
However, I have found that one of my inner layers is at 50 K higher temperature than all of the surrounding shields and even the inner 4 K cavity.

Things I have tested:
1) turning off all radiation results in 4K on all layers, hence it is not accidental conduction
2) adjusting the temperature of the outer-most surface changes that layer's temperature, even though the shields' temperatures vary minimally.

Thus, I suspect somehow, radiation is transmitting through all of my shields, so I must be setting some boundary conditions incorrectly, but I cannot figure it out.

Note: I have made the model using both full 3D as well as 2D axisymmetry, but both give the same result.

Thank you for any assistance in advance.