why COMSOL is solving so slowly

Hi All,

I am running a case with radiation heat transfer. The 3D geometry is quite simple. Number of degrees of freedom solved for: 56826 (plus 39748 internal DOFs), and element number is around 24K. I use the segragated solver.

And I found that: the time for assembly in each step is around 15 minutes, and memory usage seems OK, around 8GB.

I wonder whether this calculation speed is normal or not.

Thanks.