3D instability in a cylinder with a cold cover

Sketch of the problem

Stability diagram for n=20 and different Biot numbers Stability diagram for Bi=20 and different n Stability diagram for Bi=20 and large n   3D temperature perturbation for: Grcr=40,900, Bi=0.5, n=20, k=9 Grcr=4600, Bi=20, n=20, k=5 Grcr=6770, Bi=20, n=34, k=9