Testing case: transient heat with Neumann BCs only (no Dirichlet, no Robin)
k = 10
rho = 1
cp = 1e6
Bottom heat flux: +10000 W/m2
Top heat flux: -5000 W/m2
Time interval: [0, 3.0] seconds
Initial conditions: 0 °C
Reference point C: x=Dfuel/2, y=0, z=0
