Thermal shocks occur when an object is rapidly warmed or cooled via a strong heat exchange at the boundary. There are situations where the thermal boundary layer is so thin that temperature spots may develop at the surface. This is enforced when the discretization is relatively coarse and unable to describe the thermal boundary layer.

A detailed examination of the system of equations reveals the volume of influence at a node depends on the size and on the number of elements sharing that node. In turn, the thermal inertia of that volume of influence affects the temperature changes vs. time. Unless the mesh is fully regular, the volume of influence is likely to be different at each node, although often with similar order of magnitude. The resulting non-uniform distribution of thermal inertia leads to locally non-uniform temperature changes. Hence temperature spots may develop when the temperature boundary layer is thinner than the typical element size.

The scope of these spots is very limited in space and time, so that their somewhat unrealistic or unphysical character is easily dampened by the overall solution. In addition, energy conservation is satisfied. In other words, the inner energy change matches the energy lost or acquired via heat transfer through the boundary.