  The Navier-Stokes-Fourier model for a 3D thermoconducting viscous fluid,
where the evolution equation for the temperature T contains a term proportional
to the rate of energy dissipation, is investigated analitically at the light of
the rotational invariance property. Two cases are considered: the Couette flow
and a flow with a radial velocity between two rotating impermeable and porous
coaxial cylinders, respectively. In both cases, we show the existence of a
maximum value of T, T_max, when the difference of temperature Delta T=T_2-T_1
on the surfaces of the cylinders is assigned. The role of T_max is discussed in
the context of different physical situations.
