  It is well known that the full Navier-Stokes-Fourier system does not possess
a strong solution in three dimensions which causes problems in applications.
However, when modeling the flow of a fluid in a thin long pipe, the influence
of the cross section can be neglected and the flow is basically
one-dimensional. This allows us to deal with strong solutions which are more
convenient for numerical computations. The goal of this paper is to provide a
rigorous justification of this approach. Namely, we prove that any suitable
weak solution to the three-dimensional NSF system tends to a strong solution to
the one-dimensional system as the thickness of the pipe tends to zero.
