Fully developed (axially periodic) flow and heat transfer in
serpentine pipes, consisting of U-bends alternating with straight
segments, were predicted by Computational Fluid Dynamics. The
curvature d (ratio of pipe radius a to curvature radius c) was made
to vary between 0.1 and 0.5, the ratio g of straight tract length l to
curvature radius c between 0 and 8, the friction-velocity Reynolds
number Ret ¼ uta/n between 5 and 40 and the Prandtl number
between 1 and 100. A few additional test cases were run with
different geometrical parameters and boundary conditions in order
to perform comparisons with literature results.
A finite-volume method based on completely hexahedral grids
was used. A careful grid-independence assessment was conducted,
leading to the adoption of grids including a number of cells
between ~1 106 and ~21 106, depending on the geometry. The
flow was found to become unsteady as the friction velocity Reynolds
number exceeded a critical value Re*
t which in most caseswas
intermediate between 35 and 40. This corresponded to a bulk
Reynolds number Ud/n between ~200 and ~800 depending on the
geometry