Laminar forced convective heat transfer in helical pipe flow

Laminar forced convective heat transfer in a helical pipe with circular cross section subjected to wall heating was investigated numerically by three-dimensional (3D) direct numerical simulations (DNS) comparing with the experimental data obtained by Shatat (2010). The study was performed for three Prandtl numbers, Pr = 8.5, 7.5 and 4.02, over the wide range of torsion. In 3D steady calculations, we found the appearance of fully-developed axially invariant flow regions, where the averaged Nusselt number (averaged over the peripheral of the pipe cross section) were calculated, being in good agreement with the experimental data. Because of the effect of torsion on the heat transfer characteristics, the averaged Nusselt number exhibits repetition of decrease and increases as torsion increases from zero for all Reynolds numbers. It was found that there exists two maximums and two minimums of the averaged Nusselt number. It is interesting that the global minimum of the Nusselt number occurs at β≅0.1 and the global maximum at β≅0.55.