Fully developed laminar flow and heat transfer in serpentine pipes

In the present work, fully developed laminar flow and heat transfer in serpentine pipes were investigated by numerical simulation. The curvature δ = a/c was made to vary between 0.1 and 0.5 while the parameter γ = l/c was made to vary between 0 and 8; for each geometry, the friction velocity Reynolds number Reτ = uτa/ν was made to vary between a very low value (5), yielding almost creeping flow, and the highest value Reτ∗ still yielding steady laminar flow (∼35-40 in most cases). For Reτ≤Reτ∗ results were obtained for values of the Prandtl number between 1 and 100; predicted values of the friction coefficient and of the Nusselt number were compared with experimental results and correlations proposed in the literature. For Reτ>Reτ∗ convergence to steady flow was not achieved and an oscillatory behaviour of the solution was observed, indicating a transition to unsteady regimes which deserves a more focused study.