Natural convection of an inclined helical coil in a duct

The natural convection heat transfer of a helical coil in a duct was measured experimentally. The RaD was fixed at 4.55 × 106 and the pitch to diameter ratio varied from 1 to 5, the number of turns from 1 to 10, and the inclination of the helical coil from horizontal to vertical. To achieve a high Rayleigh number, mass transfer experiments were performed based on the analogy between heat and mass transfer. The measured NuD for a single turn of the helical coil was close to the prediction derived from the McAdams heat-transfer correlation developed for a horizontal cylinder. The heat transfer of the helical coil varied with respect to the pitch, number of turns, and duct height, demonstrating the complexities associated with velocity, preheating, and chimney effects. It is expected that the results from this study will contribute to a phenomenological understanding of natural convection heat transfer in compact heat exchangers.