Measurements of natural convection heat transfer of a helical coil varying the pitch and the turn

A helical coil is gaining interest as the part of a compact heat exchanger since it allows large heat transfer area. Many small modular reactor designs adopt the helical coil steam generator. We measured the local and total heat transfers of the helical coil using ring bundles to confirm the influences of pitches and turns. The pitch to coil diameter ratio was varied from 1.08 to 3.97 and the turns from 2 to 12, with the Ra of 3.63 × 10⁷. Based on the analogy between heat and mass transfers, mass transfer experiments were performed replacing heat transfer ones. For a small pitch, the heated plume from the lower ring provides preheated plume to the upper ring, resulting in an impaired heat transfer. However, for a large pitch, initial velocity is provided, enhancing the heat transfer. The comprehensive heat transfer influences also depend on the coil turns. The measurements of total heat transfer showed the peak at around the pitch to coil diameter ratio range from 1.50 to 2.02 regardless of the number of coil turns.