Review of two-phase flow and heat transfer phenomena in helically coiled tubes

Vaporizing and condensing heat transfer inside a helically coiled tube are intrinsically attractive for zero- or microgravity applications because of the self-induced radial acceleration field. This field, which can be thousands of times the Earth's gravitational field, decisively separates the phases and suppresses the fog flow regime. The liquid phase, deposited on the wall, moves more slowly than the vapor phase in the core and hence is subject to lower radial accelerations than the vapor core. A secondary flow is induced in the vapor core, which acts through interfacial shear to distribute the liquid around the entire surface up to 90 to 95 per cent quality, at least at low pressures. The liquid and vapor remain in thermodynamic near-equilibrium and superheated vapor can be produced directly. Condensation has been little studied in this geometry, but similar flow phenomena are expected to occur. This paper surveys the literature and known industrial applications, suggesting design procedures for preliminary evaluation and suggesting experimental programs needed for more confident engineering design in microgravity situations