HEAT-TRANSFER AND PRESSURE-DROP CHARACTERISTICS OF SPIRALLY FLUTED ANNULI .2. HEAT-TRANSFER

This paper is the second of two papers that present the results of a c omprehensive study of hear transfer and pressure drop in annuli with s pirally fluted inner tubes for the laminar, transition, and turbulent flow regimes. Fourteen fluted tubes with varying geometries were studi ed, with up to three outer smooth tubes for each fluted tube. Flow pat terns and transitions between flow regimes investigated through visual ization tests, friction factor data (from Part I), and tube surface-te mperature measurements were used to explain the enhancement phenomena. The fluted inner tubes induced a significant degree of swirl in the f low, and transition occurred in the 310 < Re < 1000 range. A Nusselt n umber correlation was developed in terms of the fluted annulus frictio n factor developed in Part I and geometric parameters. Nusselt numbers were between 4 and 20 times the smooth annulus values in the low Re r ange, while turbulent enhancements were between 1.1 and 4.0. These enh ancement values can be used in conjunction with friction factor increa se values reported in Part I to determine appropriate ranges of applic ability for spirally enhanced annuli.