This paper is the second of two papers that present the results of a comprehensive study of heat transfer and pressure drop in annuli with spirally fluted inner tubes for the laminar, transition, and turbulent flow regimes. Fourteen fluted tubes with varying geometries were studied, with up to three outer smooth tubes for each fluted tube. Flow patterns and transitions between flow regimes investigated through visualization tests, friction factor data (from Part I), and tube surface-temperature measurements were used to explain the enhancement phenomena. The fluted inner tubes induced a significant degree of swirl in the flow, and transition occurred in the 310 < Re < 1000 range. A Nusselt number correlation was developed in terms of the fluted annulus friction factor developed in Part I and geometric parameters. Nusselt numbers were between 4 and 20 times the smooth annulus values in the low Re range, while turbulent enhancements were between 1.1 and 4.0. These enhancement values can be used in conjunction with friction factor increase values reported in Part I to determine appropriate ranges of applicability for spirally enhanced annuli.

Issue Section:
Forced Convection
Keywords:
Augmentation and Enhancement, Forced Convection, Heat Exchangers
Topics:
Annulus, Heat transfer, Pressure drop, Flow (Dynamics), Friction, Turbulence, Forced convection, Heat exchangers, Temperature, Visualization
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