HEAT-TRANSFER AND PRESSURE-DROP CHARACTERISTICS OF SPIRALLY FLUTED ANNULI .1. HYDRODYNAMICS

This paper is the first of two papers that present the results of a co mprehensive study of hear transfer and pressure drop in annuli with sp irally fluted inner tubes for the laminar, transition, and turbulent f low regimes. To understand the underlying physical phenomena responsib le for heat transfer enhancement, flow mechanisms documented elsewhere are combined with pressure drop measurements to propose friction fact or correlations for the low Re range (Re < 800) and the high Re range (800 < Re < 43,500). Friction factors were found to be functions of th e flute depth, pitch and angle, and the annulus radius ratio. These co rrelations are used in the second paper to develop Nusselt number corr elations in terms of the fluted annulus friction factor. Transition in these annuli occurred in the 310 < Re < 1000 range. In Part II of thi s study, this early transition is shown to be responsible, in part, fo r significant heat transfer enhancement. Friction factor increases wer e typically between 1.1 and 2.0 in the laminar regime, and up to IO in the turbulent regime. These enhancement values can be used in conjunc tion with heat transfer enhancement values reported in Part II to dete rmine appropriate ranges of applicability for spirally enhanced annuli .