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RESEARCH PAPERS: Forced Convection

Heat Transfer and Pressure Drop Correlations for Twisted-Tape Inserts in Isothermal Tubes: Part I—Laminar Flows

[+] Author and Article Information
R. M. Manglik, A. E. Bergles

Heat Transfer Laboratory, Rensselaer Polytechnic Institute, Troy, NY 12180-3590

J. Heat Transfer 115(4), 881-889 (Nov 01, 1993) (9 pages) doi:10.1115/1.2911383 History: Received July 01, 1992; Revised March 01, 1993; Online May 23, 2008

Abstract

Laminar flow correlations for f and Num are developed based on experimental data for water and ethylene glycol, with tape inserts of three different twist ratios. The uniform wall temperature condition is considered, which typifies practical heat exchangers in the chemical and process industry. These and other available data are analyzed to devise flow regime maps that characterize twisted-tape effects in terms of the dominant enhancement mechanisms. Depending upon flow rates and tape geometry, the enhancement in heat transfer is due to the tube partitioning and flow blockage, longer flow path, and secondary fluid circulation; fin effects are found to be negligible in snug- to loose-fitting tapes. The onset of swirl flow and its intensity is determined by a swirl parameter, Sw = Resw/y, that defines the interaction between viscous, convective inertia, and centrifugal forces. Buoyancy-driven free convection that comes into play at low flow rates with large y and ΔT w is shown to scale as Gr/Sw2 ≫ 1. These parameters, along with numerical baseline solutions for laminar flows with y = ∞ , are incorporated into correlations for f and Num by matching the appropriate asymptotic behavior. The correlations describe the experimental data within ±10 to 15 percent, and their generalized applicability is verified by the comparison of predictions with previously published data.

Copyright © 1993 by The American Society of Mechanical Engineers
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