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International Heat Transfer Conference 8

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

HEAT TRANSFER AND PRESSURE DROP IN HELICALLY COILED TUBES

Volker Gnielinski
Institut fur Thermische Verfahrestechnik Universitat Karlsruhe (TH) D-76128 Karlsruhe, Germany

DOI: 10.1615/IHTC8.1360
pages 2847-2854

Abstract

Centrifugal forces in a fluid flowing through a curved pipe cause secondary flows increasing the heat transfer and the pressure drop. The effects of the curvature of the tube can be described by the characteristic parameter (d/D). In the case of an elliptical cross section of the pipe the aspect ratio γ = (a/b) additionally influences the velocity profile. Based on experimental data from the literature, equations are presented to calculate pressure drop and heat transfer. The friction factors result from equations for the circular pipe enlarged by factors containing the Dean-number for laminar flow or (d/D) for turbulent flow. In case of an elliptical cross section the Dean number is modified and the hydraulic diameter is used. The critical Reynolds number can be calculated for both cross-sections from the same equation. In laminar flow the heat transfer coefficient depends strongly on (d/D). With fully developed turbulent flow the heat transfer coefficients can be correlated by the same equation as for the straight tube, when the friction factor of the coil instead of that of the tube is inserted. For the transition region an interpolating equation is given.

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