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Research Papers: Natural and Mixed Convection

A New Analysis of Heat Transfer Deterioration on Basis of Turbulent Viscosity Variations of Supercritical Fluids

[+] Author and Article Information
Mahdi Mohseni

Ph.D. Student
e-mail: mohseni@qut.ac.ir

Majid Bazargan

Associate Professor
e-mail: bazargan@kntu.ac.ir
Department of Mechanical Engineering,
K. N. Toosi University of Technology,
P.O. Box 19395-1999,
15 Pardis Street, Mollasadra Avenue,
Tehran 1999 143 344, Iran

1Present address: Assistant Professor, Department of Mechanical Engineering, Qom University of Technology, P.O. Box 37195-1519, Qom, Iran.

2Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received November 21, 2011; final manuscript received June 23, 2012; published online October 5, 2012. Assoc. Editor: W. Q. Tao.

J. Heat Transfer 134(12), 122503 (Oct 05, 2012) (7 pages) doi:10.1115/1.4007313 History: Received November 21, 2011; Revised June 23, 2012

A two-dimensional computational fluid dynamics (CFD) code has been used to study the anomalies encountered in convection heat transfer to upward turbulent flows of supercritical fluids in tubes. In this study, the effect of turbulent viscosity variations on heat transfer deterioration (HTD) and the mechanisms involved have been investigated. The results show that the suppression of the flow turbulence which leads to the deterioration of heat transfer can be partially due to the decrease in the turbulent viscosity as a result of density decrease along a heated flow. Before this study the buoyancy and the thermal acceleration effects were called as the main two known mechanisms for the heat transfer deterioration.

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Figures

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Fig. 1

Variations of the wall temperature and corresponding heat transfer coefficient for flow conditions of case I

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Fig. 2

Variations of the wall temperature and corresponding heat transfer coefficient for flow conditions of case II

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Fig. 3

Typical variations of the properties of carbon dioxide at supercritical pressure of 8.12 MPa

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Fig. 4

Radial variations of turbulent kinetic energy at different flow cross sections before deterioration region started. Note that the deterioration occurs around bulk enthalpy of Hb = 246 kJ/kg.

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Fig. 5

Contour of turbulence intensity, I = u ′/uave, near the wall for case II. The line r/R = 1 is on the wall.

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Fig. 6

Variations of the velocity profiles and their radial gradients before deterioration region started for case I. Note that the deterioration occurs around bulk enthalpy of Hb = 246 kJ/kg.

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Fig. 7

Radial variations of fluid density (a) and turbulent viscosity (b) at different flow cross sections before deterioration region started

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Fig. 8

Effect of variations of the turbulent viscosity on wall temperature for case I (a) and heat transfer coefficients for case II (b)

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Fig. 9

Variations of the heat transfer coefficients along the tube for three situations of real fluid, zero gravity fluid, and constant density fluid for case I (a) and case II (b)

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