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Research Papers: Forced Convection

Effect of Turbulent Prandtl Number on Convective Heat Transfer to Turbulent Flow of a Supercritical Fluid in a Vertical Round Tube

[+] Author and Article Information
Mahdi Mohseni

Department of Mechanical Engineering, K.N.Toosi University of Technology, 15 Pardis Street, Mollasadra Avenue, P.O. Box 19395-1999, Tehran 1999 143 344, Iranm_mohseni@dena.kntu.ac.ir

Majid Bazargan1

Department of Mechanical Engineering, K.N.Toosi University of Technology, 15 Pardis Street, Mollasadra Avenue, P.O. Box 19395-1999, Tehran 1999 143 344, Iranbazargan@kntu.ac.ir

1

Corresponding author.

J. Heat Transfer 133(7), 071701 (Mar 30, 2011) (10 pages) doi:10.1115/1.4003570 History: Received September 23, 2009; Revised February 01, 2011; Published March 30, 2011; Online March 30, 2011

A two-dimensional numerical model is developed to study the effect of the turbulent Prandtl number Prt on momentum and energy transport in a highly variable property flow of supercritical fluids in a vertical round tube. Both regimes of enhanced and deteriorated heat transfer have been investigated. The equations of the Prt leading to the best agreement with the experiments in either regime of heat transfer were specified. The results of this study show that the increase in the Prt causes the heat transfer coefficients to decrease. When the buoyancy force increases, a better agreement with the experimental data is reached if values lower than 0.9 are used for the Prt. A decrease in the Prt values results in an increase in turbulent activities. From the effect that the Prt has on heat transfer coefficients, it may be deduced that the buoyancy effects in the upward flow of a supercritical fluid lead to the decrease in the Prt value and hence to the increase in the heat transfer coefficients. Furthermore, the value of the Prt in the laminar viscous sublayer as expected does not have a significant effect on heat transfer rate. The effect of the turbulence model on the extent to which the Prt influences the rate of heat transfer is also examined. The results obtained are shown to be valid regardless of the turbulence model used.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Flow geometry and the boundary conditions

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Figure 2

Radial variations of various Prt relations: K—Kays (30); KC—Kays and Crawford (24); MKH—Myong, Kasagi, and Hirata (28); and HKM—Hollingsworth, Kays, and Moffat (29); at an arbitrary cross section of the flow for Case 1 flow conditions

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Figure 3

Comparison of the heat transfer coefficients predicted by the present model using various constant Prt values as well as Prt relations introduced in Fig. 2 with the experiments of Bae and Kim (31), for Case 1 flow conditions

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Figure 4

Comparison of the heat transfer coefficients predicted by the present model using Prt relations introduced in Fig. 2 with the experiments of Song (32), for Case 2 flow conditions

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Figure 5

Effect of various constant values of Prt on heat transfer coefficients predicted by the present model for Case 2 flow conditions

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Figure 6

Effect of Prt on heat transfer coefficients for Case 3 flow conditions. The experimental data are those of Bae (33). Prt relations are the same as in Fig. 2.

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Figure 7

Variations of turbulent viscosity for different Prt in a radial distance near the wall corresponding to r/R=0.994 under Case 2 flow conditions

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Figure 8

Variations of turbulent viscosity for different Prt in a flow cross section corresponding to Hb=320 kJ/kg under Case 2 flow conditions

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Figure 9

Comparison of the heat transfer coefficients predicted by the present model using two Prt values with the experiments of Yamagata (34) for Case 4 flow conditions

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Figure 10

Comparison of the heat transfer coefficients with various Prt using AKN turbulence model with the experiments of Song (32) for Case 2 flow conditions

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