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Research Papers: Forced Convection

Effect of Buoyancy on the Mechanism of Heat Transfer Deterioration of Supercritical Water in Horizontal Tubes

[+] Author and Article Information
Huixiong Li

e-mail: huixiong@mail.xjtu.edu.cn

Weiqiang Zhang

State Key Laboratory of Multiphase Flow in Power Engineering,
Xi'an Jiaotong University,
No. 28 West Xian-Ning Road,
Xi'an 710049, China

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received April 29, 2012; final manuscript received February 19, 2013; published online June 17, 2013. Assoc. Editor: Louis C. Chow.

J. Heat Transfer 135(7), 071703 (Jun 17, 2013) (9 pages) Paper No: HT-12-1199; doi: 10.1115/1.4023747 History: Received April 29, 2012; Revised February 19, 2013

In order to get insights into the mechanisms governing the heat transfer deterioration (HTD) of supercritical water, systematical numerical simulations were carried out in the present study for the flow and heat transfer of supercritical pressure water in horizontal smooth tubes. The numerical results were found in very good agreement with the corresponding experimental data, validating the reliability and accuracy of the numerical model and the computational method. It was found that from these profiles along the top generatrix of the wall of the horizontal tube, there exists a thin fluid layer in which the thermo-physical properties of the fluid, including the specific heat capacity, thermal conductivity, density and viscosity, all approach its minimum at a roughly identical axial position of the tube with the increasing of the bulk fluid enthalpy along the flow direction. The maximum wall temperature of the top generatrix, obviously show the occurrence of HTD. It was especially interesting that the axial position of the maximum top generatrix wall temperature (HTD position) just coincided with the axial positions of the minimum of the above-mentioned thermophysical properties in the near top generatrix layer, which reveals the inherent connection between the HTD and the minimum value of the above-mentioned thermophysical properties of the supercritical water. It was concluded that the HTD of supercritical water in horizontal tubes was evidently due to the vertical stratification and the accumulation of light supercritical pressure fluid (very high enthalpy but low density) in the near top generatrix region. Also, the HTD phenomena under supercritical condition was similar to that of the film boiling of the subcritical pressure water. This result clearly reveals why the axial position of the HTD occurred on the top wall of horizontal tubes (with bulk fluid enthalpy of roughly 1750 kJ/kg) is axially far ahead of the position corresponding to the critical point of the supercritical water (with bulk fluid enthalpy of roughly 2150 kJ/kg) in terms of the bulk fluid enthalpy.

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References

Figures

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Fig. 1

Thermophysical properties of water with temperature (data source from [2])

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Fig. 2

Sketch map of the tube

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Fig. 3

The mesh configuration in the cross-sectional slice

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Fig. 4

Comparison of the inner wall temperature under different heat flux: (a) enhanced heat transfer; (b) deteriorated heat transfer

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Fig. 5

Comparison of the numerical results and the experimental data

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Fig. 6

Variation of inner wall temperature with enthalpy along tube circumferential direction: (a) distributions of temperature along various generatrix of the horizontal tube; (b) secondary vortex distribution at different enthalpy

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Fig. 7

Dimensionless temperature in the tube vertical plane (φ=90 deg) and horizontal plane (φ=0 deg)

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Fig. 8

Dimensionless velocities in the tube vertical plane (φ = 90 deg) and horizontal plane (φ = 0 deg)

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Fig. 9

Dimensionless parameters Gr and J versus enthalpy at P = 24.5 MPa, G = 700 kg/m2s, qw = 400 kW/m2

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Fig. 10

Variation of flow parameters at different positions

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Fig. 11

Variation of the mass flux in different enthalpy

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Fig. 12

Variation of turbulence kinetic energy, turbulence shear stress: (a) turbulence kinetic energy; (b) turbulence shear stress

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