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Research Papers: Heat Transfer Enhancement

Heat Transfer Enhancement of MHD Flow by Conducting Strips on the Insulating Wall

[+] Author and Article Information
Hulin Huang1

Academy of Frontier Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, P.R. Chinahlhuang@nuaa.edu.cn

Bo Li

Academy of Frontier Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, P.R. China

1

Corresponding author.

J. Heat Transfer 133(2), 021902 (Nov 02, 2010) (6 pages) doi:10.1115/1.4002436 History: Received March 29, 2009; Revised July 31, 2010; Published November 02, 2010; Online November 02, 2010

Due to the magnetohydrodynamic (MHD) effect, which degrades heat transfer coefficients by pulsation suppression of the external magnetic field, on the electrically conducting flow, the wall with nonuniform electrical conductivity is employed in a MHD-flow system for heat transfer enhancement. The nonuniform electrical conductivity distribution of the channel wall could create alternate Lorentz forces along the spanwise direction, which can effectively produce flow disturbance, promote mixture, reduce the thickness of the boundary layer, and enhance heat transfer. So, the heat transfer performances enhanced by some conducting strips aligned with the mean flow direction on the insulating wall for free surface MHD flow are simulated numerically in this paper. The flow behaviors, heat transfer coefficients, friction factors, and pressure drops are presented under different Hartmann numbers. Results show that in the range of Hartmann numbers 30Ha100, the wall with nonuniform conductivity can achieve heat transfer enhancements (Nu/Nu0) of about 1.2–1.6 relative to the insulating wall, with negligible friction augmentation. This research indicates that the modules with three or five conducting strips can obtain better enhancement effect in our research. Particularly, the heat transfer augmentation increases monotonically with increasing Hartmann numbers. Therefore, the enhancement purpose for high Hartmann number MHD flow is marked, which may remedy the depressing heat transfer coefficients by the MHD effect.

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Figures

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Figure 1

Schematic of the physical model

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Figure 2

Comparison between numerical and Smolentsev’s results

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Figure 3

Electric current paths in x∗=2.6 plane (Ha=30): (a) insulating wall and (b) nonuniform electrical conductivity wall

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Figure 4

Lorentz force Fx distribution in x∗=2.6 plane (Ha=30): (a) insulating wall and (b) nonuniform electrical conductivity wall

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Figure 5

Velocity distribution in x∗=2.6 plane: (a) Ha=30 and (b) Ha=70

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Figure 6

Turbulent viscosity distribution in the x∗=2.6 plane: (a) Ha=30 and (b) Ha=70

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Figure 7

Distribution of local Nu/Nu0 and local f/f0 (at x∗=2.6 plane): (a) local Nu/Nu0 at different positions and (b) local f/f0 at different positions

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Figure 8

Distribution of the mean Nusselt number, mean friction factor, and pressure drop

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Figure 9

Distribution of the mean Nusselt number, mean friction factor, and pressure drop: (a) mean Nusselt number, (b) mean friction factor, and (c) pressure drop

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Figure 10

Global thermal performance for different models

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