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Research Papers: Forced Convection

Influence of Reynolds Numbers on the Flow and Heat Transfer Around Row of Magnetic Obstacles

[+] Author and Article Information
Xidong Zhang

College of Energy and Power Engineering,
Nanjing Institute of Technology,
Nanjing 211167, China;
College of Astronautics,
Nanjing University of Aeronautics and
Astronautics,
Nanjing 210016, China
e-mail: zhangxd@nuaa.edu.cn

Guiping Zhu, Yin Zhang, Hulin Huang

College of Astronautics,
Nanjing University of Aeronautics
and Astronautics,
Nanjing 210016, China

Hongyan Wang

College of Energy and Power Engineering,
Nanjing Institute of Technology,
Nanjing 211167, China

1Corresponding author.

Presented at the 2016 ASME 5th Micro/Nanoscale Heat & Mass Transfer International Conference. Paper No. MNHMT2016-6455.Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received May 29, 2016; final manuscript received February 12, 2017; published online March 7, 2017. Assoc. Editor: Chun Yang.

J. Heat Transfer 139(5), 051701 (Mar 07, 2017) (6 pages) Paper No: HT-16-1318; doi: 10.1115/1.4036004 History: Received May 29, 2016; Revised February 12, 2017

An incompressible electrically conducting viscous fluid flow influenced by a local external magnetic field may develop vortical structures and eventually instabilities similar to those observed in flows around bluff bodies (such as circular cylinder), denominated magnetic obstacle. The present investigation analyzes numerically the three-dimensional flow and heat transfer around row of magnetic obstacles. The vortex structures of magnetic obstacles, heat transfer behaviors in the wake of magnetic obstacles, and flow resistance are analyzed at different Reynolds numbers. It shows that the flow behind magnetic obstacles contains four different regimes: (1) one pair of magnetic vortices, (2) three pairs namely, magnetic, connecting, and attached vortices, (3) smaller vortex shedding from the in-between magnetic obstacles, i.e., quasi-static, and (4) regular vortex shedding from the row of magnetic obstacles. Furthermore, downstream cross-stream mixing induced by the unstable wakes can enhance wall-heat transfer, and the maximum value of percentage heat transfer increment (HI) is equal to about 35%. In this case, the thermal performance factor is more than one.

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Figures

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Fig. 1

Schematic representation of flow region and related geometrical parameters. The north (N) and south (S) magnetic poles are separated by a distance H = 0.03 m. The origin of the coordinate axes is placed at the geometrical center of magnetic obstacles.

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Fig. 2

Comparison of wake structure from a magnetic obstacle (a) and (d) present simulation, (b) and (e) numerical simulation of Votyakov et al. [7], and (c) and (f) experiments of Samsami et al. [24]

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Fig. 3

Time traces of the spanwise component of velocity (v) at monitoring points M1 and M2 at N = 9: (a) Re = 400, (b) Re = 500, and (c) Re = 600

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Fig. 4

Instantaneous mass flow streamlines on the z = 0 plane at N = 9. The solid rectangle shows the borders of the external magnet: (a) Re = 100, (b) Re = 400, (c) Re = 500, and (d) Re = 600.

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Fig. 5

Local Nusselt number Nu/Nu0 (a) and local skin friction coefficient fc/fc0 (b) over the heated surface on the side wall y = −25 as a function of coordinate x

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Fig. 6

Variations of the percentage increment of the overall heat transfer (HI) and pressure drop penalty (ΔPpenalty)

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Fig. 7

Global thermal performance factor η = (Nu/Nu0)/(fc/fc0)1/3 at different Reynolds numbers

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