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Research Papers: Heat Transfer Enhancement

Heat Transfer Enhancement in Turbulent Ribbed-Pipe Flow

[+] Author and Article Information
Changwoo Kang

Department of Mechanical Engineering,
Inha University,
Incheon 22212, Korea
e-mail: cwkang@inha.edu

Kyung-Soo Yang

Professor
Department of Mechanical Engineering,
Inha University,
Incheon 22212, Korea
e-mail: ksyang@inha.ac.kr

1Present address: Laboratoire Ondes et Milieux Complexes (LOMC), UMR CNRS 6294, Université du Havre, 53, Rue de Prony, CS80540, Le Havre Cedex 76058, France.

2Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received June 15, 2016; final manuscript received December 28, 2016; published online March 15, 2017. Assoc. Editor: Danesh K. Tafti.

J. Heat Transfer 139(7), 071901 (Mar 15, 2017) (8 pages) Paper No: HT-16-1390; doi: 10.1115/1.4035712 History: Received June 15, 2016; Revised December 28, 2016

The present study aims at explaining why heat transfer is enhanced in turbulent ribbed-pipe flow, based on our previous large eddy simulation (LES) database (Kang and Yang, 2016, “Characterization of Turbulent Heat Transfer in Ribbed Pipe Flow,” ASME J. Heat Transfer, 138(4), p. 041901) obtained for Re = 24,000, Pr = 0.71, pitch ratio (PR) = 2, 4, 6, 8, 10, and 18, and blockage ratio (BR) = 0.0625. Here, the bulk velocity and the pipe diameter were used as the velocity and length scales, respectively. The ribs were implemented in the cylindrical coordinate system by means of an immersed boundary method. In particular, we focus on the cases of PR ≥ 4 for which heat transfer turns out to be significantly enhanced. Instantaneous flow fields reveal that the vortices shed from the ribs are entrained into the main recirculating region behind the ribs, inducing velocity fluctuations in the vicinity of the pipe wall. In order to identify the turbulence structures responsible for heat transfer enhancement in turbulent ribbed-pipe flow, various correlations among the fluctuations of temperature and velocity components have been computed and analyzed. The cross-correlation coefficient and joint probability density distributions of velocity and temperature fluctuations, obtained for PR = 10, confirm that temperature fluctuation is highly correlated with velocity-component fluctuation, but which component depends upon the axial location of interest between two neighboring ribs. Furthermore, it was found via the octant analysis performed for the same PR that at the axial point of the maximum heat transfer rate, O3 (cold wallward interaction) and O5 (hot outward interaction) events most contribute to turbulent heat flux and most frequently occur.

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References

Figures

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Fig. 1

Flow configuration and grid system (every other grid point is plotted in each direction for clarity): (a) r–z plane (schematic) and (b) r–θ plane

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Fig. 2

Instantaneous velocity vectors and contours of the circumferential vorticity component (ωθ) in an r–z plane for p/e = 4: (a) t = 0, (b) t = 0.1, (c) t = 0.2, and (d) t = 0.3

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Fig. 3

Instantaneous velocity vectors and contours of the circumferential vorticity component (ωθ) in an r–z plane for p/e = 8: (a) t = 0, (b) t = 0.1, (c) t = 0.2, and (d) t = 0.3

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Fig. 4

Distribution of local mean turbulent kinetic energy between two neighboring ribs at R−r≈0.04e

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Fig. 5

Distribution of normalized local mean Nusselt number between two neighboring ribs

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Fig. 6

Cross-correlation coefficients of velocity and temperature fluctuations along the radial direction for p/e = 10 at some selected locations: (a) z/e= 2.0, (b) z/e= 5.5, and (c) z/e=9.8

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Fig. 7

Joint probability density distributions at (R−r)/e≈0.04, z/e=2.0 for p/e = 10

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Fig. 8

Joint probability density distributions at (R−r)/e≈0.04, z/e=5.5 for p/e = 10

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Fig. 9

Joint probability density distributions at (R−r)/e≈0.04, z/e=9.8 for p/e = 10

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Fig. 10

Definition of octants

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Fig. 11

Octant contributions near the wall at z/e=2.0 for p/e = 10: (a) axial turbulent heat flux, (b) radial turbulent heat flux, and (c) probability of octant events

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Fig. 12

Octant contributions near the wall at z/e=5.5 for p/e = 10: (a) axial turbulent heat flux, (b) radial turbulent heat flux, and (c) probability of octant events

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Fig. 13

Octant contributions near the wall at z/e=9.8 for p/e = 10: (a) axial turbulent heat flux, (b) radial turbulent heat flux, and (c) probability of octant events

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