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Research Papers: Heat Transfer Enhancement

Characterization of Turbulent Heat Transfer in 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

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received February 27, 2015; final manuscript received October 1, 2015; published online January 5, 2016. Assoc. Editor: Danesh / D. K. Tafti.

J. Heat Transfer 138(4), 041901 (Jan 05, 2016) (9 pages) Paper No: HT-15-1150; doi: 10.1115/1.4032150 History: Received February 27, 2015; Revised October 01, 2015

In the current investigation, we performed large eddy simulation (LES) of turbulent heat transfer in circular ribbed-pipe flow in order to study the effects of periodically mounted square ribs on heat transfer characteristics. The ribs were implemented on a cylindrical coordinate system by using an immersed boundary method, and dynamic subgrid-scale models were used to model Reynolds stresses and turbulent heat flux terms. A constant and uniform wall heat flux was imposed on all the solid boundaries. The Reynolds number (Re) based on the bulk velocity and pipe diameter is 24,000, and Prandtl number is fixed at Pr = 0.71. The blockage ratio (BR) based on the pipe diameter and rib height is fixed with 0.0625, while the pitch ratio based on the rib interval and rib height is varied with 2, 4, 6, 8, 10, and 18. Since the pitch ratio is the key parameter that can change flow topology, we focus on its effects on the characteristics of turbulent heat transfer. Mean flow and temperature fields are presented in the form of streamlines and contours. How the surface roughness, manifested by the wall-mounted ribs, affects the mean streamwise-velocity profile was investigated by comparing the roughness function. Local heat transfer distributions between two neighboring ribs were obtained for the pitch ratios under consideration. The flow structures related to heat transfer enhancement were identified. Friction factors and mean heat transfer enhancement factors were calculated from the mean flow and temperature fields, respectively. Furthermore, the friction and heat-transfer correlations currently available in the literature for turbulent pipe flow with surface roughness were revisited and evaluated with the LES data. A simple Nusselt number correlation is also proposed for turbulent heat transfer in ribbed pipe flow.

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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) geometry, (b) r–θ plane, and (c) r–z plane

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Fig. 2

Streamlines of the mean flow; (a) p/e = 2, (b) p/e = 4, (c) p/e = 6, (d) p/e = 8, and (e) p/e = 10

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Fig. 3

Mean streamwise-velocity profiles in wall units for Re = 24,000, e/D = 0.0625

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Fig. 4

Comparison of roughness function (ΔU+)

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Fig. 5

Friction factor versus p/e for Re = 24,000, e/D = 0.0625

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Fig. 6

Contours of nondimensionalized mean temperature for Re = 24,000, e/D = 0.0625; (a) p/e = 2, (b) p/e = 4, (c) p/e = 6, (d) p/e = 8, and (e) p/e = 10

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Fig. 7

Distribution of local mean Nusselt number between two neighboring ribs

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Fig. 8

Distribution of local mean Nusselt number between two neighboring ribs for p/e = 10, ——, present; – – – –, Ahn et al. [16] (LES, channel, Re = 30,000, BR = 0.1); ▪, Ahn et al. [16] (Experiment, rectangular duct, Re = 30,000, BR = 0.1); ○, Cho et al. [40] (Experiment, rectangular duct, Re = 30,000, BR = 0.1); ◻, Liou et al. [7] (Experiment, rectangular duct, Re = 13,000, BR = 0.13)

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Fig. 9

Distribution of local mean Nusselt number between two neighboring ribs for p/e = 18

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Fig. 10

Instantaneous velocity vectors and contours of nondimensionalized temperature in an r–z plane for Re = 24,000, e/D = 0.0625; (a) p/e = 2, (b) p/e = 4, and (c) p/e = 8

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Fig. 11

Instantaneous velocity vectors and contours of the circumferential vorticity component (ωθ) in an r–z plane for Re = 24,000, e/D = 0.0625; (a) p/e = 2, (b) p/e = 4, and (c) p/e = 8

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Fig. 12

Instantaneous contours of turbulent kinetic energy (k¯) in an θ–z plane at R−r≈0.04e for p/e = 10

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Fig. 13

Instantaneous contours of local Nusselt number in an θ-z plane on the wall for p/e = 10

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Fig. 14

Instantaneous velocity vectors and vortical structures (Q) in an θ–z plane at R−r≈0.187e for p/e = 10

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Fig. 15

Variation of mean Nusselt number with p/e

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Fig. 16

Friction correlation for repeated-rib pipe flow

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Fig. 17

Heat transfer correlation for Pr = 0.71

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