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Research Papers

Forced Convection Heat Transfer in Channels With Rib Turbulators Inclined at 45 deg

[+] Author and Article Information
Giovanni Tanda, Roberto Abram

DIPTEM/TEC, University of Genova, via all’Opera Pia 15a, I-16145 Genova, Italy

J. Turbomach 131(2), 021012 (Jan 29, 2009) (10 pages) doi:10.1115/1.2987241 History: Received September 13, 2007; Revised July 25, 2008; Published January 29, 2009

Local and average Nusselt numbers and friction factors are presented for rectangular channels with an aspect ratio of 5 and angled rib turbulators inclined at 45 deg with parallel orientations on one and two surfaces of the channel. The convective fluid was air, and the Reynolds number varied from 9000 to 35,500. The ratio of rib height to hydraulic diameter was 0.09, with the rib pitch-to-height ratio equal to 13.33 or 6.66. Experiments were based on the use of heating foils (for the attainment of uniform heat flux condition) and of the steady-state liquid crystal thermography (for the identification of isotherm lines and the reconstruction of local heat transfer coefficient). Local results showed quasiperiodic profiles of Nusselt number in the streamwise direction, whose features were strongly affected by the value of rib pitch and by the spanwise coordinate. For all the investigated geometries a heat transfer augmentation, relative to the fully developed smooth channel, was found; when inclined rib turbulators were placed on two opposite surfaces of the channel, the full-surface Nusselt number was higher (by 10–19%) than that for the one-ribbed wall channel, but pressure drop penalties also increased by a factor of about 3. For both the one- and two-ribbed wall channels, the best heat transfer performance for a constant pumping power, in the explored range of Reynolds number, was generally achieved by the larger rib pitch-to-height ratio (=13.33).

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Figures

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Figure 1

Schematic layout of the experimental setup and test section

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Figure 2

Geometry of the rib-roughened heated surface

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Figure 3

Smooth channel normalized Nusselt number

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Figure 12

Normalized full-surface Nusselt number versus the normalized friction factor. Open symbols: 1RW channel; filled symbols: 2RW channel; and semi-filled symbols: literature data from Park (11) (2RW, AR=4, p/e=10, e/D=0.078, and α=45 deg), from Chandra (37) (1RW, AR=2, p/e=8, e/D=0.0625, and α=90 deg), and from Tanda (44) (1RW, AR=5, p/e=13.33, e/D=0.09, and α=90 deg).

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Figure 13

Normalized full-surface Nusselt number versus the smooth-channel Reynolds number for fixed pumping powers. Open symbols: 1RW channel; filled symbols: 2RW channel; and semi-filled symbols: literature data from Tanda (44) (1RW, AR=5, p/e=13.33, e/D=0.09, and α=90 deg).

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Figure 11

Normalized friction factor versus the Reynolds number. Open symbols: 1RW channel; filled symbols: 2RW channel.

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Figure 4

Typical liquid crystal image for the ribbed heated plate

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Figure 5

Local heat transfer coefficient h(W/m2 K) along the ribbed heated surface for p/e=13.33, Re=29,000, 1RW channel

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Figure 6

Streamwise Nusselt number at various spanwise stations for p/e=13.33. 1RW channel: (a) Re=9000 and (b) Re=35,500; 2RW channel: (c) Re=9000 and (d) Re=35,500.

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Figure 7

Streamwise Nusselt number at various spanwise stations for p/e=6.66. 1RW channel: (a) Re=9000 and (b) Re=35,500; 2RW channel: (c) Re=9000 and (d) Re=35,500.

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Figure 8

Per-module Nusselt number for p/e=13.33. Open symbols: 1RW channel; filled symbols: 2RW channel.

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Figure 9

Per-module Nusselt number for p/e=6.66. Open symbols: 1RW channel; filled symbols: 2RW channel.

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Figure 10

Normalized full-surface Nusselt number versus the Reynolds number. Open symbols: 1RW channel; filled symbols: 2RW channel.

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