Flow and Heat Transfer Characteristics in Rectangular Channels With Staggered Transverse Ribs on Two Opposite Walls

[+] Author and Article Information
Rong Fung Huang1

Department of Mechanical Engineering, National Taiwan University of Science and Technology, 43 Keelung Road, Section 4, 106 Taipei, Taiwan, ROCrfhuang@mail.ntust.edu.tw

Shyy Woei Chang

Department of Marine Engineering, National Kaohsiung Marine University, 142 Hai-Chuan Road, Nan-Tzu District, 811 Kaohsiung, Taiwan, ROC

Kun-Hung Chen

Department of Mechanical Engineering, National Taiwan University of Science and Technology, 43 Keelung Road, Section 4, 106 Taipei, Taiwan, ROC


Corresponding author.

J. Heat Transfer 129(12), 1732-1736 (Apr 06, 2007) (5 pages) doi:10.1115/1.2768101 History: Received November 18, 2006; Revised April 06, 2007

The flow characteristics and the heat transfer properties of the rectangular channels with staggered transverse ribs on two opposite walls are experimentally studied. The rib height to channel height ratio ranges from 0.15 to 0.61 (rib height to channel hydraulic diameter ratio from 0.09 to 0.38). The pitch to rib height ratio covers from 2.5 to 26. The aspect ratio of the rectangular channel is 4. The flow characteristics are studied in a water channel, while the heat transfer experiments are performed in a wind tunnel. Particle image velocimetry (PIV) is employed to obtain the quantitative flow field characteristics. Fine-wire thermocouples imbedded near the inner surface of the bottom channel wall are used to measure the temperature distributions of the wall and to calculate the local and average Nusselt numbers. Using the PIV measured streamline patterns, various characteristic flow modes, thru flow, oscillating flow, and cell flow, are identified in different regimes of the domain of the rib height to channel height ratio and pitch to rib height ratio. The vorticity, turbulence intensity, and wall shear stress of the cell flow are found to be particularly larger than those of other characteristic flow modes. The measured local and average Nusselt numbers of the cell flow are also particularly higher than those of other characteristic flow modes. The distinctive flow properties are responsible for the drastic increase of the heat transfer due to the enhancement of the momentum, heat, and mass exchanges within the flow field induced by the large values of the vorticity and turbulence intensity. Although the thru flow mode is conventionally used in the ribbed channel for industrial application, the cell flow could become the choice if the heat transfer rate, instead of the pressure loss, is the primary concern.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Test section configuration of wind tunnel for thermal measurements. Side view shows test section, heaters, and insulators. Bottom view of test section shows attachment locations of type-T thermal couples.

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Figure 2

Typical velocity vectors and streamline patterns measured by PIV in symmetry plane at Rehyd=14,000: (a) thru flow I, (b) thru flow II, (c) deflected flow, (d) and (e) cell flow

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Figure 3

Characteristic flow regimes on the domain of h∕B and p∕h

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Figure 4

Turbulence intensities measured by PIV in symmetry plane at Rehyd=14,000: (a) and (b) distribution along separation line evolving from tip of second rib on bottom wall of channel, and (c) and (d) axial distributions near bottom wall at y∕B=0.04

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Figure 5

Heat transfer characteristics: (a) and (b) axial distributions of normalized Nusselt numbers, heat flux 1100W∕m2, (c) variations of normalized area-averaged Nusselt numbers with Reynolds number, and (d) correlation of area-averaged Nusselt number

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Figure 6

(a) friction factor and (b) thermal performance



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