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Research Papers

Heat Transfer and Friction Augmentation in High Aspect Ratio, Ribbed Channels With Dissimilar Inlet Conditions

[+] Author and Article Information
Carson D. Slabaugh, Lucky V. Tran, J. S. Kapat

 Center for Advanced Turbines and Energy Research, Laboratory for Turbine Aerodynamics, Heat Transfer, and Durability, University of Central Florida, Orlando, FL 32816

Bobby A. Warren

 Siemens Energy Inc., Orlando, FL 32826

J. Turbomach 134(6), 061013 (Sep 04, 2012) (11 pages) doi:10.1115/1.4006283 History: Received November 28, 2010; Revised February 10, 2011; Published September 04, 2012; Online September 04, 2012

This work is an investigation of the heat transfer and pressure-loss characteristics in a rectangular channel with ribs oriented perpendicular to the flow. The novelty of this study lies in the immoderate parameters of the channel geometry and transport enhancing features. Specifically, the aspect ratio (AR) of the rectangular channel is considerably high, varying from 15 to 30 for the cases reported. Also varied is the rib-pitch to rib-height (p/e), studied at two values, 18.8 and 37.3. Rib-pitch to rib-width (p/w) is held to a value of two for all configurations. Channel Reynolds number is varied between approximately 3000 and 27,000 for four different tests of each channel configuration. Each channel configuration is studied with two different inlet conditions. The baseline condition consists of a long entrance section leading to the entrance of the channel to provide a hydrodynamically developed flow at the inlet. The second inlet condition studied consists of a cross-flow supply in a direction perpendicular to the channel axis, oriented in the direction of the channel width (the longer channel dimension). In the second case, the flow rate of the cross-flow supply is varied to understand the effects of a varying momentum flux ratio on the heat transfer and pressure-loss characteristics of the channel. Numerical simulations revealed a strong dependence of the local flow physics on the momentum flux ratio. The turning effect of the flow entering the channel from the cross-flow channel is strongly affected by the pressure gradient across the channel. Strong pressure fields have the ability to propagate farther into the cross-flow channel to “pull” the flow, partially redirecting it before entering the channel and reducing the impingement effect of the flow on the back wall of the channel. Experimental results show a maximum value of Nusselt number augmentation to be found in the 30:1 AR channel with the aggressive augmenter (p/e = 37.3) and a high momentum flux ratio: Nu/Nuo  = 3.15. This design also yielded the friction with f/f0  = 2.6.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Channel designs tested

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Figure 2

Experimental setup with fully developed inlet

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Figure 3

Overall experimental setup with cross-flow inlet

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Figure 4

Detailed view of experimental setup with cross-flow inlet

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Figure 5

Velocity vectors (m/s) with cross-flow Reynolds number = 125,000, test section Reynolds number = 7000. Channel AR is 15:1.

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Figure 6

Velocity vectors (m/s) with cross-flow Reynolds number = 125,000, test section Reynolds number = 26,000. Channel AR is 15:1.

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Figure 7

Velocity vectors (m/s) with cross-flow Reynolds number = 125,000, test section Reynolds number = 3500. Channel AR is 30:1.

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Figure 8

Velocity vectors (m/s) with cross-flow Reynolds number = 125,000, Test section Reynolds number = 17,000. Channel AR is 30:1.

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Figure 9

Pressure contours (Pa) forcing flow activity in non-ribbed portion at channel Reynolds number = 15,000

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Figure 10

Flow activity in non-ribbed portion at channel Reynolds number = 15,000

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Figure 11

Velocity vectors (m/s) at the channel inlets with cross-flow Reynolds number = 250,000, test section Reynolds number = 15,000, channel AR = 30:1

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Figure 12

Locally averaged Nu/Nuo versus X/Dh for Channel A (all flow configurations)

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Figure 13

Locally averaged Nu/Nuo versus X/Dh for Channel B (all flow configurations)

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Figure 14

Locally averaged Nu/Nuo versus X/Dh for Channel C (all flow configurations)

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Figure 15

Channel-averaged Nu/Nuo versus Reynolds number (all channels and flow configurations)

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Figure 16

Channel-averaged f/fo versus Reynolds number for Channel A (all flow configurations)

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