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Research Papers

# Heat Transfer at High Rotation Numbers in a Two-Pass 4:1 Aspect Ratio Rectangular Channel With $45deg$ Skewed Ribs

[+] Author and Article Information
Fuguo Zhou, Sumanta Acharya

Turbine Innovation and Energy Research (TIER) Center, College of Engineering, Louisiana State University, Baton Rouge, LA 70803

J. Turbomach 130(2), 021019 (Mar 24, 2008) (12 pages) doi:10.1115/1.2752185 History: Received October 08, 2006; Revised January 10, 2007; Published March 24, 2008

## Abstract

Heat transfer measurements are reported for a rotating 4:1 aspect ratio (AR) coolant passage with ribs skewed $45deg$ to the flow. The study covers Reynolds number (Re) in the range of 10,000–70,000, rotation number (Ro) in the range of 0–0.6, and density ratios (DR) between 0.1 and 0.2. These measurements are done in a rotating heat transfer rig utilizing segmented copper pieces that are individually heated, and thermocouples with slip rings providing the interface between the stationary and rotating frames. The results are compared with the published data obtained in a square channel with similar dimensionless rib-geometry parameters, and with the results obtained for a 4:1 AR smooth channel. As in a 1:1 AR channel, rotation enhances the heat transfer on the destabilized walls (inlet-trailing wall and outlet-leading wall), and decreases the heat transfer ratio on the stabilized walls (inlet-leading wall and outlet-trailing wall). However, the rotation-induced enhancement/degradation for the 4:1 rectangular channel is much weaker than that in the square ribbed channel, especially in the inlet (the first passage). The results on the inlet-leading wall are in contrast to that in the smooth channel with the same AR, where rotation causes heat transfer to increase along the inlet-leading wall at lower Reynolds number ($Re=10,000$ and 20,000). Higher DR is observed to enhance the heat transfer on both ribbed walls in the inlet (the first passage) and the outlet (the second passage), but the DR effects are considerably weaker than those in a ribbed square channel. Measurements have also been parameterized with respect to the buoyancy parameter and results show the same general trends as those with respect to the rotation number. In addition, pressure drop measurements have been made and the thermal performance factor results are presented.

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## Figures

Figure 1

Experimental setup: (a) rotation rig; (b) experimental apparatus

Figure 2

Heat transfer model and the ribbed copper elements: (a) lower portion of the 45deg ribbed model; (b) 45deg ribbed copper element with heater and spacer; (c) ribs configuration on the leading and trailing walls

Figure 3

Comparisons with previous studies at stationary conditions, P∕e=10, T refers to trailing wall; and L refers to leading wall: (a) Nu∕Nu0 distributions in the inlet; (b) Nu∕Nu0 distributions in the inlet, bend, and outlet; and (c) Reynolds number effects in the inlet

Figure 4

Re number effects with variation of rotation number at DR=0.13 (a) inlet-trailing wall; (b) inlet-leading wall; (c) outlet-trailing wall; and (d) outlet-leading wall

Figure 5

Rotation effects in comparisons with Johnson (7) at Re=25,000 and DR=0.13: (a) inlet (the first passage); (b) bend; and (c) outlet (the second passage)

Figure 6

Rotation effects with variable Re numbers at DR=0.13 (DR=0.10 for Re=70,000): (a) inlet-trailing wall; (b) inlet-leading wall; (c) outlet-trailing wall; and (d) outlet-leading wall

Figure 7

DR effects in comparisons with Johnson (7) on the middle copper plates at Re=25,000: (a) present: X∕Dh=5.70; Johnson (7): X∕Dh=8.50; (b) present: X∕Dh=5.70; Johnson (7): X∕Dh=8.50; (c) present: X∕Dh=24.37; Johnson (7): X∕Dh=25.50; and (d) present: X∕Dh=24.37; Johnson (7): X∕Dh=25.50

Figure 8

Average DR effects at Re=10,000: (a) inlet; and (b) outlet

Figure 9

Buoyancy effects in comparisons with Johnson (7) on the middle copper plates at Re=25,000: (a) present: X∕Dh=5.70; Johnson (7): X∕Dh=8.50; (b) present: X∕Dh=5.70; Johnson (7): X∕Dh=8.50; (c) present: X∕Dh=24.37; Johnson (7): X∕Dh=25.50; and (d) present: X∕Dh=24.37; Johnson (7): X∕Dh=25.50

Figure 10

Average buoyancy effects at Re=10,000, inlet

Figure 11

Friction factor and thermal performance factor versus Re number in the inlet at Ro=0: (a) Friction factor in the inlet; and (b) TPF in the inlet

Figure 12

Friction factor and thermal performance factor versus Ro number in the inlet with DR=0.15 and Re=25,000 (a) friction factor in the inlet; and (b) TPF in the inlet

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