RESEARCH PAPERS: Heat Transfer Enhancement

Heat Transfer Augmentation by Ion Injection in an Annular Duct

[+] Author and Article Information
Walter Grassi

 LOTHAR (LOw gravity and THermal Advanced Research Laboratory), Department of Energetics, “L. Poggi,” University of Pisa, via Diotisalvi 2, 56126 Pisa, Italyw.grassi@ing.unipi.it

Daniele Testi

 LOTHAR (LOw gravity and THermal Advanced Research Laboratory), Department of Energetics, “L. Poggi,” University of Pisa, via Diotisalvi 2, 56126 Pisa, Italyd.testi@ing.unipi.it

J. Heat Transfer 128(3), 283-289 (Aug 23, 2005) (7 pages) doi:10.1115/1.2150838 History: Received January 21, 2005; Revised August 23, 2005

The thermofluid-dynamic effects of ion injection from sharp metallic points added perpendicularly to the inner wire of a short horizontal annulus were experimentally investigated. A dielectric liquid (FC-72 by 3M) was weakly forced to flow in the duct, which was uniformly heated on the outer wall. A dc voltage as high as 22kV was applied to the inner electrode, while the heated wall was grounded. Both the laminar and the turbulent mixed-convection regimes were obtained, varying the imposed flow rate. Once an electric field is applied, the flow is dramatically modified by the jets of charged particles, which transfer their momentum to the neutral adjacent ones. Different injection strengths were obtained on the emitters, because the shape of the point tips was not controlled at the microscale. Nusselt number distributions were obtained azimuthally and longitudinally, monitoring the wall temperatures. In all cases, heat transfer turned out greatly enhanced in the proximity of the emitters, without a significant increase in pressure drop through the test section and with a negligible Joule heating, making this technique very attractive for application in compact heat exchangers.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

Schematic of the test loop

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Figure 2

Detail of the EHD test section

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Figure 3

Position of the points in configuration 2

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Figure 4

Nu distribution at Re=2220 and Grh=1.40×108

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Figure 5

Drawing of the microasperities at the point tip

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Figure 6

Presumed dynamics of the jets from the points in configuration 1

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Figure 7

Nu distribution at Re=740 and Grh=1.40×108

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Figure 8

Nu vs ξ at Re=2220 and Grh=1.40×108 and Grh=2.47×108 (dotted curves)

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Figure 9

⟨Nu⟩ vs ξ at Grh=1.40×108

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Figure 10

⟨Nu⟩ vs ξ in vertical aiding flow at Grh=3.89×108(3)

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Figure 11

⟨Nu⟩ vs Re (Secs. B and D) at Grh=1.40×108



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