Research Papers

Anisotropic Thermal Response of Packed Copper Wire

[+] Author and Article Information
Andrew A. Wereszczak

Oak Ridge National Laboratory,
Oak Ridge, TN 37831
e-mail: wereszczakaa@ornl.gov

J. Emily Cousineau, Kevin Bennion

National Renewable Energy Laboratory,
Golden, CO 80401

Hsin Wang, Randy H. Wiles, Timothy B. Burress

Oak Ridge National Laboratory,
Oak Ridge, TN 37831

Tong Wu

Department of Electrical Engineering
and Computer Science,
University of Tennessee,
Knoxville, TN 37996

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received September 6, 2016; final manuscript received February 5, 2017; published online April 19, 2017. Assoc. Editor: Hongbin Ma. The United States Government retains, and by accepting the article for publication, the publisher acknowledges that the United States Government retains, a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for United States government purposes.

J. Thermal Sci. Eng. Appl 9(4), 041006 (Apr 19, 2017) (9 pages) Paper No: TSEA-16-1256; doi: 10.1115/1.4035972 History: Received September 06, 2016; Revised February 05, 2017

The apparent thermal conductivity of packed copper wire test specimens was measured parallel and perpendicular to the axis of the wire using laser flash, transient plane source, and transmittance test methods. Approximately 50% wire packing efficiency was produced in the specimens using either 670- or 925-μm-diameter copper wires that both had an insulation coating thickness of 37 μm. The interstices were filled with a conventional varnish material and also contained some remnant porosity. The apparent thermal conductivity perpendicular to the wire axis was about 0.5–1 W/mK, whereas it was over 200 W/mK in the parallel direction. The Kanzaki model and an finite element analysis (FEA) model were found to reasonably predict the apparent thermal conductivity perpendicular to the wires but thermal conductivity percolation from nonideal wire-packing may result in their underestimation of it.

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Fig. 1

Top (a) and side (b) views of a radially sectioned, copper-wire-wound laminated steel electric motor

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Fig. 2

Sectioned view showing the copper-wire packing within slot liners. Arrows in the bottom image represent the direction of potential heat transfer from the copper wires.

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Fig. 3

Polished cross sections of the two wire sizes used to fabricate test specimens. is the diameter and t is the thickness.

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Fig. 4

Schematic (a) of wire orientations in the processed cubes, and examples of (b)-(c) the two orientations of ground sections thereof

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Fig. 5

Slab-sectionings of the processed cubes for thermal conductivity specimen testing

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Fig. 6

Test specimen harvesting (a) for laser flash testing, and test setups for (b) transient plane source and (c) thermal transmission testing

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Fig. 7

Apparent thermal conductivity perpendicular to wires as a function of sample thickness using transmittance test method for (a) 925-μm-diameter or 19-Ga and (b) 670-μm-diameter or 22-Ga copper core wires. Indicated bars on the measurements represent 95% confidence bands. FEA low and high bounds represent fill-factors from density and image analysis estimations, respectively.

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Fig. 8

Percolation pathways that potentially provide localized, preferential thermal conduction. Potential pathways are illustrated for two mutually orthogonal sections of packed-copper wire.

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Fig. 9

Predicted apparent thermal conductivity as a function of packing efficiency (after Kanzaki et al. [9]) for the two examined wire diameters compared to measured responses

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Fig. 10

Calculated apparent thermal conductivity perpendicular to the wires as a function of thermal conductivity of the wire-coating material and interstices material (after Kanzaki et al. [9]). The thermal conductivities of the wire-coating and interstices material are set equal in this example.



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