Anisotropic Thermal Response of Packed Copper Wire

Abstract

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 FEA model were found to reasonably predict the apparent thermal conductivity perpendicular to the wires but thermal conductivity percolation from non-ideal wire-packing may result in their underestimation of it.