Measurement of Thermal Conductivity of PbTe Nanocrystal Coated Glass Fibers by the 3ω Method

Abstract

Fiber-based thermoelectric materials can conform to curved surfaces to form energy harvesting devices for waste heat recovery. Here we investigate the thermal conductivity in the axial direction of glass fibers coated with lead telluride (PbTe) nanocrystals using the self-heated 3ω method particularly at low frequency. While prior 3ω measurements on wire-like structures have only been demonstrated for high thermal conductivity materials, the present work demonstrates the suitability of the 3ω method for PbTe nanocrystal coated glass fibers where the low thermal conductivity and high aspect ratio result in a significant thermal radiation effect. We simulate the experiment using a finite-difference method that corrects the thermal radiation effect and extract the thermal conductivity of glass fibers coated by PbTe nanocrystals. The simulation method for radiation correction is shown to be generally much more accurate than analytical methods. We explore the effect of nanocrystal volume fraction on thermal conductivity and obtain results in the range of 0.50−0.93 W/mK near room temperature. KEYWORDS: Thermoelectric, flexible, thermal conductivity, 3ω, radiation, finite difference method F lexible thermoelectric materials such as nanocomposites 1 and fibers 2 can significantly impact waste heat recovery and solid-state cooling because of the advantages of lightweight, flexibility, and higher tolerance to thermal expansion. Particularly, flexibility can allow thermoelectric devices to be installed on curved surfaces such as automobile exhaust pipes, power plant steam pipes, manufacturing industry cooling pipes, and so forth. Our previous studies 2 showed that thermoelectric fibers made from glass fibers coated with an ultrathin layer of PbTe nanocrystals (300 nm thick) can possess a similar thermoelectric figure of merit compared to traditional rigid bulk bismuth telluride modules. The module assemblies require several millimeters of thickness, which highlights a great potential for high performance with much reduced raw material cost for the coated fibers. In this paper, we present an investigation of the thermal conductivity of our thermoelectric fibers at the single fiber level using the 3ω method to further understand the thermal transport in the axial direction. Through simulations based on the finite-difference method, we successfully model the radiation effect and extract the thermal conductivity at the single fiber level. Our simulation method for radiation correction appears to be much more accurate than conventional analytical methods. Furthermore, we measure and simulate several samples to determine the thermal conductivities of composite fibers of varying composition; from 0% PbTe to 35.8% PbTe by volume fraction.Several methods have been developed to measure the thermal properties of wire-like samples in the axial direction. These include the self-heating 3ω method, 3 dc thermal bridge

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