Thermophysical property measurement of electrically nonconductive fibers by the electrothermal technique

摘要

The transient electrothermal technique is a powerful tool to obtain thermal properties of fine fibers. However, the technique suffers from several inherent pitfalls, which affect measurement accuracy, especially with application to coated, nonconductive samples. In this paper, measurement challenges are described and quantified for several associated parameters and physics including: sample length, time of Joule-heating initiation, sample resistance including measurement uncertainty as well as evolving resistance for coated samples, coating influence, lateral surface heat losses, vacuum level, and variable heat generation. Several methods to overcome these challenges to ensure good measurement accuracy are provided. These methods are applied to the measurement of thermal conductivity and thermal diffusivity of gold-coated glass fibers (nonconductor). The resulting measured thermal conductivity of 1.35 Wm~(-1)K~(-1), and thermal diffusivity of 7.6 × 10~(-7) m~2 s~(-1) compare well to literature values. Additionally, an analytic formula is developed along with limiting conditions for simplified application, which accounts for neglected heat losses. The result is a factor that can be applied to correct a more straightforward heat model of the sample, which neglects heat losses. To further validate the method and quantify measurement variability, a detailed uncertainty analysis is performed using methods based on the Taylor series method for propagation of uncertainty and Monte Carlo simulation. The resulting measurement uncertainty is found to be ～7% for thermal conductivity and ～4% for thermal diffusivity.