Computational study on anisotropic thermal characterization of multi-scale wires using transient electrothermal technique

• Numerical models of the anisotropic heat transfer of multi-scale wires using the TET technique were successfully developed.
• Thermal diffusivity was predicted more accurately by considering anisotropic heat transfer and radiation heat loss.
• Effects of wire morphologies and measurement conditions on thermal characterization of wires were studied comprehensively.
• Simulation results are useful for experimentalists optimizing their thermal measurement conditions using the TET technique.

Numerical models predicting anisotropic heat transfer of multi-scale wires using the transient electrothermal (TET) technique were successfully developed. Compared to previous models, the developed models are more realistic and accurate by taking into account the anisotropic thermal conduction in both axial and radial directions and the radiation heat loss from the wire surface to the measurement ambient. In the TET technique, the to-be-measured wire is placed between two electrodes. By feeding a step DC to the wire, its temperature increases and eventually reaches the steady state. The temperature evolution is probed by measuring the variation of voltage/resistance over the wire, which is then used to determine the axial and radial thermal diffusivities of the wire. For the first time, the developed models are solved using implicit finite difference method, giving more accurate predictions than the previous models using Green's function. The obtained results are in excellent agreement with the experimental data. Using the validated models, the effects of various wire morphologies (radius of 10–200 μm, length of 5–20 mm), and experimental conditions (DC supply of 5–50 mA and ambient temperature of 0–25 °C) on the thermal characterization of the wires were also quantified. Our results are beneficial to experimentalists on optimization of measurement conditions of the experiments characterizing the thermal properties of multi-scale wires such as carbon-based microfibers.