Analysis of the electrothermal technique for thermal property characterization of thin fibers

Abstract

The transient electrothermal technique has been developed to measure the thermal conductivity and thermal diffusivity of electrically conductive or non-conductive nano-to-microscale fibers. In this work, a full theoretical model is developed in detail including the effects of radiation heat loss and non-constant heating as a result of sample temperature rise during measurement, and is compared to the more commonly used reduced model, which neglects these effects. Non-dimensional parameters are derived representing radiation heat loss and non-constant heating to identify the true parameter dependences on these effects. A numerical model is used to perform parametric analyses on the experimental setup providing results that were fitted with the full and reduced models to find thermal conductivity and thermal diffusivity. Additionally, the numerical model was used to investigate nonlinear radiation heat losses and spatially non-uniform heating effects resulting from uneven coating of the conductive layer on electrically non-conductive samples. As a result, these influences are shown to require careful consideration in the application of this technique. A clear linear relationship was found between the non-dimensional parameters and measurement error, which provides a measure for the proper estimation of systematic error induced by these effects. Using the reduced model for data reduction results in measurement percentage error equal to ten times the radiation and non-constant heating dimensionless parameters under the assumption of linear radiation heat losses (small sample temperature rise compared to ambient temperature).