High-accuracy compensation of radiative heat loss in Thomson coefficient measurement

Abstract

We report a simple and accurate method to address the inevitable radiative heat loss in the Thomson coefficient measurement. The additional steps required are the measurement of the Joule heat arising from the ac current, measurement of the electrical resistance of the sample, and calculation of the ratio of the two measurement signals arising from the Joule and Thomson effects. The underlying concept is that most of the radiative heat loss that occurs during the measurement of Joule and Thomson heats can be compensated for by calculating the ratio of the two signals. This is because the heat loss during the Joule heat measurement will be highly similar to that during the Thomson heat measurement. Heat transfer analysis indicates that radiative heat loss is reduced by at least a factor of six. Once the Thomson coefficient is measured, accurate Seebeck and Peltier coefficients can be obtained in a single run. This approach was demonstrated by performing measurements on fine platinum wires in the temperature range of 80 K-300 K. The difference between the compensated and uncompensated curves became significant as the temperature increased; moreover, this difference was proportional to the cube of the temperature for a long fine-wire sample, where there is substantial radiative heat loss. Thus, the proposed approach is completely different from a conventional one, wherein the measurement accuracy degrades owing to inevitable radiative heat loss without prior knowledge of the thermal conductivity and emissivity of the sample.