Validation of commercial Bi2Te3-based thermoelectric generator modules for application as metrological reference samples

Abstract

Traceability and the definition of uncertainty budgets are considered as necessary prerequisites for a meaningful characterization of thermoelectric generator modules (TEM). Due to the lag of standardized measurement techniques and characterization guidelines users and developers of measurement facilities cannot express uncertainty budgets on a normative base, but can only rely on own experiences and act according to best practise approaches. Reference samples are an appropriate method to investigate the accuracy of measurements and to provide insides into strengths and weaknesses of the employed characterization methods. Such references are still not available to date for measurements on TEM. In order to overcome this deficit this article discusses the applicability of commercially available Bi2Te3-based TEM to serve as metrological reference samples.Four TEM types from different manufacturers were investigated with regard to their stability, which was assessed on the base of the internal electric resistance Ri in the course of different experiments. The modules have been tested under constant temperature differences (ΔT = 150 °C / 175 °C) but variable mechanical pressure (2 MPa ≤ p ≤ 3.5 MPa). Further experiments have been conducted under constant pressure (p = 3 MPa) and variable temperature differences in order to determine the short-term stability. The long-term stability was assessed from thermal cycling experiments with observation times between 117 h and 443 h in dependence of the observed module stability. Significant differences could be observed regarding the stability of Ri, which ranged from very stable module types with maximum changes of ΔRi < 2.5% to modules with a relatively weak stability showing ΔRi > 13%. The sample-to-sample variation (homogeneity) of Ri was tested in a last step on five modules from two most stable types.