A new guarded heat flow apparatus for thermal characterization of thermoelectric modules up to 500°C

F. Hemberger1, J. Wachtel1, A. Göbel1 and H. Ebert1

1Bavarian Center for Applied Energy Research (ZAE Bayern), Germany

Keywords: guarded heat flow apparatus,
property: thermal conductivity, thermal resistance,
material: thermoelectric module

The use of thermoelectric modules for the conversion of thermal waste heat using the Seebeck effect is a highly promising technique for environmentally friendly generation of electrical power.

The energy efficiency of these modules is inversely proportional to their effective thermal conductivity. Nevertheless, a good thermal contact to the heat source and the heat sink is also needed. Furthermore, a high operation temperature on the hot side of the module is desired in order to maximise the electrical output. Hence, the determination of the effective thermal conductivity at high temperatures is an important task during development and testing of thermoelectric modules. Due to the fact that thermoelectric modules are not homogeneous materials, a stationary measurement method is preferred for the measurement of the effective thermal conductivity.

In this work the setup and first test results of a new guarded axial heat flow apparatus are presented. Key feature of our design is the vast temperature range from liquid nitrogen at the cold side up to 500°C on the hot side of the apparatus. Due to interchangeable reference bodies for the heat flow determination, it is possible to investigate specimen with a thermal resistance from 0.0002 to 0.02 m²K/W. The setup is suitable for specimen diameters of 30 or 50 mm. In order to investigate the thermal contact resistance as a function of the external load, it is possible to adjust the mechanical pressure on the specimen between 0.1 and 5.0 bar. Additionally, measurements can be performed under vacuum or different gas atmospheres.

Also presented are the calibration results for the used reference materials. Their thermal conductivity was determined as a function of temperature using laser flash technique and differential scanning calorimetry. A detailed analysis of the total measurement uncertainty of the new measurement setup will be given too.

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