Fraunhofer Institute for Physical Measurement Techniques IPM
Fraunhofer Institute for Physical Measurement Techniques IPM

Innovative system design for optimized thermal coupling

© Fraunhofer IPM
In the assembly device, Peltier strips were bonded to copper fins with thermally conductive adhesive. A Peltier strip consists of two curamic plates covered with copper pads, to which the thermoelectric legs of p- and n-doped material are soldered. The legs are thus thermally connected in parallel and electrically in series. Copper wires were soldered to the strips for contacting.
© Fraunhofer IPM
This demonstrator setup achieved heat flow densities for heating of > 30,000 W/m² and for cooling of about 12,000 W/m². The effect can be used to precisely temper the tube.

In the case of Peltier elements, alternatives to the usual planar design are occasionally required with regard to thermal coupling. As part of a research project, we developed and manufactured strips made of thermoelectric material, which we have connected in series and arranged around a thin-walled tube. This »tube pelt« concept is aimed at very precisely tempering tubes made of a shape memory material so that they can be used as actuators in a very small available space. The tubes are made of the thermal shape memory alloy Nitinol. By changing the temperature, a change of the material’s initial crystalline structure (martensite) into an expanded state (austenite) is induced. This transition from the martensitic to the austenitic phase entails a movement so that the stroke can be thermally controlled and used as an actuator. Thermal coupling is crucial here: the greater the pressure, the better the compensation of unevenness; at the same time, too much force on the material (in our case bismuth telluride) may damage the thermoelectric legs. As an unsymmetrical assembly or shear forces might also destroy the legs, the assembly of the »tube pelt« was realized using a specially developed assembly device. This demonstrator setup achieved heat flow densities for heating of > 30,000 W/m² and for cooling of about 12,000 W/m².