Π Unileg Thermoelectric Structure for Cycling Robustness at High Temperature and Low Manufacturing Cost

Abstract

Unileg-type thermoelectric generators have proven to be a good choice for hightemperature applications, because their composition from a single thermoelectric material avoids different thermal expansion coefficients, giving the structure good mechanical strength and increased lifespan during thermal cycling. These structures are usually composed of a thermoelectric pellet with metallic electrical conductors joining the hot and cold ends of consecutive pellets. The novel unileg structure described herein is designed to deal with one of the main issues with traditional devices, viz. the physical and chemical stability of the solder between the pellet and the conductor at the hot side. The material for which this structure is proposed is a p-type Ca 3 Co 4 O 9 semiconductor oxide, due to its chemical stability at high temperature and good machinability. This final requirement is related to the main innovation of the structure, viz. a partial cut that divides the pellet longitudinally, leaving two legs joined by an uncut section, forming a section similar to the letter . The metallic conductor stripe usually employed in unileg thermoelectric generator manufacturing is replaced by a coating of conductive material, in this case silver, on one of the legs resulting from the cut. Due to these operations, one of the legs is practically short-circuited and acts as an electrical conductor for the unileg structure, eliminating the need for soldering at the hot end of the pellet.

Fabrication and thermoelectric conversion of thermoelectric concrete brick with buried unileg N-type CaMnO3 thermoelectric module inside

“…The unileg structure of the TEG module offers an easy-to-manufacture structure, which also reduces this thermal expansion mismatch. Moreover, this structure gives good mechanical strength and increases the lifespan of the TEG module 29 . The p/n-type TEG structure may operate at different incompatible ZT values, which harms the overall performance of the TEG module.…”

“…The p/n-type module structure creates several joining points that cause internal resistance of the TE module 26 . Typical operating environments of TEGs involve temperature fluctuations 28 also caused thermal expansion mismatch between the p-type and n-type legs of the TEGs structure [28][29][30] . The unileg structure of the TEG module offers an easy-to-manufacture structure, which also reduces this thermal expansion mismatch.…”

U-type unileg thermoelectric module: A novel structure for high-temperature application with long lifespan

“…Here, the integration of electrode and conductor reduced the total number of contacts in the thermoelectric device and further decreased the thermal stress. Therefore, the unileg module with pn-junction can be considered as a promising structure for low-stress design [13].…”