Thermoelectric Modules For High Temperature Waste Heat
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Thermoelectric Modules For High Temperature Waste Heat Ryoji Funahashi1, 2*, Toshiyuki Mihara1, 2, Masashi Mikami1, Saori Urata1 National Inst. of Adv. Indust. Sci. and Tech., Ikeda, Osaka 563-8577, Japan 2 CREST, Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012, Japan 1
ABSTRACT A new adhesive material has been developed in order to obtain practically usable thermoelectric modules composed of oxide thermoelectric legs. The thermoelectric module composed of 8-pair oxide legs has been fabricated. Both hot- and cold-sides of the module were covered by alumina plates. Open circuit voltage VO and maximum power Pmax reach 0.38 V and 0.30 W, respectively at 803 K of a hot-side temperature TH and 362 K of a temperature differential ∆T between TH and cold-side temperature TC. Generating power was repeated 11 times at 873-993 K of TH and at 200-290 K of ∆T. The module was cooled down to room temperature after each generation. At third measurement internal resistance RI of the module increased by 30 %. This is due to destruction of junctions because of thermal strain. No deterioration, however, was observed in thermoelectric properties for the oxide legs. 1. INTRODUCTION In view of global energy and environmental problems, research and development have been promoted in the field of thermoelectric power generation as a means of recovering vast amounts of waste heat emitted by automobiles, factories, and similar sources. Waste heat from such the sources offers a high-quality energy source equal to about 70 % of total primary energy, but is difficult to reclaim due to its source amounts being small and widely dispersed. Thermoelectric generation systems offer the only viable method of overcoming these problems by converting heat energy directly into electrical energy irrespective of source size and without the use of moving parts or production of environmentally deleterious wastes. The requirements placed on materials needed for this task, however, are not easily satisfied. Not only must they possess high conversion efficiency, but must also be composed of non-toxic and abundantly available elements having high chemical stability in air even at temperatures of 800−1000 K. Thermoelectric modules are composed of intermetallic compounds, such as Bi2Te3, Pb−Te, and Si−Ge. Practical applications of materials like these have, however, been delayed by problems such as their low melting or decomposition temperatures, their content of harmful or scarce elements, and their cost. Recently, oxide compounds have attracted attention as promising thermoelectric materials because of their potential to overcome the above-mentioned problems [1−7]. Though fabrication of thermoelectric modules using oxide materials has been reported [8, 9], their performance is much lower than that expected considering the properties of their starting materials. This is thought to be because the contact resistance at electrodes in which oxide/metal junctions are usually formed is very high, thus severely limiting the magnitude of out
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