Oxide thermoelectric materials are considered to be promising ones because of their durability against high temperature in air, low cost for producing and toxicity etc. Thermoelectric modules using p-type Ca3Co4O9 (Co-349) and n-type CaMnO3 (Mn-113) have been produced using Ag paste to form junctions. Moreover, thermoelectric power generation units have been demonstrated to recover waste heat from industrial furnaces and incinerators. The maximum out-put power was obtained over 700 W from the water-cooled thermoelectric unit. In order to improve the convenience of thermoelectric generation, water should be unwanted for cooling. After increase in the out-put power and durability of the thermoelectric modules using oxide materials, the air-cooled thermoelectric generation units have been developed.
The power factor is doubled by repetition of hot-forging technique for the Co-349 bulks. The out-put power of the thermoelectric module composed of Co-349 and Mn-113 devices is enhanced by 2 times. The maximum power density of the module was increased to 0.72 W/cm2 against the total cross-sectional surface of the devices at 1073 K of the heat source temperature (TH) by water cooling at 293 K (Tc).
The durability against high temperature, heat cycling, and vibration of the oxide modules was investigated quantitatively. Long life time tests have been carried out for the oxide modules up to 1073 K of the heat source temperature by water circulation at 293 K under the air atmosphere. No degradations in both generated power are observed up to 1073 K of TH. The durability against heat cycling was investigated between 873 and 373 K of TH in air. The maximum out-put power is kept constant during 200 times of the heat cycling.
The air-cooled thermoelectric units have been developed using heat pipes for the cold side. The maximum out-put power reaches 2.2 W at 823 K of the heat source temperature. The power generation can be shown by lighting LED lamps, charging the smart phone and portable TV, and wireless transmission of data and moving images by the temperature sensor and web camera, respectively using the combustion of natural gas or firewood as the heat sources.