Evaluation of a Thermoelectric Device Utilizing Porous Medium
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Evaluation of a Thermoelectric Device Utilizing Porous Medium Hideyuki Yasuda, Itsuo Ohnaka, Yoichi Inada, Kimitaka Nomura Department of Adaptive Machine Systems, Osaka University, Suita, Osaka 565-0871, Japan. [email protected] ABASTRACT A thermoelectric device consisting of the porous part and the bulk part was proposed. Increase of heat exchange area due to porous medium will improve the efficiency of heat exchange between heating/cooling sources and the device. Estimation based on physical properties of FeSi2 indicated that generated power of the partially porous device per unit area can be several times higher than that of the bulk one in case of gas heating / cooling system. The partially porous thermoelectric devices were produced. In measurement of power, it has been confirmed that generated power per unit area of the partially porous FeSi2 devices was roughly 10 times higher than that of the conventional device. The proposed porous device will exhibit its advantage in the case of low heat transfer coefficient between the device and the heating / cooling sources. INTRODUCTION Thermoelectric materials, which convert heat into electricity or electricity into heat, and system for the power generation, have been extensively studied. Development of microstructure that enhances the value of the figure-of-merit and discovery of new thermoelectric materials with a high figure-of-merit have been taken into attention in order to improve the efficiency of thermoelectric energy conversion. It is also required to design power generation or cooling / heating devices and systems in order to exhibit the best performance which is expected from the figure-of-merit. From a view point of thermo-fluid mechanics, it is generally difficult to achieve good device performance because of low thermal conductivity of heating/cooling sources when heating / cooling sources are gas. Echigo et al have proposed a novel thermoelectric power generation system and a cooling/heating system using porous thermoelectric devices [1-3]. A flammable gas flows through the porous device and combustion occurs at the end of device. The flowing gas drives thermal energy from the cold side to the hot side like a heat pump, because heat exchange efficiently occurs at the large interface of the porous medium. As a result, large temperature difference between inlet and outlet of the porous device is caused without any additional cooling system. Materials processing for the porous thermoelectric device has been also reported [4,5]. Another thermoelectric device has been proposed, which consisted of the porous parts and the bulk part [6]. A characteristic feature of porous medium is large amount of surface area in comparison with its volume, causing efficient heat exchange between solid and fluid. This paper presents a model of the partially porous device to evaluate the generated power and experimental
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