Power and Efficiency Calculation and Evaluation of Material Properties in Thermoelectric Power Generators
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Power and Efficiency Calculation and Evaluation of Material Properties in Thermoelectric Power Generators Konstantinos Zorbas, Euripides Hatzikraniotis, and Konstantinos M Paraskevopoulos Dept. of Physics, Aristotle University of Thessaloniki, Section of Solid State Physics, University Campus, Thessaloniki, GR 54124, Greece ABSTRACT Thermoelectric elements convert a portion of thermal energy into electrical energy, developing the Seebeck effect. A number of thermoelectric elements can be connected electrically in parallel and/or in series shaping a thermoelectric generator (TEG) device. The generator efficiency, η, is determined by comparing the amount of electricity produced (PTEG) to the total amount of heat induced (QH).The possible use of such a device for the recovery of wasted heat can considerably help the world effort for energy savings and the reduction of greenhouse gases. A measuring system and a modeling approach which takes into account the thermal contact resistances have been developed, allowing the characterization of TEG devices under various loads and temperature gradients and thus, the evaluation of material properties. The model was applied on investigating the expected gained power and efficiency, at different places of the exhaust pipe of an intermediate size car with the use of conventional thermoelectric elements. Furthermore, the reliability of a TEG module was examined and the repercussion on fuel consumption is discussed. INTRODUCTION Thermoelectric generators make use of the Seebeck effect in semiconductors for the direct conversion of heat into electrical energy, which is of particular interest for systems of highest reliability or for waste heat recovery. A generator usually consists of several pairs of alternating p- and n-type semiconductor blocks (generator legs), which are arranged thermally parallel and connected electrically in a series circuit. The heat flow, which is partially converted into electrical power, is induced by heating one side of the arrangement while the opposite side is cooled. The conversion efficiency η is defined as the ratio of the generated electrical power PTEG and the heat input into the module QH. To accurately determine the efficiency of a generator, the heat induced and the electrical power produced must be carefully measured. Generator efficiencies are often calculated from the measured material properties [1]. This method indirectly yields generator efficiency through the figure of merit, requiring separate measurements of absolute Seebeck, of which electrical and thermal conductivities are susceptible to a tolerance of errors. More direct measurements of the figure of merit have been demonstrated and are useful to obtain generator efficiency, but the measurement accuracy is limited to testing under small temperature gradients [2-4]. Thermoelectric generator efficiency can, also, be determined through comparative heat flow, and this method offers a more direct and realistic measurement of generator’s efficiency [5]. Thermoelectrics is a pr
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