Thermoelectric-hydraulic performance of a multistage integrated thermoelectric power generator B.V.K. Reddy, Matthew Barry, John Li, Minking K. Chyu ⇑ Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA 15261, USA article info Article history: Received 2 May 2013 Accepted 18 September 2013 Keywords: Flow channel Integrated Numerical model Performance Thermoelectrics Waste-heat recovery abstract A thermoelectric element made of p- and n-type semiconductor plates bonded onto a highly thermal and electrical conducting inter-connector material with an integrated ﬂow channel can be treated as an inte- grated thermoelectric device (iTED). The performance of an iTED with multiple elements connected elec- trically in series and thermally in parallel has been investigated using numerical simulations. The top and bottom surfaces of the device are subjected to a constant cold temperature while the inter-connector channel walls are exposed to a hot ﬂuid. The thermoelectric-hydraulic behavior of an iTED is analyzed in terms of heat input, power output, conversion efﬁciency, produced electric current, Ohmic and Seebeck voltages, and pressure drops for various hot ﬂuid ﬂow rates Re and inlet temperatures T in , thermoelectric material sizes d, and number of modules N. For a single module iTED with ﬁxed d and T in values, the power output and efﬁciency are increased ﬁve- and twofold, respectively at Re = 500 when compared with the values of Re = 100. For given Re and d values, increasing T in resulted in enhanced device perfor- mance. Furthermore, increasing d increased internal resistance and resulted in a decrease of heat input. The inﬂuence of d on power output is phenomenal; for a given set of geometric and thermal boundary conditions, there exists an optimum d where a maximum power output is achieved. The addition of mod- ules N resulted in a signiﬁcant improvement in power output and a reduction in produced electric current and efﬁciency. For instance, device with N = 5 showed more than a twofold increase in power output and nearly a 33% reduction in both efﬁciency and electric current when compared to N = 1 values. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction There is an ever-increasing amount of green-house gas and waste-heat released into the atmosphere from the fossil-fuel power generation plants, automobiles, and industrial heating or cooling systems in response to continual energy demands. Approx- imately two -thirds of the supplied energy into these systems is rejected as a waste-heat to the surroundings. There is an urgent need to explore novel, environmentally-friendly technologies that can replace or improve the performance of the existing systems. Solid-state thermoelectric devices are a viable technology for recovering waste-heat and convert it into electricity while mitigat- ing the emission of green-house gases. Thermoelectric devices (TEDs) are constructed by joining two different electrically and thermally conductive materials at a junction. Using the Seebeck effect, TEDs work as electric power generators when the two material junctions are exposed to a temperature differential. Similarly, TEDs act as a refrigerators via the Peltier effect when an electric current is applied across the ter- minals, creating a temperature differential at the material junction [1]. However, the current thermoelectric materials with a ﬁgure of merit 1.5 achieve thermal conversion efﬁciencies of 5–15% and coefﬁcients of performance (COP) of 0.5–1. Due to their scalable, reliable, stable, compact and noise free operation, TEDs are suitable in novel applications such as waste-heat recovery from exhaust streams and other low-grade heat sources, electric power genera- tion for remote radio and satellite stations, pocket electronics, bio-thermal batteries to power pacemakers, localized cooling in electronic components and space cooling in automobile seats. The efﬁciency of TEDs has been increased via the methods of nano-structuring and fabrication [2–4], novel designs [5–10] and use of new bulk materials [1]. Caillat et al. [5] developed a seg- mented TED using novel p- and n-type materials, and achieved a conversion efﬁciency of 15%. El-Genk et al. [6] reported peak efﬁ- ciencies of 16.69% and 7.4% respectively for skutterudite and SiGe segmented TEDs. Further, Punnachaiya et al. [7] studied cascaded TEDs and showed a low conversion efﬁciency of 0.47% with T h = 96 °C and temperature differential (T h –T c ) of 25 °C. Liang et al. [8] investigated the performance of a multistage TED and 0196-8904/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.enconman.2013.09.040 ⇑ Corresponding author. Tel.: +1 412 624 9720; fax: +1 412 624 4846. E-mail addresses: bvkreddy680@gmail.com (B.V.K. Reddy), mmb49@pitt.edu (M. Barry), johnli407@yahoo.com (J. Li), mkchyu@pitt.edu (M.K. Chyu). Energy Conversion and Management 77 (2014) 458–468 Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman