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TECHNICAL PAPERS: Thermal Systems

Enhancing Thermoelectric Energy Recovery via Modulations of Source Temperature for Cyclical Heat Loadings

[+] Author and Article Information
R. McCarty

Department of Mechanical and Aerospace Engineering, University of Dayton, 300 College Park, Dayton, OH 45469-0210robin.mccarty@wpafb.af.mil

K. P. Hallinan

Department of Mechanical and Aerospace Engineering, University of Dayton, 300 College Park, Dayton, OH 45469-0210kevin.hallinan@notes.udayton.edu

B. Sanders

Air Force Research Laboratories, VAS, 2210 Eight Street, Wright-Patterson, AFB, OH 45433-7542brian.sanders@wpafb.af.mil

T. Somphone

Department of Mechanical Engineering, Tuskegee University, 333 Engineering Building, Tuskegee, AL 36088

J. Heat Transfer 129(6), 749-755 (Sep 19, 2006) (7 pages) doi:10.1115/1.2717238 History: Received August 26, 2005; Revised September 19, 2006

Recent improvements in thermoelectric (TE) materials have expanded the potential to use this technology to generate electricity from waste heat in a variety of applications. The performance of a TE generator improves when the temperature difference across the generator is as large as possible given the constraints associated with its application. This paper considers the use of a “thermal switch,” located physically between the heat source and the TE device, to modulate the heat flow through the TE device. A control schema is envisioned which permits heat to flow from the source to the TE device only when the source temperature is near maximum, yielding a higher time-averaged temperature drop across the TE and therefore a higher efficiency. A numerical model is used to evaluate the benefits of an active thermal switch in series with a TE generator relative to a baseline case defined by the absence of a thermal switch for both time-varying and constant heat inputs. The results demonstrate that modulating the heat flow through the TE device and maintaining the source temperature at a near constant maximal value is capable of improving the time-averaged TE device energy recovery efficiency. For some conditions, improved efficiencies of more than five times are realized. The requisite physical conditions necessary for achieving these improvements are also identified.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Physical model considered

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Figure 2

Overall TE generator efficiency, η¯, for Case 1 with and without source temperature control, β=0.85, ω̂=0.5, R̂P,HIGH=1, R̂SINK=0.01, ĈSINK=0.1, and TOFF=148°C

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Figure 3

Source temperature for Case 1 with and without source temperature control, β=0.85, ω̂=0.5, R̂P,HIGH=1, R̂SINK=0.01, ĈSINK=0.1, and TOFF=148°C

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Figure 4

(a) Source and hot/cold side of TE temperature histories for Case 1 with active control once system reached steady state, β=0.85, ω̂=0.5, R̂P,HIGH=1, R̂SINK=0.01, ĈSINK=0.1, TOFF=148°C; and (b) source and hot/cold side of TE temperature histories for Case 1 without active control once system reached steady state, β=0.85, ω̂=0.5, R̂P,HIGH=1, R̂SINK=0.01, ĈSINK=0.1, and TOFF=148°C

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Figure 5

Source and TE heat flow transients for Case 1 with active control once system reached steady state, β=0.85, ω̂=0.5, R̂P,HIGH=1, R̂SINK=0.01, ĈSINK=0.1, and TOFF=148°C.

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Figure 6

Conceptual thermal switch design considered

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