Cost-effective waste heat recovery using thermoelectric systems
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Ali Shakourib) Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907; and Department of Electrical Engineering, Baskin School of Engineering, University of California Santa Cruz, Santa Cruz, California 95064 (Received 14 November 2011; accepted 22 February 2012)
Optimizing thermoelectric (TE) materials and modules are important factors, which can lead to widespread adoption of waste heat recovery systems. The analytic co-optimization of the TE leg, heat sink, and the load resistance shows that all parameters entering the figure-of-merit (Z) do not have the same impact on cost/performance trade-off. Thermal conductivity of the TE material plays a more important role than the power factor. This study also explores the impact of heat losses and the required contact resistances. Finally, we present the theoretical cost performance ($/W) of TE waste heat recovery systems for vehicle waste heat recovery application, assuming hot side gas temperature of 600 °C and a cooling water temperature of 60 °C.
I. INTRODUCTION
Saving natural resources such as fossil fuels is a significant mission for energy technology developments. At the same time, reducing production cost is a key challenge in commercializing the new technology and making it feasible to compete with existing technologies.1 Recovering energy from vehicle exhaust waste heat using thermoelectric (TE) power generators is especially promising.2–4 Some of the major car companies are already planning to introduce these generators embedded in their engine exhaust systems.5,6 On the other hand, due to the moderate conversion efficiency of TE systems, some experts have expressed concerns about the potential growth of TE energy systems and their bigger impact to help solve our energy challenge.7 These concerns are exasperated due to material scarcity.8 The price ($/kg) of TE material may not be reduced to the point of commercial feasibility, so that the current module design remains the central cost concern. Abundant and nontoxic materials with nanoscale modifications are currently under research and development,9–11 but they have not yet achieved the required performance or the robustness needed for commercialization. We recently presented the system optimization for TE waste heat recovery that focused on minimizing the overall material cost.12 We found that a dramatic improvement in the cost performance ($/W) of the TE generator systems can be achieved by co-optimizing the heat sink and by using
Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] This paper has been selected as an Invited Feature Paper. DOI: 10.1557/jmr.2012.79 J. Mater. Res., Vol. 27, No. 9, May 14, 2012
heat concentration (fractional area coverage of TE elements) in TE modules.12 The components of the material figure-of-merit Z, i.e., power factor and thermal conductivity, are indeed a key to determine the system performance. However, there has been little discussion regarding the impact of the power factor and thermal conductiv
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