Date of Award

8-2016

Degree Type

Thesis

Degree Name

Master of Science in Mechanical Engineering (MSME)

Department

Mechanical Engineering

First Advisor

Xianfan Xu

Committee Chair

Xianfan Xu

Committee Member 1

Stephen D. Heister

Committee Member 2

Amy M. Marconnet

Abstract

In facing the limited energy source reserves and environmental problems, thermoelectric generators (TEGs) are one of the promising waste heat recovery systems. The modern TEGs for exhaust stream (e.g. from automobiles) can improve the fuel economy by around 5%, taking advantage of the recent developed thermoelectric (TE) materials.

In this work, we aimed at designing a TEG as an add-on module for a gas-phase heat exchanger with maximized power output, and without negative impact (e.g. maintaining a minimum heat dissipation rate from the hot side). We first developed a parametric optimization algorithm using response surface method (RSM) and genetic algorithm (GA) for the numerical model. The numerical model handles varied types of heat exchangers (cross flow and counter flow) with the finite volume method and calculates the thermoelectric modules (TEMs) with thermal resistance network analyses. TEMs based on filled-skutterudite and bismuth telluride are used respectively in higher and lower temperature regions. The RSM results also provide knowledge on sensitivity and interaction of parameters. The combined RSM-GA optimization algorithm will be generally useful for the parametric design of TEGs, especially before much knowledge acquired on the TEG parameters.

The regenerative concept for TEG (R-TEG) is then introduced. Instead of developing advanced high figure-of-merit (ZT) high-temperature TE materials, we use a gas phase heat exchanger (precooler) to lower the temperature of the hot gas and at the same time regenerate hot air from the cold air supply for Bi2Te3-based TEGs, avoiding the use of high-temperature thermoelectric materials. It is found that the regenerative TEGs can achieve a similar power output compared with TEGs using high-temperature TE materials such as filled-skutterudites (combined filled-skutterudites and Bi2Te 3-based TE materials), by obtaining a higher heat scavenging rate. Thus, the regenerative TEGs also show a similar absolute efficiency, defined according to the total available enthalpy from the hot gas. This could represent a paradigm shift in the TEG research and development, that much lower-cost, reliable, and readily available Bi2Te3-based materials and modules can be used for high-temperature applications, and will ultimately enable the widespread deployment of TEGs for real world waste heat recovery applications.

Lastly, a single module TEG is developed experimentally for both characterization of TEMs and low-cost diagnoses of component performance inside TEGs. A commercialized Bi2Te3-based module is tested. Temperatures along the streams and across the TEM packaging are investigated. A better-defined single module TEG with internal detailed information available can be used as a reduced size experimental model to validate the numerical result.

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