Date of Award

Fall 2014

Degree Type


Degree Name

Doctor of Philosophy (PhD)


Mechanical Engineering

First Advisor

Stephen D. Heister

Second Advisor

Xianfan Xu

Committee Chair

Stephen D. Heister

Committee Member 1

Xianfan Xu

Committee Member 2

Timothy S. Fisher

Committee Member 3

Yue Wu


The demand for improved fuel efficiency in automobiles has placed an emphasis on exhaust system waste heat recovery as a 40% of the fuel's chemical energy is lost to the environment in modern spark ignition engines. To advance fuel economy, researchers are currently evaluating technologies to exploit exhaust stream thermal power using thermoelectric generators (TEGs) that operate using the Seebeck effect. Thermoelectric generators have the potential to recover some of this waste energy in the exhaust stream potentially improving fuel economy by as much as 5%. ^ Attempts are made to maximize the electrical power generation by optimizing the thermoelectric generator geometry for a prescribed volume. A plate-fin heat exchanger configuration is assumed and consideration is given to pressure drops associated with the fins placed in the exhaust flow path; and the cross-sectional changes across thermoelectric generator inlet-exit ports. Multiple filled skutterudites based thermoelectric modules are employed in the higher temperature regions and Bismuth Telluride modules are used at lower temperature regions of the device. Power is optimized for rectangular configurations featuring longitudinal and transverse flow through the device and for hexagonal and cylindrical topologies as well. Optimal designs that maximize power output for fixed volume and number of thermoelectric elements are obtained for all configurations. In general, the rectangular configuration with transverse flow has the best overall performance. ^ System modeling of thermoelectric (TE) components is performed to maximize thermoelectric power generation. One-dimensional heat flux and temperature variations across thermoelectric legs have been solved using iterative numerical approach as a tool to optimize both TE module and TEG designs. Design trades are explored assuming the use of skutterudite as thermoelectric material that has potential for application to automotive applications where exhaust gas and heat exchanger temperatures typically vary from 100°C to 600°C. Dependencies of parameters such as leg geometry, fill fractions, electric current, thermal boundary conditions, etc., on leg efficiency, thermal fluxes and electric power generation have been studied in detail. Optimal leg geometries are computed for various automotive exhaust conditions. ^ Axial conduction in the wall liner is further modeled numerically and its impact on temperature distribution in gas stream, wall liner, and temperature difference across thermoelectric junctions are presented. The developed model is simulated to establish TEG output sensitivity to liner materials and thicknesses for both zero and non-zero axial conduction cases. Further, the axial conduction sensitivity to inlet conditions is considered and the effect on TEG output statistics are presented.