DESIGN, OPTIMIZATION, AND APPLICATION OF THERMOELECTRIC HEAT EXCHANGERS IN THE MARINE ENVIRONMENT

DESIGN, OPTIMIZATION, AND APPLICATION OF THERMOELECTRIC HEAT

EXCHANGERS IN THE MARINE ENVIRONMENT

By Travis Thornton Wallace

Thesis Advisors: Dr. Paul Wlodkowski and Dr. Zhihe Jin

An Abstract of the Thesis Presented
in Partial Fulfillment of the Requirements for the
Degree of Master of Science
(in Mechanical Engineering)
December 2012
 

This thesis summarizes the accomplishments of the Thermoelectric Research Program that began at Maine Maritime Academy (MMA) in 2008. Starting as a mechanical and economic feasibility study of integrating thermoelectric technology into the marine industry, the initial project tested a 180 Watt (W) rated thermoelectric generator (TEG) from Hi-Z Technology, Inc. (Hi-Z) onboard MMA’s R/V Friendship and in the exhaust flow of an SR30 microturbine. Because initial testing was completed and the testing yielded results higher than the unit’s rating, it was determined that the use of thermoelectrics is feasible in the marine industry, although only with larger rated units than the 180W unit. From this initial study to the present, the thermoelectric research program has accomplished an integration of a proven technology into the marine industry by redesigning the conventional TEG design and optimized it for use in the industry, which has proven to be a pioneering and significant effort.
The program evolved into designing a simulation of a large ship’s electrical system through both an analytical approach as well as a physical approach. To this end, a MATLAB mathematical modeling program was written to predict larger TEG units. An encapsulated lifeboat was retrofitted with a diesel electric drive system, which included a diesel generator set, an electric motor, a transformer, and a variable frequency drive, which is the same setup that would be found on a larger ship. The vessel was converted into a hybrid system by installing the 180W Hi-Z TEG in the exhaust path of the diesel generator set. The objective of TEG power generation is introduction into the electrical grid, but the output of the TEG is a variable voltage direct current (DC), while the requirement is a constant alternating current (AC) voltage source. To accomplish both of these tasks, the TEG was wired to microinverters that were in turn wired to the output lugs of the transformer, thus making the vessel a true hybrid vessel.
A new TEG design concept was necessary in order to reach the required by the marine industry. The design needed to be based on existing marine technology to facilitate its integration within commercial fleets, i.e. one with which marine engineers have great familiarity. Accordingly, the design was based on the plate type heat exchanger. This design allows for the TEG to be expandable if more capacity is needed and it is instantly recognizable by marine engineers to aid serviceability. After building and testing this design, flaws were found in the current wiring method as the wiring resistance impeded the optimal output of the unit. The convective heat transfer was adequate, but it was determined that it could be improved by adding more fins to the exhaust path. These two design modifications will be adopted in future models.
Finally, to ensure long term reliability of TEGs in marine applications, the thermal stresses experienced by a thermoelectric element in steady state will be investigated using thermoelectricity and the thermal stress theory.