The effects of greenhouse gases have seen a significant rise in recent years due to the use of fossil fuels like gasoline and diesel. Conversion of the energy stored in these fossil fuels to mechanical work is an extremely inefficient process which results in a high amount of energy rejected in the form of waste heat. Thermoelectric materials are able to harness this waste heat energy and convert it to electrical power.
Thermoelectric devices work on the principle of the Seebeck effect, which states that if two junctions of dissimilar materials are at different temperatures, an electrical potential is developed across them. Even though these devices have small efficiencies, they are still an extremely effective way of converting low grade waste heat to usable electrical power. These devices have the added advantage of having no moving parts (solid state) which contributes to a long life of the device without needing much maintenance. The performance of thermoelectric generators is dependent on a non-dimensional figure of merit, ZT. Extensive research, both past and ongoing, is focused on improving the thermoelectric generator's (TEG's) performance by improving this figure of merit, ZT, by way of controlling the material properties. This research is usually incremental and the high performance materials developed can be cost prohibitive.
The focus of this study has been to improve the performance of thermoelectric generator by way of improving the heat transfer from the exhaust gases to the TEG and also the heat transfer from TEG to the coolant. Apart from the figure of merit ZT, the performance of the TEG is also a function of the temperature difference across it, By improving the heat transfer between the TEG and the working fluid, a higher temperature gradient can be achieved across it, resulting in higher heat flux and improved efficiency from the system. This area has been largely neglected as a source of improvement in past research and has immense potential to be a low cost performance enhancer in such systems. Improvements made through this avenue, also have the advantage of being applicable regardless of the material in the system. Thus these high performance heat exchangers can be coupled with high performance materials to supplement the gains made by improved figure of merits.
The heat exchanger designs developed and studied in this work have taken into account several considerations, like pressure drop, varying engine speeds, location of the system along the fuel path, system stability etc. A comprehensive treatment is presented here which includes 3D conjugate heat transfer modeling with RANS based turbulence models on such a system. Various heat transfer enhancement features are implemented in the system and studied numerically as well as experimentally. The entire system is also studied experimentally in a scaled down setup which provided data for validation of numerical studies. With the help of measured and calculated data like temperature, ZT etc, predictions are also presented about key metrics of system performance. / Ph. D.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/47919 |
| Date | 07 May 2014 |
| Creators | Pandit, Jaideep |
| Contributors | Mechanical Engineering, Ekkad, Srinath V., Huxtable, Scott T., Priya, Shashank, Pitchumani, Ranga, Ngo, Khai D. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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