Growing concerns regarding climate change, the increase in demand for energy and the efficient utilization of energy have become of major interest in applications of heating and power generation. A large portion of the energy input to these applications is lost, due to their typical inefficiencies, in the form of waste thermal energy which, if captured and utilized, can offer an abundant source of energy for electricity generation and heating purposes. The use of thermoelectric generators (TEGs) of different designs in waste heat recovery applications has been pursued over the past few decades as the generation of electrical power using TEGs has become viable compared to other conventional systems at low temperatures. This study focuses on the implementation of an annular design for integrated TEG modules in a heat exchanger device for waste heat recovery and the investigation of the effect of different TEG design parameters on the device performance.
The integration of the annular TEG design in the heat exchanger was studied using a developed numerical model to investigate the interaction between the heat transfer and the thermoelectric effects and evaluate the performance under specific operating conditions. The heat transferred from the exhaust to the water flow through the TEGs was modelled using a thermal network for the heat flow, coupled with an electrical circuit for the power output. The model was validated using experimental results of the first generation of the TEG device with good agreement (3-6 %) between the predicted and measured performance results: power output, efficiency and the exhaust and water flow temperatures.
With the objectives of maximizing the power output and improving the power characteristics, a half annular TEG design was presented. It was able to generate the same power output with double the voltage and half the current, thus improved the power characteristics required for functional operation, compared to the full annular design. The effect of the annular TEG design dimensions on the device performance was studied for a multi-row heat exchanger using the numerical model. The results showed that a maximum power output can be obtained at optimum TEG diameter ratio and thickness.
In addition, the TEGs performance was studied under different electrical connection configurations in series and in parallel. The series connection between TEG rows showed better power output characteristics with lower current output, minimal power loss due to temperature mismatch and higher voltage output. The effect of heat exchanger design considerations such as the axial heat conduction was also investigated using the numerical model and the results were compared with an ANSYS model for verification. Good agreement was demonstrated and the results showed a decrease in the total power output of multiple TEG rows when axial conduction of heat was allowed between the TEGs hot-side surfaces in the heat exchanger.
A dimensions map was created for annular TEGs integrated in a heat exchanger combining the effects of varying the TEG diameter ratio and thickness on the power output. Further, a dimensionless design parameter (β) was introduced to locate the maximum power region on the map. Using the map as a design tool, the dimensions of the annular TEG modules in a heat exchanger were determined to maximize the power output under a typical current output constraint in order to improve the system power characteristics. Using the map, it was shown that the current output could be reduced by 46 % of its value at the maximum power available on the map and the resultant power output could be maintained at 98 % of its maximum value. This also resulted in a 48% reduction in the TEG material volume and an increased voltage output of the device. As a result, the power output was maximized, the current output was limited to reduce losses in the power management system components and material volume reduction was achieved which would increase the device power density and reduce its overall cost. / Thesis / Master of Applied Science (MASc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/22255 |
| Date | January 2017 |
| Creators | Zaher, Mohammed |
| Contributors | Cotton, James, Mechanical Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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