Abstract
Thermoelectricity (TE) is an attractive technology dealing with the conversion of unused heat energy into electrical power and vice versa. Thermoelectric conversion systems share the advantages of being reliable, silent in operation, environmentally friendly and compact systems without moving parts. The areas of research that need to be taken into consideration to develop superior TEG devices are efficiency, manufacturing, and modeling of these systems. The low energy conversion efficiency in thermoelectric materials hampers the applications of thermoelectric generators (TEGs). Besides the efficiency of thermoelectric materials and the construction shape of TE modules are other crucial factors that can also directly affect TEG reliability and performance. The conventional methods used for TEG fabrication are generally limited to flat or rectangular geometries. Another drawback of TEGs is the lack of accurate numerical modeling of these systems. Simulation and optimization of TE systems are necessary to prevent over or under design which leads to saving a lot of time and money. This thesis addresses the modeling limitation of TEGs by introducing numerical simulation guided of TEGs for waste heat recovery applications. In this thesis, the background of TE modeling is addressed by defining the governing equations of TE energy conversion process. A numerical technique of TEG simulation using ANSYS software is introduced to obtain the TE performance and the reliability assessment of these systems. Different TE leg and module configurations (flat and annular TEGs) which can significantly benefit the energy conversion field in terms of developing future thermoelectric systems with improved efficiency and reliability are presented. Energy conversion efficiency in TE systems is enhanced when the temperature gradient between the hot and cold surfaces of TEGs is maximized. This, however, dramatically increases the thermal stresses built-up within the thermoelectric modules which lowers the TEG reliability. A promising method to reduce thermal stresses in TEG systems is considering unileg TEGs system instead of traditional unicouple configuration. The concept of flat and annular unileg TE systems is introduced and the thermoelectric efficiency and reliability of these systems are quantified using finite element simulations. Implemented TE modeling for waste heat recovery applications such as exhaust pipe system and IC engine oil pan are also introduced in this work. The feasibility of replacing flat TE systems with the annular unicouple and the annular unileg systems is explored for exhaust gas heat recovery applications in automobiles to assess the real-life usage of the proposed systems. Another TE application is the (IC) engine oil pan, unlike the radiator and exhaust system applications of thermoelectricity described above, in this thesis, a novel implementation of TE systems within the oil pans of internal combustion (IC) engines, where a higher amount of heat is generated and lost to the environment is presented. For future work, the manufacturability of the TE system and the comparison of existing TE applications by performing additive manufacturing (3D printing) are also discussed for present and future work. By using binder jetting additive manufacturing method, the accuracy of fabricating smaller TE element sizes can be examined, furthermore, the binder jetting method can be used to fabricate different and complex configurations of TE modules.