Geometry Optimization Of Two-stage Thermoelectric Generators Using Simplified Conjugate-gradient Method.

Thermoelectric devices can convert thermal energy directly into electrical energy, or they can work in reverse and use electrical energy to create a temperature gradient for cooling or heating applications. The absence of moving parts, wide range of operating temperatures, scalability, and modular capabilities makes thermoelectrics attractive for energy generation applications. They have been considered for use with vehicle exhausts, co-generation, and other energy recovery from lost heat in thermodynamic cycles. Thermoelectric devices have relatively low efficiencies but there have been recent advances in thermoelectric materials potentially. As material advancements continue and a wider range of power generation applications will be considered, module and system level modeling becomes critical for the design of the next generation of thermoelectric systems.The aim of this thesis is to develop an approach that integrating computer-aided analysis and optimization method, and then apply the approach to design and optimize millimeter scale devices, including the thermoelectric generators. The optimization framework consists of a model generator, a direct solver, and numerical optimizer. Therefore, the Simplified Conjugate-Gradient Method(SCGM) is employed to build the optimizer by MATLAB and the general-purpose finite element code by COMSOL is used to be the direct solver and model generator.In application of the approach to the optimization of the geometric thermoelectric generators, a multi-objective and multi-parameter optimization is implemented to design the optimal structure of two stage bismuth-telluride and skutterudites based TEG(thermoelectric generator) module. constant wall-temperature and heat flux as boundary conditions. The leg length, and cross section area(footprint area) ratio of semiconductor columns to TEG module significantly affect the TEG performance, and hence are all incorporated into the present optimization study.The optimal design obtained by multi-objective optimization makes a proper balance between the output power and conversion efficiency, so that the both are improved simultaneously.The maximum rate of increase happens at Th=700℃, which is 42.9% and 31.4% for Power the Efficiency, respectively. For the fixed heat flux which under qh<=10suns, the rate of increase are about 50% for power and efficiency.