Geometry Optimization Of Two-Stage Thermoelectric Generator And Thermoelectric Cooler Using NSGA-Ⅱ

Thermoelectric materials are materials that use thermoelectric effect to convert heat to electricity and vice versa,and it is a main component for thermoelectric generator and thermoelectric cooler.It has received extensive attention for its modularity,no moving part,no pollution.It is widely used in the field of waste heat recovery,aerospace,biomedicine,electronic device heat dissipation,et al.However,due to the limitation of the performance of the materials,its optimal thermoelectric conversion efficiency always corresponds to an optimal operating temperature range,therefore from the perspective of matching the optimal efficiency with corresponded operating temperature range,to optimize the geometric parameters of thermoelectric system in order to improve its conversion efficiency,which is one of the hot issues in system research.Based on that,the study conducted the optimal design research in TEG and TEC system.The main work of this thesis is to optimize the geometric parameters of two-stage TEG and TEC using NSGA-II,and select the most compromising solution on Pareto front using decision making method,and analysis the performance of optimized model.In multi-objectives optimization of TEG,power density and entropy generation rate are used as the objective functions;load resistance,the height of lower TE legs,the N/P cross-section ratio of upper and lower stage TE legs and the angle between N and P legs are used as variables.The influence of load resistance on voltage,power,efficiency,entropy generation rate and exergy destruction rate are investigated.For TEC,two-stage parallel TEC and two-stage series TEC model were built respectively.Exergy efficiency and irreversibility are used as objective functions;electric current,the height of lower stage TE legs and ratio of channel width and thickness of fin are used as variables.And performance of two types of TEC is compared.The results show that for TEG,the suitable thermoelectric materials will significantly improve the performance of TEG;as the TEG power density increases,the entropy generation rate will also increases;when the total volume of thermoelectric materials is fixed,the optimized TEG model exists an optimal N/P cross-section ratio and load resistance,and the performance of the TEG system is poor when the load resistance is much greater or less than its internal resistance.For TEC,increasing the current within a certain range will increases the exergy efficiency as well as COP(Coefficient of Performance),but will also increases the irreversible loss of the model;when the total volume of the thermoelectric material is fixed,the optimized TEC model exists an optimal length ratio between upper and lower stage TE legs.When the temperature difference between hot and cold side is the same,the two-stage parallel TEC saves about 50% of the power consumption compared to the two-stage series TEC,however,the parallel type circuit design is more complicated than the series type circuit design.The methods used in this paper and research results have certain theoretical and practical guiding significance for the development of high-performance thermoelectric generation systems and thermoelectric cooling systems.