| Thermoelectric power generation is a technology that convert heat directly into electricity by using thermoelectric materials,which has the advantages of compact structure,no moving parts,long service life,no emissions and no maintenance.Thermoelectric power generation(nuclear energy as heat source)has become the only option for power supply in extreme environments such as interplanetary exploration missions and submarine microwave relay stations.At the same time,thermoelectric power generation also has very good application prospects in the utilization of waste heat of fuel for aviation,automobiles and other transportation equipment.However,the low thermoelectric conversion efficiency of thermoelectric materials severely restricts their application.In order to improve the conversion efficiency of thermoelectric power system,in addition to the development of thermoelectric materials with better performance,another important way is to conduct reasonable structural design for thermoelectric modules.At the same time,the thermal stress generated during the operation of the TEG greatly affects the service life of the modules,accurately evaluating the thermal stress of TEG and analyzing its key factors is one of the key issues in the design of thermoelectric modules.This paper has carried out three fields: From the perspective of shape optimization,the best thermoelectric leg shape is theoretically obtained,and the validity of the conclusion is confirmed by detailed numerical simulation;Secondly,the nonlinear analysis model of segmented TEG considering the material temperature dependence was developed to provide accurate and rapid analysis tools for subsequent material selection design.Finally,the thermal stress distribution of TEG is analyzed by numerical method,and the influence of the number of thermoelectric element and designable parameter are discussed,so as to provide reference for improving the temperature difference between cold and hot ends and improving the overall heat transfer performance.The specific research contents are as follows:(1)Theoretical analysis and numerical verification of shape optimization for thermoelectric leg with variable cross sections of thermoelectric generator.It is a hot topic to improve the thermoelectric conversion efficiency of TEG by adjusting the variable cross-section of the legs.In this paper,the optimal shape of thermoelectric generator under the condition of arbitrary cross section of leg is discussed,and the validity of the conclusion is proved by detailed numerical analysis.The results show that varying the cross-section of the leg can realize the change of internal electric resistance of TEG,but the variation function for the cross-section of the leg is not the key.The key to achieve the highest efficiency is the rational ratio of external electric load to internal electric resistance.Therefore,considering the manufacturing process,it is recommended to adopt constant cross-section legs design and adjust the external load resistance.In addition,the optimal geometric shape of the TEG leg to produce maximum output power is a constant cross-section.(2)A analysis model of the segmented thermoelectric generator considering the temperature dependence of the material.The performance of thermoelectric materials is closely related to the operating temperature,and its high thermoelectric conversion efficiency is often applicable in a relatively narrow temperature range.The segmented design of the thermoelectric leg can maximize the thermoelectric conversion capability of each thermoelectric material,so as to improve the overall thermoelectric conversion performance.The rapid and accurate analysis model of the segmented thermoelectric generator is the basis for the design of multi-segmental thermoelectric generators.In this paper,a analysis model of the segmented thermoelectric generator considering the temperature dependence of the material is eatablished,and the validity of the proposed analysis model is verified by comparing with the detailed numerical simulation results.Based on the proposed model,the influence of the interface position of the leg for conversion efficiency performance is discussed,and the optimal thermoelectric leg sectional position is given.(3)Thermal stress evaluation and influencing factors analysis of thermoelectric module.In this paper,a thermoelectric-structure numerical model of thermoelectric generator was built,the plastic deformation of the material is considered,the influence of the number of thermoelectric elements,the thickness of ceramic substrate and copper sheet on the thermal stress of the thermoelectric device were discussed.The results show that the maximum stress of the copper sheet and thermoelectric leg appears at the corners of the joints;Due to the interaction between the thermoelectric modules,the stress of the thermoelectric generator composed of multiple thermoelectric modules increases by nearly 1 times compared to a single thermoelectric module.In addition,to save copper sheet and TE materials,thinner ceramic substrates and copper sheets are more conducive to reducing thermal stress. |
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