Prediction Of Output Performance And Fatigue Life On Embedded Thermoelectric Devices

Thermoelectric device is an equipment that can directly convert heat and electricity into each other,and it is widely used in power generation and refrigeration because of their advantages of small size,low cost and no pollution.In traditional thermoelectric generators（TEGs）,the mismatch of thermal expansion coefficients among components will lead to large thermal stress,especially in the hot side when TEGs are operated over a broad temperature range.And then penetration strain even microcracks will be generated in the hot side of TEGs,which will seriously affect the output performance and service lifespan of the TEGs.In order to solve this problem,a new embedded TEG with a stepped ceramic plate is proposed in this study.The performance and service lifespan of embedded TEGs are analyzed using COMSOL5.4 Multiphysics finite element analysis software.The main research contents and the conclusions obtained are as follows.（1）For embedded TEGs,the hot side metal electrode,the barrier layer and part of the TE legs are sequentially embedded in blind holes of the hot side ceramic plate,while the cold side is remained as the same as the traditional TEGs.The thermal stress distribution and output performance of the embedded TEGs with different TE leg heights and ceramic plate thicknesses were investigated.The results show that the metal Cu electrode at the hot side in the embedded TEGs separates the heat and electrical conduction,and the embedded structure reduces the damage to the Cu electrode at the hot side by thermal stresses comparing with the traditional TEGs.In addition,the embedded structure has a positive effect on the output performance.The peak output power of the embedded TEGs is higher than that of the traditional planar TEG（H₁=1 mm）by 22.2%.（2）Compared with planar TEG,embedded TEGs have better output performance and lower thermal stress in the key position,and then higher thermal fatigue life in temperature cycling.By quantitative analysis based on COMSOL simulation,when the TE leg height H₃ of all TEGs is kept the same,the embedded TE module b（H₁=0.6 mm）and d（H₁=1 mm）have31%and 68%higher lifetime than the traditional TE module a（H₁=1 mm）,respectively.Second,the fatigue life analysis of the embedded TEGs with different leg heights and ceramic plate thicknesses reveals that the minimum number of failure cycles can be improved as the thickness of the ceramic plate at the hot side increases.（3）Due to the difference in resistivity between p-type and n-type TE materials,the TEGs will have a large internal resistance,resulting in unoptimized output performance.The resistance of the two TE legs is necessary to be adjusted by controlling the cross-sectional area of the TE legs.It is found that the maximum unit output power of the optimized embedded TEG can be increased from 53.19 m W/mm² to 55.49 m W/mm²,and the conversion efficiency is increased from 7.81%to 8.16%compared with that of symmetric embedded TEG.（4）The structure of the embedded TEGs adds a certain degree of difficulty to the preparation of the device,the blind hole of the hot side ceramic plate can be prepared into a pyramid shape in the actual machining process,which is convenient for assembly and processing.The effect of the change of the device’s hot side structure on the output performance is studied by finite element analysis.It is found that the conversion efficiency and unit output power of the embedded TEG with different parameters（blind hole taper angleαand TE leg taper angleβ）remain above 95%,compared with the embedded TEG.