| Thermoelectric(TE)devices are green energy conversion sets that utilize the TE effect of TE materials to achieve direct conversion between thermal energy and electrical energy in the form of carriers(electron,hole)transport.At present,TE conversion efficiency is relatively low,so that the application of TE devices are greatly restricted.How to improve the TE conversion efficiency has become a research hot-spot in TE field.In this paper,the preparation and output performance of Half-Heusler(HH)medium-temperature TE device have been studied,and it is expected to provide a reference for improving the performance of TE device.Firstly,based on the TE theory and Galerkin finite element method,the calculation model of thermal-electric coupling analysis suitable for the conditions of small temperature difference and large temperature difference was established,which provided a theoretical basis for further study of the output performance of TE devices.Secondly,the ANSYS finite element software was used to simulate the HH unicouple TE device.For the steady-state condition,effects of the leg sizes,the thickness of the ceramic substrate and the heat source temperature on the output performance of TE device were studied,the structure design of TE device was also optimized,and the optimal values of geometric parameters were obtained.The results show that the leg sizes,the thickness of the ceramic substrate and the heat source temperature have a significant effect on the output performance of TE device.At the same time,there is an optimized basic model that the length,width and height of the legs are 2 mm,that the thickness of the ceramic substrate is 0.7 mm,and that the heat source temperature is 600 ?,and it's maximum conversion efficiency can reach 7.22 %.Once again,the ANSYS finite element software was used to simulate the segmented unicouple TE device.For the steady-state condition,the Bi2Te3 low-temperature TE materials were combined with the HH medium-temperature TE materials into the segmented legs,and the effects of the thickness of Bi2Te3 on the output performance of TE device was studied.The results show that the segmented TE device can show better output performance than the single material TE device.At the same time,when the height of Bi2Te3 is 0.4 mm,that is 20% of the total leg height,the maximum conversion efficiency of the segmented TE device is40 % higher than that of the single material TE device.Then,the COMSOL Multiphysics finite element software was used to simulate the HH medium-temperature TE module.For the steady-state condition,the output performance of TE module composed of 71 pairs of unicouple device was calculated based on the previously optimized basic model.The results show that the TE module can achieve an electrical outputof 13 V/48 W at a temperature difference of 500 ?.However,when the TE module is sealed with a ceramic ring,more than 70 % of the heat is conducted to the cold side of TE module via the ceramic ring,with the result that the conversion efficiency of the entire module is only2.7 %.Finally,the HH medium-temperature TE device was prepared with the filler solder Ag72 Cu,the brazing process was discussed,and the volt-ampere characteristics of devices was tested,then the aging and contact resistance of devices under different working conditions was studied.The results show that the solder Ag72 Cu can be used for the welding of HH medium-temperature TE device with the brazing temperature of 825 ?.The prepared devices can achieve an electrical output of about 0.11 V/0.46 W at a temperature difference of about500 ?,and the output performance is relatively stable.Meanwhile,the HH medium-temperature TE devices may be able to work for a long time in the low vacuum of5.0 × 10-4 Pa and the temperature of 600 ?.And the contact resistance between the p-/n-type HH medium-temperature TE materials and the solder Ag72 Cu is small. |
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