|
ИСТИНА |
Войти в систему Регистрация |
ФНКЦ РР |
||
The simulation of spark plasma sintering for the preparation of inhomogeneous thermoelectric materials for energy generatorsкнига
- Авторы: Bulat L.P., Novotelnova A.V., Tukmakova A.S., Yerezhep D., Osvenskii V.B., Sorokin A.I.
- Год издания: 2017
- Место издания: Nova Science Publishers, Inc Hauppauge, New York, United States
- ISBN: 978-153611325-9;978-153611103-3
- Монография
- Аннотация: Thermoelectric generators (TEG) are known to give a possibility to utilize waste heat. Therefore, the improvement of TEG’s efficiency is an actual problem. TEG efficiency depends on the efficiency of materials (thermoelectrics) used having a high figure of merit Z. One of the ways to increase Z is the preparation of bulk nanocrystalline thermoelectrics. Apparently, ball milling with simultaneous spark plasma sintering (SPS) is the most effective method of nanothermoelectrics fabrication. It predicts recrystallization process and allows to obtain thermoelectrics with both efficiency and mechanical properties improved. On the other hand, the way to increase the efficiency is the use of TEGs with thermoelectric legs functionally graded and segmented. In fact, each thermoelectric of a given composition has the highest Z value at a fixed temperature, while the temperature difference in a generator legs can reach 500-600°C. Consequently, it is necessary to change material properties along the length of the leg in order to obtain its high efficiency. However, the sintering of such material requires special conditions. First of all, a sufficient temperature difference along the vertical axis ΔTz in the sintered sample should exist. Thus, the improvement and optimization of SPS demands clear comprehension of thermal and electric processes taking place during the sintering. A simulation model based on experimental setup parameters has been created with the use of finite elements method. The ways of ΔTz formation in the Bi2Te3 sample have been analyzed in the cases of different tooling modification. Initially, ΔTz can be reached due to asymmetric tooling with a die that is in a contact with a lower graphite insert. Then, two ways of ΔTz increasing have been proposed. One of the ways implies an additional extension of the lower part of a die. In this case, the value of ΔTz rise up to 80 K. Another way implies an electric insulation insertion in the tooling in order to pass the major part of electric current through the upper punch and the sample. It has been shown that the increasing of insulation thickness a contributes to ΔTz growth up to hundreds of degrees. The value of radial temperature difference ΔTr does not exceed 15 K if an extended die is applied. However, in the case of insulation utilization ΔTr can reach tens of degrees. Also, it has been established that the increase of ΔTr on the upper surface of the sample corresponds to a decrease of ΔTr on the lower surface of the sample, and vice versa. Moreover, the insulation thickness has its single optimal value corresponding to the minimal value of radial temperature difference. The results obtained can be used for further analysis and improvement of SPS process of inhomogeneous materials assigned for the utilization in TEGs. © 2017 Nova Science Publishers, Inc. All rights reserved.
- Добавил в систему: Ережеп Дархан