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_МЕЖДУНАРОДНЫЙ НАУЧНЫЙ ЖУРНАЛ «ИННОВАЦИОННАЯ НАУКА» №01-2/2017 ISSN 2410-6070_
ТЕХНИЧЕСКИЕ НАУКИ
УДК 621.362
Д.К. Абрашин
магистрант 1 год обучения Санкт-Петербургский национальный исследовательский университет информационных технологий, механики и оптики (Университет ИТМО)
Г. Санкт-Петербург, Российская Федерация
ПЕРСПЕКТИВЫ ЭНЕРГОСБЕРЕГАЮЩИХ СИСТЕМ ОХЛАЖДЕНИЯ НА ОСНОВЕ ТЕРМОЭЛЕКТРИЧЕСКИХ ГЕНЕРАТОРОВ
Аннотация
В работе изучены основные типы термоэлектрических элементов и генераторов (ТЭГов), кратко описаны сферы их применения и принципы действия. Дано представление об исследованиях, проводящихся в данной области в России и за рубежом. Поднята проблема необходимости использования выделяемой приборами тепловой энергии.
Ключевые слова
Термоэлектрический генератор, элемент Пельтье, системы охлаждения, сбережение электроэнергии.
D.K. Abrashin
undergraduate of 1st year
St. Petersburg National Research University of the Information Technologies,
Mechanics and Optics (University ITMO) St. Petersburg, Russian Federation
PERSPECTIVES OF ENERGY-EFFICIENT COOLING SYSTEMS BASED ON THERMOELECTRIC GENERATORS
Abstract
In this paper the main types of thermoelectric elements and generators (TAG) have been studied (TEGs) and briefly described their scope and principles of action. The representation about the research that is being conducted in this field in Russia and abroad has been given.Also, the issue of the needful usage of thermal energy has been represented.
Keywords
Thermoelectric generator, a Peltier element, cooling system, Energy conservation.
Introduction. Today the problem of creating an inexpensive and energy-efficient cooling-system is actual for a number of reasons: modern devices and computing systems emit in its work a large amount of thermal energy that makes owners of these devices to increase expenses on the cooling system, most of which also consumes a lot of energy.
In the current situation, creation of a device which would be capable to not only cool, but also convert at least part of the generated thermal energy into the electrical one can significantly reduce the cost for these devices service and maintenance.
Like such a device may be a thermoelectric generator (hereinafter TEG) that is a technical device (an electric generator) intended for the direct conversion of thermal energy into electricity through using thermocouples (thermoelectric materials) that are present in its design.
The problem of the development, application and improvement of TEGs has been studied by many Russian and foreign scientists: D.A. Booth, B.L. Aliyevsky, A.F. Ioffe, Gang Chen and others.
TEGs. TEG's action is based on direct conversion of thermal energy into the electrical one by thermocouple. Electrical energy is produced because of Seebeck effect: if in the ground junction of two dissimilar conductors the
_МЕЖДУНАРОДНЫЙ НАУЧНЫЙ ЖУРНАЛ «ИННОВАЦИОННАЯ НАУКА» №01-2/2017 ISSN 2410-6070_
temperature difference is maintained then so-called the thermoelectric effect occurs or directed motion of the electrons (electromotive force, thermoelectric power).
In the context of this problem another important thermoelectric effect is the Peltier effect. The essence of the effect is that while the electric current passes at the place of the contact (junction) of the two dissimilar conductors (thermocouple) emission or absorption of vapour occurs.
Thermoelectric converters that use this effect, are called elements of Peltier or TEC (from the English Thermoelectric Cooler).
In the middle of the XX century academician A.F. Ioffe proposed to use semiconductors as thermocouples. This was due to higher thermoelectric power coefficient (Seebeck coefficient) than that of metals and a lower thermal conductivity. Modern semiconductor TEGs are capable of giving 5-13% efficiency, which is not enough for their large-scale using. However, they are still used as an additional source of energy for a number of reasons: long life, high reliability, stability of parameters, vibration resistance [6].
In accordance with the conduction semiconductors are divided on the n-type and p-type. The n-type semiconductor has an impure nature and conducts electricity like metals. The alloys added to the semiconductors for appearance of n-type semiconductors are called donors. The term «n-type» comes from the word «negative», indicating a negative charge carried by the free electron.
The p-type semiconductor besides its impure nature is characterized by hole conduction. The alloys added in this case are called acceptors. «P-type» comes from the word «positive», indicating the positive charge of the major carriers.
In 2014, the fellow of Massachusetts Institute of Technology (MIT) Gang Chen demonstrated a new version of the TEG which was used as a material for half-Heusler thermocouples; it is alloys with a strong crystal lattice, which provides greater stability at high temperatures. Generator was named GMZ Energy. The generator can withstand temperatures of about 600 °C on its hot side while maintaining the temperature of 100 °C on its cold side. At such a temperature difference of 4 square centimeters in size module can produce 7.2 watts of power [2].
At the same time, in Russia the same original version of the TEG has been proposed, which uses nanostructured films; it is islet metal films on dielectric substrates having low thermal conductivity. Islet structures are very flexible in terms of the optimization of their physical properties, including coefficients of thermal conductivity and thermoelectric power. With such structures, it is possible to achieve and exceed the current value of efficiency for TEG, despite the fact that new materials have advantages such as the manufacturability, reliability and small size.
This development is being realized by the limited liability company «New Energy Technologies»; it is the Russian innovative company which is a resident of the innovation center «Skolkovo». Also, there are other residents of «Skolkovo» engaged in the search for new solutions in the field of thermoelectricity: companies «SmS tenzoterm Rus», LLC «Metemp», LLC «FEMTOINTEH».
Universities keep up with companies. For example, with assistance from the University ITMO the international laboratory called «Direct conversion of energy and nano-engineering of thermoelectric structures» has been created which studies nanostructured thermoelectric elements for generation of electricity and has a purpose to develop and create high-efficient thermoelectric materials.
Areas of application TEGs. Today, the Peltier elements are used for cooling in semiconductor lasers, CCD (CCD arrays, or CCD - sharge-coupled device), for example, in infrared sensors: night vision devices, thermal imagers, etc. Peltier elements also are implemented in molecular biology, where they are used in a PCR thermocycler; it is devices for carrying out the polymerase chain reaction (PCR). Different PCR steps should take place at temperatures over 90 °, 70 ° - 72 ° and about 60 °. This cycle is repeated many times. A Peltier element assistance is required for rapid cooling the sample tubes from 90 ° to 70 °.
TEGs are used in the aerospace industry, but a heat source for them is not natural heat waste of the equipment but thermal energy generated by the decay of radioactive isotopes, such as plutonium-238. Therefore, these TEGs are called radioisotope ones or RTGs.
Such devices are used, for example, in the automatic interplanetary station (AWS) NASA New Horizons, designed for study of Pluto and its satellite Charon. On interplanetary Cassini device, developed in the framework of the program of studying the planet Saturn, its rings and satellites Cassini-Huygens, three RTGs are located, each of which contains 11 kilograms of plutonium-238 [3].
The Seebeck effect is used in some measuring devices and sensors. Temperature sensors, fixing the appearance
_МЕЖДУНАРОДНЫЙ НАУЧНЫЙ ЖУРНАЛ «ИННОВАЦИОННАЯ НАУКА» №01-2/2017 ISSN 2410-6070_
of an electric current, are capable of giving highly accurate results. Also, these devices effectively cope with the definition of heat loss in a variety of industries, heat generation registration of exothermic reactions, etc.
TEGs are used actively in oil and gas production. There free heat from the burning of associated gas can be used to generate electricity. The devices provide a variety of remote operation control systems, telemechanics and other devices that must operate for a long time without maintenance by people in remote and inaccessible areas.
Now technology Energy Harvesting are becoming increasingly popular, based on the implement of low-power stand-alone electronic devices that operate without the need for battery replacement. The wireless sensors, sensors, the systems of control parameters and transmission of information in remote or moving parts of equipment receive energy from TEGs. Another area of application is heating control system of premises inside the house and readings from various meters accounting consumable resources («smart home») [4].
Today developed TEGs are being developed that can convert heat taken from car exhaust into electrical energy. To do this, we do a search for new thermoelectric materials - cheap, safe and capable of operating at high temperatures (above 800 C). Electrically conductive materials have high heat conductivity, so while heat distributing cold side of the thermocouple becomes hot too which leads to a decrease in electricity generation. This fact forces manufacturers of TEGs to seek artificial methods of maintaining a temperature gradient, which not only complicates the design of products, but also significantly increases their costs.
Thermoelectric materials.The search for materials that would meet the requirements of mass production is being done by both foreign and Russian companies. For example, the LLC «SmS tenzoterm Rus» is occupied with creating devices (SmS) on the basis of samarium monosulfide. Due to the properties of the substance they have to surpass the existing analogues for a variety of parameters. The company plans to develop both TEGs and cooling devices and strain gauges.
The team «Metemp» LLC at NUST «MISA» does researches on materials based on oxides, Heusler alloys, skutterudites, silicon-germanium alloys. All these materials can efficiently convert thermal energy into electrical one at a range of up to 1100 °C in the case of alloys based on silicon and germanium. The technological base «MISA» NUST allows you to create the necessary structures, up to the nanostructured material. This effect of nanostructuring allows you to create phonon scattering centers, which significantly reduces the thermal conductivity and increases the efficiency of materials [7].
The efficiency of a thermoelectric material is determined by such indicators as the ratio of thermoelectric figure of merit (Eng. Coefficient of merit). Coefficient of merit is represented as the dimensionless index ZT:
where T is absolute temperature, a - Seebeck coefficient of the material, o - its electrical conductivity, and x -thermal conductivity [5].
Figure 1 shows typical values of thermoelectric figure of merit (coefficient of merit) for many industrial and advanced materials, working in various temperature ranges.
i* Pn-
f 5
'J о
S Ь
I I
н n
500
1000 Г, С
10
10
10
: % J L BioiisSbn.i; 1
k /N • » \ • • ш Bi>Te2.7Sco.3
* V"* • \ * • . AgPb|KSbTe;o
• \ - • \ Sn)Te* * •..... ZT = 2 • • . .
7 *• ---"----N • •. Ga^Sei РЬТсЧ • r-rJ£T = 1
\ *-" SiGe
-ZT = 0.1 SrTio.nNbo.iOjOD) ....... i
500
1000
Г, к
1500
Figure 1 - Thermoelectric figure of merit of the range of used and advanced materials[1]
_МЕЖДУНАРОДНЫЙ НАУЧНЫЙ ЖУРНАЛ «ИННОВАЦИОННАЯ НАУКА» №01-2/2017 ISSN 2410-6070_
Advanced materials are as follows: bismuth tellurides III (Bi2Te3), lead (PbTe), germanium (GeTe) and antimony III (Sb2Te3); bismuth selenide III (Bi2Se3), antimony III (Sb2Se3) and gadolinium (GdSe); samarium monosulfide (SmS), magnesium silicide (Mg2Si).
Conclusion. Summarizing all the above, we can conclude that in spite of the low efficiency, TEGs have a huge potential: they are used in various fields of science and technology and the improvement of production technology of thermoelectric materials can significantly improve their performance and ensure mass production of TEGs for civilian use in the nearest time.
Список использованной литературы The list of the used literature
1. Biryukov A.V, Repnikov N.I, Simkin A.V, V.V. Hovaylo. Thermoelectric efficiency of low-temperature generating materials, the possibility of its improvement // Herald of Chelyabinsk State University - 2015. - N° 7 (362). - P. 21-29. 2
2. Gang Chen, Zhifeng Ren, Shuo Chen, Wei-Shu Liu, Hengzhi Wang, Hui Wang, Bo Yu. Methods of synthesizing thermoelectric materials // US Patent 9,306,145, 2016
3. Roger D. Launius Powering Space Exploration: US Space Nuclear Power, Public Perceptions, and Outer Planetary Probes // Smithsonian Institution, Washington, DC 20650, 2008, p.23
4. Chris R Bowen, John Taylor, E. LeBoulbar, R. Vaish Pyroelectric Materials and Devices for Energy Harvesting Applications // Energy & Environmental Science 7 (12) - 2014. - P. 21
5. Zhongliang Ouyang, Dawen Li Modelling of segmented high-performance thermoelectric generators with effects of thermal radiation, electrical and thermal contact resistances // Scientific Reports 6 - 2016. - P. 20
6. Wei-Hsin Chena, Po-Hua Wua, Xiao-Dong Wangb, Yu-Li Linc Power output and efficiency of a thermoelectric generator under temperature control // Energy Conversion and Management - 2016. - P. 404-415
7. RousseauM. Thermoelectricity: modernity [electronic resource] // Polit.ru - M., 2014. - URL: http://polit.ru/article/2014/10/09/sk_therm_electro/ (reference date: 05.11.16).
© Abrashin D.K., 2017
УДК 004
В.М. Алексеев
ректор, Академия подготовки главных специалистов (Краснодар)
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Аннотация на русском языке
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