Presented By:
ShreyasiSahu
DevanshuSharma
PrateekMurkute
SamyakDhone

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Introduction:-
Thermoelectrics is one of various technologies being considered for producing electricity from waste heat energy.To achieve performance levels comparable to internal combustion engines and dynamic power converter technologieswould require maximum efficiency level depending on that system’s thermal and electrical losses . As a result, the key to improving existing space power technology and expanding the range and scale of terrestrial generators, for both civilian and military applications, lies for the most part in the development of new, much more efficient materials and devices.
Principle:-
The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice versa. A thermoelectric device creates a voltage when there is a different temperature on each side (known as the Seebeckeffect ). Conversely when a voltage is applied to it, it creates a temperature difference (known as the Peltier effect). At atomic scale (specifically, charge carriers), an applied temperature gradient causes charged carriers in the material, whether they are electrons or electron holes, to diffuse from the hot side to the cold side, similar to a classical gas that expands when heated; hence, the thermally induced current.
Working:-
The core component of a thermoelectric module is a thermocouple. A thermocouple consists of two dissimilar semiconductors (referred to as p-type and n-type to describe dissimilar electrical conduction mechanisms in the two materials) connected together by a metal plate. Electrical connections at the top complete an electric circuit. Thermoelectric cooling (TEC) occurs when current passes through this thermocouple, in which case the thermocouple cools on one side and heats on the other by a phenomenon known as the Peltier effect. Conversely thermoelectric generation (TEG) occurs when the couple is put in a thermal gradient (i.e., the top is hotter than the bottom), in which case the device generates a current, thereby converting heat into electrical power by a phenomenon referred to as the Seebeck effect.
Thermoelectric materials:-
Thermoelectric materials show the thermoelectric effect in a strong and/or convenient form.Mostly all materials have a nonzero thermoelectric effect, in most materials it is too small to be useful. However, low cost materials that have a sufficiently strong thermoelectric effect (and other required properties) could be used for applications including power generation, refrigeration and a variety of other applications.The primary criterion for thermoelectric device viability is the figure of merit given by:
which depends on the Seebeck coefficient, S, thermal conductivity, λ, and electrical conductivity, σ. The product (ZT) of Z and the use temperature, T, serves as a dimensionless parameter to evaluate the performance of a thermoelectric material.Device efficiency is proportional to ZT, so ideal materials have a large Z value at high temperatures.
Materials such as Bi2Te3 and Bi2Se3 comprise some of the best performing room temperature thermoelectrics with a temperature-independent thermoelectric effect, ZT, between 0.8 and 1.0. Nanostructuring these materials to produce a layered superlattice structure of alternating Bi2Te3 and Bi2Se3 layers produces a device within which there is good electrical conductivity but perpendicular to which thermal conductivity is poor. The result is an enhanced ZT (approximately 2.4 at room temperature for p-type). Note that this high value has not entirely been independently confirmed.
 Since the 1950s, the main approach to developing advanced thermoelectric materials was focused on identifying, characterizing, and optimizing bulk degenerate semiconductors
 p-type TAGS materials (GeTe-AgSbTe2 compositions) with peak ZT values around 1.2.
 Solid solutions, such as Bi2–xSbxTe3–ySey and Si1–xGex, have been used to tune the band gap for maximizing ZT values
 A more recent strategy consists of replicating the nanoscale features responsible for enhanced ZT values in bulk materials using advanced synthesis techniques.
 Significant increase in ZT in some bulk materials, such as silver antimony lead telluride and its alloys, attributed mostly to the formation of “self-assembling” nanoclusters inside a host matrix.
Applications:-
Recoverable Industrial Waste Heat
 Extremely large amounts of waste heat energy are generated through inefficiencies of power-generating plants and manufacturing industries.
 Manufacturing industries overall reject about 33% of their energy as waste heat directly to the atmosphere or to thermal management systems because of their inability to recycle the excess energy
 U.S. manufacturing sector alone, more than 3,000 TWh of waste heat energy is lost each year, an amount equivalent to more than 1.72 billion barrels of oil.
 Aluminum, glass,metalcasting,non-metal,melting, ceramic sintering, and steel manufacturing all have process furnaces discharging high-temperature waste heat combustion gases and melt pool gases (such as aluminum melting at 1,025 K and glass melting near 1,700K).
 Recent U.S. studies6 on nearterm waste heat recovery applications determined that between 0.9 TWh and 2.8 TWh of electricity might be produced each year for materials with average ZT values ranging from 1 to 2. Solar Thermal
 There has long been interest in solar thermal power systems where the solar energy is concentrated and turned into a high-temperature heat source, and then converted to electricity by using a dynamic or static Carnot engine.
 Largescale power plants relying on dynamic converters (such as turbines operating on the Rankine cycle) have been built in recent years, with thermal-to-electric conversion efficiencies in the 20% to 30% range for moderate heat source temperatures around 800 K.
 Concept consists of concentrating and splitting the solar energy spectrum into a low wavelength portion directed at PV cells and a high wavelength portion directed generatinghigh grade heat for thermoelectric modules. Photovoltaic cells efficiently convert the ultraviolet and visible light and removing the infrared portion of the spectrum helps maximize their conversion efficiency by maintaining low operating temperatures.
Automotive Exhaust Waste Heat
 The automobile industry has also recently developed a strong interest in a waste exhaust heat to supplement or replace the alternator and thus decrease fuel consumption.
 Current estimates of available waste thermal power range from 20 kW to 400 Kw for light-duty vehicle systems, depending on engine size and operation.
Space technology
 Thermoelectric power sources have consistently demonstrated their extraordinary
reliability and longevity for deep space missions (67 missions to date, more than 30
years of life)
 The NASA Jet Propulsion Laboratory is leading collaborative research and development on novel advanced bulk materials capable of long-term operation at temperatures up to 1,300 K at more than 20% conversion efficiency.
Conclusion:-
Thermoelectric technology has some unique advantages in terms of ease of integration for retrofitting existing industrial equipment, hybridizing with other power technologies as topping or bottoming cycles, unique scalability and modularity, and low maintenance requirements. However, thermoelectrics are often seen as a low performance, immature, and costly technology for application to the megawatt- class power generation systems. Most recent studies point to the fact that the ZT values of state-of-practice materials only lead to thermoelectric generators of marginal performance. In the last 15 years, significant progress in materials synthesis and processing coupled with better understanding of how to engineer superior thermoelectric materials has brought some very promising results.Because of its fairly low power level (~1 kW), moderate temperature range, and potential large scale use, automobile thermoelectric waste heat recovery constitutes a unique opportunity to design, develop, validate and demonstrate technologies that are critical to a widespread application of thermoelectric generators.