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Zeichen Journal ISSN No: 0932-4747

ANALYSIS AND IMPLEMENTATION OF THERMO- USING GRAPHENE Sneha Panchal, Sai Parab ,SanatRathod , RajtaraIngavale , Ujvalatade LokmanyaTilak College of

Abstract-This project proposes to develop an influence electric potential will exist between them. When an generator from waste from various sources. A electrical potential occurs, electrons will start to flow, Radioisotope (RTG) is an making current. This is a way different technique than that electrical generator that uses an array of , employed by atomic stations on Earth. That process which is a state device that converts heat generated by is called fission, gets very high efficiency rates by literally the decay of a radioactive material directly into electrical "splitting" unstable radioactive materials (such as uranium) through a phenomenon called the Seebeck into smaller parts. Fission generates very large amounts of effect.Due to the various advantages of Thermoelectric heat, but is much more complex than and not as reliable as power generators it has arisen asalternative green simply using the heat produced by radioactive decay. . This type of generator which has no moving Basically, fission gives you a huge release of energy and parts has been used which leads it’s application in a power uses rapidly. An RTG gives a steadier and much sources in satellites, Navigation and unnamed remote smaller amount of energy. Thermoelectric have enabled the control where use is not practical. RTGs use heat human race to take the first exploratory steps into the outer from the natural radioactive decay of plutonium-238, in the Solar System and beyond into interstellar space. By virtue form of plutonium dioxide. Such devices are often of having no moving parts (including no moving fluids) relatively simple, are often efficient, and that they are often thermoelectric elements have shown themselves to be readily adaptable to microcircuit interfacing. Due to unique extremely reliable and long-lived. shape and characteristics, graphene are most frequently used nanofillers. They could potentially use to generate 1.1 Thermo Electric Generator: enough power or running a small ultra-low power operations, if graphene films are closely stacked together, A thermoelectric power generator is a strong state tool that with minimum cost in a wide variety of applications for provides direct power conversion from both research and industries. (warmness) because of a gradient into electrical power based on “Seebeck impact”. In truth, this Key Words :-Thermoelectric generator , seebeck effect, phenomenon is applied to thermocouples which might be , graphene. extensively used for temperature measurements. Based totally on this Seebeck effect, thermoelectric devices can 1. Introduction act as electric energy generators.

A radioisotope thermoelectric generator, or RTG, uses the Schematic of a single thermo-couple: radioactive materials which generate heat as they decompose into non-radioactive materials. The heat used is An ordinary thermoelectric energy module is proven converted into by an arrangement of schematically. Within the following discern: n-kind and p- thermocouples which then power the spacecraft. A kind thermo factors are linked in collection thermocouple may be a device which converts thermal by tremendously- carrying out steel strips to shape a energy directly into . Basically, it's made thermocouple. The two sides of the thermocouple are from two sorts of metal which will both conduct electricity. maintained at two exclusive . Due to this They are connected to every other during a closed-loop temperature distinction, waft of the rate providers’ takes system. If the two metals are at different temperatures, an place in each n-kind and p-type pellets constituting to the distinction across load resistance.

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Fig 2 Complete structure of Thermo electric Generator

The semiconductor thermo elements which are sandwiched among the ceramic plates are linked thermally in parallel and electrically in series to form a thermoelectric tool (module). Multiple pair of are usually assembled collectively to shape a thermoelectric module and in the module a couple of thermo elements is referred to as a thermocouple. The junctions connecting the thermo elements between the new and cold plates are interconnected the usage of noticeably engaging in steel (e.G. Copper) strips. Fig 1 Single structure of thermocouple

1.2 A typical Thermoelectric Power Generator:

A thermoelectric module is made from a number of thermocouples linked together electrically in collection and thermally in parallel. The diagram under indicates the 3- dimensional view of the standard Thermo electric powered Generator. Whilst warmness is absorbed on one facet of a TEG (crimson arrow) the movable price vendors begin to diffuse, ensuing in a uniform attention distribution inside the TEG alongside the temperature gradient, and generating the distinction inside the electric ability on each sides of the Fig. 3 Thermo Elements Sandwiched between Ceramic TEG. To maximize the electricity technology output, p-bars Plates and n-bars (see circles) are related collectively in a mobile electrically in series and thermally parallel. Due to the Electrons present at hot side of material is more energized , electrons flow through the n-type than the electrons present at cold side. These hot energized element to the colder side while in the p-type elements, the electrons will flow from the hot side to the cold side. positive charge carriers flow to the cold side.. This Electricity will flow continuously, if the circuit is complete. illustrates how connecting the p-bar and the n-bar augments Semiconductor materials are the foremost efficient, and are the voltage of each bar and the voltage of each unit cell. combined in pairs of “p type” and “n type”. The electrons flow from hot too cold in the “n type”, while the holes flow 1.3 Working Principle of TEG: from hot to cold in the “p type.” This allows them to be combined electrically in series. Thermoelectric energy technology is based on a phenomenon called “Seebeck effect” observed by means of Thomas Seebeck in 1821. The See beck impact was first discovered in 1822 by using Seebeck, who determined an electric drift when one junction of assorted metals, jointed at locations, was heated whilst the other junction became kept at a decrease temperature.

2 Analysis

2.1. Performance of TEG:

Thermal Conductivity of the materials used, Thermal Expansion Coefficient of the materials used, Specific Heat of the materials used, Resistivity of the materials used and

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See beck coefficients of the materials used are some of the factors that govern the performance of TEG. Figure of merit and its efficiency is also taken into consideration.

The ability of a material to conduct heat is known as the . The thermoelectricmaterials selected Higher the ZT, greater the efficiency, subject to certain for the TEG module must have high thermal conductivity. provisions, particularly that the two materials in the couple have similar Z. S.I unit = W/ (m-K) ZT is therefore a method for comparing the potential efficiency of devicesusing different materials. Values of 1 Thermal Expansion Coefficient is the change in the are considered good; values in the 3–4 range are essential size of material with change in temperature. for thermoelectric to compete with mechanical devices in

efficiency. To date, the best reported ZT values are in the S.I unit = /•C (or) / •K 2–3 range.

Efficiency of a thermoelectric device for electricity

generation is given by η. Specific Heat is the per unit of the

substance where heat capacity is the amount of heat

supply to increase the change in the temperature.

S.I unit =J/ kg/ K

Resistivity tells how strongly a material opposes the flow of electric current. 3 Graphene Based Thermoelectric Generator : S.I unit = Ω-m Graphene is a two-dimensional(2D) material with high Seebeckcoefficient, represented by ‘S’, of a material electric conductivity, elasticity, stiffness, bio-compability measures the magnitude of an induced thermoelectric and stability at high temperature i.e above 3400K. For same voltage in response to a temperature difference across that applications such as TEG, such properties make it material. If the temperature difference ΔTbetween the two universally suitable material and a potential candidate for ends of a material is small, then the thermopower of a post-silicon electronic era. Different carbon material material is defined approximately as, including carbide compound and graphite and chemically modified graphene , which is usually referred to as reduce graphene oxide (rGO) or simply graphene oxide (GO). GO is adaptable to wide variety of application and is prepared by colloidal suspension with advantages such as low cost, flexible, scalable. In this paper we propose a study analysis A thermoelectric voltage of ΔV is seen at the terminals. and development of graphene based efficient TEG. Fig(a) The negative sign indicates the flow of electrons and shows the fabrication steps of graphene based TEG. The positive sign means flow of holes. fabrication steps include mainly 4 steps : Layering, depositing GO, deoxidization and finally testing. S.I unit = V/ •C 3.1 About Graphene The figure of merit Z for thermoelectric devices is defined as, Graphene may be a single layer (monolayer) of carbon

Where σ is the electrical conductivity, κ is the thermal conductivity, and S is the . The atoms, tightly bound during a hexagonal honeycomb dimensionless figure of merit ZT is formed by multiplying lattice. It is an allotrope of carbon in the form of a plane of Z with the average temperature. sp2-bonded atoms with a molecular bond length of 0.142 nanometers. Layers of graphene stacked on top of every other form graphite, with an interplanar spacing of 0.335 nanometers. The separate layers of graphene in graphite are

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held together by van der Waals forces, which may be overcome during exfoliation of graphene from graphite.

Graphene is the thinnest compound known (one atom thick). It is the lightest material known (with 1 square metre weighing around 0.77 milligrams) and also the strongest compound discovered ,stronger than steel (between 100-300 times stronger) with 130 GPa tensile strength and a Young's modulus of 1 TPa - 150,000,000 psi), the best conductor of heat at room temperature (at (4.84±0.44) × 10^3 to (5.30±0.48) × 10^3 W·m−1·K−1) and also the simplest conductor of electricity known (studies have shown electron mobility at values of more than 200,000 cm2·V−1·s−1). Other notable properties of graphene are its potential suitability for use in spin and its uniform absorption of light across the Fig 4.1 Graphene (10mm*10mm*300mm) visible and near-infrared parts of the spectrum (πα ≈ 2.3%).

4. Construction and experimental procedure for 2D and 3D thermoelectric device:

4.1Construction and experimental procedure for 2D thermoelectric device:

Graphenea make monolayer graphene of dimension

10mm*10mm*300nm on an SiO2 substrate is considered for the experiment. The two ends of monolayer graphene is connected to voltage through silver (Au) paste which is covered 1mm in the substrate end. The in graphene layer is introduced by electrical field method that is by applying electrical field above the graphene layer. For positive electric field the layer acts as a “N” type doping and for negative electric field the layer acts a “P” type. By applying heat in the “PN” junction of Fig 4.1.2 Schematic of the experimental set-up of 2D graphene layer, through external convection heating, the thermos-electric device. thermo-voltage across the two ends can be measured. By varying the electric field potential, the doping concentration 4.2 Construction and experimental procedure for of “N” and “P” layer can be changed. Thus the effect of 2D thermoelectric device: change in doping concentration on thermo-voltage for a fixed temperature difference can be studied. The hot end Theexperimental set up includes semiconductor based “PN” junction temperature and the temperature at the two thermoelectric device, a PI controller with a thermocouple, ends of graphene are measured with the help of a LED, multi-meter, electric heater (for heating ) and a thermocouple. Like different doping concentration, the flask.The thermoelectric device consists of 2 regions- hot thermo-voltage for different temperature difference can region and cold region. The hot and cold regions of the also be measured. thermoelectric device are placed as shown in the figure. The temperature of the hot region is increased with the help of water. The flask containing the water is kept on the hot region and the temperature of the water is controlled with the help of PI controller. The temperature of the cold region is decreased with the help of dry ice. The temperature of the former was set to 60o C and the temperature of dry ice is -78.5o C. Due to this temperature difference the LED starts glowing. Once the temperature of the water reaches

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60o C, the PI controller stops and the temperature of the water starts reducing. As the temperature reduces the POWER brightness of the LED also reduces. The values of the 8000 and currents are measured in small intervals and power (P=V*I) is calculated from the measured values. 6000

4000

2000

0 0 10 20 30POWER40 50 60 70

Fig 4.3.1 Plot of power versus temperature for the experimental setup

120 Voltage and current 100 Fig 4.2 Experimental set-up for thermo-electric device 80 4.3 Result of 3D thermo-electric device: 60 40 Sr.No. Temperature Voltage Current 1 60 67.3 97 20 2 58 59 83.5 3 56 54 76.6 0 4 55 50 70 0 10 20 30 40 50 60 70 5 53 44.8 62 Voltage Current 6 51 39.6 54 7 49 36.9 49.9 8 47 31 40.8 Fig 4.3.2 Plot of current and voltage versus temperature 9 45 28.5 36.7 for the experimental setup 10 43 25.7 32.1 11 41 21.2 25.3 From the experiment performed the result obtained were 12 39 17.7 19.89 tabulated in table 4.3 and variation of voltage, current and 13 38.5 16.8 18.39 power with respect to the temperature difference are plotted 14 38 16.6 18.23 in fig 4.3.1 and 4.3.2. It is observed that current, voltage 15 37.5 16.2 18.02 and power is directly proportional to temperature difference. Higher the temperature difference greater the voltage and current, hence higher the power. Table 4.3: shows the results obtained from the experiment conducted on 3D thermoelectric device. 5 Conclusion:

From above thesis we infer, Thermoelectric technology can be used to generate a small amount of electrical power, typically in the μW or mW range, if a temperature difference is maintained between two terminals of a thermoelectric module. In Graphene based TEG Seebeck coefficient is higher than the any other induced voltage method. Seebeck coefficient increases as graphene layer increases. Moreover, Graphene based thermos TEG is more Efficient, Reliable, compact, light in weight and

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free, all above stated advantages leads potentially a wide 10. E. A. Skrabek and D. S. Trimmer, “Properties of the variety of applications in and engineering General TAGS System”, Chapter 22 of CRCHandbook of Thermoelectrics, David M. Rowe, editor, CRC Press, Inc., Boca Raton, Florida, 1995. [12]C. J. Goebel, “SNAP-19 Pioneer 10 and 11 RTG 6. Reference: Deep Space Performance”, Paper 759 130, Record of the 10th Intersociety Energy Conversion Engineering 1. Woerner, D., et al. "Next-Generation Radioisotope Conference, held in Newark, Delaware, 18-22 August1975. Thermoelectric Generator Study Final Report." JPL D-

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(2012). Vision and voyages for planetary science in 12. W. M. Brittain and E. A. Skrabek, “SNAP 19 RTG thedecade 2013-2022. National Academies Press Performance Update for the Pioneer and Viking Missions”, . Proceedings of the 18th Intersociety EnergyConversion

Engineering Conference, held in Orlando, Florida, 21-26 3. Rowe, D. M. (Ed.). (2005). Thermoelectrics handbook: August 1983 macro to nano. CRC press.

13. A. A. Pitrolo, B. J. Rock, W. C. Remini, and J. A. 4. G. L. Bennett, J. J. Lombardo, and B. J. Rock, “U.S. Leonard, “SNAP-27 Program Review”, Paper Radioisotope Thermoelectric Generator Space Operating 699023,Proceedings of the 4th Intersociety Energy Experience (June 1961 - December 1982)”, paper 839171, ConversionEngineering Conference, held in Washington, Proceedings of the 18th IntersocietyEnergy Conversion D. C., Engineering Conference, held in 22-26 September 1969. Orlando, Florida, 21-26 August 1983. (This paper was

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