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Transcript of Nano tech
Bansari Patel Improved
Thermoelectric figure of merit(ZT) using
(n-type Cosb3 based nanocomposites) ZT INTRODUCTION ZT=((α^2 σ)/k)T Thermoelectric (TE) devices based on Seebeck effect use a temperature difference across the device to drive the diffusion of charge carriers.
N-type and a P-type thermo element connected electrically in series by a conducting strip. Nowadays Nanomaterials are widely used for TE materials.
Bi2Te3 is one of the most widely used nanostructured TE materials. Thermoelectric Module (A) The Traditional Junction
Current & heat Flow in same diretion.
Long current path through shunt & tall narrow TE elements
(B) The stack Junction
Current flow perpendicular to heat flow.
Short current path through shunt Ref (1):
Carroll, D. L. (n.d.). Thermoelectric “ Fabrics ” based on carbon nanotube composites.Center for Nanotechnology and Molecular Materials, Department of Physics. Wake Forest University, Winston-Salem NC 27109 Thermally/electrically insulating layers Ref (1) ZT is figure of merit,
α is see back co-efficient
σ & k are the electrical & thermal conductivity respectively,
T is absolute temperature ZT is figure of merit,
φte is the thermoelectric efficiency,
Th & Tc are the temperature of hot & cold end respectively Ref:
W. J. Xie, H.J.Kang & team Members, Nano letters 10 (2010) 3283
Nano Energy (2012) 1, 42-56 Zhong lin Wang (T)
T.Caillat, A. Borshchevsky, and J.-P. Fleurial, J. Appl. Phys. 80, 4442 (1996)
Applied physics letters 91, 172116 (2007) Nanocomposites offer a promising approach to incorporate nanostructured constituents to bulk thermoelectric materials. n-type CoSb3 nanocomposites were prepared by hot pressing the mixture of nanoscale and microsized CoSb3 powders synthesized by solvothermal method and melting, respectively. Microstructure analysis shows that the bulk materials are composed of nano- and micrograins. The nanocomposite structures are effective in reducing thermal conductivity more than electrical conductivity, hence in improving the thermoelectric performance. A dimensionless figure of merit of 0.71 is obtained for the nanocomposite with 40 wt % nanopowder inclusions, about 54% increase of that without nanopowder inclusions. The nanostructures induced by uniaxial compression in Ce0.29Fe1.40Co2.60Sb11.24 bulk thermoelectric material is reported. High-resolution transmission electron microscope images reveal that the nanostructures consist of Ce0.31Fe1.38Co2.62Sb11.56 crystals & Fe0.34Co0.66Sb1.99 minicrystal/noncrystal with grain sizes about 5–20 nm. It is shown that the Seebeck coefficient is increased by 21%, the phonon thermal conductivity is reduced by 19%, while the electrical conductivity rises slightly at 300 K. This leads to a surprising increase in the power factor by 51%. The significant increase of Seebeck coefficient and the remarkable reduction of phonon thermal conductivity are believed to be due to quantum effect and size effect of the nanostructures, respectively. Nanostructures
thermoelectric properties Schematic representation of a nanocomposite material. Red cubes of nanometre dimensions (eg Ag and Sb rich regions) are embedded in the blue host material (eg PbTe)2 large Seebeck coefficients could be achieved in nanostructured materials. These are composite materials where nanometre regions of material A are embedded inmaterial B (fig 4). The increase in the Seebeck coefficient comes from changes in the electronic structure when the dimensionality of a material is reduced. This concept was proven in carefully grown quantum dot thin-films but has been found difficult to translate to bulk materials. However, fortunately, the large number of interfaces innanostructured materials are very efficient at reducing the lattice thermal conductivity. This happens because lattice vibrations behave like waves in a solid. The propagation of waves with wavelengths shorter than the size of the nanodomains are not affected but waves of similar lengthare scattered very effectively. It is this effect that leads to a large reduction in thermal conductivity. Ref: (Education in chemistry (2012))
Bubobna et al, Nat. Mater., 2011, 10, 429
D Kraemer et al, Nat. Mater., 2011, 10, 532 (DOI:10.1038/nmat3013) TEM image (a),
SAED pattern (a1),
HRTEM image(b), and
optical diffraction pattern(b1) of a triplet crystal structure in the as-prepared Ce0.29Fe1.40Co2.60Sb11.24 bulk thermoelectric material. Light-Weight Flexible Carbon Nanotube Based Organic Composites increase thermoelectric PowerFactors Thermoelectric(TE) Power Factors Typical organic materials have low thermal conductivities that are best suited to thermoelectrics, but their poor electrical properties with strong adverse correlations have prevented them from being feasible candidates. Our composites, containing single-wall carbon nanotubes, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and/or polyvinyl acetate, show thermopowers weakly correlated with electrical conductivities, resulting in large thermoelectric power factors in the in-plane direction of the composites,160 μW/m 3 K2 at room temperature, which are orders of magnitude larger than those of typical polymer composites. Furthermore, their high electrical conductivities, 105 S/m at room temperature, make our composites very promising for various electronic applications. The optimum nanotube concentrations for better power factors were identified to be 60 wt % with 40 wt % polymers. It was noticed that high nanotube concentrations above 60 wt % decreased the electrical conductivity of the composites due to less effective nanotube dispersions. The thermal conductivities of our 60 wt % nanotube composites in the out-of-plane direction were measured to be 0.20.4 W/m 3 K at room temperature. Scanning electron micrographs of cold-fractured cross sections along the out-of-plane direction
The less amount of the stabilizer (PEDOT:PSS) resulted in thicker and less dispersed nanotubes K Ref: Choongho Yu,* Kyungwho Choi, Liang Yin, and Jaime C. Grunlan YU et al VOL-5 , NO. 10, 7885–7892 , 2011 Carbon Nanotube (CNT)
wt % Power factor
(α^2 σ) Electrical Conductivity
(σ) Applications Future Aspects Applications for thermoelectric modules cover a wide spectrum of product areas. These include equipment used by military, medical, industrial, consumer, scientific/laboratory, and telecommunications organizations. Uses range from simple food and beverage coolers for an afternoon picnic to extremely sophisticated temperature control systems in missiles and space vehicles.
Thermoelectricity from window glasses
Thermoelectric generator harvests waste from the exhaust gases coming out of the automobile.
Implantable Medical Devices such as Pacemakers, defibrillators, bio-thermal battery, etc. The ability to create thermoelectric nanomaterials has led to remarkable progress in enhancing thermoelectric properties Photographic film maker Fujifilm developed a thermoelectric conversion material using an organic polymer material. It exhibited a thermoelectric convertor module using the materials at Nanotech 2013, in Tokyo. Thank You