Papers by Keyword: Thermoelectricity

Abstract: Polyaniline (PANI) has been considered for thermoelectric (T.E) applications due to its facile preparation methods, easy doping-dedoping processes and its environmental stability. Like other conducting polymers (CPs), it has low thermal conductivity (usually below 1 Wm^-1K^-1) which is favorable for T.E applications, however studies have shown that it still suffers from low power factors as a result of low electrical conductivity. For this reason, PANI has been compounded with other materials such as polymers, inorganic nanoparticles and carbon nanoparticles to enhance its electrical conductivity, power factors (PF) and ultimately zT value.This work is focused on the synthesis and characterization of n-type polyaniline nanocomposites doped with reduced graphene oxide (rGO). The rGO was prepared through oxidation of graphite and subsequent reduction and incorporated into polyaniline through in situ polymerization and the resulting nanocomposites were characterized. Addition of rGO resulted in enhancement of the electrical conductivity of polyaniline from 10^-3 S/cm to 10^-1 S/cm which is two orders of magnitude higher. This contributed to the enhanced PF, an indication that thermoelectric behavior of conducting polymers can be boosted through compounding with inorganic materials.

Abstract: Substituting V/Nb in Fe₂VAl causes an initial increase of the unit cell volume as well as an increaseof the structural disorder. Although V and Nb are isoelectronically, slight changes of the electronicdensity of states N(E) right at the Fermi energy are obtained. While for a 10 % substitution of V/Nbthe absolute value of N(E_F) keeps almost constant, the slope of N(E) grows. As a result, the Seebeckeffect grows in comparsion to the starting material Fe₂VAl, reaching values of about 100 μ V/K at roomtemperature. The latter is one of the largest found so far for p-type substituted Fe₂VAl.

Abstract: This paper is intended for the analysis of the fabrication of Thermoelectric Materials with emphasis on the use of Powder Technology including the use of Powder Technology. Main characteristics of them are considered. The recycling of thermoelectric material pieces is shown.

Abstract: A new system for converting combustion heat into electric power was proposed on the basis of countercurrent burner with thermoelectric element embedded in a wall separating incoming fresh mixture and combustion products. The wall serves as heat exchanger between combustion products and the fresh mixture. Numerical simulations showed that almost whole combustion heat may be transferred through the thermoelectric element in such system and the total thermal efficiency attained a value close to the conversion efficiency of the thermoelectric device itself.

Abstract: Use of spark plasma sintering (SPS) allows improving thermoelectric figure of merit Z of bulk nanothermoelectrics but required parameters of SPS process for achievement of best Z can be defined only empirically. In the present study the finite elements method for investigation of electric and thermal processes which occur in volume and on boundaries of sintering particles is applied. As a geometrical model a structural cell of a sintered sample, containing contact “a truncated cone - a plate” has been chosen. Temperature distributions in the volume of a sample depending on amplitude, on-off time ratio and duration of impact of the electric current has been obtained for solid solution based on bismuth telluride using the energy balance equation and the equation of electric current continuity. Under certain conditions nonlinear and nonlocal processes start to arise. The calculated temperature distributions at different sintering conditions were comparing with empirically defined experimental parameters that lead to improved value of Z. The comparison allows formulating recommendations to achieve best conditions of SPS process for increase of Z. The present method can be used for management of SPS fabrication process for different application, not only for thermoelectrics.

Abstract: Thin films of sodium cobalt oxide and zinc aluminium oxide were prepared onto ceramic substrates by a bipolar pulsed-dc magnetron sputtering system using a NaCoO₂ target and a ZnAlO target, respectively, under an argon atmosphere. Energy dispersive spectroscopy analysis revealed that the as-deposited films from the NaCoO₂ target comprised Na, Co, O elements, while those from the ZnAlO target contained Zn, Al, O elements. Cross-sectional view estimation by the scanning electron microscope indicated that the as-deposited Na-Co-O (NCO) and Zn-Al-O (ZAO) films had the thickness of 0.63 μm and 0.58 μm, respectively. X-ray diffraction analysis showed that the NCO thin films were grown in amorphous phase while the ZAO thin films exhibited hexagonal structure. From thermoelectric properties measurement, the p-NCO and n-ZAO films were found to exhibit the thermoelcectric power factor of 0.03 and 14.39 μW/mK², respectively. A thermoelectric module made from three pairs of the p-n thin film stripes provided the open-circuit voltage up to 26.0 mV for a temperature difference of 79.3 K. However, the module was unable to produce useful electrical current due to its high internal series resistance contributed from the NCO films.

Abstract: Abstract. Besides the material property and dimensional optimization of the thermoelectric module, temperature distribution uniformity on the hot junction of the module surface highly affects the outputs of the thermoelectric power generation system. This paper reports the findings on the effects of non-uniform input temperature distribution on the performance of thermoelectric power generation system. To assure the investigation, heat transfer model and finite element formulation of thermoelectric module having non-linear material property have been developed. In addition to the experimental data from a real thermoelectric device, thermoelectric power generation system modeling and simulation using finite element packaging ANSYS software was carried out. For the simulation, temperature dependent thermoelectric material properties such as the Seebeck coefficient, thermal and electrical conductivity have been considered. The experimental and simulation results indicate that keeping the temperature distribution uniform on the hot junction of the thermoelectric module results higher efficiency, higher power, voltage and current outputs than the non-uniform temperature distribution.

Abstract: To enhance the Seebeck coefficient and reduce the thermal conductivity and meanwhile keep an excellent electrical conductivity, the disordered structure was introduced into the ordered CoSb3 nanocrystalline by increasing hot-pressing temperature. The results show that the introduced disordered structure can increase the Seebeck coefficient from 125 VK-1 to 390 VK-1 measured at 773K, the thermal conductivity can be reduced from 1.94 Wm-1K-1 to 1.73 Wm-1K-1. Even though the electrical conductivity is decreased from 74000 Sm-1 to 14000 Sm-1, a largely enhanced figure of merit of 1.21 at 773 K still can be obtained for the sample hot-pressed at 943 K. Therefore, introducing the disordered structure into an ordered structure can be considered as an effective way to enhance the figure of merit.

Abstract: The thermoelectric SiC structural materials for supersonic vehicles can convert intense aerodynamic heat to electricity simply by temperature difference. A general model of nose tip is developed to predict the thermal-electrical energy con-version performance of the thermoelectric SiC materials. The temperature distributions of model was obtained by solving the Navier-Stokes (N-S) equations and the heat conduction equation. The largest temperature difference between the hot side and cold side of the hypothetical thermoelectric module is about 275 K. With the thermoelectric properties assumed constant in the presence of temperature gradient, the output power and thermoelectric efficiency of the model are calculated. The maximum of thermoelectric efficiency and output power of the model are 0.4×10^-3 W and 1.6×10^-4 %, respectively, at a current of 0.014 A. The thermoelectric performance of the model shows great potential for the application of SiC ceramic structures to thermoelectric generation from aerodynamic heat on supersonic vehicles.

Abstract: Blanking is one of the most widely used manufacturing technologies in sheet metalprocessing, because nearly each sheet must be trimmed out of a semi-finished part or has to beblanked after a forming process to get the precast part in the manufacturing chain. In general, a highquantity of blanked parts should be manufactured without reworking the tool. Therefore a capableprocess is indispensable to avoid inadequate part quality or premature failure of the tool because ofwear. The blanking process is affected by tool parameters, the press and the material properties ofthe blanked part.However, another important factor is the occurring temperature in the shearing zone of the sheetmetal due to the dissipation of nearly 95% of the plastic work during blanking and, in addition,frictional heating. This temperature impacts the blanking process features such as tool-wear andresulting cut edge quality. It has been presumed to be negligible by a lot of authors yet. In contrastsome publications with experimental and analytical research assume that the temperature reachesvalues up to 1000°C. Therefore, this report outlines a thermoelectric method to measure theresulting temperature distribution during the blanking process on the cutting edge of the blankingpunch. The feasibility of the investigated measurement concept is shown on a concrete example.