Papers by Keyword: Thermoelectric

Abstract: This paper reports on experimental comparisons of coefficient of performance (COP) of a thermoelectric coolingsystem which cooled the hot side of the TEC by water (wc), ethylene glycol (egc) and nanofluids (nfc) The nanofluids is composed of ethylene glycol with silver nano(35 nm).The TEC was composed of the TE cooling modules, heat exchanger, and the air cooled heat sink at the cold side of the TE modules.Experiments were conducted with various current input 1 - 4.5 A to find out the optimum current input condition. To consideration of cooling capacity and COP of system was measured the hot and cold side temperature of TEC. Results shown that, the cooling capacity was increased with current input. The maximum cooling capacity of nfc, egc and wc are about 72, 62 and 41 W, respectively. Considered with highest COP found that the optimum current input is approximately 2.5 A. The maximum COP of nfc, egc and wc are about 2.01, 1.7 and 1.12, respectively. Therefore, the proposed TEC-nfc concept is expected to contribute to wider applications of the TE cooling system.

Abstract: Output performance prediction of thermoelectric generators (TEG) is a valuable work for TEG structure optimization (i.e. shape of thermocouple and other electrical or thermal conducting components) and material selection. Considering the basic thermoelectric effects, as well as the thermal resistances between the thermocouple and the heat source, heat sink, this paper describe a physical model with Thomson effect for a simplified thermoelectric module. A new method to solve the temperature of the thermocouple hot and cold conjunctions which directly affect the voltage, current and output power, is proposed. And an experiment test of a commercial Bi₂Te₃ thermoelectric module is undertaken to testify the physical model and the solution method. The study shows that the calculation results are in good accordance with the experiment data, which prove the accuracy of the physical model and the solution method. This paper can provide a novel analytical method for TEG performance prediction.

Abstract: The aim of this experiment was to use mechanical chopper coupling with CO₂ laser ablation to reduce thermal effect on thermoelectric thin film fabrication. The average power at 10 W of sealed tube CO₂ laser together with the mechanical chopper was used for the thermoelectric (TE) thin film fabrication on silicon substrate in vacuum system. The 1.02 ms of pulse duration with 600 Hz of repetition rate were generated by the optimized speed of chopper at 4500 rpm with 8 channels of circular apertures which were used for the reduction of thermal effect on the bismuth antimony telluride (Bi-Sb-Te) target. The experiment results illustrated the thickness and the thin films fabricated by using 10 seconds of exposure time with the chopper, illustrated the smaller grain size than without the chopper while the thickness increased as the exposure time increased at constant speed of chopper. The output efficiency referred to the ratio of the thickness per target lost in unit time which increased from 19.6 to 181.8 μm/g per hour, due to the increase of the exposure time with the chopper while without the chopper resulted in 55.0 μm/g per hour caused by the higher temperature raise on the thermoelectric target which affected to the as-deposited thin films and the re-evaporation occurred. In this experiment, the chopper speed was measured by the digital tachometer, the target loss was analyzed by the digital analytical balance and the morphology of the 60⁰ tilted surface of thin film was characterized by scanning electron microscope (SEM).

Abstract: The article utilizes thermo-electric performance experiments to study four fixed volume kinds of electrolytes (Tap Water, Mineral Water, Sea Water, and Al₂O₃ Nanofluids) under different operating temperatures, distances and areas of electrodes due to the impact of the output currents. The experimental results showed that the rise in operating temperature will significantly affect the magnitude of the output current because of heat convection inside the fluid. And the output current of the seawater was much larger than those of the nanofluids, tap water and mineral water between 27 °C and 90 °C. Its maximum value was up to 4.2 mA. However, the seawater presented unstable for output current. The Al₂O₃ nanofluids had the most stable among them and its output current was about 1.08 mA. If seawater combined with Al₂O₃ nanoparticles, they will be able to achieve a complementary role in the future development.

Abstract: The thermoelectric phenomenon can be used for a wide application spectrum. Typically, the Seebeck effect of metallic materials is used for temperature measurement in common thermocouples. However, there is also a high potential for adapting the effect in nondestructive testing due to a high sensitivity of the thermoelectric properties to a variety of material characteristics.Different studies point out an influence of plastic deformations on the thermoelectric behavior of metals, but a detailed and quantitative analysis and description is not provided yet. There is an increasing interest in detecting the changes of properties by nondestructive characterization of plastically deformed materials. Especially in metal forming, the knowledge about the correlation between the degree of deformation and the thermoelectric behavior can help to check formed metal parts. On that account, the influence of plastic deformations on the thermoelectric behavior, in particular the Seebeck coefficient, of four steel alloys is introduced in this paper.An apparatus based on the integral measuring method was built up to measure the relative Seebeck coefficient to a reference material at different temperature gradients and for several degrees of plastic deformation. Well defined values of plastic deformation are realized by cold rolling. With this compressive forming technology a logarithmic deformation φ up to 2.11 was set for all steel alloys. Besides a high degree of deformation, a uniform strain over the sample thickness can be obtained by rolling.With increasing plastic deformation a significant change of the relative Seebeck coefficient can be observed in a defined temperature range for all investigated steels. The plastic deformation is accompanied by an increase of dislocation density into the lattice structure of the metal. These line defects provoke the formation of new scattering centers and thus the electron motion is disturbed. By the combination of metallurgical examinations and measurements of micro hardness, the relation between the thermoelectric behavior and the plastic deformation of steels can be clearly illustrated.

Abstract: The studies on the thermoelectric (TE) properties of 3,4,9,10-Perylenetetracarboxylic dianhydride (PTCDA) and a conducting polymer Poly(ethylenedioxythiopene): poly(styrenesulfonate) (PEDOT:PSS)–PH1000 are presented. PTCDA and PEDOT:PSS have been used as a potential n-type material and a p-type material for the TE device, respectively. The Seebeck coefficients, open circuit voltage and the output power have been obtained for the fabricated TE device. The Seebeck effect was observed on this TE device where the output power in the range of 1 nW/cm2 to 5 nW/cm2,was successfully deduced from this TE device. It was found that the association of PEDOT:PSS and PTCDA have been acting well in this TE device. However, a higher TE performance, in the future could be developed, by applying a thermal treatment and introducing a suitable dopant to this n-type material which may increase the mobility of the electrons and the Seebeck coefficient.

Abstract: Half-heusler TiCoSb1-xSnx (0.00≤x≤0.05) alloys were prepared by mechanical alloying of elemental powders, and consolidated by vacuum hot pressing. Sn doped half-Heusler phases of TiCoSb was successfully produced in all doping ranges by vacuum hot pressing using as-milled powders without subsequent annealing. However, a little fraction of CoSb phase appeared after hot pressing. Thermoelectric properties as functions of temperature were evaluated for hot pressed specimens. Seebeck coefficients showed to change in conductivity by doping and the absolute value revealed relatively low. It is shown that electrical conductivity is relatively high and thermal conductivities are compatibly low. Sb doping up to x=0.02 in TiCoSb1-xSnx was shown to be effective on thermoelectric properties in this study.

Abstract: The Nd-doped SrO(SrTiO₃)_n (n=1,2) bulk samples were prepared by combining a sol-gel method and spark plasma sintering (SPS). The microstructures of the precursor powders were characterized by X-ray powder diffraction (XRD) and scanning electron microscope (SEM), thermogravimetric (TG) and differential scanning calorimetry (DSC). The oxides of (Sr_1-xNd_x)_n+1Ti_nO_3n+1(n=1,2;x=0.05, 0.1) were prepared by solid-state reaction of the precursor powders with post-spark plasma sintering for the first time and the thermoelectric properties showed that electrical resistivity ρ and the absolute values |S| of Seebeck coefficient increased with temperature and depended on the dopant concentration, indicating a n-type degenerate semiconductor behavior. Compared with the total thermal conductivity κ (4.1-5.2 Wm^-1K^-1) at room temperature, the estimated electronic thermal conductivity κ_e (0.2-0.7 Wm^-1K^-1) were very small, indicating that lattice contribution was predominant in the RP phase compounds. The largest dimensionless figure of merit ZT, 0.13 at 905K, was obtained the 10 at.% Nd-doped Sr₃Ti₂O_7. This synthetic method provides a simple way to prepare thermoelectric oxides.

Abstract: The efficiency of a thermoelectric device depends on material properties through the figure of merit, Z = σS²/κ, where σ, S, and κ are electrical conductivity, Seebeck coefficient, and thermal conductivity, respectively. To maximize the thermoelectric figure of merit of a material, high electrical conductivity, high Seebeck coefficient, and low thermal conductivity are required. This work has focused on the synthesis of a mesoporous titania films for its application in thermoelectric generation. The mesoporous titania film was synthesized with titanium tetraisopropoxide. The triblock copolymer, Pluronic P-123 (EO₂₀ PO ₇₀EO ₂₀) was used as surfactant in 1-propanol. As a result, an improvement of electrical conductivity and reduced annealing with a lowering of thermal conductivity by distributions of pores were found to be effective to enhance the thermoelectric property.

Abstract: Thermoelectricity has gained special interest due to its potential applications, especially the advancements in the electronic devices with very low power consumption. Thermoelectric materials can be used to make energy conversion devices that generate power from thermal sources. Multiferroic oxides, in particular cobaltates, have been actively studied as a new type of thermoelectric material (1). The crystal structure of these cobaltates offers a possibility to manipulate Seebeck coefficient, electric conductivity, and thermal conductivity to optimize the figure of merit ZT. The theoretical explanation and experimental observations by some investigators proved the candidature of multiferroic materials for thermoelectric generation. Many semiconducting multiferroic oxides are showing spin dependent Seebeck coefficient (2-3). Moreover, most of these oxides are inherently stable at high temperatures in air, making them a suitable material for high temperature applications. In this work we have investigated the multiferroic and thermoelectric properties of thinfilms of doped cobalt oxide matrices. The observations confirmed that these materials are suitable for thermoelectric generation.