Thermoelectric Properties of Combustion-Synthesized Lanthanum-Doped Strontium Titanate

The possibility of combustion synthesis of perovskite-oxide thermoelectric materials with the attendant saving of energy and time and without deterioration in the thermoelectric properties was investigated by evaluating the thermoelectric properties of lanthanum-doped strontium titanate (Sr 1Àx La x TiO 3 , 0 x 0:1). The materials were successfully combustion synthesized and spark plasma sintered with 98.0-99.6% of true density, and their thermoelectric properties were evaluated from room temperature to 850 K. The optimal lanthanum doping amount ratio x in the considered temperature range was from 0.06 to 0.08, in which Sr 0:92 La 0:08 TiO 3 sample showed the maximum ZT of 0.22 at 800 K. This value was close to the highest recorded ZT at the same temperature up to now, and the ZT of most samples are higher than those synthesized by the conventional solid state reaction method. Thus, combustion synthesis is promising for producing perovskite-oxide thermoelectric materials for high-temperature application

Technology of Latent Heat Storage for High Temperature Application : A Review

To save energy and reduce CO2 emissions, the utilization of solar energy and waste heat using latent heat storage (LHS) has emerged as an attractive solution because of advantages such as large density of heat storage, constant-temperature heat supply, and repeatable utilization without degradation. This review describes research trends in LHS technologies using phase-change materials (PCMs) based on papers published from 2001–2009, and state-of-the-art LHS technologies for high-temperature applications over 100°C, such as solid–solid PCM, encapsulation of PCMs, PCM composites, solar power generation with LHS, and waste heat recovery systems

A large thermoelectric figure of merit of La-doped SrTiO3 prepared by combustion synthesis with post-spark plasma sintering

We investigated figure of merit of La-doped SrTiO3 prepared by combustion synthesis (CS) with post Spark Plasma Sintering (SPS), on which effect of sintering time was mainly examined. The samples of Sr0.92La0.08TiO3, CSed from oxides, carbonates, metal and sodium perchlorate, was prepared by SPS at 1573 K for 1, 5, 15 and 30 min to measuring thermoelectric properties from RT to 1173 K. In conclusion, only 5-min-sintered product recorded a maximum value of 0.37 in figure of merit at 1045 K

Combustion synthesis of doped LaGaO3 perovskite oxide with Fe

La0.7Sr0.3Ga0.7Mg0.1Fe0.2O3-δ (LSGMF73712) has been proposed as a new substitute for solid electrolyte in SOFC (solid oxide fuel cells). It has several merits, such as lower operating temperature of SOFC, high transport number of oxide ion and higher electronic conductivity. In this study, the doped-lanthanum gallium with Fe was produced by combustion synthesis, and the effect of particle sizes on sintering behaviors of La(Sr)Ga(Mg)FeO3-δ samples by spark plasma sintering (SPS) was analyzed by comparing with the traditional solid-state reaction method. In the experiments of the combustion synthesis, lanthanum oxide, strontium carbonate, metallic gallium, pure iron, metallic magnesium and sodium perchlorate were mixed uniformly and were ignited at one end of the sample under the argon atmosphere to complete the combustion process without any additional energy. Not only could this method shorten the processing time, but also it could minimize the sintering temperature in the production. As a result, the product showed definite peaks of lanthanum galliumin X-ray diffraction (XRD) patterns and the product could be sintered at a lower temperature 1473 K by SPS method, in comparison to a conventional solid-state reaction method. Moreover, the sintering temperature of the products could further decrease in a lower temperature 1273K after ball-mill treatment

Thermoelectric Properties of Combustion-Synthesized Lanthanum-Doped Strontium Titanate

The possibility of combustion synthesis of perovskite-oxide thermoelectric materials with the attendant saving of energy and time and without deterioration in the thermoelectric properties was investigated by evaluating the thermoelectric properties of lanthanum-doped strontium titanate (Sr1−xLaxTiO3, 0≤x≤0.1). The materials were successfully combustion synthesized and spark plasma sintered with 98.0–99.6% of true density, and their thermoelectric properties were evaluated from room temperature to 850 K. The optimal lanthanum doping amount ratio x in the considered temperature range was from 0.06 to 0.08, in which Sr0.92La0.08TiO3 sample showed the maximum ZT of 0.22 at 800 K. This value was close to the highest recorded ZT at the same temperature up to now, and the ZT of most samples are higher than those synthesized by the conventional solid state reaction method. Thus, combustion synthesis is promising for producing perovskite-oxide thermoelectric materials for high-temperature application

Feasibility of an Advanced Waste Heat Transportation System Using High-temperature Phase Change Material (PCM)

A waste-heat transportation (HT) system whose operation depends on the latent heat (LH) of high-temperature phase change material (PCM) is effective in reducing carbon dioxide (CO2) emission from industries. This paper describes 1) the use of the binary eutectic mixture NaOH/Na2CO3 as a PCM to realize the HT system, 2) the feasibility of HT system using this PCM from viewpoints of energy requirements, exergy loss, and CO2 emissions. In this study, we examined the thermophysical properties of the PCM and its chemical stability with reference to the heat transfer medium of the HT system by differential scanning calorimetry and thermogravimetry-differential thermal analysis. We observed that NaOH/Na2CO3 had a LH of fusion of 252 kJ/kg and a melting point (MP) and a freezing point (FP) of 285±1°C that was suitable for the HT system. There were no significant changes in the chemical and physical properties after aging for 500 h during phase change when dibenzyltoluene was used as the heat transfer medium. On the contrary, in the system analysis, the operating data in the proposed system—as well as in a conventional heat supply system—were calculated based on heat and material balances. The results show it has only 9.5% of the energy requirements, 39.7% of the exergy loss, and 19.6% of the CO2 emissions of conventional systems that lack heat-recovery capabilities

Thermoelectric Properties of Combustion Synthesized and Spark Plasma Sintered Sr1-xRxTiO3 (R = Y, La, Sm, Gd, Dy, 0<x≤0.1)

Thermoelectric properties of combustion synthesized and spark plasma sintered rare-earth-doped (Y, La, Sm, Gd and Dy) SrTiO3 was investigated from room temperature to 870 K toward the viewpoint of energy and time saving without deterioration in thermoelectric properties. All the rare-earth-doped SrTiO3 were successfully synthesized and sintered with high purities and high densities. With temperature increasing, the absolute value of Seebeck coefficient increased and the electric conductivity decreased; the power factor of all the samples decreased except Y-doped sample in the experimental temperature range. In all the samples, the La-doped SrTiO3 and the Y-doped SrTiO3 had the highest and the lowest power factor, respectively. The dimensionless figure of merit ZT of La-doped samples with different doping amount was evaluated and the maximum ZT was 0.22, which was obtained at 800 K from Sr0.92La0.08TiO3 sample. Comparing Y and La-doped samples prepared by our method with that of conventional solid-state reaction method, the thermoelectric properties of our samples were relatively higher. Thus the combination of combustion synthesis and spark plasma sintering has a potential to prepare perovskite-oxide materials with relatively higher thermoelectric properties for high-temperature application

Improvement on Heat Release Performance of Direct-contact Heat Exchanger Using Phase Change Material for Recovery of Low Temperature Exhaust Heat

Latent heat storage using a phase change material (PCM) is a promising method for utilizing the exhaust heat from steelworks. The purpose of this study was to improve the heat release performance of a direct-contact heat exchanger using a PCM and heat transfer oil (HTO). Erythritol (with a melting point of 391 K), which is a kind of sugar alcohol, was selected as a PCM. A vertical stainless steel cylinder with an inner diameter of 200 mm and height of 1400 mm was used as the heat storage unit (HSU). A ring-shaped injector with 18 holes positioned vertically downward was placed at the bottom of the HSU. Each hole in this injector had a diameter of 2.5 mm. We investigated the effects of the height of the PCM in the HSU, the HTO flow rate, and an increase in the number of injection-nozzle holes on the temperature effectiveness and heat exchange rate as indices of the heat release performances. As results, we found that an increase in the number of nozzle holes accelerated the uniform distribution of the HTO in the liquid PCM, prevented the HTO drift flow and adverse solidification of the PCM, and improved the heat release performance under the condition of a high HTO flow rate

Design of Cascaded Oxide Thermoelectric Generator

This paper describes the design of two- and three-stage cascaded oxide thermoelectric generators (TEGs) for high-temperature heat recovery using reported data to optimize energy conversion efficiency. We used the general intermetallic compounds Bi2(Se,Te)3 and (Bi,Sb)2Te3 for the low-temperature stages and oxides of TiO1.1, La-doped SrTiO3, NaxCo2O4, and Al-doped ZnO for the higher-temperature stages. A two-stage TEG with TiO1.1 as the p-type material and La-doped SrTiO3 as the n-type material was found to have the highest efficiency at heat-source temperatures below 852 K, while the three-stage TEG was slightly more efficient than the two-stage TEG for heat-source temperatures above 852 K. For the three-stage TEG, the optimal boundary temperature of the second and third stages was calculated to be 698 K; at this temperature, the maximum energy conversion efficiency, 13.5%, was obtained at a heat-source temperature of 1223 K. The results showed that the designed two- and three-stage cascaded oxide TEGs have high potential for heat recovery from high-temperature waste

Thermoelectric Properties of Solution Combustion Synthesized Al-Doped ZnO

Thermoelectric properties of Al-doped ZnO prepared by solution combustion synthesis using urea as fuel and sintered by spark plasma sintering were investigated for developing an energy- and time-saving synthesis method to decrease its thermal conductivity without a significant deterioration in other thermoelectric properties. The desired materials were successfully synthesized and sintered. The thermoelectric properties of the synthesized products subjected to planetary ball milling (PBM) treatment before sintering were compared with those of synthesized products not subjected to PBM treatment; the results showed that the former products had a larger power factor and higher thermal conductivity than the latter products. The thermal conductivity of all as-synthesized products was in the range of 8.3–19.7 W·m−1·K−1 at room temperature, which was significantly lower than that of the products synthesized by a conventional solid-state reaction method. (Zn0.99Al0.01)O obtained by PBM had the highest dimensionless figure of merit ZT of 0.050 at 863 K. From these results, it is inferred that solution combustion synthesis is an effective method for synthesizing Al-doped ZnO with relatively low thermal conductivity for high-temperature thermoelectric applications