Double-perovskites YBaCo2−xFexO5+δ cathodes for intermediate-temperature solid oxide fuel cells

Double-perovskites YBaCo_2−xFe_xO_5+δ (YBCF, x = 0.0, 0.2, 0.4 and 0.6) are synthesized with a solid-state reaction and are assessed as potential cathode materials for utilization in intermediate-temperature solid oxide fuel cells (IT-SOFCs) on the La_0.9Sr_0.1Ga_0.8Mg_0.115Co_0.085O_2.85 (LSGMC) electrolyte. The YBCF materials exhibit chemical compatibility with the LSGMC electrolyte up to a temperature of 950 °C. The conductivity of the YBCF samples decreases with increasing Fe content, and the maximum conductivity of YBCF is 315 S cm⁻¹ at 325 °C for the x = 0.0 sample. A semiconductor-metal transition is observed at about 300-400 °C. The thermal expansion coefficient of the YBCF samples increases from 16.3 to 18.0 × 10⁻⁶ K⁻¹ in air at temperatures between 30 and 900 °C with increase in Fe content. The area-specific resistances of YBCF cathodes at x = 0.0, 0.2 and 0.4 on the LSGMC electrolyte are 0.11, 0.13 and 0.15 Ω cm² at a temperature of 700 °C, respectively. The maximum power densities of the single cells fabricated with the LSGMC electrolyte, Ce_0.8Sm_0.2O_1.9 (SDC) interlayer, NiO/SDC anode and YBCF cathodes at x = 0.0, 0.2 and 0.4 reach 873, 768 and 706 mW cm⁻², respectively. This study suggests that the double-perovskites YBCF (0 ≤ x ≤ 0.4) can be potential candidates for utilization as IT-SOFC cathodes.     

太阳能富集地区住宅建筑非平衡保温研究——拉萨市供暖期太阳辐射分析与室内热环境测试

在有供暖需求的太阳能资源富集地区,由于太阳辐射强烈,住宅建筑各个朝向外墙,尤其是南北向的外墙所接收的太阳辐射量差异很大,为了更有效地利用太阳能并降低保温成本,这种差异应表现在建筑围护结构保温性能的设计中.本文通过对拉萨市标准年气象数据库的分析得到了其住宅建筑各朝向外墙供暖季内获得的太阳辐射量.与内地城市相比,拉萨市太阳能资源丰富且朝向差异很大,非平衡保温具有一定的实际意义.另外,冬季现场测试表明无供暖建筑的南北朝向房间热环境有所不同,南向房间测试周期内基本处于人体舒适范围内,而北向房间始终偏冷,远离人体热舒适区域,有供暖需求.     

Thermal management of a proton exchange membrane fuel cell stack with pyrolytic graphite sheets and fans combined

This work characterizes the thermal management of a proton exchange membrane fuel cell (PEMFC) stack with combined passive and active cooling. A 10-cell PEMFC stack with an active area of 100 cm² for each cell is constructed. Six thermally conductive 0.1-mm-thick Pyrolytic Graphite Sheets (PGSs) are cut into the shape of flow channels and bound to the six central cathode gas channel plates. These PGSs, which are lightweight and have high thermal conductivity, function as heat spreaders and fins and provide passive cooling in the fuel cell stack, along with two small fans for forced convection. Three other cooling configurations with differently sized fans are also tested for comparisons (without PGSs). Although the maximum power generated by the stack with the configuration combining PGSs and fans was 183 W, not the highest among all configurations, it significantly reduced the volume, weight, and cooling power of the thermal management system. Net power, specific power, volumetric power density, and back work ratio of this novel thermal management method are 179 W, 18.54 W kg⁻¹, 38.9 kW m⁻³, and 2.1%, respectively, which are superior to those of the other three cooling configurations with fans.     

Influence of temperature on the fatigue strength of compressed-hydrogen tanks for vehicles

The influence of environmental temperatures on the fatigue strength of compressed-hydrogen tanks for vehicles was investigated. The fatigue strength of Type-3 tanks was found to decrease in a low-temperature environment and increase in a high-temperature environment. The Type-3 tank has been subjected to autofrettage to improve fatigue strength. The investigation clarified that the effect of autofrettage changes according to the environmental temperature due to the difference between the coefficients of thermal expansion of carbon fiber reinforced plastic and aluminum alloy. This causes fatigue strength to change with changes in temperature. The Type-4 tank has a very long fatigue life and did not break after 45,000 cycles in a room-temperature or low-temperature environment. In a high-temperature environment, however, the tank broke in fewer than 45,000 cycles. The fatigue of carbon fiber reinforced plastic was promoted in the high-temperature environment, resulting in breakage of the tank. These results indicate that the fatigue strength of the tanks is influenced by the environmental temperature.     

Using SVM based method for equipment fault detection in a thermal power plant

Due to the growing demand on electricity, how to improve the efficiency of equipment in a thermal power plant has become one of the critical issues. Reports indicate that efficiency and availability are heavily dependant upon high reliability and maintainability. Recently, the concept of e-maintenance has been introduced to reduce the cost of maintenance. In e-maintenance systems, the intelligent fault detection system plays a crucial role for identifying failures. Data mining techniques are at the core of such intelligent systems and can greatly influence their performance. Applying these techniques to fault detection makes it possible to shorten shutdown maintenance and thus increase the capacity utilization rates of equipment. Therefore, this work proposes a support vector machines (SVM) based model which integrates a dimension reduction scheme to analyze the failures of turbines in thermal power facilities. Finally, a real case from a thermal power plant is provided to evaluate the effectiveness of the proposed SVM based model. Experimental results show that SVM outperforms linear discriminant analysis (LDA) and back-propagation neural networks (BPN) in classification performance.     

服装标识对人体舒适性的影响因素分析

通过对服装标识及其引起人体不适性的现状进行概述和分析,进而对服装标识影响人体舒适性的相关因素分物理和化学两个方面进行分析和探讨,并推出服装标识影响人体舒适性因素的相关函数关系组,期望对服装标识不适性问题的解决提供理论参考.     

Micro-scale energy dissipation mechanisms during dynamic fracture in natural polyphase ceramic blocks

The dynamic fracture of natural polyphase ceramic (granite) blocks by high-speed impact at 207 m/s, 420 m/s and 537 m/s has been investigated. An electromagnetic railgun was used as the launch system. Results reveal that the number of fragments increases substantially, and the dominant length scale in their probability distributions decreases, as the impact energy is increased. Micro-scale studies of the fracture surfaces reveals evidence of localized temperatures in excess of 2000 K brought on by frictional melting via fracturing and slip along grain boundaries in orthoclase and plagioclase, and via transgranular fracture (micro-cracking) in quartz. The formation of SiO₂- and TiO₂-rich spheroids on fracture surfaces indicates that temperatures in excess of 3500 K are reached during fracture.     

Fabrication and performance evaluation of electrolyte-combined α-LiAlO2 matrices for molten carbonate fuel cells

To improve the unit cell performance and stability, molten carbonate fuel cell (MCFC) matrices were fabricated using synthetic α-LiAlO₂ powder and they showed mechanical and microstructural stability under thermal cycle tests. The pure α-LiAlO₂ matrix demonstrated stability with high open-circuit voltage (OCV) and maximum power density during many thermal cycle tests (more than 15 repetitions). Furthermore, to minimize the change in stack height during stack start-up and to improve mechanical and microstructural stabilities of the matrix, the electrolyte-combined α-LiAlO₂ matrix was optimized by controlling the mixing ratio of synthetic α-LiAlO₂ and Li/K carbonate powders. The suitable electrolyte content was fixed at approximately 50 vol.% for the homogeneously filled pores of the pure α-LiAlO₂ matrix. These matrices showed good microstructural stability during five thermal cycle tests in an air atmosphere at 923 K and with improved unit cell performance (0.127 W cm⁻²) under MCFC operating conditions.In unit cell and thermal cycling tests, the optimized matrices were stable through more than 20 repetitions.     

Thermal diffusion in the modified Frazier schemes with column heights varied at a constant increment for improved performance

The effects of column number and column-height increment on the degree of separation in the modified Frazier scheme of thermal diffusion columns with the total sum of column heights fixed, has been investigated. The equations, which may be employed to predict the optimal column number and the optimal column-height increment for the maximum separation, have been derived. Considerable improvement in performance is obtainable if the column number and column-height increment in a modified Frazier scheme with the total sum of column heights fixed, are properly assigned under a certain flow-rate operation, instead of using the conventional Frazier scheme of constant column height with the same total sum of column heights.     

DISCUSSION ON: A Fundamental Study of Synthetic Sapphire as a Bearing Material

Thermal reactive diffusion (TRD) coating on a DIN 1.2367 die steel substrate was performed in a powder mixture consisting of ferrovanadium, ferrochromium, ammonium chloride, alumina, and naphthalene at temperatures of 1000, 1050, and 1100°C for 2–4 h. The carbide layers were characterized using the microstructure, microhardness, X-ray diffraction, and chemical analysis. Wear scars were analyzed on scanning electron microscopy (SEM) micrographs with an energy-dispersive X-ray spectroscopy module. Depending on the coating process time and temperature, the thicknesses of the vanadium carbide and the chromium carbide layers formed on the substrate were obtained in a range from 7 to 30 μm and 5 to 17 μm, respectively. The maximum hardness values of vanadium carbide and chromium carbide layers were measured as 2537 and 1973 HV, respectively. The test samples coated using the TRD method were analyzed with regard to abrasive wear behavior using three different loads (1, 2, and 3 N) and speeds of 40, 80, and 160 rpm in fixed-ball micro-abrasion tests. Depending on the load and speed values applied, the grooving and rolling mechanisms were found to be predominant abrasion mechanisms on the worn surfaces.