Garnet-like Li7-xLa3Zr2-xNbxO12 (x = 0−0.7) solid state electrolytes enhanced by self-consolidation strategy

Garnet-like Li₇La₃Zr₂O₁₂ electrolytes with Nb doping are synthesized by self-consolidation method. Different from conventional methods such as cold or hot isostatic pressing, not any pressing assistance is employed throughout the preparation process. Although the preparation process is dramatically simplified, both density and ionic conductivity of the obtained samples are enhanced. Nb-doped content plays a key role in the sintering of the packed precursor powders and in the structure stabilization of the obtained bulk samples. The optimized 0.60?mol Nb-doped sample with relative density of 94%, fine particle boundaries, and solitary cubic structure possesses the maximum total ionic conductivity of 5.22?×?10^?4?S?cm^?1 at 30?°C, which is comparable to the highest reported value of the samples prepared by conventional pressing methods. This work verifies that self-consolidation strategy is effective, reliable, and productive for the preparation of cubic Li₇La₃Zr₂O₁₂ electrolyte, which would significantly facilitate the development of ceramic electrolyte membrane technology.     

铁氧化物在流化床温度和CO气氛下的形态迁移及其对NO催化还原

利用小型固定床实验台实验研究了铁氧化物在典型流化床温度和CO还原性气氛下的形态迁移及其生成物对NO的催化还原作用，采用分级还原结合X射线衍射（XRD）表征分析，确定铁氧化物与CO和NO反应后生成物的价态及各种铁氧化物对NO的还原机制。结果表明，Fe₂O₃在实验条件下可依次被CO还原为Fe₃O₄、FeO和单质铁，反应过程中随着还原度的增加，还原速率逐级下降，从Fe₂O₃还原到Fe₃O₄的速率最高，FeO还原到Fe速率最低，在实验温度范围内，床温升高有利于提高Fe₂O₃到Fe₃O₄的还原速率和还原度。不同形态的铁氧化物对NO的催化还原特性不同，Fe₂O₃及其部分还原后生成的Fe₃O₄都不能直接与NO反应，Fe₂O₃对CO催化还原NO的效果很弱，而Fe₃O₄对CO还原NO的反应却有很强的催化作用，而进一步还原生成FeO与单质铁还可直接与NO反应。     

Large eddy simulation of a 660 MW utility boiler under variable load conditions

Large eddy simulation (LES) has become a promising tool for pulverized coal combustion with the development of computational fluid dynamics (CFD) technologies in recent years. LES can better capture the unsteady features and turbulent structures of coal jet flame than Reynolds averaged Navier Stokes (RANS). The coal-fired power plants in China are now required to be operated in a wide load range and quickly respond to the electric grid. The boiler performance of variable loads should be evaluated in terms of flow, heat transfer, and combustion processes. In this paper, LES was applied to simulate a 660 MW ultra-supercritical boiler under BMCR (boiler maximum continue rate), 75%THA-100, and 50%THA-100 conditions. The predicted gas velocities agree well with the thermal calculation and the temperature error is less than 130 K. The simulation results show that the operation load has significant effects on the boiler performance. It is also proved that LES can provide guidance for the design and operation of advanced coal-fired boilers.     

An engineering method for complex structural optimization involving both size and topology design variables

This work presents an engineering method for optimizing structures made of bars, beams, plates, or a combination of those components. Corresponding problems involve both continuous (size) and discrete (topology) variables. Using a branched multipoint approximate function, which involves such mixed variables, a series of sequential approximate problems are constructed to make the primal problem explicit. To solve the approximate problems, genetic algorithm (GA) is utilized to optimize discrete variables, and when calculating individual fitness values in GA, a second-level approximate problem only involving retained continuous variables is built to optimize continuous variables. The solution to the second-level approximate problem can be easily obtained with dual methods. Structural analyses are only needed before improving the branched approximate functions in the iteration cycles. The method aims at optimal design of discrete structures consisting of bars, beams, plates, or other components. Numerical examples are given to illustrate its effectiveness, including frame topology optimization, layout optimization of stiffeners modeled with beams or shells, concurrent layout optimization of beam and shell components, and an application in a microsatellite structure. Optimization results show that the number of structural analyses is dramatically decreased when compared with pure GA while even comparable to pure sizing optimization.     

基于连续介质损伤力学的7075铝合金高温成形极限理论预测与数值仿真

开展7075铝合金高温单向拉伸试验和成形极限试验，获得了不同温度和应变率的应力-应变曲线和成形极限曲线。结果表明，在较高的温度和应变率时7075铝合金的强度减小、成形性提高。为描述7075铝合金高温损伤演化过程，提出一种改进的连续介质损伤模型，并建立了耦合损伤的多轴统一黏塑性本构模型。基于试验结果，运用NSGAII遗传算法标定了模型中的参数，标定后的本构模型可以很好地预测7075铝合金的高温热力行为和极限应变。通过有限元软件Abaqus的用户材料子程序VUMAT，该本构模型被编入到Abaqus软件中进行数值仿真计算。结果表明，仿真获得的成形极限曲线和应变场分布与试验和理论结果吻合度好，进一步证明了所建立的耦合损伤的多轴本构模型的正确性及其在高温成形极限有限元仿真中的适用性。     

A decoupled method to identify affecting mechanism of crosswind on performance of a natural draft dry cooling tower

The natural draft dry cooling tower (NDDCT) has been increasingly used for cooling in power generation in arid area. As crosswind affects the performance of a NDDCT in a complicated way, and the basic affecting mechanism is unclear, attempts have been made to improve the performance of a NDDCT based on limited experiences. This paper introduces a decoupled method to study the complicated crosswind effects on the inlet and outlet of a NDDCT separately by computational fluid dynamics (CFD) modeling and hot state experiments. Accordingly, the basic affecting mechanism of crosswind on the NDDCT performance is identified. Crosswind changes the inlet flow field of a NDDCT and induces mainstream vortices inside the tower, so as to degrade the ventilation. Besides, low crosswind deflects the upward plume at the outlet to further degrade the ventilation, while high crosswind induces the low pressure area at the outlet to reduce the ventilation degradation.     

Simultaneous improvement of thermal conductivity and mechanical properties for mechanically mixed ABS/h-BN composites by using small amounts of hyperbranched polymer additives

Recently, thermal interface materials (TIMs) are in great demands for modern electronics. For mechanically mixed polymer composite TIMs, the thermal conductivity and the mechanical properties are generally lower than expected values due to the sharply increased viscosity and poor filler dispersion. This work shows that addition of a small amount of polyester-based hyperbranched polymer (HBP) avoided the trade-off in mechanically mixed ABS/hexagonal boron nitride (h-BN) composites. After adding 0.5 wt% HBP, the maximum h-BN content in the composites increased from 50 to 60 wt%. The out-of-plane, in-plane thermal conductivity, and tensile strength of ABS/h-BN with 50 wt% h-BN were 0.408, 0.517 W/mK, and 18 MPa, respectively, and were increased to 0.729, 0.847 W/mK, and 32 MPa by adding 0.5 wt% HBP, while 0.972, 1.12 W/mK, and 29.5 MPa were achieved for ABS/h-BN/HBP with 60 wt% h-BN. The morphological and rheological results proved that these enhancements are due to the improved h-BN dispersion by decreasing viscosity of composites during mixing. Theoretical modeling based on the modified effective medium theory confirmed such results and showed that the interfacial thermal resistance also decreased slightly. Thus, this work demonstrates a facile and scalable method for simultaneously improving the thermal conductivity and mechanical properties of thermoplastic-based TIMs.     

胡海陶瓷艺术作品选登

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