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991.
Jinghuai Zhang Zhe Leng Shujuan Liu Milin Zhang Jian Meng Ruizhi Wu 《Journal of Alloys and Compounds》2011,509(20):L187-L193
Mg–3.4 wt.% Al-based alloy modified with 2.4 wt.% Ce-rich and 0.3 wt.% Y-rich misch metals was prepared by high-pressure die-casting. The microstructure, thermal stability of intermetallic phases and mechanical properties were investigated. The cross-section of test bar is divided into the fine skin region and the wide core region by a narrow band. Two intermetallic phases Al11RE3 and Al2RE, with the former being the dominant one, are mainly distributed at the interdendritic regions. The Al11RE3 intermetallics possess high volume fraction, fine acicular/lamellar morphology and layered arrangement. It is suggests that each rare earth element has the individual preference for the above two Al–RE intermetallics. The thermal stability of Al11RE3 is conditioned. It is basically stable at temperature up to 200 °C within 800 h, while almost all Al11RE3 intermetallics transform to Al2RE at higher temperature of 450 °C for 800 h. The alloy exhibits remarkably improved tensile and compressive yield strengths at room temperature and 200 °C and they are the results of the reinforcement of dendrite boundaries with Al11RE3 intermetallics, the fine dendritic arm spacing effect as well as the solid solution strengthening with various rare earth elements. 相似文献
992.
The short operating life of metallic diaphragm caused by fracture is one of the main disadvantages for diaphragm compressors used in hydrogen fueling stations. A new generatrix for cavity profile is proposed through optimization using the complex method to decrease the maximal radial stresses on both oil and gas sides of the diaphragm clinging to the cavity surface. In the optimization, the convex part of the cavity generatrix is subjected to a constraint that the generatrix has a lower slope than the deformed diaphragm under a uniform pressure load. This constraint aims to avoid cavity dead volume at the end of the gas discharge process. Thus, an analytical solution for the deflection of an edge-clamped metallic diaphragm under a uniform pressure load is firstly developed. The solution employs the principle of minimum energy and the Rayleigh-Ritz method, which based on the theory of thin plates with large deflections. Experimental measurements, as well as the finite elements method (FEM), are employed to validate the solution. The analytical results are found to be in good agreement with the results of measurements and FEM simulations. Secondly, the stress of the diaphragm with a specific deflection is calculated, and the radial stress concerning both gas side and oil side of the diaphragm is taken as the objective function. Finally, a new generatrix is obtained through the optimization. The radial stress of the diaphragm clinging to the new cavity profile is validated via the FEM simulation, and results match well with each other. It also approves that the cavity dead volume is eliminated by the new generatrix at the end of the gas discharge process. Moreover, the maximal and the centric radial stress of the working diaphragm were compared between the new generatrix and the traditional generatrix under the same design parameters, the maximal and the centric radial stress of the diaphragm decreased by 8.2% and 13.9%, respectively. Based on the proposed design method, effects of the cavity volume, cavity radius, diaphragm thickness and diaphragm material properties on the maximal radial stress of the working diaphragm are further discussed. 相似文献
993.
This paper studies the influence of a High-Porosity Mesh (HPM) stent on the hemodynamic characteristics in the intracranial aneurysm based on the Computational Fluid Dynamics (CFD). An idealized basilar tip aneurysm model and a HPM stent model are built. The pulsating blood flow in a cardiac cycle is computationally simulated for non-stented and stented models, to provide a wealth of information of the spatio-temporally varying blood flow field. The influence of the stent placement on the hemodynamic characteristics is analyzed in terms of distributions of velocity, pressure, Wall Shear Stress (WSS) and Energy Loss (EL), which are believed to play an important role in the development and rupture of the aneurysm. The numerical results clearly show that the velocity, pressure, WSS and EL of the blood flow in the aneurysm are reduced by 30%-40% when the HPM stent is implanted. These computational results may provide valuable hemodynamic information for clinical neurosurgeon. 相似文献
994.
Amphiphilic diblock copolymers of polystyrene-b-poly(methacrylic acid) were synthesized by means of atom transfer radical polymerization. First, the polystyrene with a bromine atom at the chain end (PS-Br) was prepared using styrene as the monomer, 1-bromoethyl benzene as the initiator, and CuCl/2,2′-bipyridyl (bpy) as the catalyst ([1-bromoethyl benzene]/[CuCl]/[bpy] = 1:1:3). The polymerization was well controlled. Second, the diblock copolymer of polystyrene-b-poly(tert-butyl methacrylate) was synthesized also by atom transfer radical polymerization using PS-Br as the macro-initiator, CuCl/bpy as the catalyst, and tert-butyl methacrylate (tBMA) as the monomer. Finally, the amphiphilic diblock copolymer, PS-b-PMAA, was obtained by hydrolysis of PS-b-PtBMA under the acid condition. The molecular weight and the structure of aforementioned copolymers were characterized with gel permeation chromatography, infrared, and nuclear magnetic resonance. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2381–2386, 2001 相似文献
995.
以栅元为模块进行特征线跟踪的中子输运方程解法 总被引:3,自引:1,他引:2
为解决复杂几何条件下中子输运方程的求解问题,分析了特征线法理论模型,探讨了以栅元为模块的高效特征线产生方法,以及与之相关的空间角度离散和边界条件处理问题.采用自行研制的特征线法数值计算软件--PEACH,对经济合作组织核能机构(OECD/NEA)UO2和MOX燃料混合装载的7群(C5G7MOX)基准问题的数值进行了检验.结果表明,无论是计算Keff还是棒功率分布该方法都具有很高的精度. 相似文献
996.
《Journal of food engineering》2009,90(4):390-398
Because of its fast and volumetric nature, radio frequency (RF) heating has been looked upon as a way to overcome the problems associated with conventional heating methods used for disinfestation of fruits. But non-uniform heating within fruits is a major obstacle in adaptation of this technology. In this study, RF heating patterns influenced by dielectric properties (DPs) of fruits were investigated both experimentally and mathematically. A computer simulation model was developed using FEMLAB 3.4, a commercial software for solving Maxwell’s electromagnetic and Fourier’s heat transfer equations. Orange, apple, grapefruit, peach, and avocado fruits, selected for these studies were subjected to RF heating in a water filled container equipped with a mechanism to keep fruits rotating and moving during RF heating in a 27.12 MHz, 12 kW parallel plate RF unit. DPs of constitutional parts of the selected fruits were measured by open-ended coaxial probe method. The study showed that dissimilarity in peel and pulp DPs greatly influenced the RF heating behavior of the fruits. Core heating was prominent in apple, peeled orange and grapefruit; whereas subsurface/peripheral heating in whole oranges and grapefruit, and avocado. The computer model was an effective tool in characterizing and explaining the heating patterns in the fruits based on DPs. The study helped in better understanding the complex RF heating characteristics of fruits, which may be useful in assessing the design feasibility of product specific RF energy based treatment protocol. 相似文献
997.
Yongchang Feng Liangxing Li Feilong Zhan 《Numerical Heat Transfer, Part A: Applications》2013,63(11):1263-1279
ABSTRACTA numerical study is presented for two-dimensional convection melting of solid gallium in a rectangular cavity. The bottom wall of the cavity is uniformly heated and a uniform magnetic field is applied separately in both horizontal and vertical directions. The lattice Boltzmann (LB) method considering the magnetic field force is employed to solve the governing equations. The effects of magnetic field on flow and heat transfer during melting are presented and discussed at Rayleigh number Ra = 1 × 105 and Hartmann number Ha = 0, 15, and 30. The results show that the magnetic field with an inclination angle has a significant impact on the flow and heat transfer in the melting process. For a small Hartmann number, similar melting characteristics are observed for both horizontally applied and vertically applied magnetic fields. For a high value of Hartmann number, it is found that in the earlier stage of melting process, the flow retardation effect caused by the horizontally applied magnetic field is less obvious than that caused by the vertically applied magnetic field. However, the opposite is true in the later stage. 相似文献
998.
The effects of residual strain and grain boundary character distribution on sensitisation of type 304 stainless steel at 525 °C were evaluated using electrochemical potentiokinetic reactivation (EPR) technique. The results indicated that a very low level of residual strain and a high fraction of annealing twins significantly improved the resistance to sensitisation. Image analysis indicated that the fraction of area attacked during the EPR test correlated well with the EPR data. The volume loss, calculated using atomic force microscopic examinations, during the EPR tests also correlated well with the EPR results. 相似文献
999.
1000.
Simulation-based life cycle assessment of energy efficiency of biomass-based ethanol fuel from different feedstocks in China 总被引:2,自引:0,他引:2
Interests in biomass-based fuel ethanol (BFE) have been re-boosted due to oil shortage and environmental deterioration. Biomass-based fuel ethanol is renewable and, apparently, environmentally friendly. Biomass-based E10 (a blend of 10% ethanol and 90% gasoline by volume) is a promising conventional gasoline substitute, because vehicle engines require no modifications to run on E10 and vehicle warranties are unaffected. This paper presented life cycle assessments (LCAs) of energy efficiency of wheat-based E10 from central China, corn-based E10 from northeast China, and cassava-based E10 from southwest China. The respective energy flow-based evaluation model of wheat-, corn-, and cassava-based E10 was built based on data from pilot BFE plants. Monte Carlo method is applied to deal with the uncertain parameters and input and output variables of the evaluation model because of its wide application and easy development of statistical dispersion of calculated quantities. According to the assessment results, the average energy input/output ratio of wheat-based fuel ethanol (WFE), corn-based fuel ethanol (CFE), and cassava-based fuel ethanol (KFE) is 0.70, 0.75, and 0.54, respectively, and biomass-based E10 vehicle can have less fossil energy demand than gasoline-fueled ones. 相似文献