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[en] The mechanisms of fatigue life improvement by pre-twinning process in a commercial rolled magnesium (Mg) alloy have been investigated using real-time in situ neutron diffraction under a continuous-loading condition. It is found that by introducing the excess twinned grains through pre-compression along the rolling direction the fatigue life was enhanced approximately 50%, mainly resulting from the prolonged detwinning process and inhibited dislocation slip during reverse tension. Moreover, after pre-twinning, the reduction of the rapid strain hardening during reverse tension leads to a compressive mean stress value and more symmetric shape of stress–strain hysteresis loop. The pre-twinning has significant impacts on the twinning-detwinning characteristics and deformation modes during cyclic loading and greatly facilitates the twinning-detwinning activities in plastic deformation. The cyclic straining leads to the increase of contribution of tensile twinning deformation in overall plastic deformation in both the as-received and pre-twinned sample. The mechanisms of load partitioning in different groups of grains are closely related to the deformation modes in each deformation stage, while the fatigue cycling has little influence on the load sharing. The pre-twinning process provides an easy and cost-effective route to improve the low-cycle fatigue life through manufacturing and processing, which would advance the wide application of light-weight wrought Mg alloys as structural materials. - Highlights: • The low-cycle fatigue life of a rolled Mg alloy was improved 50% after pre-twinning. • The deformation mechanisms were investigated by in situ neutron diffraction. • Load partitioning in different grains under various deformation modes was examined. • Relationship between macroscopic behavior and microscopic response was established.
[en] We adapt the simulated annealing approach for reconstruction of the 3D microstructure of a LiCoO2 cathode from a commercial Li-ion battery. The real size distribution curve of LiCoO2 particles is applied to regulate the reconstruction process. By discretizing a 40 × 40 × 40 μm cathode volume with 8,000,000 numerical cubes, the cathode involving three individual phases: 1) LiCoO2 as active material, 2) pores or electrolyte, and 3) additives (polyvinylidene fluoride + carbon black) is reconstructed. The microstructural statistical properties required in the reconstruction process are extracted from 2D focused ion beam/scanning electron microscopy images or obtained by analyzing the powder mixture used to make the cathode. Characterization of the reconstructed cathode gives important structural and transport properties including the two-point correlation functions, volume-specific surface area between phases, tortuosity and geometrical connectivity of individual phase. - Highlights: • Simulated annealing approach is adapted for 3D reconstruction of LiCoO2 cathode. • Real size distribution of LiCoO2 particles is applied in reconstruction process. • Reconstructed cathode accords with real one at important statistical properties. • Effective electrode-characterization approaches have been established. • Extensive characterization gives important structural properties, say, tortuosity
[en] Highlights: • Two types of heat-integrated processes, SWP and SCWP, are presented. • From economic aspects, it is verified that SWP is superior to SCWP. • From aspects of energy utilization, it is verified that SCWP is superior to SWP. • From aspects of CO_2 capture, it is verified that SCWP is superior to SWP. - Abstract: The design of hydrogen production, purification, compression and carbon dioxide capture is developed as two types of heat-integrated processes. The SWP (SMR + WGS + PCC) is mainly composed of the steam methane reforming (SMR) reactor, the low temperature water–gas-shift (WGS) reactor and the process of hydrogen purification, compression and carbon dioxide capture (PCC), and the SCWP (SMR + CO2R + WGS + PCC) primarily consists of the SMR reactor, the carbon dioxide reforming of methane (CO2R) reactor, the WGS reactor and the PCC. From economic aspects, it is expectable that the SWP process is superior to the SCWP process due to lower energy demand and less equipment. From aspects of energy utilization and CO_2 capture, it is verified that the SCWP process is superior to the SWP process
[en] Highlights: • Two hybrid power plant configurations based on torrefied biomass co-gasification (TBCG) are evaluated. • The carbon boundary points (CBPs) are found using a specific optimization algorithm. • The pre-SOFC configuration is superior to the post-SOFC one in terms of the maximum net system efficiency. • With regard to global warming, the post-SOFC configuration has lower specific CO_2 emissions. • The energy penalty of the post-SOFC configuration can be reduced based on heat integration design. - Abstract: This study developed a clean hybrid power plant using a combination of integrated torrefied biomass co-gasification (TBCG), solid oxide fuel cell (SOFC), and calcium looping (CaL) CO_2 capture. Based on pre-SOFC (Design I) and post-SOFC (Design II) configurations, thermodynamic analysis is adopted to examine the performance of hybrid power generation plants. The carbon boundary points (CBPs) for different torrefied biomass blending ratios (TBBRs) are found using specific optimization algorithms to maximize the syngas yield. From the viewpoint of energy utilization, the simulation results show that Design I is superior to Design II. However, the CO_2 emissions of Design II are lower than those of Design I by 94.19%, although it has an accompanying energy penalty of 4.17%. Due to its use of the internal heat recovery approach, the energy penalty of Design II falls to 1.09%. As a whole, Design II with the heat integration design is recommended for use in hybrid power plants.
[en] The Mn-rich Ni50Mn25+xGa25-x (x=0-5) alloys were developed to investigate the structural transitions and magnetic properties. Structural transitions from austenite to 5M, 7M, and non-modulated martensite were observed with the increase of Mn content. The lattice parameter a elongates, as where b and c contract, and the unit cell volume reduces with increasing Mn content. The martensitic transformation start temperatures Ms increase monotonically from 10.7 deg. C for x=2 to 102.7 deg. C for x=5. The saturation magnetization was measured at 5 K, where all the samples exhibit a martensitic structure. The average magnetic moments per Mn atom vary from 4.38 μB to 2.93 μB for x=0 to x=5. The negative effect of excess Mn atoms changes from -3.00 μB for x=2 to -7.25 μB for x=5. The excess Mn atoms modify the electronic structures of the unsubstituted Mn atoms, resulting in the sharp decrease of the magnetic moments of the unsubstituted Mn atoms with increasing Mn content. Structural incommensurability was observed with 7M for powder and non-modulated for bulk samper in a specific range of compositions and proved to be reversible when performing martensitic transformation. The 7M and non-modulated martensites Ni50Mn30Ga20 possess similar saturation magnetizations and Curie temperatures. The non-modulated martensite was estimated to have a lower free energy than 7M, and should be more stable for a reverse martensitic transformation, leading to a higher austenite start temperature As, which is consistent with the experimental result
[en] Condensation heat of air-conditioner in household and public is a kind of indispensable waste heat, which is necessary to recover and reuse it. Herein, phase change material is widely used in exhaust heat recover and storage. In the present work, expanded graphite(EG) was introduced to stearic acid-acetamide(SA-AC) eutectic mixture, aiming at obtaining composite phase change material(CPCM) with high thermal conductivity, large heat storage capacity and favorable thermal repeatability for efficient heat recover. DSC results exhibited its remarkable energy storage capacity with a latent heat of CPCM of 186.8 J g−1 compared to most of the organic eutectic composite. The second law of thermodynamics was used to explain the phase change characteristics of the SA-AC/EG CPCMs corresponding to the pristine SA-AC eutectic mixture. The thermal conductivity of the CPCM was enhanced by 17.59 times comparing to pristine SA-AC. The results of thermal conductivity and infrared thermal images confirmed the CPCM possessed prominent heat storage efficiency. The thermo-physical properties of the SA-AC/EG CPCM after 500 accelerated thermal cycles were slightly decreased which did no distinct influence on heat storage. Due to the low cost and remarkable properties, the SA-AC/EG CPCM was a promising candidate for energy conservation by condensation heat recovery of air-conditioner. - Highlights: • SA-AC/EG CPCM was obtained with optimum mass ratio of 90 wt.% SA-AC eutectic mixture. • The intrinsic latent heat of SA-AC was enhanced due to the EG porous filler. • The thermal conductivity of CPCM was significantly enhanced by a factor of 17.59. • CPCM possessed favorable heat storage capacity with appropriate melting temperature. • The second law of thermodynamics was used to explain phase change characteristics.
[en] A unified algorithm for solving Langevin equations with deeply asymptotic parameters is proposed and tested. The method consists of identifying solvable linear friction and implementing the force evaluations by use of the Runge-Kutta method. We apply the present scheme to the periodic motion of an overdamped particle subjected to a multiplicative white noise. The accurate calculations for the temporal velocity of the particle and its correlation function can be realized by introducing an inertial term. It is shown that the fluctuation around the steady quantity increases with decreasing time step in the overdamped white-noise algorithm, however, a massive white-noise technique greatly reduces this spurious drift, and the result can converge to the correct value if the added inertia approaches zero. The other application is the simulation of generalized Langevin equation with an exponential memory friction, this allows us to treat a weak non-Markovian process
[en] In the design of the cost function in the nonlinear finite control set model predictive control (FCS-MPC) system, the traditional method based on weighting factors demonstrates some limitations, such as the weighting factors adjusting and heavy predictive calculation due to the increased number of voltage vectors applied in controlling multilevel converters. This paper proposes a simplified FCS-MPC method based on common mode voltage satisfactory optimization, which could considerably reduce the predictive calculation by the optimized switch combination and simplify the cost function design. Moreover, satisfactory optimization is adopted to achieve the accuracy control of common-mode voltage amplitude without adjusting process of weighting factors. The simulation and experimental results verify the feasibility of this control strategy.