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Zhang T.,Du W.Y.,Zhan C.Y.,Wang M.M.,Deng H.W.,Xie Z.M.,Li H. 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.8
The synergistic effect of ZrC nanoparticle pining and Re solution in W matrix on the thermal stability of tungsten was studied by investigating the evolution of the microstructure, hardness and tensile properties after annealing in a temperature range of 1000e1700 C. The results of metallography, electron backscatter diffraction pattern and Vickers micro-hardness indicate that the rolled W-1wt%Re-0.5 wt% ZrC alloy has a higher recrystallization temperature (1600 Ce1700 C) than that of the rolled pure W (1200 C), W-0.5 wt%ZrC (1300 C), W-0.5 wt%HfC (1400e1500 C) and WeK-3wt%Re alloy fabricated by the same technology. The molecular dynamics simulation results indicated that solution Re atoms in W matrix can slow down the self-diffusion of W atoms and form dragging effect to delay the growth of W grain, moreover, the diffusion coefficient decrease with increasing Re content. In addition, the ZrC nanoparticles can pin the grain boundaries and dislocations effectively, preventing the recrystallization. Therefore, synergistic effect of solid solution Re element and dispersed ZrC nanoparticles significantly increase recrystallization temperature
M. Q. Zeng,J. L. Tu,M. Zhu,W. Wang,J. W. Liu,Z. C. Lu 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.9
The effects of plasma discharge intensity on the microstructure evolution of ball-milled tungsten (W)–carbon (C)–cobalt (Co)mixtures and the formation mechanism of ultrathin plate-like tungsten carbide (WC) grains prepared by ball milling with andwithout plasma discharge were investigated. It was found that increasing the plasma discharge intensity during ball millingobviously promoted the formation of a thin flake-like W phase because of the electroplasticity effect and simultaneouslylowered the carburization temperature between W and C. A combination of high hardness and transverse rupture strength of92.9 HRA and 3659 MPa, respectively, was obtained for the WC–8Co alloy fabricated by plasma milling at a gas pressure of5 × 103 Pa with a dielectric barrier discharge layer thickness of 3 mm. These properties were mainly attributed to the markedlylowered activation energy of the WC phase and generation of highly oriented ultrathin plate-like WC grains by plasma milling. The combination of the flake-like structure of the plasma-milled W aggregate and high specific interfacial area and shortdiffusion distance of W/C were readily inherited by the ultrathin plate-like WC grains in the sintered WC–Co hardmetals.
Wang Y.-J.,Mao Z.-J.,Park K.-W. 한국생물환경조절학회 2004 한국생물환경조절학회 학술발표논문집 Vol.- No.-
To evaluate the biological and physiological response of Picea koraiensis Nakai to elevated CO₂ and nitrogen. 3-year old seedlings were planted in an ambient and 700 ppm CO₂ at low (2mM NH₄N0₃) or high nitrogen (l6mM NH₄NO₃) supplying treatments for 3 months. Photosynthetic parameters were measured monthly. Seedlings were harvested at monthly intervals and growth parameters of root system, stem and needle fractions were evaluated. The result showed that height of the seedlings grown at both of elevated CO₂× high nitrogen and elevated CO₂× low nitrogen supplying treatments increased significantly more than that of at ambient CO₂ treatments. Seedlings grown at elevated CO₂× high nitrogen produced more root biomass than at elevated CO₂× low nitrogen and ambient CO ₂× high nitrogen treatments. This result suggested that the root growth response of Picea koraiensis seedlings was greater in elevated CO₂× high nitrogen regime, which is very important for carbon sequestration in soil. Amaxof the seedlings grown at elevated CO₂× high nitrogen increased during the three months significantly, and Amaxof the seedlings grown at the other three treatments decreased significantly, suggesting that the interaction between elevated CO₂ and high nitrogen supplying stimulates the Amax of Picea koraiensis. Amax of the seedlings grown at elevated CO₂× low nitrogen showed higher than other three treatments in the first month of the experiment, but decreased in succedent two months, suggesting that elevated CO₂ promotes the photosynthesis of the seedlings. However long term growth in elevated CO₂× low nitrogen supplying condition resulted in an acclimatory decreased in leaf photosynthesis.
Surface tension-affected laminar film condensation problems
Hua Sheng Wang,John W. Rose 대한기계학회 2007 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.21 No.11
Following Nusselt [1] there were few developments in the theory of laminar film condensation until the advent of digital computers in the 1950s. Approximations used by Nusselt, namely neglect of inertia, convection and surface shear stress (for the free convection case) were then found to give very accurate results for the normal practical range of vapour-to-surface temperature difference. Subsequent developments treated the gas phase and dealt with superheated vapour, condensation in the presence of a non-condensing gas and condensation of mixtures. The temperature discontinuity at the vapour-liquid interface has been studied experimentally and theoretically since the 19<SUP>th</SUP> century and more recently in the 1960s by experiments using liquid metals. In the present paper the focus is on the condensate film and, in particular, the role played by surface tension which is important for condensation on finned surfaces and in microchannels, owing to abrupt changes in curvature of the condensing surface. The way in which surface tension affects condensation heat transfer and difficulties which arise are first illustrated by reference to condensation on a smooth horizontal tube, where the effect of surface tension on heat transfer is minimal. Practically more relevant cases of condensation in microchannels and on finned surfaces and are then discussed and recent results presented.
Y.Wang,S.W.H. de Haan,A. van Zwam 전력전자학회 2007 ICPE(ISPE)논문집 Vol.- No.-
Design for optimizing the efficiency of interleaved power converters requires considering many design parameters, such as the magnetizing inductance of the transformer, switching frequency, number of parallel units and parallel semiconductors. Because of the number of parameters and the non-linear relationships among the parameters, a multidimensional design optimization is not straightforward. In this paper the sensitivity of the efficiency in dependency of the value of principal design parameters is investigated by a loss model built in Mathcad file. The results are used to find a set of parameters for optimal efficiency. In addition, the results can be utilized to make trade-offs between some conflicting requirements such as efficiency versus cost.