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11.
In relation to nuclear reactor accident and safety studies, experiments on hot-leg U-bend two-phase natural circulation in a loop with a relatively large diameter pipe (10.2 cm inner diameter) were performed for understanding the two-phase natural circulation and flow termination during a small break loss of coolant accident in LWRs. The loop design was based on the scaling criteria developed under this program and the loop was operated either in a natural circulation mode or in a forced circulation mode using nitrogen gas and water. Various tests were carried out to establish the basic mechanism of the flow termination as well as to obtain essential information on scale effects of various parameters such as the loop frictional resistance, thermal center and pipe diameter. The void distribution in a hot-leg, flow regime and natural circulation rate were measured in detail for various conditions. The termination of the natural circulation occurred when there was insufficient hydrostatic head in the downcomer side. The superficial gas velocity at the flow termination could be predicted well by the simple model derived from a force balance between the frictional pressure drop along the loop and the hydrostatic head difference. The bubbly-to-slug flow transition was found to be dependent on axial locations. It turned out that the formation of cap bubbles in the large diameter pipe caused the increased drift velocity, which would affect the prediction of the void fraction in the hot leg. 相似文献
12.
新一代超小型DIP-IPM 总被引:1,自引:0,他引:1
为了满足空调、洗衣机、冰箱等白色家电对高效、高性能的需要,三菱电机开发了新一代超小型第四代(Ver.4)双列直插封装的智能功率模块(Dual-In-linePackageIntelligentPowerModule,简称DIP-IPM)。本文首先分析了第四代超小型DIP-IPM内部电路的构成和功能,然后详细介绍了第四代DIP-IPM生产过程中的关键技术,包括无铅化、高热传导性绝缘片、chip-to-chip导线直接连接以及ASIC技术,最后与第三代(Ver.3)DIP-IPM进行了比较。 相似文献
13.
Rong-Jun Xie Mamoru Mitomo Wonjoong Kim Young-Wook Kim Guo-Dong Zhan Yoshio Akimune 《Journal of the American Ceramic Society》2002,85(2):459-465
Starting from three powder mixtures of 80 vol% SiC (100α, 50α/50β, 100β) and 20 vol% YAG, liquid-phase-sintered silicon carbide ceramics were prepared by hot pressing at 1800°C for 1 h under 25 MPa, and then by hot forging or annealing at 1900°C for 4 h under an applied stress of 25 MPa in argon. The phase transformation and texture development in the as-hot-pressed, hot-forged, and annealed SiC ceramics were investigated via X-ray diffraction (XRD) and the pole figure measurements. The 6H → 4H polytypic transformation was observed in samples consisting of both α- and β-SiC phases when subjected to compressive deformation but absent in the case of annealing, suggesting the deformation-enhanced solubility of aluminum in SiC. Deformation was also found to enhance the 3C → 4H transformation in the sample containing entirely β-phase, which is due to the accelerated solution-precipitation process assisted by grain boundary sliding. The current study showed that the β- →α-phase transformation had little effect on texture development in SiC. Hot forging generally produced the strongest texture, with the calculated maximum of 2.2 times random in samples started with pure α-SiC phase. The mechanism for texture development was explained based on the microstructural observations. 相似文献
14.
By using an oxynitride glass composition from the Y-Mg-Si-Al-O-N system as a sintering additive, the effect of atmosphere on densification was investigated during the liquid-phase sintering of SiC, and the resulting microstructure and mechanical properties of the sintered and subsequently annealed materials were investigated. SiC ceramics that were densified with 10 wt% oxynitride glass showed higher sinterability in a nitrogen atmosphere. Oxynitride glass enlarged the stability region of β-SiC and suppressed β→ alpha phase transformation, which resulted in an equiaxed microstructure. Grain growth of fine-grained SiC in some extent (up to ∼300 nm) was beneficial in improving both room-temperature strength and toughness. The best results were obtained when the ceramics were hot-pressed at 1800°C for 1 h in a nitrogen atmosphere and subsequently annealed at 1900°C for 3 h in an argon atmosphere. The room-temperature flexural strength and fracture toughness of the material were 847 MPa and 3.5 MPa·m1/2 , respectively. 相似文献
15.
In emulsion polymerization, the Smith and Ewart theory gives about two or three times the number of polymer particles obtained by experiment. In this paper, a reaction model is proposed which, from the standpoint of reactor design, can give an adequate explanation of the whole course of an emulsion polymerization of monomer highly insoluble in water. Among other things, the generating process of polymer particles is examined in detail. It is demonstrated experimentally that a new parameter proposed here, which represents the degree of difficulty of monomer initiation in micelles, is indispensable in explaining that process. Also confirmed is that monomer initiation takes place more easily in polymer particles than in micelles. According to the new model, the progress of polymerization, i.e., monomer conversion, the number of the polymer particles, and properties of polymer thus produced can be estimated with satisfactory accuracy. Furthermore, approximate equations are derived for easier estimation. 相似文献
16.
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18.
Cross-rolling, in which the roll axis is tilted by 7.5° towards the TD-direction, was carried out on a commercial magnesium alloy. The (0002) texture intensity of the cross-rolled specimen was lower than that of the unidirectionally rolled specimen, and the (0002) texture of the cross-rolled specimen was inclined about 10° towards the TD-direction. Also, the grain size of the cross-rolled specimen was smaller than that of the unidirectionally rolled specimen. As a result of the Erichsen tests at 433-493 K, the press formability of the cross-rolled specimen was higher than that of the unidirectionally rolled specimen. The high formability of the cross-rolled specimen is attributed to both the modification of (0002) texture and the enhancement of grain refinement by the cross-rolling. 相似文献
19.
Hideomi Koinuma Min-Sung Kim Toshiaki Asakawa Mamoru Yoshimoto 《Fullerenes, Nanotubes and Carbon Nanostructures》2013,21(3):599-612
Abstract Several new processes have been developed for the preparation of fullerenes and thin films by using a pulsed excimer laser. The irradiation of a pulsed KrF excimer laser beam onto a C60 powder target produced single phase C60 thin films when the laser energy fluence was in the range between 40 and 50mJ/cm2. By atomic force microscopy, the laser-deposited C60 thin film was verified to have a surface far smoother that the surfaces of films produced by the conventional evaporation method. The stainless steel rods coated with this film exhibited an excellent tribological property. Cluster formation from SiC and other carbides MCn(M=Ti,W,B) was investigated by laser desorption time-of-flight mass spectrometry. No clear indication was observed for the production of such clusters as (SiC)60 and (MxC60-x) from the sintered targets directly as well as from the films laser deposited from the targets. However, C60 and C70 were found to exists in the laser-deposited films, indicating a new applicability of pulsed laser processing for segregative cluster synthesis from solid solution. Preliminiary results on thin film deposition via pulsed ablation of (Ba,Na)xSi46 clathrate were also presented. 相似文献
20.
Rong-Jun Xie Naoto Hirosaki Mamoru Mitomo Takayuki Suehiro Xin Xu Hidehiko Tanaka 《Journal of the American Ceramic Society》2005,88(10):2883-2888
Rare-earth-doped Ca-α-SiAlON phosphors, with the compositions of (Ca1−3/2 x RE x ) m /2 Si12− m − n Al m+n O n N16− n (RE=Ce, Sm, and Dy, 0.5≤ m =2 n ≤3.0), were prepared by sintering at 1700°C for 2 h under 10 atm N2 . The concentration of rare earths varied from 3 to 30 at.% with respect to Ca. The photoluminescence (PL) properties were investigated as functions of the composition of the host matrix (i.e., m ) and the concentration of rare earths (i.e., x ). The results show that the emission properties can be optimized by tailoring m and x . The Ce3+ luminescence originating from the 4 f –5 d interconfigurational transitions is greatly affected by the environment surrounding the Ce3+ ions, which differs from the Sm3+ or Dy3+ luminescence arising from the 4 f –4 f intraconfigurational transitions. X-ray diffraction and scanning electron microscopy were used to explain the composition and concentration dependence of PL properties. 相似文献