• 대한기계학회논문집
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• 제14권3호
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• pp.581-593
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• 1990

본 연구에서는 교반기술에 의하여 얻어진 반응고상태의 금속에 단섬유를 첨가 하여 복합재료를 제조하였다. 그리고 제조되어진 복합재료에 있어서 섬유의 분산상 태및 기지재와의 접합관계를 조사하여 압연가공에 필요한 반응고상태인 금속복합재료 의 제조방법을 확립하였다. 균일하게 분실되어진 반용융상태의 단섬유강화형 금속복 합재료를 직접 압연하여 박판을 제조할 수 있는 가능성을 검토하였으며, 또한 제조되 어진 박판의 인장시험에 의하여 기계적 성질을 조사하였다.

• 한국주조공학회지
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• 제31권5호
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• pp.274-283
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• 2011

The vacuum die casting is a promising candidate of the stamping process for fabrication of fuel cell bipolar plate due to its advantages, such as precision casting, mass production and short production time. This study proposes vacuum die casting process to fabricate bipolar plates in fuel cell. Bipolar plates were fabricated under various injection conditions such as molten metal temperature and injection velocity. Also, according to injection velocity conditions, simulation results of MAGMA soft were compared to the experimental results. In case of melt temperature $650^{\circ}C$, misrun occurred. When the melt temperature was $730^{\circ}C$, mechanical properties were low due to dendrite microstructure. Injection velocity has to set at more than 2.0 m/s to fabricate the sound sample. When melt temperature, injection velocity (Fast shot), and vacuum pressure are $700^{\circ}C$, 2.5 m/s and 30 kPa respectively, sample had good formability and few casting defects. Simulation results are mostly in agreement with experimental results.

• 한국수소및신에너지학회논문집
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• 제23권4호
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• pp.382-389
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• 2012

Power generation cycle using ammonia-water mixture as working fluid has attracted much attention because of its ability to efficiently convert low-temperature heat source into useful work. If an ammonia-water power cycle is combined with a power cycle using liquefied natural gas (LNG), the conversion efficiency could be further improved owing to the cold energy of LNG at $-162^{\circ}C$. In this work parametric study is carried out on the thermodynamic performance of a power cycle consisted of an ammonia-water Rankine cycle as an upper cycle and a LNG cycle as a bottom cycle. As a driving energy the combined cycle utilizes a low-temperature heat source in the form of sensible heat. The effects on the system performance of the system parameters such as ammonia concentration ($x_b$), turbine 1 inlet pressure ($P_{H_1}$) and temperature ($T_{H_1}$), and condenser outlet temperature ($T_{L_1}$) are extensively investigated. Calculation results show that thermal efficiency increases with the increase of $P_{H_1}$, $T_{H_1}$ and the decrease of $T_{L_1}$, while its dependence on $x_b$ has a downward convex shape. The changes of net work generation with respect to $P_{H_1}$, $T_{H_1}$, $T_{L_1}$, and $x_b$ are roughly linear.

• 자원리싸이클링
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• 제16권5호
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• pp.36-40
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• 2007

백금은 물리화학적 특성에 기인하여 많은 분야에서 중요한 역할을 하고 있으며, 이러한 분야에서는 아주 미세한 백금의 사용을 요구하고 있다. 그러므로 본 연구에서는 액상에서 환원제를 사용하여 백금염을 환원시킴으로서 나노크기의 백금을 제조하는 방법에 대하여 알아보았다. 수용액상에서 C14TABr과 $H_2[PtCl_6]$ 상호작용은 $[C1_4TA]_2[PtCl_6]$의 유기백금염 화합물을 형성한다. 단분산 나노 백금입자를 얻기 위해서는 $C1_4TABr$과 $H_2[PtCl_6]$ 농도가 각각 cmc와 0.32 mM 이상이 되어야 한다. $H_2[PtCl_6]$와 C14TABr 농도가 증가함에 따라 백금입자 크기가 증가하였으며, 백금입자의 형태는 C14RABr농도 증가에 따라 제어가 가능하였다.

• Composites Research
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• 제23권6호
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• pp.55-60
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• 2010

본 연구에서는 열가소성 복합재료인 유리섬유/폴리프로필렌 복합재료를 이용한 복합재료 고정판의 적절한 성형조건을 찾기 위해 다양한 성형조건으로 제작된 시편의 인장실험과 굽힘실험을 수행하여 성형조건에 따른 기계적 거동을 비교하였다. 실험 결과 성형온도와 압력이 각각 $230^{\circ}C$, 3MPa일 때 가장 우수한 기계적 특성을 가짐을 확인하였다. 성형실험을 통해 결정된 성형조건을 이용한 복합재료 고정판의 성형방법으로는 고정판의 스크류 구멍을 한번에 성형하는 정형성형방법과 스크류 구멍을 후가공하는 방법을 사용하였으며, 성형실험과 굽힘실험 결과 스크류 구멍을 후가공 하는 경우 우수한 굽힘특성을 가지는 것을 확인하였다. 본 논문에서는 복합재료 고정판의 적절한 성형을 위해 유리섬유/폴리프로필렌 복합재료의 기초 성형정보와 그에 따른 고정판 성형에 대한 연구를 수행하였으며, 이 결과는 해당재료를 이용한 구조물 성형에 중요한 정보를 제공할 것으로 기대된다.

• Nuclear Engineering and Technology
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• 제52권10호
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• pp.2334-2338
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• 2020

In recent years, 3D printing technology has received significant research attention. Additionally, 3D printing technology is being applied to study radiation dosimeters of various materials. In this study, a plastic scintillator for 3D printing was developed in a laboratory and used to manufacture a plastic scintillation dosimeter (PSD) with a shape identical to that of the ionization chamber PTW31010. The 16-mm beam of Gamma Knife® Perfexion™ was irradiated to derive the absorbed dose rates of the PSD and PTW31010; they were subsequently compared with the dose rates of the treatment plan. The differences in the dose rates of the Gamma Knife treatment plan and the absorbed dose rates of PTW31010 were within 0.87%. The difference between the dose rates of the Gamma Knife treatment plan and the absorbed dose rates of the PSD were within 4.1%. A linear fit of the absorbed dose rates of four shots involving different dose rates and irradiation angles yielded an adjusted R-square value exceeding 0.9999. A total of 10 repeated measurements were conducted for the same shot to confirm its reproducibility, with a relative error of 0.56%.

• 한국주조공학회지
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• 제20권2호
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• pp.122-128
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• 2000

Strip casting process is a new technology that makes a near net shape thin strip directly from molten metal. With this process, a large amount of energy and casting cost could be decreased from the abbreviation of reheating and/or hot rolling process. Ductile cast iron which has spheroidal graphite in the matrix is the most commercial and industrial material, because of its supreme strength, toughness, and wear resistance etc. But it cannot be produced to the thin strip owing to difficulty in rolling of ductile cast iron. In this study, ductile cast iron strips are produced by the twin roll strip caster, with different chemical compositions of C, Si, and Mn contents. And then heat-treated, microstructures and mechanical properties are examined. The microstructures of as-cast strip are that of white cast iron which consists of the mixture of cementite and pearlite, but the equiaxed crystal zone of the pearlite or segregation zone of cementite exists in the center region of the strip thickness, which cannot be observed in the rapidly solidified metallic mold cast specimens. This structure is supposed to be formed from the thermal distribution of strip and the rolling force. Comparing with the structures of each strips after heat treatment, increasing Si content makes smaller spheroidal graphite and more compact in the matrix, furthermore the less of Mn content makes the ferrite matrix be obtained clearer and easier. As a result of the tensile test of graphitization heat-treated strips, the yield strengths are about 250 MPa, the tensile strengths are about $430{\sim}500$ MPa, and the elongations are about $10{\sim}13%$. In the case of the strip which has the smaller and more compact spheroidal graphite in the ferrite matrix, the higher tensile strength and better drawability could be obtained.

• Nuclear Engineering and Technology
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• 제42권1호
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• pp.97-108
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• 2010

Fluid-elastic instability and turbulence-induced vibration of steam generator U-tubes of a nuclear power plant are studied numerically to investigate the effect of design changes of support structures in the upper region of the tubes. Two steam generator models, Model A and Model B, are considered in this study. The main design features of both models are identical except for the conditions of vertical and horizontal support bars. The location and number of vertical and horizontal support bars at the middle of the U-bend region in Model A differs from that of Model B. The stability ratio and the amplitude of turbulence-induced vibration are calculated by a computer program based on the ASME code. The mode shape with a large modal displacement at the upper region of the U-tube is the key parameter related to the fretting wear between the tube and its support structures, such as vertical, horizontal, and diagonal support bars. Therefore, the location and the number of vertical and horizontal support bars have a great influence on the fretting wear mechanism. The variation in the stability ratios for each vibrational mode is compared with respect to Model A and Model B. Even though both models satisfy the design criteria, Model A shows substantial improvements over Model B, particularly in terms of having greater amplitude margins in the turbulence-excited vibration (especially at the inner region of the tube bundle) and better stability ratios for the fluid-elastic instability.

• Nuclear Engineering and Technology
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• 제41권6호
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• pp.821-830
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• 2009

In this paper, modal testing and finite element modeling results to identify the modal parameters of a nuclear fuel rod as well as its cladding tube are discussed. A vertically standing full-size cladding tube and a fuel rod with lead pellets were used in the modal testing. As excessive flow-induced vibration causes a failure in fuel rods, such as fretting wear, the vibration level of fuel rods should be low enough to prevent failure of these components. Because vibration amplitude can be estimated based on the modal parameters, the dynamic characteristics must be determined during the design process. Therefore, finite element models are developed based on the test results. The effect of a lumped mass attached to a cladding tube model was identified during the finite element model optimization process. Unlike a cladding tube model, the density of a fuel rod with pellets cannot be determined in a straightforward manner because pellets do not move in the same phase with the cladding tube motion. The density of a fuel rod with lead pellets was determined by comparing natural frequency ratio between the cladding tube and the rod. Thus, an improved fuel rod finite element model was developed based on the updated cladding tube model and an estimated fuel rod density considering the lead pellets. It is shown that the entire pellet mass does not contribute to the fuel rod dynamics; rather, they are only partially responsible for the fuel rod dynamic behavior.

• Nuclear Engineering and Technology
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• 제45권3호
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• pp.323-334
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• 2013

During a hypothetical core-disruptive accident (CDA) in a sodium-cooled fast reactor (SFR), degraded core materials can form roughly conically-shaped debris beds over the core-support structure and/or in the lower inlet plenum of the reactor vessel from rapid quenching and fragmentation of the core material pool. However, coolant boiling may ultimately lead to leveling of the debris bed, which is crucial to the relocation of the molten core and heat-removal capability of the debris bed. To clarify the mechanisms underlying this self-leveling behavior, a large number of experiments were performed within a variety of conditions in recent years, under the constructive collaboration between the Japan Atomic Energy Agency (JAEA) and Kyushu University (Japan). The present contribution synthesizes and gives detailed comparative analyses of those experiments. Effects of various experimental parameters that may have potential influence on the leveling process, such as boiling mode, particle size, particle density, particle shape, bubbling rate, water depth and column geometry, were investigated, thus giving a large palette of favorable data for the better understanding of CDAs, and improved verifications of computer models developed in advanced fast reactor safety analysis codes.