• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.122-125
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• 2008

Generally, in shipbuilding, large curved block components which have large curvature radius along various directions are used for huge ships such as LPG-vessel and oil tanker ships. Lots of the blocks are manufactured by line heating method which uses a heat source to bend the thick plate materials. The conventional forming process is entirely dependent on the experience of experts because it is done by manual method thus the curvatures and qualities are not uniform even for same part. However, it is hard to adopt the press forming process using die tool sets fur the manufacturing because of the characteristics of the industry that based on the small quantity and variety in the products. In this study, flexible forming technology using numbers of punches is investigated based on the simulation to substitute for the conventional forming method. Thick plate material model was applied to the proposed process to verify the feasibility for hull structure block forming process. The press forming processes were simulated by adopting the explicit-to-implicit sequential solution. Moreover, experiment of the flexible forming process was also conducted and its results were compared with that of simulation.

• Journal of information and communication convergence engineering
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• 제1권3호
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• pp.133-138
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• 2003

The preparation of $Al_{2}O_{3}-SiO_{2}$ thin films from less than one micron to several tens of microns in thickness had been prepared from metal alkoxide sols. Two methods, dip-withdrawal and electrophoretic deposition, were employed for thin films and sheets formation. The requirements to be satisfied by the solution for preparing uniform and strong films and by the factors affecting thickness and other properties of the films were examined. For the preparation of thin, continuous $Al_{2}O_{3}-SiO_{2}$ films, therefore, metal-organic-derived precursor solutions contained Si and Al in a chemically polymerized form has been developed and produced in a clear liquid state. In the process of applying to substrates, this liquid left a transparent, continuous film that could be converted to crystalline $Al_{2}O_{3}-SiO_{2}$ upon heating to $1000^{\circ}C$. And, a significant change of the film density took place in the crystallization process, thus leading to the strict requirements as to the film thickness, which could survive crystallization.

• 대한기계학회논문집B
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• 제32권2호
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• pp.100-106
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• 2008

An experimental study was carried out in a small-scale test furnace to investigate the performance, such as $NO_X$ emission, enhancement of heat transfer, uniformity of temperature, and etc, of oscillating combustion applied in radiant tube burner system. A premixed type burner and a cyclic oscillating control valve were designed and used. The fuel, used commercial LPG in this study, was only oscillated using the cyclic oscillating control valve. As oscillating combustion was applied in radiant tube burner system, it is found that $NO_X$ emission, compared to no oscillation, could be reduced by 38% at $90{\sim}120rpm\;(1.5{\sim}2.0Hz)$. However, as oscillating frequency was increased, effect of abatement of $NO_X$ emission is gradually reduced. From the measurement of furnace heating time from $100^{\circ}C$ to $720^{\circ}C$, heat transfer is increased by 11.5% at the oscillation of 120rpm. Temperature distribution of radiant tube surface is more uniform at oscillation of 120rpm with decrease of the peak temperature and increase of low temperature. From these results, it is confirmed that oscillating combustion is useful in radiant tube burner system.

• 대한방사선기술학회지:방사선기술과학
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• 제16권1호
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• pp.101-106
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• 1993

In order to assure safety of both patient and operator, and to provide uniform quality radiographs, it is necessary to perform periodic calibration of diagnostic X-ray equipment. A basic parameter of diagnostic equipment's and its image sharpness is the size(and shape the energy distribution) of the focal spot as viewed along the central X-ray beam. This size determines the resolution possible with the equipment and also determines the heat characteristics of an anode. A fine focus tube gives high resolution but causes high local heating of target. In past, the pin-hole and star pattern image measurement for evaluation of resolution have been widely used, but it produced blurring and inaccuracy of image. So newly inverted Ug-meter has advantage in more convenient measurement method and less out-put bias than other image measurement. The authors intended to compare measured focal size between Ug-meter and focal spot test tool, changed state from setting to now of units.

• 한국결정성장학회지
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• 제7권4호
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• pp.536-547
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• 1997

축방향으로 균일한 자장이 가하여진 Czochralski 도가니에서 도가니와 성장결정이 다양한 각속도로 회전하는 경우에 대하여 유동장, 온도장 및 산소의 농도장이 수치적으로 연구되었다. 도가니 벽의 가열에 의한 부력의 효과와 자유표면에서 온도차이에 의한 열모세관효과로 인한 용융물질의 유동은 도가니와. 성장결정의 회전에 따른 원심력에 의하여 차등적으로 억제될 수 있다. 이 원심력에 가장 큰 영향을 주는 인자는 도가니의 회전속도이며 이것이 초크랄스키 결정성장과정에서 속도장, 온도장, 농도장에 큰 영향을 주고 있다. 도가니의 회전속도가 작을 때에는 성장결정의 회전이 원심력을 효과적으로 발생시킨다.

• 대한기계학회논문집B
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• 제21권1호
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• pp.15-23
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• 1997

An experimental investigation of two-dimensional steady natural convection cooling in a vertical open top cavity with conducting side walls of finite thickness is presented. The various heat-generating discrete heaters are located on one vertical wall of the cavity. When each heater dissipates different amount of power, the purpose of the work is to obtain the optimal array condition of the heaters. The four cases of non-uniform heating conditions are considered. The temperature fields in the cavity were visualized by the interferometer and local temperatures of the vertical wall were measured by thermocouples. The heaters were arranged in two configurations: flush-mounted on a vertical wall or protruding from the wall about 4.5 mm. The vertical wall was constructed out of copper or epoxy-resin sheet. Experiments have been conducted for air with constant Prandtl number(Pr=0.7), the aspect ratio of 4.6, 7.5, 9.5, power input in the range of 0.9 W ~ 4.2 W. For the enhancement of the cooling effectiveness, the upper and lower of vertical wall would give the better position for the heaters of higher heat flux.

• 한국화재소방학회논문지
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• 제9권1호
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• pp.10-19
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• 1995

Study on combined natural convection-radiation In partially open square enclosures filled with absorbing-anisotropic scattering media is performed. A heater block located in the enclosure causes the natural circulation of the fluid in the enclosure which results In significant in-flow of the cold fluid through the partially open wall. Four different locations of the heater are considered to observe the effect of the heater locations on the resulting heat transfer. Results obtained from the combined convection-radiation analyses show much stronger circulation of t he fluid inside the enclosure as compared to those obtained from the pure convection analyses. As the ratio of the open area is Increased, the inflow of the cold fluid and the circulation of the fluid inside the enclosure is increased causing lower fluid temperature Inside the enclosure. It is shown that the location of the heater influences the circulation and heat transfer significantly by showing stronger circulations and more uniform temperature distributions for the cases where the heater is located on the bottom wall as compared to those for the cases where the heater is located on the upper part wall of the enclosure. For pure absorbing medium, the expected circulation in the fluid is relatively week as compared to those with absorbing-scattering medium due to the smaller wall heating as the radiant heat is used to heat the fluid instead. The forward anisotropic scattering phase function is shown to increase the fluid circulation further as compared to the isotropic scattering medium.

• 한국전기전자재료학회논문지
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• 제33권5호
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• pp.344-349
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• 2020

Modern thin film deposition processes require high deposition rates, low costs, and high-quality films. Atmospheric pressure plasma-enhanced chemical vapor deposition (AP-PECVD) meets these requirements. AP-PECVD causes little damage on thin film deposition surfaces compared to conventional PECVD. Moreover, a higher deposition rate is expected due to the surface heating effect of atomic hydrogens in AP-PECVD. In this study, polycrystalline silicon thin film was deposited at a low temperature of 100℃ and then AP-PECVD experiments were performed with various plasma powers and hydrogen gas flow rates. A deposition rate of 15.2 nm/s was obtained at the VHF power of 400 W. In addition, a metal foam showerhead was employed for uniform gas supply, which provided a significant improvement in the thickness uniformity.

• 한국분말재료학회지
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• 제21권5호
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• pp.382-388
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• 2014

Fe-TiC composite powder was fabricated by high-energy milling of powder mixture of (Fe, TiC) and (FeO, $TiH_2$, C) as starting materials, respectively. The latter one was heat-treated for reaction synthesis of TiC phase after milling. Both powders were spark-plasma sintered at various temperatures of $680-1070^{\circ}C$ for 10 min. with sintering pressure of 70 MPa and the heating rate of $50^{\circ}C/min$. under vacuum of 0.133 Pa. Density and hardness of the sintered compact was investigated. Fe-TiC composite fabricated from (FeO, $TiH_2$, C) as starting materials showed better sintered properties. It seems to be resulted from ultra-fine TiC particle size and its uniform distribution in Fe-matrix compared to the simply mixed (Fe, TiC) powder.

• 설비공학논문집
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• 제28권7호
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• pp.275-282
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• 2016

MILD (Moderate and Intense Low-oxygen Dilution) combustion using oxygen as an oxidizer is considered as one of the most promising combustion technologies for high energy efficiency and for reducing nitrogen oxide and carbon dioxide emissions. In order to investigate the effects of nozzle angle and oxygen velocity conditions on the formation of oxygen-MILD combustion, numerical and experimental approaches were performed in this study. The numerical results showed that the recirculation ratio ($K_V$), which is an important parameter for performing MILD combustion, was increased in the main reaction zone when the nozzle angle was changed from 0 degrees to 15 degrees. Also, it was observed that a low and uniform temperature distribution was achieved at an oxygen velocity of 400 m/s. The perfectly invisible oxy-MILD flame was observed experimentally under the condition of a nozzle angle of $10^{\circ}$ and an oxygen velocity of 400 m/s. Moreover, the NOx emission limit was satisfied with NOx regulation of less than 80 ppm.