• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.583-588
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• 2002

The purpose of the study is to evaluate fracture toughness on the Laser and the electron beam welded joints of high tensile steels (HT500, HT550, HT650) by using 3-point bend CTOD and Charpy impact test. WM (weld metal) CTOD tests have been carried out using two kinds of CTOD specimen, the Laser beam welding (108mm length, and 24mm width, and 12mm thickness) and the electron beam welding (l71mm length, and 38mm width, and 19mm thickness). WM Charpy impact specimen is a standard V-notch type, and the temperature of the experiment is changed from -45 to 20 degree of centigrade. FE-analysis is also performed in order to investigate the effect of stress-strain fields on fracture characteristics. Results of the standard V-notch Charpy test are influenced by strength mis-match effect and the absorbed energy vE depends on crack path, and The transition temperature of Laser beam welded joints is more higher than that of electron beam welded joints. Results of the 3-point bend test give low critical CTOD and the crack path is in the weld metal of al specimens. These results indicate fracture toughness characteristics of the welded joints and transition temperature of HT500 are similar both a Laser beam welded joint and an electron beam welded joint. But the fracture toughness and the transition temperature of the electron beam welded joints of HT550 and HT650 are higher than those o the Laser beam welded joints.

• 한국재료학회지
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• 제25권10호
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• pp.559-565
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• 2015

The ductile-brittle transition behavior of two austenitic Fe-18Cr-10Mn-N-C alloys with different grain sizes was investigated in this study. The alloys exhibited a ductile-brittle transition behavior because of an unusual brittle fracture at low temperatures unlike conventional austenitic alloys. The alloy specimens with a smaller grain size had a higher yield and tensile strengths than those with a larger grain size due to grain refinement strengthening. However, a decrease in the grain size deteriorated the low-temperature toughness by increasing the ductile-brittle transition temperature because nitrogen or carbon could enhance the effectiveness of the grain boundaries to overcome the thermal energy. It could be explained by the temperature dependence of the yield stress based on low-temperature tensile tests. In order to improve both the strength and toughness of austenitic Fe-Cr-Mn-N-C alloys with different chemical compositions and grain sizes, more systematic studies are required to understand the effect of the grain size on the mechanical properties in relation to the temperature sensitivity of yield and fracture stresses.

• Bulletin of the Korean Chemical Society
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• 제7권2호
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• pp.124-129
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• 1986

The effects of molecular attraction and orientations for the energy mismatch variance, vibrational energy level and double-quantum transition, in the vibration-vibration energy exchange, have been considered. The contribution of molecular attraction increases the exchange rate of the purely repulsive interaction, in general, significantly, but which becomes smaller as the temperature is increased. As the energy mismatch is increased, its contribution is also increased, but which is small. However, its contribution for the double-quantum transition is very paramount. At each orientation, the exchange rate constants have been calculated and compared with the results for rotational average, and it is found that the exchange rate is a strong function of the orientation angles of colliding molecules. We have also discussed about the system having the strong interaction such as the hydrogen bond, and it is found that for this system the preferred orientation should be considered in order to calculate the exchange rates.

• Korean Chemical Engineering Research
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• 제47권4호
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• pp.481-487
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• 2009

본 연구에서는 기체(공기)-액체(용융탄산염) 이상 흐름계(용융염산화 공정)에서 공기유속(0.05~0.22 m/sec) 및 탄산용융염의 온도($870{\sim}970^{\circ}C$)가 흐름영역 전이특성에 미치는 영향을 공기 체류량의 drift-flux 및 차압요동의 추계학적 해석을 통하여 규명하였다. 흐름영역이 시작되는 공기 체류량값은 공기체류량-drift flux 그래프를 통하여 구하였다. 흐름영역 전이가 시작되는 공기 체류량 값은 탄산용융염의 온도가 증가함에 따라서 증가하였는데 이는 탄산용융염의 온도가 증가함에 따라서 액상의 점도와 표면장력의 감소로 인한 계의 안정화 때문이며 계의 특성에 가장 큰 영향을 미치는 기포특성(평균기포크기 및 상승속도)을 drift-flux 모델식을 적용하여 추정하였다. 흐름영역전이 특성을 좀 더 정량적으로 특성화하기 위하여 차압요동신호를 상공간투영 및 Kolmogorov entropy를 이용하여 해석하였다. Kolmogorov entropy는 탄산용융염의 온도가 증가함에 따라 감소하였으며 공기유속이 증가함에 따라서 증가하였으나 흐름영역에 따라서 다른 경향성을 나타내었고 흐름영역이 시작되는 공기유속값은 공기체류량의 drift-flux 해석으로 유도된 결과와 동일하였다.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 1991년도 추계학술발표회논문집
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• pp.18-22
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• 1991

Far Infrared radiators should have functionality to convert thermal energy into electron wave. In order to apply the Far Infrared to the substance, the absorption characteristics of the substance should be considered. In this paper, interrelation of emissivity with emission energy according to temperature in the range of 2.5$\mu$m to 25$\mu$m after the transition element oxides (MnO2, Fe2O3, CuO, Co3O4) of first grade reagent were molded in press, then they were calcinated in 1050˚C, and they were used as samples.

• 한국조명전기설비학회지:조명전기설비
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• 제9권6호
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• pp.32-40
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• 1995

Far Infrared radiators should have functionality to convert thermal energy into an electromagnetic wave. In order to apply the Far Infrared to the substance, the absorption characteristics of the substance should be considered. In this paper, interrelation of emissivity with emission energy according to temperature in the range of [$2.5\mu\textrm{m}$] to 25[$\mu\textrm{m}$] after the transition element oxides (MnO2, Fe2O3, CuO, Co3O4) of first grade reagent were molded in press, then they were sintered in [$1050^{\circ}C$], and they were used as samples.

• Progress in Superconductivity
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• 제11권2호
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• pp.112-117
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• 2010

We examine phase transition of the spin density wave and $\pi$ phase shifted superconductivity in the Fe pnictide superconductors. The phase diagram is described in the plane of the temperature T and the doping x with the combination of Ginzburg-Landau expansion of the free energy near the multi-critical temperature $T_c$ and the self-consistent numerical iterations of the gap equations. The phase separation or coexistence is determined by computing the 4-th order terms of the free energy which is confirmed by the numerical calculations. We can show the phase coexistence when the spin density wave is incommensurate. And the first order phase transition is observed near the boundary between commensurate and incommensurate spin density wave.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2004년도 임시총회 및 추계학술발표회
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• pp.399-402
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• 2004

An aquifer thermal energy storage (ATES) model is simulated by FEFLOW according to the scenario of heat pump operation in two layered confining aquifer. The scenario is consisted of 4 steps: 90 days pumping (west well) and waste water injection (east well: 35 $^{\circ}C$), 90 day s stop, 90days pumping (east well) and waste water injection (west well: 5 $^{\circ}C$), and 95 days stop. The injection of the waste water is limited in the second layer and the first layer is aquitard. The temperature distribution at the surface shows low difference with reference temperature and opposit aspect with that of the second layer because the thermal transition through the first layer is very slow. Even though the simulated thermal transition in the aquifer system have a difference with real ATES system, optimal design and operate system can be developed with field tests and operational experience.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1997년도 춘계학술발표회논문집(2)
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• pp.129-136
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• 1997

The automated ball indentation(ABI) test was utilized to develop a semi-nondestructive method for estimating the fracture toughness( $K_{JC}$ ) in the transition temperature range. The key concept of the method is that the indentation deformation energy to the load at which the mean ball-specimen contact pressure reaches the fracture stress is related to the fracture energy of the material. ABI tests were performed for the reactor pressure vessel(RPV) base and weld metals at the temperatures of-15$0^{\circ}C$~$0^{\circ}C$ and the fracture toughness (estimated $K_{JC}$ ) was calculated from the indentation load-depth data. For all steels the temperature dependence of the estimated fracture toughness was almost the same as that ASTM $K_{JC}$ master curve The reference temperatures( $T_{o}$)of the steels were determined form the estimated $K_{JC}$ versus temperature curves. The reference temperature was well correlated with the index temperature of 41J Charpy impact energy( $T_{41J}$).).).

• 한국수소및신에너지학회논문집
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• 제29권6호
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• pp.635-641
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• 2018

To select the operating condition of 0.5 MWth chemical looping combustion system, minimum fluidization velocity, transition velocity to fast fluidization and solid circulation rate were measured using mass produced new oxygen carrier (N016-R4) which produced by spray drying method for 0.5 MWth chemical looping combustion system. A minimum fluidization velocity decreased as the pressure increased. The measured transition velocity to fast fluidization was 2.0 m/s at ambient temperature and pressure. The measured solid circulation rate increased as the solid control valve opening increased. We could control the solid circulation rate from 26 to $93kg/m^2s$. Based on the measured minimum fluidization velocity and transition velocity to fast fluidization, we choose appropriate operating conditions and demonstrated continuous solid circulation at high pressure condition (5 bar-abs) up to 24 hours.