• Journal of Korean Society of Environmental Engineers
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• v.29 no.4
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• pp.466-471
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• 2007

The purpose of study is to obtain basic but important information for the operation of the greenhouse facility located in the suburb of town. Special emphasis is given on the aspect of energy saving method, which can be easilyapplicable in a practical sense. For this end numerical calculation has been made systematically in order to increase the energy efficiency by the evaluation of the temperature distribution in greenhouse. Major parameters considered are primarily the overall shape of greenhouse together with the various conditions of baffle installion inside greenhouse. Further, the performance of heating system is also carefully compared each other for a number of typical arrangements of heating duct. The performance of the computer program developed in this study is evaluated by the observation of the famous fluid trapping phenomenon occurred in staggered baffle condition in the enclosure of greenhouse. Based on the this study, a number of useful conclusions can be drawn, that is, the installation of baffles are quite effective in energy saving method with a minor modification of facility. Also, it is found that the change of the heating duct system can contribute significantly to the uniform temperature distribution in greenhouse. Further other findings obtained by numerical calculation were not only physically consistent and meaningful but also useful for the determination of optimum condition of practical operation of greenhouse.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.2
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• pp.97-104
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• 2007

An investigation has been made on the relationship between characteristics of Acoustic Emission (AE) signal in welding flaw and the stress corrosion defect in-service for the high pressure pipe steel. In order to tackle the problem of welding flaw in high pressure pipe, specimens were made by the aid of the application of both corrosion liquid usage and a quenching method after local heating. The amplitude of signal was $60{\sim}75\;dB$ in the territory which is suspected for defect, and the specimens which only have welding flaw showed gradients of 0.034, 0.034, 0.035. Moreover, there is a certain increase in gradient even though the differences are very slight. That is, corrosion specimens showed new gradients of 0.040, 0.039, 0.041 which put welding flaw and corrosion mechanism together. After pressurizing 3 minutes, AE signal has been detected from welding flaw easily in each part of the section. It is possible to predict the occurrence and also prevent the damage of stress corrosion crack which has characteristics of cleavage fracture.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.3
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• pp.279-285
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• 2012

It is necessary to install the inert gas system(IGS) for preventing fire and explosion in LNGC main diesel engine crankcase besides oil mist detector(OMD) unit with $CO_2$ gas injector. Therefore, to design the liquid nitrogen IGS, analytical work is conducted for predicting the heat input load of liquid nitrogen heater with two-phase stratified flow model. This paper also presents the effects of changes in pipe diameter, saturated pressure, and inclination angle by ship's movement on cryogenic two-phase stratified flows. It is found that the stratified model gives reasonable predictions, and the model is effective to predict the heat input load of liquid nitrogen IGS.

• Corrosion Science and Technology
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• v.13 no.3
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• pp.87-94
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• 2014

Recently, the application of bending products has been increased since the industries such as automobile, aerospace, ships, and plants greatly need the usage of pipes. For facility fabrication, bending process is one of key technologies for pipings. Induction heat bending process is composed of bending deformation by repeated local heat and cooling. Because of local heating and compressive strain, detrimental phases may be precipitated and microstructural change can be induced. This work focused on the effect of induction heat bending process on the properties of ASME SA312 TP316 stainless steel. Evaluation was done on the base metal and the bended areas before and after heat treatment. Microstructure analysis, intergranular corrosion test including Huey test, double loop electropotentiokinetic reactivation test, oxalic acid etch test, and anodic polarization test were performed. On the base of microstructural analysis, grain boundaries in bended extrados area were zagged by bending process, but there were no precipitates in grain and grain boundary and the intergranular corrosion rate was similar to that of base metal. However, pitting potentials of bended area were lower than that of the base metal and zagged boundaries was one of the pitting initiation sites. By re-annealing treatment, grain boundary was recovered and pitting potential was similar to that of the base metal.

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.2
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• pp.46-54
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• 2015

Nitrous oxide is known as green and safe propellant, and can be supplied by its own vapor pressure. So, many liquid propulsion research institutes and university laboratories use nitrous oxide as oxidizer of experimental liquid rocket engine. However, the unknown explosions occurred twice during hot fire experiments using subscale ethanol/nitrous oxide thruster. In this paper, we surmised that the explosions were caused by the decomposition of nitrous oxide in the injector body and the recondensation of nitrous oxide. Improvement and the safe handling methods are suggested.

• Journal of the Korean Vacuum Society
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• v.9 no.3
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• pp.290-295
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• 2000

In order to utilize as a pre-ionization means for reproducible ohmic plasma on KAIST-TOKAMAK, a simple, safe, economical and continuous microwave source has been developed using a home kitchen micro-wave oven. The magnetron used in the study can provide 500 W of power at 2.45 GHz. A conventional magnetron in a home kitchen microwave oven generates microwave for 8 ms at every 16 ms periodically due to the periodic (60 Hz) high voltage applied to the magnetron cathode. In order to generate continuous microwave which is suitable for tokamak pre-ionization, the magnetron operation circuit has been modified using a DC high voltage (5 kV, 1 A) power supply. It provides high-voltage with small ripple for magnetron cathode bias. Using the developed magnetron system, electron cyclotron resonace heated (ECH) plasmas were produced and the characteristics of the system were studied by diagnosing the ECH plasma using Langmuir probe and $H_{\alpha}$ emission diagnostics.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2009.06a
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• pp.63-64
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• 2009

변환시설의 해체 시 발생한 해체폐기물은 2009년 현재까지 약 354톤이며, 이들 중 탱크, 배관, 반응기, 펌프류 동의 해체금속폐기물이 약 191톤으로 54% 를 차지하고 있다. 이들 해체금속폐기물은 제염 처리공정을 통하여 전량 자체처분폐기물로 전환시키는 것을 목표로 두고 있다. 이는 오염된 금속류를 효과적으로 제염한 다음 자체처분시킴으로서 방사성폐기물에 대한 처분비용을 저감할 수 있기 때문이다. 해체금속폐기물 중 스테인레스강 해체폐기물은 질산 용액을 사용한 초음파화학제염공정으로 제염한 후 자체처분폐기물로 53톤을 전환하였다. 탄소강 해체물의 경우 스팀제염공정으로 제염한 결과 제영 효율은 좋았으나 변환시설 가동 중 유지 보수를 위하여 페인팅을 하였던 해체물의 경우 페인트를 제거하지 않을 경우 스팀제염장치로는 제염이 안 되었다. 탄소강 해체금속폐기물은 약 117톤 발생하였으며, 이들 중 모터, 펌프 등을 제외한 제염 대상 폐기물은 약 80톤이며, 이들을 용융 제염 및 감용을 위하여 기초 연구를 수행한 결과를 바탕으로 약 180kg/batch 용량의 금속용융제염 설비를 제작 설치하여 탄소강 해체금속폐기물 용융제염 처리를 수행 중에 있다. 금속용융은 장치가 간단하고 폐기물 처리량이 비교적 적고 단속적인 운전에 매우 효과적인 고주파 유도로를 사용하였다. 용융장치는 고주파 발진장지와 용해로체로 구성된 고주파 유도설비와 냉각계통으로 구성된다. 고주파발진장치는 철제 200kg을 용해할 수 있는 용량을 갖추었으며, 실험 및 실제 처리 등 용해로체의 크기 변경이 필요할 경우에는 고주파발진기의 출력 주파수를 변경할 수 있게 하였다. 용융 장치의 발진기 부분의 입력전원은 3상, 440V, 60Hz 이며, 출력전원은 200kW, 출력주파수는 lkHz, 3kHz, 5kHz로 구성되어 있으며, 회당 180kg 의 폐기물을 용융할 시에는 3kHz로 고정하여 사용하였다. 용해로체 부분 중 고주파유도가열부는 heating coil 및 절연부로 구성되어 있고, 그 외 support frame과 lever로 구성되어 있다. 용해로체와 고주파 발진장치의 냉각을 위한 냉각설비는 냉각기와 냉매의 저장을 위한 저장조로 구성되어 있으며, 냉각기의 용량은 20RT 이다. 용융로체의 직경은 약 28cm로 크기가 큰 해체물의 장입이 어려워 작은 크기로 세절을 해야만 하며，용융로의 용량을 증가시킬 경우 해체물을 작은 크기로 세절하는 비용을 절감할 수 있을 것이다. 용융 중 시료 채취는 매 배치마다 수행하였으며, 그림3과 같은 시료 채취용 주형 틀에 국자모양의 채취기로 채취하였다. 해체물의 용융시 ingot를 생성하기 위해서 주형틀에 용융물을 장입하기 전 시료를 채취하였다 그림4는 생성된 ingot이며, 이들의 방사능 농도는 배치마다 차이는 있지만 최대 0.05 Bq/g 이하로 나타나 자체처분 폐기물로 전량 전환 가능하였다 그림5 는 해체물에 함유된 우라늄과 불순물을 제거한 슬래그로 방사능농도는 약 12Bq/g 으로 나타났으며, 이들의 발생량은 약 3wt% 정도로 폐기물 발생량이 작았다. 따라서 금속폐기물의 경우 용융제염으로 처리할 경우 폐기물 발생량을 최대로 줄일 수 있어 처리 효율이 기타 처리 공정보다 효율적인 것으로 판단된다.

• Journal of Sensor Science and Technology
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• v.12 no.3
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• pp.139-148
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• 2003

$LiPO_3$ glass scintillators were fabricated, and lanthanides(except Pm) oxides or chlorides were used as an activator. For the fabrication of $LiPO_3$ glasses, optimum heating conditions were obtained, and the photoluminescence of the glasses was measured by the monochromator. For the best transparency of the glass samples, optimum heating temperature and time are $950^{\circ}C$ and 90 min, respectively. It was found that Pr, Nd, Gd, Ho, Er, Tm, Yb and Lu do not work as activator; emission spectrums of samples with them were equal to those of samples without activators. In the case of samples with Europium, the peaks of emission spectrum of $Eu^{2+}$ and $Eu^{3+}$ were 420 nm and 620 nm respectively. And samples with $Ce^{3+}$ were about 380 nm, and $Tb^{3+}$ were about 550 nm. Glass scintillators with $Be^{3+}$, $Eu^{2+}$, and $Ce^{3+}$ were found to be more applicable to neutron detection. The result of neutron detection by Ra-Be sources showed that $Ce^{3+}$ was found to be the best activator of $LiPO_3$.

• Fire Science and Engineering
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• v.25 no.6
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• pp.168-177
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• 2011

The combustion test for real box of AC outdoor unit has been performed in this study in order to estimate the fire hazard in multi-system type of AC outdoor unit which is currently used for commercial use. The result showed that in test, there was explosion inside of AC outdoor unit, and flame erupted and fire spread through upper side grill. And then this fire burnt the combustibles such as wires, electronic control board, heat exchange copper plate and plastics etc inside the unit, refrigerant gas pipe was burst due to fire, and accelerated the explosion and flame eruption to outside while the refrigerant was erupting. It is found in this test that the maximum heat release rate of AC outdoor unit is 5,830 kW, the maximum internal temperature measured with infrared camera and thermocouple is $1,201^{\circ}C$, maximum ambient temperature is $881^{\circ}C$, and flame rose higher than about 5 m. It is concluded that the fire in AC outdoor unit cause fire to combustibles around the unit, and may give big damage by generating the secondary fire. It is expected that the result obtained from the test on the real object may be applied to fire realization of AC outdoor unit and estimation of fire spreading to the combustibles around in the future computer simulation.