• Journal of Advanced Marine Engineering and Technology
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• 제28권3호
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• pp.500-508
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• 2004

The heat transfer coefficients during gas cooling process of carbon dioxide in a horizontal tube were investigated. The experiments are conducted without oil in the refrigerant loop. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater, and a gas cooler(test section). The water loop consists of a variable-speed pump, an isothermal tank, and a flow meter. The gas cooler is a counterflow heat exchanger by cooled water flowing in the annulus. The $CO_2$ flows in the horizontal stainless steel tube. which is 9.53mm in O.D. and 7.75mm in I.D. The gas cooler is 6 [m] in length. which is divided into 12 subsections, respectively. The experimental conditions considered in the study are following range of variables : refrigerant temperature is between 20 and $100^{\circ}C$. mass fluxes ranged from 200 to 400kg/($m^2$.s), average pressure varied from 7.5 to 10.0MPa. The main results were summarized as follows : The friction factors of $CO_2$ in the gas cooler show a relatively good agreement with those predicted by Blasius' correlation. The local heat transfer coefficient in the gas cooler has compared with most of correlations, which are the famous ones for forced convection heat transfer of turbulent flow. The results show that the local heat transfer coefficient of gas cooler agrees well with the correlation by Bringer-Smith except that at the region near pseudo critical temperature. while that at the near pseudo critical temperature is higher than the correlation.

• Clinical and Experimental Reproductive Medicine
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• 제18권1호
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• pp.81-87
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• 1991

There studies were carried for evaluation of the efficiency of freezing of hamster oocytes for use in a human sperm penetration assay. The hamster oocytes fully equilibrated in various cryoprotectant agents and inseminated with human sperm. After insemination with hamster oocytes, there was no difference in penetrated rates. Cumulus free oocytes equilibrated in 1.5M various cryoprotective agents and slowely cooled to temperature $-30^{\circ}C$ before rapid cooling and storage in nitrozen tank. After rapid thawing, survival rates of frozen oocytes according to cryo-protective agents were examined and the human sperm penetration assay with zona free hamster oocytes was conducted. 1. Survival rates of oocytes after cryoprotectants exposure have no significant difference (range 88-91%) and peneration rate was 51.1%. 2. Recovery and survival rate of frozen-thawed oocytes were 85.1 and 66.8%. There was no significant difference on cryoprotective agents. 3. Penetration rates of the frozen-thawed and intact oocytes were 69.0 and 77.0%, respectively. 4. Hamster oocytes cryopreservation provides a convenient way of supplying and trans-porting hamster oocytes for the assessment of the fertilizing potential of human spermatozoa.

• 수산해양기술연구
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• 제34권2호
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• pp.212-222
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• 1998

Heat transfer performance improvement by fin and groovs is studied for condensation of R-11 on integral-fin tubes. Eight tubes with trapczodially shaped integral-fins having fin density from 748 to 1654fpm(fin per meter) and 10, 30 grooves are tested. A plain tube having the same diameter as the finned tubes is also used for comparison. R-11 condensates at saturation state of 32 $^{\circ}C$ on the outside tube surface coded by inside water flow. All of test data are taken at steady state. The heat transfer loop is used for testing singe long tubes and cooling is pumped from a storage tank through filters and folwmeters to the horizontal test section where it is heated by steam condensing on the outside of the tubes. The pressure drop across the test section is measured by menas pressure gauge and manometer. The results obtained in this study is as follows : 1. Based on inside diameter and nominal inside area, overall heat transfer coefficients of finned tube are enhanced up to 1.6 ~ 3.7 times that of a plain tube at a constant Reynolds number. 2. Friction factors are up to 1.6 ~ 2.1 times those of plain tubes. 3. The constant pumping power ratio for the low integral-fin tubes increase directly with the effective area to the nominal area ratio, and with the effective area diameter ratio. 4. A tube having a fin density of 1299fpm and 30 grooves has the best heat transfer performance.

• 한국추진공학회지
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• 제9권3호
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• pp.133-144
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• 2005

기존 발사체 시스템의 성능을 향상시키는 방법의 하나로 액체산소와 액체수소와 같은 극저온 추진제를 고밀도화하는 기술이 최근 활발히 개발되고 있다. 극저온 추진제 고밀도화를 통하여 발사체에서 추진제의 질량분율을 높임으로 보다 큰 유상하중을 괘도에 진입시킬 수 있다. 본 논문에서는 극저온 추진제 고밀도화의 원리 및 최근 기술동향을 소개한다. 주로 액체산소의 고밀도화에 초점을 맞추어 여러 고밀도화 방법들에 대해서 소개하였다. 고밀도화된 극저온 추진제를 탑재한 발사체의 엔진 및 발사체 전체 성능해석 결과를 통하여, 발사체 시스템의 성능 향상을 정량적으로 소개하였다 또한 향후 극저온 추진제 고밀도화 기술의 국내 위성발사체 적용을 위한 방안을 간략히 제시하였다.

• 한국산학기술학회논문지
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• 제15권10호
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• pp.6282-6288
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• 2014

본 논문은 용접 산업현장에서 많이 사용 되는 $CO_2$ 용접에서는 차량내부 및 탱크내부 용접에서 제어 패널을 볼 수 없는 곳, 작업장이 먼 곳 등에서 용접사가 용접을 하면서 용접조건에 맞는 전류와 전압을 조절할 수가 없고, 전류와 전압을 조절하기 위해 용접을 중단하고 잦은 이동으로 용접 구조물의 순간적인 냉각에 의해 용접결함이 발생된다. 본 연구에서는 기존의 $CO_2$ 용접기 3종류를 각각 사용하여 원격제어 토치의 용접에 대해 SS400 용접구조용 압연강재를 사용하여 원격제어 토치와 기존 $CO_2$ 용접 토치를 V형 맞대기 수직자세로 용접실험을 실시하고 용접 부의 표면비드 상태의 형상을 육안검사 관찰하고 또한 이를 침투탐상검사 및 굽힘 시험을 통해 용접부의 외관품질에 대하여 중점적으로 수행하여 용접결함 감소 및 기존 상용용접기에 교체사용에 대한 성능 및 호환성여부에 미치는 영향에 대해 평가하였다.

• 한국물환경학회지
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• 제27권5호
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• pp.634-645
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• 2011

A newly developed rainwater harvesting (RWH) system reliability model is evaluated for roof area of buildings in Haeundae District of Busan. RWH system is used to supply water for toilet flushing, back garden irrigation, and air cooling. This model is portable because it is based on a non-parametric precipitation generation algorithm using a markov chain. Precipitation occurrence is simulated using transition probabilities derived for each day of the year based on the historical probability of wet and dry day state changes. Precipitation amounts are selected from a matrix of historical values within a moving 30 day window that is centered on the target day. Then, the reliability of RWH system is determined for catchment area and tank volume ranges using synthetic precipitation data. As a result, the synthetic rainfall data well reproduced the characteristics of precipitation in Busan. Also the reliabilities of RWH system for each of demands were computed to high values. Furthermore, for study area using the RWH system, reduction efficiencies for rooftop runoff inputs to the sewer system and potable water demand are evaluated for 23%, 53%, respectively.

• 수산해양기술연구
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• 제60권3호
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• pp.277-289
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• 2024

Climate change has led to a significant increase in jellyfish populations globally, causing various problems. For power plants that use nearby seawater for cooling, the intrusion of jellyfish into intake systems can block the flow, leading to reduced output or even shutdowns. This issue is compounded by other small marine organisms like shrimp and salps, making it urgent to develop solutions to prevent their intrusion. This study addressed the problem using the BioSonics DT-X 120 kHz scientific fish finder to conduct preliminary tank experiments. We also deployed underwater acoustic and camera buoys around the intake of nuclear power plant, utilizing a bidirectional communication system between sea and land to collect data. Data collection took place from July 31, 2023 to August 1, 2023. While harmful organisms such as jellyfish and salps were not detected, we successfully gathered acoustic data on small fish measuring backscattering strength (SV). Analysis showed that fish schools were more prominent in the evening than during the day. The highest fish distribution was observed at 3:30 AM on July 31 with an SV of -44.8 dB while the lowest was at 12:30 PM on the same day with an SV of -63.4 dB. Additionally, a solar-powered system was used to enable real-time data acquisition from sea buoys with smooth communication between the land server and the offshore buoy located 1.8 km away. This research developed an acoustic-based monitoring system for detecting harmful organisms around the intake and provided foundational data for preventing marine organism intrusion and planning effective measures.

• Korean Chemical Engineering Research
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• 제54권1호
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• pp.11-15
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• 2016

무인항공기가 장시간 비행하기 위해서는 배터리보다 고분자전해질 연료전지(PEMFC)가 적합하다. 본 연구에서는 PEMFC에 수소를 공급하는 $NaBH_4$가수분해 반응 시스템에 대해 연구하였다. $NaBH_4$가수분해 반응 시스템의 무게를 감소시키기 위해 수소수율 향상, 응축수 회수, 안정적인 수율 유지 등에 대해 실험하였다. 반응기 압력제어를 함으로써 수소 수율을 3.4% 향상시켰다. 수소를 공랭하여 PEMFC 스택에 공급하는 과정에서 발생하는 응축수를 $NaBH_4$ 저장조에 회수하였다. 이 과정에서 응축수가 $NaBH_4$분말을 용해시켜 보충됨으로써 14%의 무게 감량효과가 있었다. 2.0 L/min의 속도로 수소를 발생시킬 때 Co-P-B촉매 2.0 g을 사용해서 10시간동안 96% 수소수율로 $NaBH_4$가수분해 반응 시스템을 안정적으로 구동하였다.

• Nuclear Engineering and Technology
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• 제45권5호
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• pp.605-612
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• 2013

Removal of decay heat from an operating reactor during a prolonged station blackout condition is a big concern for reactor designers, especially after the recent Fukushima accident. In the case of a prolonged station blackout condition, heat removal is possible only by passive means since no pumps or active systems are available. Keeping this in mind, the AHWR has been designed with many passive safety features. One of them is a passive means of removing decay heat with the help of Isolation Condensers (ICs) which are submerged in a big water pool called the Gravity Driven Water Pool (GDWP). The ICs have many tubes in which the steam, generated by the reactor core due to the decay heat, flows and condenses by rejecting the heat into the water pool. After condensation, the condensate falls back into the steam drum of the reactor. The GDWP tank holds a large amount of water, about 8000 $m^3$, which is located at a higher elevation than the steam drum of the reactor in order to promote natural circulation. Due to the recent Fukushima type accidents, it has been a concern to understand and evaluate the capability of the ICs to remove decay heat for a prolonged period without escalating fuel sheath temperature. In view of this, an analysis has been performed for decay heat removal characteristics over several days of an AHWR by ICs. The computer code RELAP5/MOD3.2 was used for this purpose. Results indicate that the ICs can remove the decay heat for more than 10 days without causing any bulk boiling in the GDWP. After that, decay heat can be removed for more than 40 days by boiling off the pool inventory. The pressure inside the containment does not exceed the design pressure even after 10 days by condensation of steam generated from the GDWP on the walls of containment and on the Passive Containment Cooling System (PCCS) tubes. If venting is carried out after this period, the decay heat can be removed for more than 50 days without exceeding the design limits.

• 한국산학기술학회논문지
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• 제16권2호
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• pp.1339-1347
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• 2015

본 연구는 현장의 GMAW 용접기에 더블 와이어 릴을 겸비한 원격제어토치의 시스템에 관한 것이다. 산업현장 용접에서는 용접기 본체로부터 와이어 송급장치까지의 거리가 약 30m 떨어져 있고 송급장치로부터 토치까지의 거리는 약 3~5m 정도이다. 이에 따라 차량 및 탱크 내부의 용접에서 제어 패널을 볼 수 없는 곳이나 작업장이 먼 곳 등에서 용접사가 용접을 하면서 용접조건에 맞는 전류와 전압을 조절할 수가 없고 또한 용접와이어가 완전히 소모되면 용접을 중단하고 와이어 릴을 갈아 끼워야하는 번거로운 문제점이 있다. 이 때문에 전류와 전압 조절 및 와이어를 교체하기 위해 용접을 중단하고 잦은 이동으로 용접구조물의 순간적인 냉각에 의해 용접결함이 발생된다. 본 연구에서는 이러한 제반 문제를 감소하기 위해 기존의 GMAW 용접기의 제반기능을 토대로 간소화 및 합리화하여 더블 와이어 릴을 겸비한 원격제어토치를 자체 제작하였다. 실험은 SM50A 용접구조용 압연강재 6mm를 사용하여 와이어 더블 릴을 겸비한 원격제어 토치와 기존 $CO_2$ /MAG 용접토치를 V형 맞대기 수직자세로 용접을 실행하였다. 용접 완료 후 용접부의 표면비드 상태의 형상을 육안검사 관찰하고 또한 이를 방사선투과검사를 통해 용접부의 내부 용접품질에 대하여 용접현상을 분석하였다. 이 연구를 통해 용접결함 감소, 원가절감 및 기존 상용용접기에 교체사용에 대한 성능 및 호환성여부에 미치는 영향에 대해 평가하였다.