• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 추계학술대회 논문집
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• pp.1726-1735
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• 2008

Seoulmetro has operated the air cooling equipment for 57 stations to improve services focused on our customers who use Seoulmetro during the summer season and has established every year. However, a new set of problems has arisen with the cooling tower to support a heat exchange of cooling water. The most important matter is loss of efficiency in the cooling tower. The leading cause of this problem is that we use an indoor type. As the cooling tower room is located in the underground of the city because of the residents near the station. Therefore It is difficult to establish the cooling tower on the ground. But it is unsuitable for the location requirements of the underground type because it has a limited space to set up the air cooling equipment, for example, the cooling tower and a ventilating opening. As a result of such an unfavorable condition, the cooling tower doesn't work efficiently and the warmth of cooling water because of insufficiency of a heat exchange and a refrigerator's technical obstacle such as a high-temperature and a high-pressure has arisen. To prevent this situation, the operator tend to reduce refrigerant. Accordingly, the efficiency of the air conditioning is getting lower and lower. Study wishes to analyze the matter to improve indoor cooling tower efficiency and recommend a best practice for a person who manage the establishment.

• 한국안전학회지
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• 제27권5호
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• pp.229-234
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• 2012

Operator's action time is evaluated from MAAP4 analysis used in conventional probabilistic safety assessment(PSA) of a nuclear power plant. MAAP4 code which was developed for severe accident analysis is too conservative to perform a realistic PSA. A best-estimate code such as RELAP5/MOD3, MARS has been used to reduce the conservatism of thermal hydraulic analysis. In this study, operator's action time of core cooling recovery operation is evaluated by using the MARS code, which its Fussell-Vessely(F-V) value was evaluated as highly important in a small break loss of coolant(SBLOCA) event and loss of component cooling water(LOCCW) event in previous PSA. The main conclusions were elicited : (1) MARS analysis provides larger time window for operator's action time than MAAP4 analysis and gives the more realistic time window in PSA (2) Sufficient operator's action time can reduce human error probability and core damage frequency in PSA.

• 대한기계학회논문집B
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• 제21권9호
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• pp.1185-1197
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• 1997

Three-dimensional flow within a film-cooling hole, which is normally oriented to the main flow, has been measured by using a straight five-hole probe for the blowing ratios of 1.0 and 2.0. The length-to-diameter ratio of the injection hole is fixed to be 1.0 throughout the whole experiments. The result shows that the secondary flow within the hole is strongly affected by the main flow and flow separation at the hole inlet. The higher blowing ratio provides less influence of the main flow on the injectant flow. The three-dimensional flow at the hole exit is considerably altered due to the strong interaction between the injectant and main flow. The aerodynamic loss produced inside the injection hole is mainly attributed to the inlet flow separation.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1998년도 춘계학술발표회논문집(1)
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• pp.647-652
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• 1998

The YGN Units 3&4 plant conditions during shutdown operation were reviewed to identified the possible even scenarios following the loss of shutdown cooling. The Thermal hydraulic analyses were performed for the five cases of RCS configurations under the worst event scenario, unavailable secondary cooling and no RCS inventory makeup, using the RELAP5/MOD3.2 code to investigate the plant behavior, From the analyses results, times to boil, times to core uncovery and times to core heat up were estimated to determined the containment closure time to prevent the uncontrolled released of fission products to atmosphere, These data provide useful information to the abnormal procedure to cope with event.

• Journal of Advanced Marine Engineering and Technology
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• 제32권4호
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• pp.596-602
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• 2008

The cooling system is one of the most concerning factor for the reliability of the electric propulsion ship. Generally, a drive system operation in higher temperature decreases the device's reliability and power efficiency. The management of power loss and temperature of switching devices is indispensable for the reliability of the power electric system. In this paper, the switching devices are molded by IGBT, and the propulsion system is consisted of MIIR(Motor with Inverter Internal to Rotor). The system composition interacts with each other to calculate the loss and temperature of device. The calculation result is used for modeling and designing of the control and monitoring system for the electric propulsion system.

• Nuclear Engineering and Technology
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• 제45권4호
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• pp.459-468
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• 2013

During a station blackout (SBO), the initiating event is a loss of Class IV and Class III power, causing the loss of the pumps, used in systems such as the primary heat transporting system (PHTS), moderator cooling, shield cooling, steam generator feed water, and re-circulating cooling water. The reference case of the SBO case does not credit any of these active heat sinks, but only relies on the passive heat sinks, particularly the initial water inventories of the PHTS, moderator, steam generator secondary side, end shields, and reactor vault. The reference analysis is followed by a series of sensitivity cases assuming certain system availabilities, in order to assess their mitigating effects. This paper also establishes the strategies to mitigate SBO accidents. Current studies and strategies use the computer code of the Integrated Severe Accident Analysis Code (ISAAC) for Wolsong plants. The analysis results demonstrate that appropriate strategies to mitigate SBO accidents are established and, in addition, the symptoms of the SBO processes are understood.

• 한국초전도ㆍ저온공학회논문지
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• 제5권1호
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• pp.76-80
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• 2003

A contractible heat pipe is designed and tested to improve cooling performance of conduction cooled superconducting magnet. When the heat pipe temperature drops below the triple point temperature, heat pipe working fluid freezes to create low pressure. From this moment the heat pipe does net work any more (OFF state) and it just works as a heat leak path when the temperature of the first stage is higher than that of the second stage. Considering small cooling capacity of the second stage around 4.2 K, the conduction loss is not negligible. Therefore, the contractible heat pipe, made of a metal bellows and copper tubes, was considered to eliminate the conduction loss. Nitrogen and argon are as working fluid of heat pipe. The copper block is cooled down with these heat pipe and the cooling performance for each heat pipe is compared. At off state, the bellows is contracted due to the low pressure of heat pipe and the evaporator section of the heat pipe is detached about 3 mm from the second stage cold head of the cryocooler. In this way, we tan eliminate the conduction loss through the heat pipe wall.

• 조명전기설비학회논문지
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• 제29권9호
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• pp.71-80
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• 2015

This paper proposes a convenient thermal modeling method for loss distribution control method of 3-level Active NPC(Neutral Point Clamped) inverter. In the drawback of conventional 3-level NPC, the generated losses can occur unbalance in each switching device, as a result, thermal utilization of designed system has been decreased. In order to compensate unbalanced losses, Active NPC inverter performed loss balancing control with thermal modeling during operation of each switching device. Therefore, this paper deals with a convenient thermal modeling method based on newton's law of cooling rather than conventional thermal modeling method. Both simulation and experimental results based on 10kW 3-level Active NPC inverter confirm the validity of the analysis performed in the study.

• Nuclear Engineering and Technology
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• 제55권8호
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• pp.3102-3113
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• 2023

Following the Fukushima nuclear disaster, the simulation of accidents in the spent fuel pool has become more noticeable. Despite the low amount of decay heat power, the consequences of the accidents in a spent fuel pool (SFP) can be severe due to the high content of long-lived radionuclides and lack of protection by the pressure vessel. In this study, the loss-of-cooling accident (LOFA) for the VVER-1000/V446 spent fuel pool is simulated by employing RELAP5 and MELCOR 1.8.6 as the best estimate and severe accident analysis codes, respectively. For two cases with different total power levels, decay heat of spent fuels is calculated by ORIGEN-II code. For modeling SFP of a VVER-1000, a qualified nodalizations are considered in both codes. During LOFA in SFP, the key sequences such as heating up of the pool water, boiling and reducing the water level, uncovering the spent fuels, increasing the temperature of the spent fuels, starting oxidation process (generating Hydrogen and extra power), the onset of fuel melting, and finally releasing radionuclides are studied for both cases. The obtained results show a reasonable consistency between the RELAP5 and MELCOR codes, especially before starting the oxidation process.

• 설비공학논문집
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• 제10권1호
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• pp.88-94
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• 1998

The thermal performance of cooling towers is affected mainly by the velocity, temperature and humidity of the entering air, In this paper, the effects of these variables are experimentally investigated for both counter-flow and cross-flow cooling towers. The cooling performance is reduced by up to 50% as the relative humidity of the entering air is increased from 40% to 80%. The higher air velocity and lower coolant flow show better cooling performance. The coolant loss rates in the present experimental conditions are in the range of 0.4 to 1.7%