• Proceedings of the Korean Nuclear Society Conference
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• 2002.10a
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• pp.113.1-113
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• 2002

• International Journal of High-Rise Buildings
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• v.1 no.2
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• pp.99-105
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• 2012

The higher the building height and the larger the temperature difference between the outdoor and indoor space, the more remarkable is the draft driven by the stack effect in high-rise buildings. Moreover, the stack effect can bring about the deterioration of habitability and the degradation of the performance of the indoor control system in high-rise buildings. In this study, as a measure to attenuate the stack effect, the E/V shaft cooling method was proposed and its performance was compared with the conventional stack effect control method for strengthening the air-tightness of the building using a numerical simulation method. The total decreasing ratios on the stack effect in a building were compared, and the probabilities of the secondary problems were analyzed. The results show that the E/V shaft cooling is very effective to decrease the stack effect in a high-rise building in terms of the reduction performance and application. Moreover, this method does not cause secondary problems, such as stack pressure transition to other walls, unlike the conventional stack effect mitigation method.

• Nuclear Engineering and Technology
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• v.56 no.8
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• pp.2893-2905
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• 2024

Passive safety systems are integrated into the latest generation of Light Water Reactors (LWRs), including small modular reactors. This paper employs the US-NRC TRACE thermal hydraulic code to examine the performance of a passive safety condenser known as SACO, designed to serve as the ultimate heat sink for dissipating decay heat during accident scenarios. The TRACE model is constructed with reference to the PKL/SACO test facility. The safety condenser (SACO) is interconnected with the PKL facility via the secondary side of steam generator 1, effectively serving as a third natural circulation cooling loop during accident scenarios. In the present research, the thermal-hydraulic behavior of the PKL facility is investigated in the presence of the SACO passive safety system during an extended SBO with Loss of AC Power accident scenario. This SBO can be categorized into three distinct phases depending on the activation of the SACO system and the refilling process of the SACO pool. The first phase is depressurizing using primary and secondary relief valves, the second phase is cooling down using SACO system, and the third phase is the refilling of SACO pool. The findings indicate that the SACO system effectively manages to dissipate all decay heat, even though there is temporary evaporation of the SACO water pool. Furthermore, this study provides sensitivity analysis for the assessments of system codes on the selection of maximum time step.

• Nuclear Engineering and Technology
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• v.45 no.4
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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.

• Journal of Power System Engineering
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• v.16 no.2
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• pp.24-29
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• 2012

In this paper, an analysis on performance and exergy of R404A refrigeration system using R744 secondary refrigerant was performed numerically to optimize the design for the operating parameters. The operating parameters considered in this study include subcooling and superheating degree, internal heat exchanger and compression efficiency, evaporation and condensation temperature in the R404A refrigeration cycle and temperature difference of cascade heat exchanger. The main results are summarized as follows : The COP(coefficient of performance) of R404A refrigeration system increases with increasing evaporation temperature. The evaporation capacity of R744 as secondary refrigerant increases with the increase in evaporation pressure of R744 secondary refrigeration. And the enthalpy in the evaporator outlet of R744 increases with the increasing evaporation pressure of R744 secondary refrigeration. Therefore, it is important to analysis for the relationship between COP of R404A refrigeration system and refrigeration capacity of R744. As cascade evaporation temperature increase, the exergy loss of condenser and compressor using R404A is the largest among all components. Therefore, the exergy loss in the condenser and compressor using R404A must be decreased to enhance the COP of R404A refrigeration system with R744 secondary refrigerant.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.11a
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• pp.33-34
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• 2005

The internal state of an automotive engine is very severe. A piston exposes burnt gas of over $2000^{\circ}$ nd is shocked by high pressure at the time of explosion. Furthermore strong friction is caused by high speed motion. A study on the cooling of the piston requires because the cooling and lubrication of the piston has an effect on the life and efficiency of engine directly. The previous system of oil jet cooled only the bottom of the piston. In order to improve the cooling efficiency, the oil gallery is made inside the piston, and oil flows into the oil gallery. The flow rate of oil at the entrance of oil gallery is important because of the cooling efficiency. The purpose of this study is the investigation of fluid flow characteristics of oil jet and flow rate into the oil gallery.

• Architectural research
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• v.16 no.4
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• pp.203-210
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• 2014

The packaged terminal air conditioner, the typical cooling system for the residential buildings, consumes a large amount of electricity in a short period time during peak hours. In order to reduce the peak load and conserve the electricity, the thermally activated building system can be used as a secondary system to handle the partial cooling load. However, the thermally activated building system may cause condensation and under-cooling. Thus, design of both systems should be performed with careful investigation in characteristics of both systems to amplify the advantages. Since the thermally activated building system has the time-delay effect which may cause under-cooling, the system is designed to handle the base load of the building. Hence, simple simulation with EnergyPlus was performed to observe the characteristics of cooling load in residential buildings. Once the possible range of the load handling ratio of the thermally activated building system was decided, characteristics of system was analyzed in terms of hardware component and operation parameters. The hardware components were analyzed in plant and system aspects and the operation parameter was evaluated in the thermal comfort aspect. As the load handling ratio increased, the thermal comfort increased due to the lower radiant mean temperatures. Within the range of thermal comfort, the several adjustments were made in setpoint temperature and electricity consumptions of difference cases were observed to decide which components and parameters were important for designing the systems.

• Nuclear Engineering and Technology
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• v.31 no.1
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• pp.68-79
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• 1999

The YGN Units 3&4 plant conditions during shutdown operation were reviewed to identify the possible event scenarios following the loss of shutdown cooling (SDC) event. For the five cases of typical reactor coolant system (RCS) configurations under the worst event sequence, such as unavailable secondary cooling and no RCS inventory makeup, the thermal hydraulic analyses were performed using the RELAP5/MOD3.2 code to investigate the plant behavior following the event. The thermal hydraulic analyses include the estimation of time to boil, time to core uncovery, and time to core heat up to determine the containment closure time to prevent the uncontrolled release of fission products to atmosphere. The result indicates that the containment closure is recommended to be achieved within 42 minutes after the loss of SDC for the steam generator (SG) inlet plenum manway open case or the large cold leg open case under the worst event sequence. The containment closure time is significantly dependent on the elevation and size of the opening and the SG secondary water level condition. It is also found that the containment closure needs to be initiated before the boiling time to ensure the survivability of the workers in the containment. These results will provide useful information to operators to cope with the loss of SDC event.

• Journal of the Korean Society for Heat Treatment
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• v.35 no.6
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• pp.319-326
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• 2022

Direct extrusions of an aluminum 7075 alloy were carried out using 1500 ton machine with and without die cooling system. Cooling of extrusion die has been performed by the flow of liquid nitrogen and controlled by laser thermometer. Billet was 180 mm in diameter and 500 mm in length. The preheating temperatures of billet, container and die were 390℃, 400℃ and 450℃, respectively. Ram speed was kept with 1.25 mm/sec first. The change of ram speed was carried out during extrusion according to the observation of surface defects such as crack or tearing. Extrudates of 8.3 m in length, 100 mm in width and 15 mm in thickness were obtained to observe and analyze surface defects by optical microscopy and EBSD (Electron BackScattered Diffraction). In case of extrusion without die cooling cracks on the surface and tearing in the corner of extrudate occurred in the middle stage and developed in size and frequency during the late stage of extrusion. At the extrusion with die cooling the occurrence of defects could be suppressed on the most part of extrudate. EBSD micrographs showed that cracks and tearings have been resulted from the same origin. Surface defects were generated at the boundaries of grains formed by secondary recrystallization due to surface overheating during extrusion.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.1
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• pp.47-54
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• 2006

[ $CO_2$ ] and propane mixtures were chosen as promising alternative refrigerants and their performance potentials were evaluated experimentally in an air-conditioning system. Pure $CO_2$ and 85/15, 75/25 and 60/40 binary blends by the charged mass percentage of $CO_2/propane$ were selected as working fluids. The effect of the inlet temperature of the secondary fluids and degree of superheat on the cooling performance was tested and discussed. The charging amounts of refrigerants were adjusted to make the system show the maximum COP. Comparisons among different refrigerants were carried out on the same compressor speed basis for a given operating condition. In addition, the temperature gliding effect of zeotropic mixtures on the system performance were analyzed based on the drop-in test results.