• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.8 no.2
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• pp.42-47
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• 2012

The containment local leakage rate testing in nuclear power plants is performed in accordance with ANSI/ANS 56.8-1994 in Korea. Two methods, the make-up flow rate and the pressure decay, are used for local leakage rate testing. Though ANSI/ANS 56.8-1994 does not define clearly the minimum test duration for the make-up flow rate method, it requires obtaining the data after reaching the stable condition. Thus the prerequisite stable condition for data acquisition and the testing time is differently applied to each NPPs. Therefore, this study presents a standardized test procedure for data stabilization and testing time through experiments to improve the test reliability.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1999.11a
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• pp.149-154
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• 1999

This paper describes a passive safety injection system with free piston Stirling pump working withabundant decay heat in the nuclear reactor during the hypothetical accident. The water column in the tube assembly connected from the hot chamber to the cold chamber in the pump oscillates periodically due to thermal volume changes of non-condensable gas in each chamber. The oscillating pressure in the water column is converted into the pumping power with a suction-and-bleed type valve assembly. In this paper a dynamic model describing the frequency of oscillation and pumping pressure is developed. It was found that the pumping pressure is a function of the temperature difference between the chambers. Also, the frequency oscillation depends on the length of the tube with water column.

• Nuclear Engineering and Technology
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• v.26 no.1
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• pp.19-31
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• 1994

The objective of this study is to conduct a thermal-hydraulic analysis on the spent fuel pool and to evaluate a parametric effect for the thermal-hydraulic analysis of spent fuel pool. The selected parameters are the Reynolds Number and the gap flow through the oater gap between fuel cell and fuel bundle. The simplified flow network for a path of fuel cells is used to analyze the natural circulation phenomenon. In the flow network analysis, the pressure drop for each assembly from the entrance of the fuel rack to the exit of the fuel assembly is balanced by the driving head due to the density difference between the pool fluid and the average fluid in each spent fuel assembly. The governing equations ore developed using this relation. But, since the parameters(flow rate, pressure loss coefficient, decay heat, density)are coupled each other, iteration method is used to obtain the solution. For the analysis of the YGN 3&4 spent fuel rack, 12 channels are considered and the inputs such as decay heat and pressure loss coefficient are determined conservatively. The results show the thermal-hydraulic characteristics(void fraction, density, boiling height)of the YGN 3&4 spent fuel rack. There occurs small amount of boiling in the cells. Fuel cladding temperature is lower than 343.3$^{\circ}C$. The evaluation of parametric effect indicates that flow resistances by geometric effect are very sensitive to Reynolds number in the transition region and the gap flow is negligible because of the larger flow resistance in the gap flow path than in the fuel bundle.

• Food Science and Preservation
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• v.23 no.6
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• pp.772-777
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• 2016

Activity of the noncontacted low temperature atmospheric pressure surface discharged plasma (LASDP) converts stable gas to ionized gas known as discharge or plasma. This ionized gas exhibits the antimicrobial activity. We examined the effects of 3 different storage treatments for 80 days on 'Setoka' : ambient storage (AS), low-tempperature storage (LTS), and low-temperature atmospheric pressure plasma+low-tempperature storage (PLTS). Total soluble solids showed no the significant differences between the 3 treatments. Acidity gradually decreased, and was 0.5% under AS after 30 days of storage. Fruit firmness increased by a few percent until 40 days of storage. Weight loss in AS was higher than for other treatments. After 80 days of storage, the decay ratio was significantly low in PLTS treatment: (AS, 50.5%; LTS, 5.6%; PLTS, 1.9%). In AS treatment, 73% of the rotten fruits were infected particularly with green and blue mold; however, only 1% of the rotten fruits were infected in case of PLTS treatment. In conclusion, LASDP treatment can prevent postharvest decay caused by fungi and is an efficacious alternative extending the shelf-life of citrus fruits.

• Wind and Structures
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• v.24 no.1
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• pp.79-93
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• 2017

Wind-induced fluctuating internal pressures in a building with a dominant opening can be described by a second-order non-linear differential equation. However, the accuracy and efficiency of the governing equation in predicting internal pressure fluctuations depend upon two ill-defined parameters: inertial coefficient $C_I$ and loss coefficient $C_L$, since $C_I$ determines the un-damped oscillation frequency of an air slug at the opening, while $C_L$ controls the decay ratio of the fluctuating internal pressure. This study particularly focused on the value of loss coefficient and its influence factors including: opening configuration and location, internal volumes, as well as wind speed and approaching flow turbulence. A simplified formula was presented to predict loss coefficient, therefore an approximate relationship between the standard deviation of internal and external pressures can be estimated using Vickery's approach. The study shows that the loss coefficient governs the peak response of the internal pressure spectrum which, in turn, will directly influence the standard deviation of the fluctuating internal pressure. The approaching flow characteristic and opening location have a remarkable effect on the parameter $C_L$.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.357.1-357.1
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• 2014

Superhydrophobic WOx nanowire (NW) arrays were fabricated using a thermal evaporation and surface chemistry modification methods by self-assembled monolayer (SAM). As-prepared non-wetting WOx NWs surface shows water contact angle of $163.2^{\circ}$ and has reliable stability in underwater conditions. Hence the superhydrophobic WOx NWs surface exhibits silvery surface by total reflection of water layer and air interlayer. The stability analysus of underwater superhydrophobicity of WOx NWs arrays was conducted by changing hydrostatic pressure and surface energy of WOx NWs arrays. The stability of superhydrophobicity in underwater conditions decreased exponentially as hydrostatic pressure applied to the substrates increased3. In addition, as surface energy decreased, the underwater stability of superhydrophobic surface increased sharply. Specifically, sueprhydrophobic stability increased exponentially as surface energy of WOx NWs arrays was decreased. Based on these results, the models for explaining tendencies of superhydrophobic stability underwater resulting from hydrostatic pressure and surface energy were designed. The combination of fugacity and Laplace pressure explained this exponential decay of stability according to hydrostatic pressure and surface energy. This study on fabrication and modeling of underwater stability of superhydrophobic W18O49 NW arrays will help in designing highly stable superhydrophobic surfaces and broadening fields of superhydrophobic applications even submerged underwater.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.601-601
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• 2013

Superhydrophobic W18O49 nanowire (NW) arrays were synthesizedusing a thermal evaporation and surface chemistry modification methods by self-assembled monolayer (SAM). As-prepared non-wetting W18O49 NWs surface shows water contact angle of $163.2^{\circ}$ and has reliable stability in underwater conditions. Hence the superhydrophobic W18O49 NWs surface exhibits silvery surface by total reflection of water layer and air interlayer. The stability analysus of underwater superhydrophobicity of W18O49 NWs arrays was conducted by changing hydrostatic pressure and surface energy of W18O49 NWs arrays. The stability of superhydrophobicity in underwater conditions decreased exponentially as hydrostatic pressure applied to the substrates increased3. In addition, as surface energy decreased, the underwater stability of superhydrophobic surface increased sharply. Specifically, sueprhydrophobic stability increased exponentially as surface energy of W18O49 NWs arrays was decreased. Based on these results, the models for explaining tendencies of superhydrophobic stability underwater resulting from hydrostatic pressure and surface energy were designed. The combination of fugacity and Laplace pressure explained this exponential decay of stability according to hydrostatic pressure and surface energy. This study on fabrication and modeling of underwater stability of superhydrophobic W18O49 NW arrays will help in designing highly stable superhydrophobic surfaces and broadening fields of superhydrophobic applications even submerged underwater.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.364-370
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• 2008

Spinning detonations propagating in a circular tube were numerically investigated with a one-step irreversible reaction model governed by Arrhenius kinetics. The time evolution of the simulation results was utilized to reveal the propagation mechanism of single-headed spinning detonation. The track angle of soot record on the tube wall was numerically reproduced with various levels of activation energy, and the simulated unique angle was the same as that of the previous reports. The maximum pressure histories of the shock front on the tube wall showed stable and unstable pitch modes for the lower and higher activation energies, respectively. The shock front shapes and the pressure profiles on the tube wall clarified the mechanisms of two modes. The maximum pressure history in the stable pitch remained nearly constant, and the single Mach leg existing on the shock front rotated at a constant speed. The high and low frequency pressure oscillations appeared in the unstable pitch due to the generation and decay of complex Mach interaction on the shock front shape. The high frequency oscillation was self-induced because the intensity of the transverse wave was changed during propagation in one cycle. The high frequency behavior was not always the same for each cycle, and therefore the low frequency oscillation was also induced in the pressure history.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.472-478
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• 2004

This paper describes the characteristics of the unsteady pressure on the stator surface induced by rotor viscous wakes. The primary object of this study is to investigate the effects of axial spacing between the rotor and the stator and three-dimensional vane geometries such as stator sweep and stator lean on the unsteady pressure fluctuations on the stator vane. To predict these fluctuations, unsteady three-dimensional Navier-Stokes analyses are performed. Furthermore, a three-dimensional analytical method using unsteady lifting-surface theory is also used to elucidate the mechanism of interaction of passing rotor wakes with downstream stator. Five different fan configurations with three sets of stator geometries, which are three radial stator configurations with different axial spacing, the swept stator and the swept and leaned stator, are used for this study. It is found that, in axial spacing between rotor and stator, the effect of radial phase skew of incoming rotor wake is important for the reduction of the induced unsteady pressure in addition to the rotor wake decay. It is also shown that incorporation of stator sweep and lean is effective to reduce this unsteady pressure.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.10a
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• pp.250-255
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• 1997

The computer simulation and mock-up test are recently applied to the practical design for the room acoustics to predict and evaluate its characteristics. In this paper, the sound field properties predicted and evaluated by the computer simulation were compared to the measured data. Comparison and analysis between simulation data and measured data were performed for the Reverberation Time, Sound Pressure Level at the various measuring positions and frequencies and Definition, Early Decay Time, Speech Transmission Index.