• Nuclear Engineering and Technology
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• v.42 no.5
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• pp.590-599
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• 2010

Recently, efficient operation and practical management of power plants have become important issues in the nuclear industry. In particular, typical aging parameters such as stress and cumulative usage factor should be determined accurately for continued operation of a nuclear power plant beyond design life. However, most of the major components have been designed via conservative codes based on a 2-D concept, which do not take into account exact boundary conditions and asymmetric geometries. The present paper aims to suggest an effective fatigue evaluation methodology that uses a prototype of the integrated model and its transfer functions. The validity of the integrated 3-D Finite Element (FE) model was proven by comparing the analysis results of individual FE models. Also, mechanical and thermal transfer functions, known as Green's functions, were developed for the integrated model with the standard step input. Finally, the stresses estimated from the transfer functions were compared with those obtained from detailed 3-D FE analyses results at critical locations of the major components. The usefulness of the proposed fatigue evaluation methodology can be maximized by combining it with an on-line monitoring system, and this combination, will enhance the continued operations of old nuclear power plants.

• Journal of the Korean Solar Energy Society
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• v.32 no.4
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• pp.96-102
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• 2012

The minimum airflow of VAV terminal boxes is a key factor for comfort, indoor air quality(IAQ) and energy cost. If the minimum airflow is not reasonable, it would waste energy and make IAQ problems. There are two types of VAV terminal box control logic. One is the single maximum, another is the dual maximum control logic. Dual maximum control logic is more efficiency way to reduce the energy consumption. It has a minimum airflow set point and a heating maximum set point. It allows the minimum airflow set point to be much lower than single maximum control logic. A building simulation was conducted to evaluate the energy consumption and the IAQ according to the control logic of the V AV terminal box. In the simulation, dual maximum control logic can save the energy up to 6.5% compared to the single maximum control logic.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.2
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• pp.142-149
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• 2004

Recently, the government introduced the thermal storage system for reducing the electric power load. Especially, the ice slurry type has gained lots of interest due to its good heat transfer and flowing characteristics. This study was peformed to understand the effects of transporting ice slurry through elbows of various angle. Propylene glycol water solution was used and about 2 mm ice particles were circulated. The experiments were carried out under various conditions, such as concentration and velocity of water solution ranging between 0∼20 wt％, 1.5∼2.5 m/s, respectively. And elbows with 4 different angles of 30$^{\circ}$, 45$^{\circ}$, 90$^{\circ}$, 180$^{\circ}$. The differential pressure and IPF (ice packing factor) between the pipe entry and exit were measured. The tendency of pressure loss and outlet IPF in elbow is that the pressure loss was reduced as concentration and flow velocity of water solution is increased, and low value appeared at 10 wt％ and 2.5 m/s. The variation of outlet IPF was compared with the inlet IPF in the range of $\pm$20％.

• International Journal of Precision Engineering and Manufacturing
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• v.9 no.4
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• pp.3-10
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• 2008

Micro-electrical discharge machining (micro-EDM) is an effective method for machining all types of conductive materials regardless of hardness. Since micro-EDM is an electro-thermal process, the energy supplied by the pulse generator is an important factor in determining the effectiveness of the process. In this study, an investigation was conducted on the micro-EDM of tungsten carbide (WC) to compare the performance of transistor and resistance/capacitance (RC) pulse generators in obtaining the best quality micro-hole. The performance was measured by the machining time, material removal rate, relative tool wear ratio, surface quality, and dimensional accuracy. The RC generator was more suited for minimizing the pulse energy, which is a requirement for fabricating micro-parts. The smaller-sized debris formed by the low-discharge energy of RC micro-EDM could be easily flushed away from the machined zone, resulting in a surface free of burrs and resolidified molten metal. The RC generator also required much less time to obtain the same quality micro-hole in WC. Therefore, RC generators are better suited for fabricating micro-structures, producing good surface quality and better dimensional accuracy than the transistor generators, despite their higher relative tool wear ratio.

• Nuclear Engineering and Technology
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• v.33 no.4
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• pp.441-456
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• 2001

ABB-CE＇s regionalization methodology for the core inlet flow distribution map is reviewed. This methodology merges the test data of fuel assembly locations which are either in symmetry or strongly correlated with others. It increases the number of available test data for each regional flow factor It makes up effectively for the deficiency due to limited number of test data. It also contributes to making the core inlet flow distribution smoother not only locally but also over the entire core, and to relieving the impacts of test errors that may happen due to some do- calibrated local pressure measurement taps. As a result, the core inlet How distribution data becomes more statistically useful and thus the conservatism involved in handling the core inlet flow factors for the thermal margin analysis is expected to be reduced. Meanwhile, the regionalized map may lose the unique local characteristics in core inlet flow distribution too much. By an alternative approach introduced in the present work, it is shown that such a disadvantage can be mitigated somewhat if the engineering judgement is made more

• Journal of the Semiconductor & Display Technology
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• v.19 no.1
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• pp.42-48
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• 2020

As global warming accelerates, eco-friendly electric cars are being developed to reduce carbon dioxide emissions, and power conversion inverters are used to drive motors. Among inverter components, DC-link capacitor is heated by high current usage, which causes problems such as performance and life-saving of inverter. Although metal cases with good thermal performance have been used to solve this problem, it is difficult to apply them in practice due to insulation problems with other parts. In this paper, the Heat-Generation influence factor of DC-link capacitor is analyzed. Variables on heat-generation are set at 3 levels for film width, inductance, and film thickness. Box-Behnken to 13 tests using the design and minimal deviations, e.g. through the experiment three times by each level. The surface of the film k type by attaching the sensor current is measured temperature. Capacitance was set to a minimum level of 200 ㎌ and had a frequency of 16 kHz with Worst case, ambient temperature of 85℃ and a ripple current of 50 Ams was applied. The temperature at the measurement point was collected in the data logger after sampling at 1 minute intervals for 2 hours after saturation with the ambient temperature. This experiment confirmed that setup factors are correlated with heat-generation.

• Membrane Journal
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• v.9 no.4
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• pp.215-220
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• 1999

The asymmetric polyimide [PI] membrane with good solvent-resisting and heat-resisting properties was prepared by using the phase inversion method from polyamic acid, and its pervaporation separation characteristics of water-acetic acid system were studied. It was appeared from the prepared membranes that the best non-solvent of polyamie acid for the phase inversion was toluene. The best heat-treatment condition for the imidization of polyamic acid was 1 hr heating at each of the temperatures, 373, 473, and 573 K The thermal durability and chemical stability during the pervaporation separation of water-acetic acid of the prepared PI membrane was superior. The pervaporation characteristics of prepared membrane were 180 of separation factor and 0.5 kg/$m^2$hr of total flux for 80 wt% acetic acid feed.

• Journal of Astronomy and Space Sciences
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• v.35 no.1
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• pp.39-46
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• 2018

In this study, the performance of ranging techniques for the Korea Pathfinder Lunar Orbiter (KPLO) space communication system is investigated. KPLO is the first lunar mission of Korea, and pseudo-noise (PN) ranging will be used to support the mission along with sequential ranging. We compared the performance of both ranging techniques using the criteria of accuracy, acquisition probability, and measurement time. First, we investigated the end-to-end accuracy error of a ranging technique incorporating all sources of errors such as from ground stations and the spacecraft communication system. This study demonstrates that increasing the clock frequency of the ranging system is not required when the dominant factor of accuracy error is independent of the thermal noise of the ranging technique being used in the system. Based on the understanding of ranging accuracy, the measurement time of PN and sequential ranging are further investigated and compared, while both techniques satisfied the accuracy and acquisition requirements. We demonstrated that PN ranging performed better than sequential ranging in the signal-to-noise ratio (SNR) regime where KPLO will be operating, and we found that the T2B (weighted-voting balanced Tausworthe, voting v = 2) code is the best choice among the PN codes available for the KPLO mission.

• Journal of Microbiology and Biotechnology
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• v.27 no.7
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• pp.1209-1215
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• 2017

Microwave sterilization was performed to inactivate the spores of biofilms of Bacillus cereus involved in foodborne illness. The sterilization conditions, such as the amount of water and the operating temperature and treatment time, were optimized using statistical analysis based on 15 runs of experimental results designed by the Box-Behnken method. Statistical analysis showed that the optimal conditions for the inactivation of B. cereus biofilms were 14 ml of water, $108^{\circ}C$ of temperature, and 15 min of treatment time. Interestingly, response surface plots showed that the amount of water is the most important factor for microwave sterilization under the present conditions. Complete inactivation by microwaves was achieved in 5 min, and the inactivation efficiency by microwave was obviously higher than that by conventional steam autoclave. Finally, confocal laser scanning microscopy images showed that the principal effect of microwave treatment was cell membrane disruption. Thus, this study can contribute to the development of a process to control food-associated pathogens.

• Korean Journal of Food Science and Technology
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• v.29 no.3
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• pp.497-501
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• 1997

Kinetic parameters on heat-induced color changes of anthocyanin pigment from purple sweet potato were determined in the temperature range of $121{\sim}141^{\circ}C$. Color change determined by a browning index $(A_{532}\;nm/A_{420}\;nm)$ followed second order reaction kinetics. Activation energy values of purple sweet potato pigment solutions of pH 2.0, 3.0, 4.0 and 5.0 were 69.57, 76.68, 81.07 and 92.98 kJ/mol, respectively, indicating that temperature dependency of the reaction increased with pH. Apparent kinetic compensation effect between preex-ponential factor and activation energy value was observed.