• 항공우주기술
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• 제3권1호
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• pp.97-102
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• 2004

우주비행체의 추진시스템은 주차 궤도에서 임무 궤도도의 진입을 위해 필요한 임펄스 및 궤도에서의 3축 자세제어에 요구되는 적절한 임펄스를 제공하는 역할을 수행한다. 다목적실용위성 2호의 추진시스템은 용접으로 조립된 단일추진제 하이드라진 시스템으로 추력기, 추진제 탱크, 압력변환기, 추진제 필터, 격리밸브 및 충전/배출 밸브 등의 주요부품들로 구성되며, 그 외 각 부품들을 연결해주는 추진제 배관과 열제어 부품들이 추가된다. 이 논문에서는 설계에서부터 조립/시험에 걸친 액체 추진시스템의 개발과정을 서술하였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 춘계학술대회 논문집 초전도 자성체
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• pp.64-67
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• 2002

The Physical and magnetic properties such as microstructure, permeability and power loss of Ni-Zn ferrite with composition of $Ni_{0.8}Zn_{0.2}Fe_2O_4$, were investigated as the function of $Bi_2O_3$ and CaO contents. The power loss increased in proportion to the amount of $Bi_2O_3$ up to 0.3 wt% but it decreased over than 0.3 wt% addition. The highest permeability of 134 was obtained to the specimen added 1.0 wt% $Bi_2O_3$ since $Bi_2O_3$ contents were strongly dominant to grain growth and size than that of CaO. $Bi_2O_3$ liquid phase created during sintering process promoted sintering and grain growth so that grain size and permeability increased compared to that of the specimens which were sintered with free-additive and CaO. Also, lots of pores existed in the specimen which was added $Bi_2O_3$ wt% with the biggest grain size.

• 한국분무공학회지
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• 제18권1호
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• pp.55-60
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• 2013

In this study, injection flow rates and material of the solenoid sealing of the injectors were improved for the development of a di-methyl Ether(DME) common-rail system. To deliver the same amount of energy provided by injection pressure of diesel $P_{inj}$ = 160 MPa, the DME injectors need to have larger diameter of nozzle hole and more No. of hole at low injection pressure of $P_{inj}$ = 40~50 MPa. The simplified nozzle flow model, which takes account of nozzle geometry and injection condition, was employed in order to design the concept of a injector nozzle such as No. of hole, diameter of hole and diameter of needle seat, etc. Injection amount and rate were tested by diesel and DME test stand. As a result, the diameter of nozzle hole were enlarged by 0.25 mm. The diameter of the orifice in the high pressure line was increased by 1.0 mm to maintain hydraulic force in the nozzle. The material of the solenoid sealing was changed to HNBR, which was strong against the corrosive. Experimental results showed that the injection amount of the DME injector drastically increased by 191.9% comparison to that of diesel at $P_{inj}$ = 40 MPa.

• Nuclear Engineering and Technology
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• 제47권3호
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• pp.332-339
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• 2015

The leak before break (LBB) concept is widely used in designing pipe lines in nuclear power plants. According to the concept, the amount of leaking liquid from a pipe should be more than the minimum detectable leak rate of a leak detection system before catastrophic failure occurs. Therefore, accurate estimation of the leak rate is important to evaluate the validity of the LBB concept in pipe line design. In this paper, a program was developed to estimate the leak rate through circumferential cracks in pipes in nuclear power plants using the Henry-Fauske flow model and modified Henry-Fauske flow model. By using the developed program, the leak rate was calculated for a circumferential crack in a sample pipe, and the effect of the flow model on the leak rate was examined. Treating the crack morphology parameters as random variables, the statistical behavior of the leak rate was also examined. As a result, it was found that the crack morphology parameters have a strong effect on the leak rate and the statistical behavior of the leak rate can be simulated using normally distributed crack morphology parameters.

• 설비공학논문집
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• 제7권3호
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• pp.366-381
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• 1995

A performance analysis of refrigeration system using the HFC-134a and scroll compressor is performed numerically. The refrigeration system mainly consists of various standard components such as heat exchanger, compressor, and expansion device. The model for heat exchanger performance is based on a tube-by-tube method which is analyzed separately by considering the cross-flow heat transfer with the outdoor air flow and pressure drop. Compressor is used the scroll-type compressor which has many merits such as high efficiency, low noise and vibration, and small in size. Short-tube is included as an expansion device. Vapour and liquid line are also considered for the performance analysis of refrigeration system. Using the modeling of various components of refrigeration system, a performance comparison of CFC-12 and HFC-134a is performed numerically for the various outdoor air temperature and various values of short-tube diameter. As the results of this study, the refrigeration system performance decreases as the outdoor air temperature increases. And the optimum short-tube diameter based on COP is 1.37mm for this system.

• Journal of the Optical Society of Korea
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• 제16권2호
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• pp.151-156
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• 2012

Reflective polarizers can be used as luminance enhancement films for LCD backlights via the polarization recycling process. The optical performances of a wire grid polarizer (WGP) as a reflective polarizer adopted in edge-lit backlights were investigated by luminance evaluation and a time-domain simulation technique. The results were compared to those of a commercial dielectric multilayer film. The luminance gain factor of WGP was smaller than that of the multilayer film by 18%. This was attributed to a much larger internal loss of WGP due to light absorption by metal wires. The internal losses of both reflective polarizers and the polarization conversion efficiency of the backlight were obtained numerically based on a phenomenological model. The optical performances of WGP were optimized by using a time-domain simulation technique. The luminance gain increased and was found to become comparable to, but slightly less than the case of the dielectric multilayer film with decreasing line width.

• Nuclear Engineering and Technology
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• 제46권2호
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• pp.183-194
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• 2014

Recently, a CANDU digital reactivity computer system (CDRCS) to measure the worth of the liquid zone controller in a CANDU-6 was developed and successfully applied to a physics test of refurbished Wolsong Unit 1. In advance of using the CDRCS, its measureable reactivity range should be investigated and confirmed. There are two reasons for this investigation. First, the CANDU-6 has a larger reactor and smaller excore detectors than a general PWR and consequently the measured reactivity is likely to reflect the peripheral power variation only, not the whole core. The second reason is photo neutrons generated from the interaction of the moderator and gamma-rays, which are never considered in a PWR. To evaluate the limitations of the CDRCS, several tens of three-dimensional steady and transient simulations were performed. The simulated detector signals were used to obtain the dynamic reactivity. The difference between the dynamic reactivity and the static worth increases in line with the water level changes. The maximum allowable reactivity was determined to be 1.4 mk in the case of CANDU-6 by confining the difference to less than 1%.

• International Journal of Air-Conditioning and Refrigeration
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• 제8권2호
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• pp.80-88
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• 2000

In order to predict thermodynamic performance of refrigeration system, it is required to know the oil concentration of the refrigerant/oil mixture. The current method is to extract the working mixture and then to measure the oil weight. In this study, oil concentration is measured in si.tu way without any extraction of the working fluid. Based on the measurement, a working equation is presented as follows, C=a +b x t +c x $t^2$ +(d + e x t +f x $t^2$) x SG. C is oil concentration, t is temperature($^{\circ}C). SG Is specific gravity of mixture and a~f is coefficients The oil concentration ranges over 0~l2 wt% and the temperature ranges over 20~50$^{\circ}C. The specific gravity and temperature are measured using the on-line densimeter and thermometer. This working equation enables to predict the oil concentration without any extraction of the mixture. This equation can be applied for R-12/Naphthenic oil and R-134a/P0E oil liquid mixtures.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
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• pp.1141-1146
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• 2009

The compressibility of clay has been expressed e-log p' graph. In natural clay, e-log p' graph are changed by deposition condition and chemical cementation as well as Atterberg limits, whereas in reconstituted clay, it is generally known that e-log p’ curve is varied with Atterberg limits. However, e-log p' graph is possible to change according to the reconstituting methods and test conditions. In this study, consolidation tests are performed as various test condition for reconstituted Busan clay. Test results show that the relationship e/$e_L$ and log p' is almost constant with $e_L$. And the compression index obtained from slurry method sample is larger than one obtained from kneading method sample. Intrinsic compression line (ICL) of Busan clay is identical with ICL suggested by Burland.

• 한국분무공학회지
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• 제9권4호
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• pp.17-23
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• 2004

Spray characteristics of a twin-hole air shrouded nonle designed for gasoline injectors was investigated by using laser diffraction particle analyzer (LDPA) and tomography reconstruction- A confined spray chamber which is optically accessible through a pair of glass windows was made to simulate the fuel injection condition in intake manifold of gasoline engine. The measurement was applied to the twin hole injector with and without an air shroud. It demonstrates that for the case with an air shroud, fine atomization is achieved and there exists a large number of fine droplets between the region of the main spray streams, which conforms with the spray visualization. The drop size distribution was investigated as a function of elapse time after fuel injection. The distribution was greatly affected by the measurement position from the injector exit. Also, the spatially resolved spray volume fraction and Sauter Mean Diameter (SMD) from line-of-sight data of the LDPA are tomographically reconstructed by Convolution Fourier transformation under the steady injection condition.