• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2007년도 동계학술발표대회 논문집
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• pp.410-415
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• 2007

The optimization of back pressure chamber is one of the most important factors in designing scroll compressors, because it has a great influence on the efficiencies and other design parameters. The design process can be divided into 2 parts. One is obtaining the optimum pressure of the chamber and keeping it in constant value. And the other is finding out the minimum inflow rate of medium with which back pressure chamber is filled. In this study we are focused on the first step. At first we added a simple structure that could change back pressure without reassembling compressor. It makes the optimum back pressure be obtained. And then we devised an equipment that the back pressure control valve assembly could be independently tested with. A spring was redesigned to decrease stiffness variation. And sealing mechanism of back pressure control valve was improved to more effective way. As a result it was verified in a real mode test that back pressure variation could be stabilized within 2.3% when discharge pressure and operating frequency varied. And the integrated structure of back pressure control valve is expected to contribute to an effective manufacturing process.

• 항공우주시스템공학회지
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• 제1권4호
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• pp.37-41
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• 2007

Labyrinth seal is most common way to protect the bearings installed in Reaction wheel. In spite of wide applications, no such research was found about the sealing utility of the Labyrinth seal in the condition of vacuum and high temperature. In this research, we tried to verify the utility of Labyrinth seal. Numerical analysis had been executed to predict the benefit of the Labyrinth seal and also experiments were performed to verify the utilization. Two Bearings were installed at the vacuum chamber, one was assembled with Labyrinth seal and the other was stand alone. After executing the vacuum test, it was found to be the stand alone bearing had lost more weight than the one that was assembled with the labyrinth seal. In this result, it is verified that the Labyrinth seal has useful function to preserve the lubricant that affects to the life-cycle of the Bearing.

• 대한기계학회논문집B
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• 제25권3호
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• pp.366-372
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• 2001

The ice plugging process consists of placing liquid nitrogen around a pipe and removing heat until the water in the pipe freezes and provides a solid plug or seal against fluid movement. This technique enables us to repair or inspect a pipe system without shutdown of entire system. A set of test apparatus for investigation of the liquid freezing phenomena during ice plugging is prepared. This study shows the characteristics of the liquid freezing and the heat transfer with various pipe and freezing jacket conditions. And in case there is flow of the fluid inside the pipe, the flow rate which can be able to form the ice plug is identified with the effect of the pipe diameter and freezing jacket length on the plug formation. The permissible maximum flow rate for the complete plug formation is approximately proportional to the freezing jacket length at the same pipe diameter condition.

• Advances in aircraft and spacecraft science
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• 제5권3호
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• pp.319-334
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• 2018

In this study, the failure mode and energy absorption capabilities of a composite shock absorber device, during an emergency landing are evaluated. The prototype has been installed and tested in laboratory simulating an emergency landing test condition. The crash absorber presents an innovative configuration able to reduce the loads transmitted to a helicopter fuselage during an emergency landing. It consists of a composite tailored tube installed on the landing gear strut. During an emergency landing this crash absorber system should be able to absorb energy through a pre-designed deformation. This solution, compared to an oleo-pneumatic shock absorber, avoids sealing checks, very high values of the shock absorber pressure, and results to be lighter, easy in maintenance, inspect and use. The activities reported in this paper have become an attractive research field both from the scientific viewpoint and the prospect of industrial applications, because they offer benefits in terms of energy absorbing, weight savings, increasing the safety levels, and finally reducing the costs in a global sense.

• Nuclear Engineering and Technology
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• 제53권10호
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• pp.3438-3448
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• 2021

Dynamic seals are one of the critical components of Absorber Rod Drive Mechanism of Fast Breeder Reactors, requiring separate experimental development. Their significance can't be overemphasized considering that the availability and re-usability of Control Rod Drive Mechanisms of Fast Breeder Test Reactor is governed by the failure rate of dynamic seals (bellows). For prototype and subsequent Fast Breeder Reactors in India, choice of the dynamic seal is changed to an in-house designed & developed labyrinth type V-ring seal. The present work is related to the numerical investigations carried out to gain insights into the sealing mechanism and the thermal behaviour of these seals. The results indicate that the seal geometry is very important for obtaining optimum performance. By changing the geometry of the present seal, performance enhancement by more than 50% in important indices is obtained. Further, the results point out that caution shall be exercised when the seal material & its operating temperature are changed. Also, the numerical model developed in this study will be useful for developing more robust dynamic seals in future.

• 대한치과의사협회지
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• 제57권10호
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• pp.569-578
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• 2019

The purpose of this retrospective study was to compare outcome of preformed stainless steel crown restorations according to depth of caries in primary molars. The study subjects consisted primary molars having dentin caries extending at least one-fourth of dentin without signs and symptoms of irreversible pulpitis. A total 295 primary molars received preformed stainless steel crown restorations without any base materials were included in this study. Survival rates were compared using a Kaplan-Meier analysis test. There was no significant difference between depth of caries and survival period in primary molars. And also there was no significant difference with or without pulp therapy. The results of this study suggest that neither the amount of caries nor pulp therapy affect the survival period of primary molars significantly. Proper restoration is more important to achieve sealing for stopping caries progression.

• 한국분무공학회지
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• 제27권4호
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• pp.181-187
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• 2022

For carbon neutrality, direct-injection hydrogen engines are attracting attention as a future power source. It is essential to estimate the transient injection rate of hydrogen for the optimization of hydrogen injection in direct injection engines. However, conventional injection rate measurement techniques for liquid fuels based on the injection-induced fuel pressure change in a test section are difficult to be applied to gaseous fuels due to the compressibility of the gas and the sealing issue of the components. In this study, a momentum flux measurement technique is introduced to obtain the transient injection rate of gaseous fuels using a force sensor. The injection rate calculation models associated with the momentum flux measurement technique are presented first. Then, the volumetric injection rates are estimated based on the momentum flux data and the calculation models and compared with those measured by a volumetric flow rate meter. The results showed that the momentum flux measurement can detect the injection start and end timings and the transient and steady regimes of the fuel injection. However, the estimated volumetric injection rates showed a large difference from the measured injection rates. An alternative method is suggested that corrects the estimated injection rate results based on the measured mean volumetric flow rates.

• 한국항공우주학회지
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• 제44권11호
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• pp.949-956
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• 2016

태양광 복사에 의한 기계적 부품의 강성 및 강도 저하, 변색 등의 영향이 다양한 항공우주 산업분야에서 관찰되고 있다. 이러한 현상에 대한 연구를 위해 자연 상태의 태양광에 대한 노출 시험을 수행할 수 있지만 균일한 시험환경 구현이 어렵고 과다한 시간과 비용이 요구된다는 문제점이 있다. 이를 극복하고자 본 논문에서는 자연 상태의 태양광 복사강도($1,120W/m^2$)를 가속화 할 수 있는 시험 장치를 개발하고, 섬유강화 복합재료에 사용되는 epoxy polymer에 대한 가속화 시험을 통하여 태양광 복사에 따른 색 변화 특성을 연구하였다. 시험 시편은 인장 시험 규격인 ASTM-D638에 따라 제작하였으며, 시험 기간에 따른 색변화 특성에 관한 가속계수와 역제곱 모형을 산출하였다. 본 연구를 통해 복사강도가 증가할수록 동일한 변화량에 도달하기까지 소요되는 시간을 단축할 수 있다는 것을 확인하였다.

• 한국산업보건학회지
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• 제24권4호
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• pp.518-527
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• 2014

Objectives: The adverse health effects attributed to exposure to radon have been well known over the world. However, the efforts for prevention and mitigation of radon have not been taken in Korea so far. The purpose of this study was to evaluate the effectiveness of mitigation methods applied for various types of houses and public buildings with high level of radon. Methods: Based on the results of "National Radon Survey" performed by the National Institute of Environmental Research(NIER) in 2010-2012, we selected 30 candidate buildings consisting of 20 houses and 10 public buildings with greater than $148Bq/m^3$ of radon level. We measured the concentration of radon in 30 buildings, using E-PERMs and RAD-7 during January to March of 2013. More than five E-PERMs and one RAD-7 per house were installed for seven days. Ten houses and five public buildings were finally chosen to be mitigated after mainly considering the level of radon and the location of buildings nationwide. Three mitigation methods such as Sealing, two types of Active Ventilation(window-shaped and wall-typed ventilations), and Active Soil Depressurization(ASD) were applied, and the concentrations of radon were measured before and after mitigation, respectively. To evaluate the effectiveness of mitigation methods, reduction rates of radon were calculated and Wilcoxon's signed-rank test was performed. Results: The mean concentration of 15 buildings just before radon mitigation was $297.8Bq/m^3$, and most of the buildings were located in Gangwon, Chungbuk, Chungnam, and Daegu areas(73.3%), and built in 1959-1998. The level of radon decreased from 48% to 90% and kept the below recommendation limit of $148Bq/m^3$ after installation of radon mitigation. Among mitigation methods applied, the reduction rate(58.7-90.4%) of radon attributed to ASD was the greatest than that of other methods, followed by Active Ventilation(48.4-78.4%) and Sealing(<22%). The effectiveness of radon reduction by window-shaped Active Ventilation(63.2-75.2%) was relatively better than that of wall-typed Active Ventilation(48.4-54.3%). Conclusions: The results of this study indicate that ASD could be more effective for radon mitigation. Moreover, our findings would be background information in future for making the strategy for radon mitigation nationwide, as well as for developing Korean-version of mitigation techniques according to types of dwellings in Korea.

• 한국식품저장유통학회지
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• 제19권3호
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• pp.328-336
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• 2012

데침 나물류의 품질유지에 효과적인 포장방법을 개발하기 위하여 포장 방법에 따른 데친 나물의 저장 중 품질변화를 조사하였다. 고사리, 토란대, 취나물, 시래기를 데친 후 비닐포장, 밀봉포장, 진공포장 방법으로 각각 개별 포장하여 $10^{\circ}C$에서 10일 동안 저장하면서 미생물 검사, 경도, pH, 냄새성분 분석을 수행하였다. pH는 데침 나물의 종류에 따라 상이했고 데친 취나물과 데친 시래기의 경우 포장방법에 따른 유의적인 차이가 있었다. 경도는 저장기간이 늘어날수록 모든 시료에서 감소하는 경향을 보였고 진공포장을 한 데친 고사리와 데친 취나물에서 경도가 상대적으로 높은 경도를 유지하였다. 데침 나물의 미생물 검사 결과 모든 시료가 저장기간 동안 호기성세균과 대장균군수가 증가하는 경향을 보였고, 대장균은 검출되지 않았다. 포장방법별 데침나물의 균수는 진공<밀봉<비닐 순으로 높게 나타났다. 전자코를 이용한 냄새성분은 전반적으로 모든 시료구에서 포장방법에 따른 냄새패턴 변화율이 차이가 났으며 제 1주성분값은 positive에서 negative로 이동하는 경향을 나타내었다. 포장방법에 있어서 진공포장방법이 냄새성분의 변화율이 가장 낮았다. 저장기간 동안의 냄새변화율은 비닐포장의 경우 데친 고사리와 데친 취나물은 저장 7일, 데친 시래기는 저장 3일 이후부터 냄새의 변화가 급격한 반면 진공포장은 저장기간 동안 냄새변화가 거의 없었다. 결론적으로 저장기간 동안 포장 조건에 따른 데친 나물의 품질 유지에 있어서 진공포장이 가장 효과적임을 확인할 수 있었다.