• 한국주조공학회지
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• 제25권4호
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• pp.173-178
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• 2005

The vacuum molding process is one of the clean-foundry molding-processes that can recycle molding sands repeatedly, because molding can be accomplished by introducing vacuum only among dry molding sands in flask. The effects of molding conditions such as sand grain fineness, vacuum pressure and coating thickness on the fluidity of A356 Al alloy were studied and the results was obtained that the fluidity length was decreased as the sand grain fineness number and coating thikness were decreased and the vacuum pressure was increased. A large amount of heat removal from the molten metal resulting from the vacuum suction during the vacuum molding process was the principal cause of this decrease in fluidity.

• International journal of advanced smart convergence
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• 제10권1호
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• pp.159-165
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• 2021

Electronic devices used in the mobile environments fabricated under the plasma conditions in high vacuum system. Especially for the development of advanced electronic devices, high quality plasma as the process conditions are required. For this purpose, the variable conductance throttle valves for controllable plasma employed to the high vacuum system. In this study, we analyzed the effects of throttle valve applications on vacuum characteristics simulated to obtain the optimum design modelling for plasma conditions of high vacuum system. We used commercial simulator of vacuum system, VacSim(multi) on this study. Reliability of simulator verified by simulation of the commercially available models of high vacuum system. Simulated vacuum characteristics of the proposed modelling agreed with the observed experimental behaviour of real systems. Pressure limit valve and normally on-off control valve schematized as the modelling of throttle valve for the constant process-pressure of below 10-3 torr. Simulation results plotted as pump down curve of chamber, variable valve conductance and conductance logic of throttle valve. Simulated behaviors showed the applications of throttle valve sustained the process-pressure constantly, stably, and reliably in plasma process.

• Journal of Microbiology and Biotechnology
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• 제8권2호
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• pp.124-128
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• 1998

The procedures currently used for determining microbiological quality of natural mineral water recommend filtration through membrane filters. In this study, we evaluated the effect of vacuum pressure for the accurate detection of bacteria from water samples seeded with Escherichia coli. We observed that the number of E. coli detected increased with increasing vacuum pressure. In order to examine the retention rate of bacteria in the holes of the membranes under the different pressures, the membrane filters were removed after filtration, washed with sterile water by vortexing, and placed on m-Endo agar plates. With all the filters tested, the number of E. coli retained within the filters at negative 600 mmHg was approximately 10 to $20\%$ higher than that obtained with 100 mmHg. These results demonstrate that the vacuum pressure exerted during the filtration procedure may affect the fixation of bacteria into some portions of openings in the membrane filter.

• 한국진공학회지
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• 제10권1호
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• pp.9-15
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• 2001

질량분석기가 장착된 초고진공챔버를 사용하여 미소체적을 갖는 평판표시소자용 패널내부에 존재하는 잔류가스의 전체압력과 분압을 성공적으로 측정하였다. 패널내부의 전체압력은 $10^{-6}$Torr범위로 측정되었으며, 전체압력의 증가에 크게 기여하는 가스분압은 아르곤, 메탄 및 헬륨 분압들이었다. 패널의 진공패키징을 위한 배기공정시 가열온도는 고진공패키징에 있어서 매우 중요하며, 가열배기 온도가 높을수록 전체압력과 메탄분압은 감소하였다.

• Applied Science and Convergence Technology
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• 제25권4호
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• pp.67-72
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• 2016

This article describes an electrical network analysis (ENA) method to calculate the pressure distribution of a vacuum system in a molecular flow regime. The vacuum system was modeled using electrical components. For an accurate analysis, a complexly combined pipe model, excluding entrance conductance, was employed and the pressure distribution was simulated using ENA. A vacuum system comprising three vacuum pumps was used for simplicity. In addition, the ENA results were compared with results from finite element analysis (FEA) and experimental measurements. The pressure distribution profiles estimated from ENA, performed using the LTSpice IV software, were in agreement with FEA and experimental results.

• 대한기계학회논문집B
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• 제27권7호
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• pp.877-882
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• 2003

The main objective of the present study is to analyze the heat transfer characteristics in the vacuum carburizing furnace. Local temperatures are measured at different locations in the self-fabricated furnace for various operating conditions using K-type thermocouples. In addition, the present study simulates the fluid flows and heat transfer in the vacuum carburizing furnace using a commercial package (Fluent V. 6.0), and compares the predictions of local temperatures with experimental data. The temperature and flow fields are predicted. It is found that the time taken for reaching the steady-state temperature under the vacuum pressure is shorter than that under the normal pressure condition. It means that the carburizing furnace under vacuum pressure condition is capable of saving the required energy more efficiently than the furnace under the normal pressure condition. Furthermore, the temperature variations predicted by the numerical simulations are in good agreement with experimental data.

• 한국진공학회지
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• 제8권1호
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• pp.1-8
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• 1999

형태와 진공특성이 다른 여러 용기와 도관들로 구성된 진공네트웍의 압력분포를 계산할 때 단면이 서로 틀린 요소들의 연결부에서 입출구효과에 의해 발생하는 압력강하를 기체가 흐르는 방향에 상관없이 자동적으로 고려할 수 있는 경계조건을 만들었다. 또 원추형 도관처럼 단면이 변화하는 요소를 포함하고 있는 경우 시스템이 방향성을 가지지 않도록 도관 내에서의 압력강하를 보정하는 방법에 대해 소개한다. 개발된 경계조건을 간단한 예제 진공시스템에 적용하여 입자평형식에 근거를 둔 연립방정식을 작성하고 해를 구하는 과정을 구체적으로 설명한다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.151-151
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• 2011

Atmospheric-pressure plasmas are used in a variety of materials processes. The lifetime of most atmospheric-pressure plasma sources is limits by electrode erosion due to energetic ion bombardment. These drawbacks were solved recently by several microplasma sources based on microstrip structure, which are more efficient and less prone to perturbations than other microplasma sources. In this work, we propose microplasma sources based on strip line and microstrip line, developed for the generation of microplasmas even in atmospheric air and analyzes these systems with microwave field simulation via comparative study with two previous microwave sources (Microstrip Spit Ring Resonator (MSRR), Microstrip Structure Source (MSS)).

• 한국정밀공학회지
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• 제30권12호
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• pp.1327-1333
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• 2013

Air bearings are widely used in precision stages because of low friction and high motion accuracy, however, they suffer from low stiffness in comparison with rolling bearings or hydrostatic bearings. So, several preloading methods using weight, magnet and vacuum force, and opposing pads have been used to increase the stiffness of the air bearings. In this paper, pressure distributions of the vacuum preloaded porous air bearings are calculated using the proposed method. And then, the load capacity and stiffness are analyzed. For the vacuum preloaded air bearings, the stiffness is increased owing to reduced bearing clearance by vacuum force. The simulation results indicate that variation of vacuum pressure with clearance in the vacuum pocket gives rise to low stiffness, so the vacuum pocket should be designed for pressure to be constantly maintained regardless of the bearing clearance by means of large effective pumping speed.

• 한국식품저장유통학회지
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• 제16권6호
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• pp.869-874
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• 2009

새로운 돔배기 절임공정을 개발하고자 상압과 감압하에 직간법과 물간법으로 염절임한 돔배기의 품질특성을 비교하였다. 무게 감소율은 물간법으로 상압하에서 절임 하였을 때 12.23%로 높았으며, 수분함량은 감압상태에서 물간법으로 절임한 돔배기가 65.46%로 높았다. 염함량은 직간법으로 감압상태에서 절임 하였을 때 3.02%로 높았으며, 보수력은 직간법으로 감압상태에서 절임한 돔배기가 60.2%로 높았다. 수분활성도는 상압상태에서 직간법으로 절임 하였을 때 0.926으로 낮았으며, 색차는 감압상태에서 물간법으로 절임한 돔배기가 9.75로 가장 낮았으며, 탄력성은 직간법으로 감압상태에서 절임한 돔배기가 91.7%로 높았다. 상압과 감압상태에서 절임한 돔배기을 비교하였을 때, 감압상태에서 절임한 돔배기의 품질특성이 더 좋은 것으로 나타났다. 따라서 감압상태에서의 절임법은 새로운 절임 가공 기술로 활용할 수 있는 가능성을 보였다.