• Journal of Power System Engineering
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• v.16 no.1
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• pp.44-50
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• 2012

팁 간격의 크기가 냉각탑용 축류팬의 성능과 누설 유동에 미치는 영향을 조사하기 위해서 서로 다른 2가지 팁 간격을 가진 경우에 대해서 점성유동을 해석하였다. 케이싱 내에서 작동하는 축류팬 주위의 유동을 연속방정식, Navier-Stokes 방정식 등을 지배방정식으로 사용하여 수치해석 하였다. 난류유동에 나타나는 레이놀즈 응력은 ${\kappa}-{\epsilon}$ 난류모델을 사용하여 계산하였다. 전체적으로 H형 격자계를 사용하였으며, 팁 주위의 유동을 해석하기 위해서 팁 영역 주위에 부분적으로 조밀한 격자를 두었다. 팁 간격이 증가하면 누설 유동의 증가로 인한 유동 손실의 증가로 전압상승과 수력효율이 감소하였다. 팬 직경에 대한 팁 간격이 0.4%에서 1.0%로 증가하면 전압상승 값이 약 10% 정도 감소하였으며, 수력효율은 약 3% 정도 감소하였다. 팁 간격이 팁 근처 날개 주위의 압력에 미치는 영향을 보면, 팁 간격이 증가하여 누설 유동이 증가하면 흡입면과 압력면의 압력차가 전연 부근에서 감소함을 알 수 있었다. 누설 와류의 중심은 코드를 따라서 흡입면으로 부터 떨어져 나가면서 형성됨을 알 수 있었다. 누설 와류의 위치를 보면 팁 간격이 증가하면 와류 중심의 위치가 흡입면 쪽으로 이동하고, 흡입면에서 떨어진 거리도 날개 후반부에서 증가 폭이 커지는 포물선 형태로 증가함을 알 수 있었다.

• 전자공학회논문지 IE
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• v.44 no.3
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• pp.1-5
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• 2007

A new field emission tip array was realized by Ti silicidation of Ti coated Si tip, which has long term durability, chemical stability, and high emission current density. The fabricated Ti silicided FE tip array under high vacuum condition of about $10^{-8}Torr$ shows that the turn-on voltage is about 40V and the emission current is about $69{\mu}A$ when the bias of 150V is applied between anode and cathode of $100{\mu}m$ distance.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.4
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• pp.1210-1215
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• 2010

The probe card are test modules which are to classify the good semiconductor chips and thin film before the packaging process. In the rapid growth a technology of semiconductor, the number of pads per unit area is increasing and pad arrays are becoming irregular. Therefore, the technology of probe card needs narrow width and lots of probe tip. In this paper, the probe tip based on the MEMS(Micro Electro Mechanical System)technology was developed a new MEMS probe tip for vertical probe card applications. For the structural designs of probe tip were performed to mechanical characteristics and structural analysis using FEM(Finite Element Method). Also, the contact force of MEMS probe tip compared with FEM results and experimental results. Finally, the MEMS probe card was developed a fine pitch smaller than $50{\mu}m$.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.9
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• pp.605-610
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• 2001

Electrostatic comb-drive microactuators with sub-micron gap were fabricated and tested. We designed and fabricated two type of electrodes which are rectangular and triangular tip. The fabricated microactuators with triangular tip resulted in the electrode gaps in the range of 0.55 ${\mu}{\textrm}{m}$~1.35 ${\mu}{\textrm}{m}$ Displacement of 1 ${\mu}{\textrm}{m}$ and electrostatic force of 2.3 $\mu$N were observed in a triangular-tip microactuator with 0.55 ${\mu}{\textrm}{m}$ gap when a DC drive voltage of 13 volts was applied. Measured 1st resonance frequency of microactuators was about 23 kHz.

• Journal of the Korean Vacuum Society
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• v.6 no.2
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• pp.103-108
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• 1997

Silicon field emitter arrays (FEAs) have been fabricated by a novel method employing a two-step tip etch and a spin-on-glass (SOG) etch-back process using double layered thermal/tetraethylortho-silicate (TEOS) oxides as a gate dielectric. A partial etching was performed by coating a low viscous photo resist and $O_2$ plasma ashing on order to form the double layered gate dielectric. A small gate aperture with low gate leakage current was obtained by the novel process. The hight and the end radius of the fabricated emitter was about 1.1 $\mu\textrm{m}$ and less than 100$\AA$, respectively. The anode emission current from a 256 tips array was turned-on at a gate voltage of 40 V. Also, the gate current was less than 0.1% of the anode current.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.181.2-181.2
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• 2005

• Journal of Sensor Science and Technology
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• v.5 no.2
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• pp.9-14
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• 1996

We have fabricated the vacuum magnetic sensor with a lateral field emitter arrays constructed on n-Si substrate, and investigated its magnetic characteristics. The device consists of 100 field-emitter tips with a $10{\mu}m$ pitch, gate, and split-anodes which are laterally structured. The electron-emission characteristics from the emitter followed the Fowler-Nordheim tunnelling theory. The sensor has good linear characteristics and high sensitivity of 825 %/T.

• 한국전산유체공학회:학술대회논문집
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• 1998.05a
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• pp.181-189
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• 1998

A numerical study based on the three-dimensional Reynolds averaged Navier-Stokes equations is presented to analyze the transonic flowfield through two-stage axial compressor. Explicit four-step Runge-Kutta scheme is used for solution algorithm, and local time step and implicit residual averaging are introduced for enhancing the convergency. Artificial dissipation model is adopted to assure the stability of solution. The solver is coupled with Baldwin-Lomax model to describe turbulence. To avoid calculating the unsteady flow, a mixing process is modeled at a station between rotating and stationary blade rows. Results show a variety of important physical phenomena. Comparison of the flowfields with and without tip clearance shows that the effect is considerable in this flowfield. Comparisons with experimental data carried out to validate the calculational results show reasonable agreements. Some remedies are also suggested to improve the revealed problems.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.4
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• pp.545-552
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• 2009

The marine medium-speed diesel engines are operated by two methods; one is the electric motors, and the other air starting motors. Even though air starting motor is dependent of the engine types and sizes, it has been widely used in this area due to its simplicity, convenience and reliability. However most of them are currently imported from overseas due to the lack of the cutting-edge technology in terms of design and manufacturing. Therefore, from the point of this view, the air starting motor needs to be produced by our own techniques. The purpose of this paper is to give the designing parameters in order to make a proper "Air Starting Motor" using CFD. The aerodynamic approaches were given to understand the internal flow characteristics of the air starting motor. In addition, we have carried out the effects of tip clearance. In the calculations the tip clearance of air starting motor has been varied between 0% and 5.7% of blade span.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.268-273
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• 2004

A study on experimental method of the model test for the impulse turbine is carried out. the wave simulator is used to reproduce the real wave condition. It controls two parameter correspond to wave height and wave frequency. The optimum design which is reported by T. Setoguchi is manufactured and tested for the validation of our test facilities. The comparison of model test show that our facilities produce little bit higher efficiency at maximum efficiency point. To increase the efficiency of turbine, the new rotor with negative tip clearance is designed and being tested.