• 대한기계학회논문집B
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• 제38권8호
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• pp.671-676
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• 2014

볼텍스 컵은 실린콘 웨이프 제조공정과 같이 민갑한 물체을 이송시키는 방법으로 제안되었다. 볼테스 컵의 상부에 위치한 노즐을 통해 공기를 공급하면 내부 실린더에서 큰 선회유동이 생성된다. 공기는 볼텍스 컵과 바닥면 사이의 틈새로 빠져나가면서 흡입압력을 생성시키고 물체를 들어 올릴 수 있게 된다. 본 논문에서는 볼텍스 컵에 관한 3차원 유동 해석을 통해 실험 결과와 해석 결과를 비교하여 해석의 신뢰성을 확인하였다. 그리고 볼텍스 컵의 길이 변화와 형상 변화를 주어 해석을 통해 흡입 압력 생성에 영향을 미치는 정도를 분석하였고, 볼텍스 컵 형상의 최적 조건을 제시하였다.

• Journal of Welding and Joining
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• 제22권2호
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• pp.51-58
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• 2004

Residual stresses, which can be produced during the welding process, play an important role in an industrial field. Welding residual stresses are exerting negative effect on the fatigue behavior and integrity of structure. In this study, as a result of the thermal elasto-plastic finite element analysis for the welds of a nuclear component, the residual stress distributions are estimated for as-welded condition. Also, finite element techniques are developed to simulate the relaxation of the residual stresses according to the various mechanical stress relieving(MSR) loads such as hydrostatic pressure loading, tensile pipe-end loading, and mechanical stress improvement process(MSIP) loading. Finally, the results of residual stress redistributions for various loading conditions are compared and reviewed qualitatively and quantitatively to find an optimum loading condition.

• 전기학회논문지
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• 제61권1호
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• pp.89-93
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• 2012

c-BN films were deposited on SKH-51 steels by electron assisted hot filament CVD method and microstructure development was studied processing parameters such as bias voltage, temperature, etching and phase transformation at boundary layer between BN compound and steel to develop a high performance wear resistance tools. A negative bias voltage higher than 200V at substrate temperature of $800^{\circ}C$ and gas pressure of 20 torr in B2H6-NH3-H2 gas system was one of optimum conditions to produce c-BN films on the SKH-51 steels. Thin layer of hexagonal boron nitride phase was observed at the interface between c-BN layer and substrate.

• Journal of Electrical Engineering and Technology
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• 제13권4호
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• pp.1663-1672
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• 2018

In recent times, gas insulated medium voltage (MV) circuit breakers (CB) form a vital component in power system network, considering its advantages such as reduced size and safety margins. Gas insulation characteristics of circuit breakers are generally measured by lightning impulse (LI) test according to IEC standard 60060-1 as a factory routine test. Considering the environmental issues of $SF_6$ gas, many research works are being carried out towards the mixture of $SF_6$ gases for high voltage insulation applications. However, few reports are only available regarding the LI withstand and streamer propagation characteristics (at both positive and negative polarity of waveform) of $SF_6/N_2$ gas mixture insulated medium voltage circuit breakers. In this paper, positive and negative polarity LI tests are carried out on 22 kV medium voltage circuit breaker filled with $SF_6/N_2$ gas mixture at different gas pressures (1-5 bar) and at different gas mixture ratios. Important LI parameters such as breakdown voltage, streamer velocity, time to breakdown and acceleration voltage are evaluated with IEC standard LI ($1.2/50{\mu}s$) waveform. Weibull distribution analysis of LI breakdown voltage data is carried out and 50% probability breakdown voltage, scale parameter and shape parameter are evaluated. Results illustrate that the $25%SF_6+75%N_2$ gas filled insulation considerably enhances the LI withstand and breakdown strength of MV circuit breakers. LI breakdown voltage of circuit breaker under negative polarity shows higher value when compared with positive polarity. Results show that maintaining the gas pressure at 0.3 MPa (3 bar) with 10% $SF_6$ gas mixed with 90% $N_2$ will give optimum lighting impulse withstand performance of 22 kV MV circuit breaker.

• 유기물자원화
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• 제7권2호
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• pp.93-104
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• 1999

본 연구는 기존의 소멸화장치를 개선하여 에너지절감과 동시에 탈취효과를 극대화시키면서 유기물의 분해능력을 극대화시키는 장치를 개발하기 위하여 실시되었다. 기존의 장치와 비교하여 3차에 걸친 열교환을 통하여 백금촉매탑에서 발생하는 폐열을 회수하여 이용하게 하였으며, 배기가스의 65%정도를 재순환하게 하였다. 또한 장치전체에 대해서는 감압을 유지하게 하여 수분의 증발을 원활하게 하였다. 미생물제재에 의하여 반응을 안정적으로 유지하는 것이 가능했으며, 또한 분해매체제는 기존의 처리용량의 20배용적을 사용했으나, 본장치에서는 15배용적에 있어서도 미생물활성화가 가능하며, 호기성분위기를 효율적을 유지하는 것이 가능했다. 배기가스의 내부순환을 시스템을 사용함에 따라 얻어지는 효과에 대하여 검토한 결과, 내부의 악취물질인 암모니아가스농도를 감소시키는 것이 가능했으며, 탈취탑으로 유입되는 배기가스가 경감됨에 따라 전력비가1/3선으로 절감되는 효과가 확인되었다. 이러한 내순환에 따라 최적공기량은 100kg처리용량에 대하여 $0.44m^3$로, 이 공기량의 변화에 따라 전력비가 비례하여 변화하는 현상이 확인되었다.

• Korean Chemical Engineering Research
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• 제45권5호
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• pp.473-478
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• 2007

공침법을 이용하여 질산은($AgNO_3$)을 수산화아파타이트(hydroxyapatite)에 흡착시켜 복합항균제를 제조하였다. 질산은의 농도, 온도, 압력, 숙성시간에 따른 흡착된 은이온양의 변화를 관찰하였고, 은-수산화아파타이트 흡착의 최적조건을 얻었다. 제조된 은-수산화아파타이트를 ICP-MS, SEM-EDAX, DSC, XRD를 이용하여 물리적 화학적 특성을 고찰하였다. 또한 제조된 은-수산화아파타이트는 진탕플라스크실험법(shake flask method, KS M-146-2003)을 이용하여 양성균인 황색포도상구균(staphylococcus aureus, ATCC 6538)과 음성균인 대장균(escherichia coli, ATCC 25922)의 항균성을 확인하였다.

• 한국축산시설환경학회지
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• 제20권4호
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• pp.155-160
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• 2014

This study was researched for use by data for the improvement of ventilation system of optimum environmental control systems. The ventilation system for windowless swine housing was installed negative pressure system that circular pipe duct for inlet was installed on the ceiling and axial flow fan for exhaust was installed on the sidewall. The temperatures in the pen was measured using infrared thermography camera and thermocouple with data-logger. The temperature measurement points was selected by infrared thermography camera is alley (G), inlet (A), front-upper (B), front-lower (C), rear-upper (D), rear-lower (E), forward fan (F). The temperature measured at those selected points for temperature distribution was $28^{\circ}C$ that was maintained setting temperature in suitably. The temperature deviations of F point and A~E points in windowless swine housing was less then average $0.5^{\circ}C$. The result of air velocity of measured points was suitable to the breeding of pigs.

• 한국분무공학회지
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• 제4권3호
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• pp.32-41
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• 1999

In this research, internal-mixing twin-fluid atomizer using sonic energy is designed and manufactured. We are trying to intimate high efficiency twin-fluid atomizer to obtain good liquid atomization in the low pressure region. Define of geometric form of atomizer, characteristics of spray is influenced by position, depth and height variation of cavity resonator, variation of sound intensity and resonant sound frequency with liquid flow rate. The liquid atomization is promoted by multi-stage disintegration of mixing flow of gas with liquid and the optimum condition of position and depth of cavity resonator according to sonic energy is obtained from the condition at a=2.5mm and L=2mm. The velocity distribution of droplets shows negative value due to recirculation region at the center of axial, and as the radial direction distance is far, the velocity distribution of droplets decrease slowly after having a maximum value. However velocity and SMD show nearly uniform distribution at the down stream and as result compared to Nukiyama and Tanasawa's equation. atomization of mixing flow with air and liquid dispersing from the outlet of the nozzle is promoted by the effect of collision at the cavity resonator.

• 한국운동역학회지
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• 제29권3호
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• pp.167-172
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• 2019

Objective: The aim of this study was to investigate the effect of midsole hardness of running shoe on muscle fatigue and impact force during distance running. Method: Ten healthy college recreational runners who were performing distance running at least three times a week participated in this experiment. They were asked to run for 15 minutes in the treadmill at 10 km/h with running shoes having three different types of midsole hardness (Soft, Medium, Hard). EMG signal and insole pressure were collected during the first and last one minute for each running trials. Data were analyzed using a one-way analysis of variance (ANOVA) with repeated measures. Results: Midsole hardness did not affect the consistency of stride length. For the median frequency of the EMG signal, only VL was affected by midsole hardness; that of medium was greater than other midsoles (p<.05). The loading rate of impact forces increased by midsole hardness (p<.01). Conclusion: Although soft midsole could attenuate impact forces at heel contact, it might have a negative effect on the fatigue of muscle which could decelerate the body after heel contact. Therefore, it is necessary to select the optimum hardness of midsole carefully for both reduction impact forces and muscle fatigue.

• 에너지공학
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• 제16권4호
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• pp.187-193
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• 2007

갑작스런 펌프 정지로 야기되는 수격현상은 과압이나 부압을 일으킬 수 있다. 과압을 줄이거나 부압을 방지하는 것은 계통설비의 피로를 피하고 작동효율을 향상시키기 위해 필요하다. 에어챔버가 설치된 펌프 관로 계에서 수격현상에 대한 현장시험을 수행하였다 또한 특성 곡선법을 사용하여 과도현상에 대한 수치해석을 수행하였다. 계통에 대한 헌장시험과 수치해석 결과를 비교하여 수치해석코드에 사용되는 주요 입력변수인 폴리트로픽 지수, 유량계수, 압력파의 속도에 대한 보정값 검증과 민감도 분석을 수행하였다. 수격현상을 최소화할 수 있는 에어챔버의 크기와 관련 변수의 영향이 현장시험과 수치해석을 통해 연구되었다.