• 대한기계학회논문집B
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• 제26권12호
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• pp.1707-1714
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• 2002

This paper deals with the development of a new method that can obtain heat transfer coefficient and reference free stream temperature simultaneously, The method is based on transient heat transfer experiments using two narrow-band TLCs. The method is validated through error analysis in terms of the random uncertainties in the measured temperatures. It is found that the errors could be reduced more than 2 times less. The general method described in this paper is applicable to many heat transfer models with unknown free stream temperature.

• 한국분무공학회지
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• 제4권3호
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• pp.15-23
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• 1999

The use of LPG as clean fuel for Diesel engine is very attractive way to reduce soot and NOx emission. In this study, a numerical study has been done to know the transient behavior of LPG fuel in chamber pressures which is held at a pressure above (0.37MPa)and below(0.15MPa)the fuel vapor pressure. Results show that the vortex formed within the start of injection at the leading edge of the spray cone and was most apparent for 0.15MPa chamber pressure case. The high speed photographs and model results showed a narrower cone angle during the quasi-steady spray period at the 0.37MPa chamber pressure compared to the 0.15MPa case. And it can be shown that more realistic vaporization process is necessary to predict the spray length well.

• KSBB Journal
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• 제6권4호
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• pp.385-388
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• 1991

자란(B. striata)의 미성숙종자로 부터 유도한 embryogenic callus를 현탁배양하고 이와같은 embryogenic cell suspensions로부터 분리한 원형질체에 electroporation 방법을 사용하여 reporter genes이 들어있는 pBI121 plasmid DNA 를 도입하고 그 발현을 확인하였다. 배양된 세포에 있어서 GUS의 활성은 plasmid DNA양의 증가와 함께 높게 나타났으며, 200-300 voltage/1180 uF에서 GUS의 활성 및 원형질체의 생존율(viability)이 가장 좋았다.

• Nuclear Engineering and Technology
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• 제56권3호
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• pp.886-892
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• 2024

The cladding temperatures and axial mass distribution computed by MAAP5 were compared with their measured values in the test bundle of the Phebus Test FPT0. The computed cladding temperatures were in good agreed with the measured values in the pre-transient phase. In the transient heat-up phase, the computed temperatures were overestimated by the Baker-Just correlation in MAAP5, but the computed temperatures could simulate the subsequently measured values. The computed mass distribution in the axial direction was in qualitative agreement with the measured one for post-test fuel damage observations. The calculated flow areas of inner and outer regions in the test bundle were compared with the photographic observations. MAAP5 computed them at the height of 0.2 m where the molten pool formed was in qualitative agreement with the photographic observations. It was found that the remaining steam flow paths might be caused by the gas-liquid two-phase flow counter-current flow limitation.

• 대한전자공학회논문지SD
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• 제39권4호
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• pp.10-18
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• 2002

본 논문에서는 IPS모드의 액정 셀에서 전압에 따른 액정 거동을 수치 해석적으로 계산하는 방법을 보고한다. 액정 거동을 해석하기 위해 복잡한 구조에 적용이 용이한 3차원 유한 요소법을 사용하여 액정 셀 내부의 전압 분포와 전계 분포를 계산하였다. 전기 에너지와 액정 분자의 탄성 에너지로 이루어지는 액정 셀 내부의 자유에너지 밀도를 고려하였으며, 에릭슨-레슬리(Ericksen-Leslie) 방정식과 라플라스(Laplace) 방정식을 해석함으로서 액정 셀의 스위칭 특성을 계산하였다. 24㎛×12㎛×4.5㎛ 사이즈의 IPS 모드 액정 셀에 대하여 1,859개의 노드와 8,640개의 사면체 요소를 생성하여 16ms까지 과도 해석하였다. 그 결과, 전극 위 부분을 제외한 영역에서 횡방향의 전계가 형성되었고, 전극 위 영역에서 전경선(disclination)이 발생하는 것을 확인하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1951-1956
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• 2004

The transient nature and complex flow geometries of two-phase gas-liquid flows cause fundamental difficulties when measuring flow velocity using an electromagnetic flowmeter. Recently, a current-sensing flowmeter was introduced to obtain measurements with high temporal resolution (Ahn et $al.^{(1)}$). In this study, current-sensing flowmeter theory was applied to measure the fast velocity transients in slug flows. To do this, the velocity fields of axisymmetric gas-liquid slug flow in a vertical pipe were obtained using Volume-of-Fluid (VOF) method and the virtual potential distributions for the electrodes of finite size were also computed using the finite volume method for the simulated slug flow. The output signal prediction for slug flow was carried out from the velocity and virtual potential (or weight function) fields. The flowmeter was numerically calibrated to obtain the cross-sectional liquid mean velocity at an electrode plane from the predicted output signal. Two calibration parameters are required for this procedure: a flow pattern coefficient and a localization parameter. The flow pattern coefficient was defined by the ratio of the liquid resistance between the electrodes for two-phase flow with respect to that for single-phase flow, and the localization parameter was introduced to avoid errors in the flowmeter readings caused by liquid acceleration or deceleration around the electrodes. These parameters were also calculated from the computed velocity and virtual potential fields. The results can be used to obtain the liquid mean velocity from the slug flow signal measured by a current-sensing flowmeter.

• 마이크로전자및패키징학회지
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• 제30권4호
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• pp.61-68
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• 2023

무연솔더에 Fe 입자를 첨가하여 Cu₃Sn 금속간화합물 성장을 억제하고 취성파괴를 방지하는 연구는 보고된 바 있으나 이러한 복합솔더를 TLP(transient liquid phase) 본딩에 적용한 경우는 아직 없다. 본 연구에서는 Sn계 무연솔더 내부에 Fe 입자의 함량을 적절히 조절하여 Sn-3.5Ag-15.0Fe 복합솔더를 제작하고 TLP 본딩에 적용하여 접합부 전체를 Sn-Fe 금속간화합물로 변화시킴으로써 고온 솔더로서의 적용 가능성을 탐색하였다. 접합공정 중에 형성되는 FeSn₂ 금속간화합물은 513℃의 고융점을 가지므로 사용 중 온도가 280℃까지 상승하는 전력반도체용 파워모듈에 안정적으로 적용이 가능하다. 칩과 기판에 ENIG(electroless nickel-immersion gold) 표면처리를 적용한 결과 접합부에 Ni₃Sn₄/FeSn₂/Ni₃Sn₄의 다층 금속간화합물 구조를 형성하였으며 전단시험시 파괴경로는 Ni₃Sn₄/FeSn₂ 계면에서 균열이 진전하다가 FeSn₂ 내부로 전파되는 양상을 보였다. TLP 접합공정 2시간 이후에는 30 MPa 이상의 전단강도를 얻었고 특히 200℃ 전단시험에서도 강도 저하가 전혀 없었다. 본 연구결과는 최근 활발히 연구되고 있는 전기자동차용 파워모듈에 적용할 수 있는 소재 및 공정으로 기대할 수 있다.

• 대한기계학회논문집B
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• 제29권6호
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• pp.671-686
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• 2005

The transient nature and complex geometries of two-phase gas-liquid flows cause fundamental difficulties when measuring flow velocity using an electromagnetic flowmeter. Recently, a current-sensing flowmeter was introduced to obtain measurements with high temporal resolution (Ahn et al.). In this study, current-sensing flowmeter theory was applied to measure the fast velocity transients in slug flows. The velocity fields of axisymmetric gas-liquid slug flow in a vertical pipe were obtained using Volume-of-Fluid (VOF) method, and the virtual potential distributions for the electrodes of finite size were also computed using the finite volume method for simulating slug flow. The output signal prediction for slug flow was carried out from the velocity and virtual potential (or weight function) fields. The flowmeter was numerically calibrated to obtain the cross-sectional liquid mean velocity at an electrode plane from the predicted output signal. Two calibration parameters are proposed for this procedure: a flow pattern coefficient and a localization parameter. The flow pattern coefficient was defined by the ratio of the liquid resistance between the electrodes for two-phase flow with respect to that for single-phase flow, and the localization parameter was introduced to avoid errors in the flowmeter readings caused by liquid acceleration or deceleration around the electrodes. These parameters were also calculated from the computed velocity and virtual potential fields. The results can be used to obtain the liquid mean velocity from the slug flow signal measured by a current-sensing flowmeter.

• 한국추진공학회지
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• 제12권4호
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• pp.33-41
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• 2008

외부로부터 일정한 열유속을 받으면서 발사대기 중인 액체추진 로켓의 극저온 산화제 탱크 내 열적거동에 대하여 열역학 방정식과 열 및 물질 전달 관계식을 이용하여 수치적으로 해석하였다. 발사대기 단계는 헬륨가스에 의한 가압과정을 포함하여 이상적인 다섯 단계로 구성된다고 하였다. 얼리지 기체영역의 해석에는 Peng-Robinson 상태방정식을 사용하였고, 액체 영역은 열적 성층화를 고려할 수 있도록 균일한 성질을 갖는 여러 개의 수평층으로 나누어 해석하였다. 전형적인 경우에 대한 계산 결과에 의하면 액체산화제의 온도상승은 1K 미만이고 액체에 녹아드는 헬륨의 양은 10g 정도였다.

• 대한기계학회논문집B
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• 제23권3호
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• pp.320-329
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• 1999

An experimental study has been performed to investigate the heat transfer characteristics of impinging jets with corrugated nozzle and wake generation plate. Three different shapes of corrugated nozzle and five different shapes of wake generation plate were tested to improve the heat transfer characteristics of impinging jet. Heat transfer coefficients were obtained by using transient method based on the liquid crystal thermography. The effects of corrugated nozzle and wake generation plate on the heat transfer characteristics of impinging jets were discussed in detail. The results showed that both the corrugated nozzle and the wake generation plate improved the heat transfer characteristics of impinging jet. Especially, heat transfer coefficients around stagnation region of impinging jets were highly increased.