• 대한토목학회논문집
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• 제13권5호
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• pp.165-172
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• 1993

균일조도 원형관에서 수행한 Nikuraclse의 실험결과에 따라 관로흐름은 층류(層流), 천이층류(遷移層流), 완난류(緩亂流), 천이난류(遷移亂流)와 전난류(全亂流)등 다섯가지로 구분되며, 천이층류는 조건에 따라 층류로부터 완난류로 천이하는 경우와 층류로부터 전난류로 바로 천이하는 경우가 있다. 각 조건은 관경의 조고에 대한 비로 결정될 수 있으며, 각 조건에 대하여 원형관 마찰계수를 양해법으로 구하는 수식을 개발하였다. 본 수식은 Nikuradse의 실험결과와 비교하여 상당히 양호한 결과를 보여준다.

• International Journal of Air-Conditioning and Refrigeration
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• 제9권2호
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• pp.8-18
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• 2001

The direct simulation Monte Carlo Method is applied to investigate the two-dimensional flow fields of a turbomolecular pump(TMP) in both molecular and transition flow regions. The pumping characteristics of the TMP are investigated for a wide range of the Knudsen number. The maximum of compression ratio and of pumping speed strongly depend on the Knudsen number in transition region, while they weakly depend on the Knudsen number in free molecular flow region. The present numerical results show good agreement with the previously known experimental data. Finally. the results of the single blade row in both molecular and transition regions are used to predict the overall performance of a TMP, which has three kinds of blade with 24-rows.

• 설비공학논문집
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• 제12권1호
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• pp.83-94
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• 2000

The performance of a turbomolecular pump(TMP) in both molecular and transition flow regions is predicted by the numerical solutions of the Boltzmann equation obtained by the direct simulation Monte Carlo method. The compression characteristics of the TMP are investigated for a wide range of the Knudsen number( Kn ). The maximum compression ratios strongly depend on Kn in transition region, while do they weakly on Kn in free molecular flow region. The present numerical results of the single blade row in both molecular and transition regions are used to predict the overall performance of a TMP, which has three kinds of blade with 24-rows.

• 전력전자학회논문지
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• 제24권5호
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• pp.372-378
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• 2019

This study proposes a new zero-current-zero-voltage-transition (ZCZVT) boost-flyback converter using a soft switching auxiliary circuit. The proposed converter integrates the boost and flyback converters to increase the voltage with a low duty ratio. The main and auxiliary switches turn the ZCZVT conditions on and off. Thus, the proposed converter has high efficiency. The voltage gain at the steady state is derived, and the inductor volt-second balance and the design guidelines are presented. Finally, the performance of the proposed converter is validated by experimental results from a 200 W, 30 V DC input, 400 V DC output, and 200 kHz boost-flyback converter prototype.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2023년도 봄 학술논문 발표대회
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• pp.99-100
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• 2023

In this study, an approach has been made to understand the effect of encapsulation thickness of the nanoencapsulated PCMs on the phase transition kinetics. Paraffin is encapsulated by silica via single pot polycondensation reaction. Different ratios of silica precursor are chosen to encapsulate paraffin. The obtained encapsulated PCMs are identified as nano sized, as well as with increasing silica precursor, thicker silica encapsulations have been manifested with shrinking core diameter. The synthesized PCMs are characterized using various characterization techniques. Isochronal kinetic studies are done in differential scanning calorimeter (DSC) to understand about their phase transformation behaviors. This study can appreciate the cognition of the large-scale applications of PCMs into the building constructions as well as the fundamental conception on the phase transition kinetics of PCMs can also be amended.

• Composites Research
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• 제37권3호
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• pp.215-218
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• 2024

Diglycidyl ether of 4,4'-dihydroxy-α-methylstilbene (DGE-DHMS)에 aniline을 2:1의 비율로 첨가한 액정에폭시올리고머인 DD-A를 합성하고 촉매성 경화제인 1-Methyl Imidazole을 이용하여 경화시키며 겔화 및 유리화 시간을 측정하여 액정 변화가 포함된 Time-Temperature-Transition Diagram을 작성하였다. 경화제의 농도가 높아질수록 겔화 및 유리화 시간이 감소함을 확인할 수 있었고 유리화 곡선은 전형적인 S-형태를 보였다.

• 한국재료학회지
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• 제23권11호
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• pp.649-654
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• 2013

The effect of interstitial elements on the ductile-brittle transition behavior of austenitic Fe-18Cr-10Mn-2Ni alloys with different nitrogen and carbon contents was investigated in this study. All the alloys exhibited ductile-brittle transition behavior because of unusual low-temperature brittle fracture, even though they have a faced-centered cubic structure. With the same interstitial content, the combined addition of nitrogen and carbon, compared to the sole addition of nitrogen, improved the low-temperature toughness and thus decreased the ductile-brittle transition temperature (DBTT) because this combined addition effectively enhances the metallic component of the interatomic bonds and is accompanied by good plasticity and toughness due to the increased free electron concentration. The increase in carbon content or of the carbon-to-nitrogen ratio, however, could increase the DBTT since either of these causes the occurrence of intergranular fracture that lead to the deterioration of the toughness at low temperatures. The secondary ion mass spectroscopy analysis results for the observation of carbon and nitrogen distributions confirms that the carbon and nitrogen atoms were significantly segregated to the austenite grain boundaries and then caused grain boundary embrittlement. In order to successfully develop austenitic Fe-Cr-Mn alloys for low-temperature application, therefore, more systematic study is required to determine the optimum content and ratio of carbon and nitrogen in terms of free electron concentration and grain boundary embrittlement.

• 한국추진공학회지
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• 제22권1호
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• pp.45-51
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• 2018

최근 이중모드 램제트 엔진에서 모드 천이는 격리부 출구 마하수의 불연속적인 변화를 일으킨다고 보고된 바 있다. 이 현상을 격리부 입구와 출구에서의 유효 유동 단면적과 압력비에 따라 나타내었으며, 이는 Non-Allowable Region (NAR)으로 설명되었지만, NAR의 발생 기구에 대한 이해는 여전히 부족한 실정에 있다. 본 연구에서는 NAR의 발생 원인에 대한 유동 메커니즘을 조사하기 위해, 앞서 수행한 수치해석 결과들의 상세 연구가 수행되었으며, 스크램제트에서 램제트로의 모드 천이발생 동안 기체역학적 특성에 대한 이해를 돕기 위해 이론해석도 수행되었다. 격리부 입구에서 유동 상태량이 수용할 수 있는 당량비의 임계값이 정해져 있는데, 이 임계값을 초과하는 당량비의 증가는 격리부 입구에서의 정압뿐만 아니라 마하수의 급격한 변화를 발생시키게 되며, 이는 NAR의 발생 원인이 된다.

• 한국초전도ㆍ저온공학회논문지
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• 제1권2호
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• pp.43-48
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• 1999

The normal zone propagation (NZP) velocity and V-I characteristics of two Bi-2223 pancake coils with different Ag/SC ratio were investigated based on the experimental results and broad resistive transition were obesved in two coils. The measured NZP velocity of coil was found to be faster due to increase of Ag/SC ratio, and agree well with calculated data from two dimensional heat balance equation.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 1999년도 제1회 학술대회논문집(KIASC 1st conference 99)
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• pp.109-112
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• 1999

The normal zone propagation (NZP) velocity and V-I characteristics of two Bi-2223 pancake coils with different Ag/SC ratio were investigated by experiment. Non-uniformity of Ic and broad restive transition was oberserbed in two coils. The NZP velocity of azimuth direction is faster than radius direction, and the NZP velocity of coil with higher Ag/SC ratio is faster than another coil with lower Ag/SC ratio.