• 한국추진공학회지
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• 제19권6호
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• pp.54-63
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• 2015

본 연구에서는 고온/고압의 연소가스에 의해 야기되는 노즐목 삭마현상의 분자수준 메커니즘을 분자동역학 시뮬레이션을 이용하여 관찰한다. 노즐목은 두 개의 그래핀으로 구성된 그래파이트로 모델링하고 분자동역학 시뮬레이션은 충분한 속도를 가지고 그래파이트에 충돌하는 $H_2O$ 분자와 $CO_2$ 분자가 지속적으로 생성되는 과정과 평형상태의 시뮬레이션으로 구성된다. 반응을 모사할 수 있는 ReaxFF 포텐셜을 사용하며, 충돌에 의해 야기되는 $H_2O$ 및 $CO_2$ 분자의 해리와 화학적 삭마와의 관계에 중점을 두고 관찰하고자 하며, 거시적인 관찰결과들과 비교하고자 한다.

• Carbon letters
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• 제2권3_4호
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• pp.192-201
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• 2001

The Carbon/Carbon composite was prepared from 3D carbon fiber preform and coal tar pitch as matrix precursor. In order to evaluate of ablative characteristics of the composite, liquid rocket system was employed Kerosene and liquid oxygen was used as propellants, operating at a nominal chamber pressure of 330 psi and a nominal mixture ratio (O/F) of 2.0. The results of an experimental evaluation were that high density composite exhibited high, while low density composites showed low erosion resistance. The erosion rate against heat flux was highly depended on the density of the materials. The morphology of eroded fiber showed differently according to collision angle with heat flux on the composite. The granular matrix which derived from carbonization pressure of 900 bar was more resistance to heat flux than well-developed flow type matrix.

• 한국기계가공학회지
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• 제10권6호
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• pp.95-101
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• 2011

Micro-abrasive jet machining(${\mu}AJM$) using mask is a fine machining technology which can carve a figure on a material. The mask should have holes exactly same as the required figure. Abrasive particles are jetted into the holes of the mask and it collide with the material. The collision break off small portion of the material. And the ${\mu}AJM$ nozzle should move all over the machining area. However, in general the carving shape is modeled as in a bitmap figure, because it often contains characters. And the mask model is also often modeled from the bitmap image. Therefore, the machining path of the ${\mu}AJM$ also efficient if it can be generated from the bitmap image. This paper suggest an algorithm which can generate ${\mu}AJM$ tool path directly from the bitmap image of the carving figure. And shows some test results and applications.

• 한국연소학회지
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• 제21권3호
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• pp.1-6
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• 2016

The effect of applied electric fields on jet flow instability was investigated experimentally by varying the direct current (DC) voltage and the alternating current (AC) frequency and voltage applied to a jet nozzle. We aimed to elucidate the origin of the occurrence of twin-lifted jet flames in laminar jet flow configuration, which occur when AC electric fields are applied. The results indicate that a twin-lifted jet flames originates from cold jet instability, caused by interactions between negative ions in the jet flow via electron attachment as $O_2+e{\rightarrow}O_2{^-}$ when AC electric fields are applied. This was confirmed by experiments in which a variety of gaseous jets were ejected from a nozzle to which DC voltages and AC frequencies and voltages were applied, with ambient air between two deflection plates connected to a DC power source. Experiments in which jet flows of several gases were ejected from a nozzle and AC electric fields were applied in coflow-nitrogen provided further evidence. The flow instability occurred only for oxygen and air jets. Additionally, jet instability occurred when the applied frequency was less than 80 Hz, corresponding to the characteristic collision response time. The effect of AC electric fields on the overall structure of the jet flows is also reported. Based on these results, we propose a mechanism to reduce jet flow instability when AC electric fields are applied to the nozzle.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.358-363
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• 2008

The spray cross-section characteristics of two-phase spray that using external-mixing nozzle injected into a subsonic cross flow were experimentally studied with various ALR ratio that is $0{\sim}59.4%$. Suction type wind tunnel was used and experiments were conducted to ambient environment. Several plain orifice nozzles with L/d of 30 and orifice diameter of 0.5 mm and orifice length 1.5 mm were tested. Free stream velocity profiles at the injection location were measured using hot wire. Spray images were captured to study collision point and column trajectory. Phase Doppler particle analyzer(PDPA) was utilized to quantitatively measuring droplet SMD, volume flux. Measuring probe of PDPA positions was moved 3-way transverse machine. SMD distributions were layered structure and peaked at the top of the spray plume and low value at bottom of the spray. Volume flux of spray was distributed to the two side region and volume flux quantity decreased when ALR ratio increased. It was found that the perpendicularly injected two-phase spray jet of external mixing into a cross flow showing that mistlike spray moved away from the test section bottom region.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.255-259
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• 2008

This paper presents the spray characteristics of the oxidizer rich preburner injector which can be used in the high-thrust rocket system. We designed the basic shape of the liquid-liquid coaxial swirl injector for the rocket oxidizer rich preburner injection system. To understand the spray angle variation with the high pressure environment, the spray visualization in the high pressure chamber was preformed. Also we measured the droplet velocity, the Sauter Mean Diameter(SMD), the volume flux and the number density with the PDPA system by using water in atmospheric pressure. The results show that the spray angle is reduced by increasing ambient pressure and maximum droplet velocity is shown from a nozzle tip and then the droplet velocity decreases as a spray moves to the downstream. The SMD decreases on the axial distance from 20 mm to 50 mm but it increases over 50 mm. That is due to the increasing number of collision with each droplet and interaction with ambient air on going downstream direction.

• Korean Chemical Engineering Research
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• 제60권2호
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• pp.300-307
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• 2022

매우 짧은 펄스 폭의 X선 자유전자 레이저(XFEL)를 이용한 시간 분해능 연속 펨토초 결정학(time-resolved serial femtosecond crystallography, TR-SFX)기법에서 반응 물질과 생체분자 결정 샘플간의 혼합률(mixing rate)과 결정 샘플과 X선 레이저 간의 충돌률(hit rate)은 생체분자의 시분해 구조 변화에 대한 정확한 이미지 획득 및 효율적인 샘플소비와 같은 TR-SFX의 분석 성능을 결정짓는 핵심인자이다. 본 연구에서는 극초단 내 일어나는 생체분자의 시분해 구조 변화 해석을 위해 초고속 믹싱 기능을 가짐과 동시에 공압 기반의 주문형 액적 젯팅이 가능한 두 가지 다른 방식의 샘플 전달시스템을 고안하였다. 한 방식은 이중 노즐을 통해 토출된 액적의 고속 충돌에 유발된 관성 믹싱을 기반으로 하고 있으며, 다른 방식은 마이크로믹서가 내장된 공압 젯팅을 기반으로 하고 있다. 먼저, 이중 노즐을 통해 토출된 액적의 충돌에 대한 동적 거동 및 액적 내부 관성 유동에 대한 믹싱에 대한 실험 및 수치해석적 연구를 수행하였다. 다음으로 마이크로믹서가 내장된 공압 젯팅 시스템의 성능을 유사한 방법을 통해 평가하였다. 본 연구에서 개발한 샘플 전달시스템은 질환을 유발하는 특정 단백질들의 기작을 규명하거나, 항체 의약품과 신약 후보 물질 탐색하는 데 있어 필수적인 3차원 생체 분자 구조분석 연구에 매우 유용하게 활용될 수 있을 것이다.

• 한국추진공학회지
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• 제3권1호
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• pp.9-14
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• 1999

작동조건이 두개의 공기충돌형 연료분사장치로부터 분사되는 이중분무 특성에 미치는 영향을 공연비 1.36∼3.54의 범위에서 실험적으로 수행하였다. 물과 질소가스가 실험유체로서 사용되었다. 분무 액적의 분포특성은 질량분포와 순간영상 촬영법에 의하여 측정되었다. 실험적 결과는 ROA(축방향에 대한 반경방향 공급압력비)의 증가에 따라 질량분포곡선의 최대값은 낮아지면서 더 넓은 영역에 걸쳐 분포하였으며 공급유체의 증가에 따른 질량중심점의 위치는 변화가 없었다. 노즐간격 증가는 간섭영역에서의 질량분포에는 커다란 영향을 미치지는 않았으나 더 넓은 영역에 걸쳐 분포하려는 특성을 보여주었다. 또한, ROA 비가 증가할수록 충돌중심점 근처에서 간섭의 영향은 작아짐을 중첩법을 이용하여 비교함으로서 잘 알 수 있었다.

• 한국재료학회지
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• 제27권9호
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• pp.501-506
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• 2017

Surface morphology and optical properties such as transmittance and haze effect of glass etched by physical and chemical etching processes were investigated. The physical etching process was carried out by pen type sandblasting process with $15{\sim}20{\mu}m$ dia. of $Al_2O_3$ media; the chemical etching process was conducted using HF-based mixed etchant. Sandblasting was performed in terms of variables such as the distance of 8 cm between the gun nozzle and the glass substrate, the fixed air pressure of 0.5bar, and the constant speed control of the specimen stage. The chemical etching process was conducted with mixed etching solution prepared by combination of BHF (Buffered Hydrofluoric Acid), HCl, and distilled water. The morphology of the glass surface after sandblasting process displayed sharp collision vestiges with nonuniform shapes that could initiate fractures. The haze values of the sandblasted glass were quantitatively acceptable. However, based on visual observation, the desirable Anti-Glare effect was not achieved. On the other hand, irregularly shaped and sharp vestiges transformed into enlarged and smooth micro-spherical craters with the subsequent chemical etching process. The curvature of the spherical crater increased distinctly by 60 minutes and decreased gradually with increasing etching time. Further, the spherical craters with reduced curvature were uniformly distributed over the etched glass surface. The haze value increased sharply up to 55 % and the transmittance decreased by 90 % at 60 minutes of etching time. The ideal haze value range of 3~7 % and transmittance value range of above 90 % were achieved in the period of 240 to 720 minutes of etching time for the selected concentration of the chemical etchant.