• 한국추진공학회지
• /
• 제7권2호
• /
• pp.7-14
• /
• 2003

본 연구에서는 마이크로 임계노즐을 통한 유출계수를 예측하기 위하여, 축대칭, 압축성 Navier-Stokes 방정식을 사용한 수치계산을 수행하였다. 수치해의 적합성을 조사하기 위하여, 다양한 난류모델과 벽함수를 적용하였으며, 수치 결과들은 종래의 실험결과와 비교하였다. 그 결과 본 수치계산법은 임계노즐을 통한 유출계수를 적절하게 예측하였으며, 특히 표준 $\kappa$-$\varepsilon$난류모델과 표준 벽함수를 적용한 경우에 유출계수를 가장 잘 예측함을 알았다. 본 연구의 결과로부터 얻어진 임계노즐벽면의 난류경계층의 배제두께는 레이놀즈수가 2000에서 20000의 범위에서 임계노즐목 직경의 약 2%에서 0.6%까지 변화하였으며, 종래의 경험식과 잘 일치하였다.

• 대한기계학회논문집B
• /
• 제29권2호
• /
• pp.205-213
• /
• 2005

The drop ejection process from a micro nozzle is investigated by numerically solving the conservation equations for mass and momentum. The liquid-gas interface is tracked by a level set method which is extended for two-fluid flows with irregular solid boundaries. Based on the numerical results, the liquid jet breaking and droplet formation behavior is found to depend strongly on the pulse type of forcing pressure and the contact angle at the gas-liquid-solid interline. The negative pressure forcing can be used to control the formation of satellite droplets. Also, various nozzle shapes are tested to investigate their effect on droplet formation.

• 한국정밀공학회지
• /
• 제19권1호
• /
• pp.219-226
• /
• 2002

The mechanical etching technique has recently been developed to a powder blasting technique for various materials, capable of producing micro structures larger than 100$\mu$ m. This paper describes the performance of powder blasting technique in micro-pocketing of stainless steel and the effect of the number of nozzle scanning and the nozzle height on the depth and width of pockets. Experimental results showed that increasing the no. of nozzle scanning and decreasing the nozzle height resulted in the increase of depth and width in pockets. Increase of width results from wear of mask film.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2007년도 제29회 추계학술대회논문집
• /
• pp.225-228
• /
• 2007

마이크로 고체 추진제 추력기는 현재의 MEMS 기술로 가장 실현 가능성이 높은 마이크로 추력기이다. 마이크로 고체 추진제 추력기의 기본 요소로는 마이크로 노즐, 마이크로 점화기, 연소 챔버 그리고 고체 추진제이다. 마이크로 노즐과 연소 챔버는 감광유리의 이방성 식각을 통해 제작이 되었다. 마이크로 점화기는 마이크로 유리 박막 백금 히터를 사용하였다. 요소들의 제작 공정을 확립 후, 요소들을 통합하여 추력기를 개발하였다. 추력기의 연소 실험을 수행하여 성공적으로 연소가 일어남을 확인하였다.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회B
• /
• pp.2763-2768
• /
• 2007

Recently, as the semiconductor production technology develops, there has been growing interest in the cooling system using micro fluid pump. Among the various types of micro fluid pump, the valve-less diffuser/nozzle has been extensively studied in recent years. However, the flat-walled diffuser/nozzle flow has not been clearly looked into due to its non-linear characteristics. In this paper, the flow characteristics of the flat-walled diffuser/nozzle have been analyzed using similitude model and simulations. Similitude models are designed so that the flow pattern is same as that of 1/10 scale flow by using high viscous fluid as working fluid. The results are compared to the simulations. It is shown that the flow characteristics of 2D simulation are different from 3D simulations at high Re region, and the measured pump efficiency is highly dependent on the pressure difference as well as the channel geometry. From these results, the desirable conditions for the efficient pump is discussed.

• 한국기계가공학회지
• /
• 제15권4호
• /
• pp.148-154
• /
• 2016

A study on the micro particle blasting was conducted to find the optimum conditions of the blasted surface of aluminum 6061. The particle type such as $Al_2O_3$ and SiC, nozzle diameter, pressure, standoff distance and injection time were used as blasting conditions. Statistical method of orthogonal arrays(ANOVA) was used to find optimum conditions of maximum depth and maximum diameter of blasted surface. Particle type, nozzle diameter, and pressure were found to be the main factors of maximum blasted depth and diameter. Maximum blasted diameter was affected by increasing pressure and nozzle diameter but saturated maximum diameter. Maximum blasted depth was affected by pressure and nozzle diameter when aluminum 6061 was blasted with $Al_2O_3$ particle. The value of surface roughness was increased as pressure and nozzle diameter increased when aluminum 6061 was blasted with SiC.

• 한국전산유체공학회지
• /
• 제22권1호
• /
• pp.43-50
• /
• 2017

Thermal flowfield of a micro turbojet engine was computationally investigated for exhaust nozzles with different aspect ratio and curvature. Special attention was paid to maximum and average temperature of the nozzle surface and the exhaust nozzle plume. The IR signatures of the micro turbojet engine nozzle were then calculated through the narrow-band model based on thermal flowfield data obtained through CFD analysis. Finally, in order to check the similarity of thermal flowfields and IR signature of the sub-scale micro turbojet engine model and the full-scale UCAV propulsion system, several non-dimensional parameters associated with temperature and optical property of plume were introduced. It was shown that, in spite of some differences in actual values of non-dimensional parameters, the scaling characteristics on spectral feature of IR signature and effects of aspect ratio and curvature of nozzle configuration remain similar in sub-scale and full-scale cases.

• 한국항공우주학회지
• /
• 제35권12호
• /
• pp.1115-1120
• /
• 2007

본 논문은 기둥 구조의 전극이 내부에 존재하는 노즐을 이용한 정전 분무 마이크로 추진 장치의 새로운 메커니즘을 제시하였다. 기둥 구조의 노즐로 인한 제팅의 효율 증진을 수치적 및 실험적으로 연구하였다. 노즐 상부에 존재하는 전극에 인가된 전압으로 인하여 액면에 형성된 전기장은 액체의 분무를 가능하게 하며 기둥 구조의 전극은 액면의 중앙 부분에 전기장이 집중되도록 하여 제팅을 효율적으로 할 수 있게 하였다. 또한 노즐 크기에 따른 필요한 인가전압의 차이에 대한 연구를 수행하였으며 본 연구로부터 수 마이크로미터의 노즐에 대해서 500V 이하의 전압에서 구동이 가능함을 보였다.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2008년도 추계학술대회B
• /
• pp.2210-2213
• /
• 2008

In the present study, effects of degree of confinement on heat transfer characteristics of a micro-scale slot jet impinging on a heated flat plate are experimentally investigated. The effects of Reynolds numbers (Re = $1000{\sim}5000$), lateral distances (x/B = $1{\sim}10$), nozzle-to-plate spacings (Z/B = $1{\sim}20$), and degree of confinement ($B_c$/B = 3, 48) on the Nusselt number are considered. The results show that the effects of the degree of confinement on the cooling performance of the micro-scale impinging slot jet are significant at lower nozzle-to-plate spacings and higher Reynolds numbers. In addition, it is shown that the cooling performance of the micro-scale unconfined slot impinging jet is 200% higher than that of the micro-scale confined slot impinging jet.

• 한국기계가공학회지
• /
• 제16권2호
• /
• pp.135-141
• /
• 2017

An experimental study of micro blasting for a rotating aluminum rod was conducted through the statistical analysis of ANOVA to obtain the effect of blasting conditions. The rotating equipment was designed and constructed with forward and backward moving for helical blasting, but rotation was used in this study. The blasting condition factors were the type of abrasive particle, nozzle diameter, pressure, standoff distance, injection time, etc. The width of the surface, the maximum depth of the sprayed surface, and ANOVA were analyzed by statistical analysis. The results showed that the contributions of the main factors were pressure, nozzle diameter, and injection particle.