• Journal of computational fluids engineering
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• v.12 no.4
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• pp.38-43
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• 2007

Owing to the rapid progress in manufacturing technology of microscale devices, there are active research works in developing microscale propulsion systems. In this study, gas flows in nozzles with size of milli and sub-millimeter are investigated by using a CFD code based on the Navier-Stokes equations. The prediction results were compared with theoretical results of quasi-one-dimensional nozzle flow and experiment data. In general, theoretical values agree very well with the CFD results. However, theoretical values begin to deviate from the CFD and experimental data for relatively small Reynolds numbers and the nozzle shape with rectangular cross section. The primary reason for this discrepancy is due to the existence of the thick boundary layer at the wall in low Reynolds flows.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.149-152
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• 2008

A slinger combustor which can be applied to micro turbojet engine has been developed with the combustor rig test. A rotating fuel injector with high speed rpm was designed, manufactured and tested to apply into slinger combustor through spray test and adequate droplet size and spray distribution were achieved. The CFD was used to analyze internal flow of the combustor. We found out that the combustor shows 11.2% of pressure loss and 99.8% of combustion efficiency at full combustor rig test.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.10a
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• pp.253-256
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• 2003

The engine core of a 65hp-turboshaft engine for UAV is developed and modified into a 55lbf-turbojet engine. Since the core engine is installed with a propelling nozzle, which has the same mass flow characteristics as the power generator of the turboshaft engine its mechanical and aerodynamic characteristics are basically the same as those of the complete engine. Engine output is not shaft power but thrust force that is easier to measure. The core engine is very useful for core test purpose. Besides, the core engine itself can be directly used for propulsion of small air vehicles.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.253-256
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• 2009

In the micro turbojet engine less than 350kw power class, it is not easy to find out the good atomization fuel injector with good spray quality. However conceptually, rotating fuel injection system can give high atomization quality by only the centrifugal force of a high speed rotating shaft of the engine without high-pressure fuel pump. With this motivation, we manufactured very small rotating fuel injector of 40 mm diameter and performed under a variety of injection orifices. We measured droplet size, velocity and spray distribution by the PDPA(Phase Doppler Particle Analyzer) system. Also spray was visualized by using high speed camera. From the test results, we could understand that the length of liquid column from the injection orifice is mainly controlled by the rotational speeds. Furthermore, droplet size(SMD) is decreased with the rotational speeds and is influenced by the diameter of the injection orifice and liquid film thickness.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.6
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• pp.1-7
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• 2017

The performance of a MEMS solid propellant thruster was predicted and analyzed through internal ballistics model and CFD analysis. The nozzle throat was $416{\mu}m$, and the area ratio of the nozzle was 1.85. As a result of the internal ballistics model, chamber pressure increased up to 197 bar and the maximum thrust was 3,836 mN. In CFD analysis, the chamber pressure of the internal ballistics model was applied as the operating pressure, and the CFD model was divided into an adiabatic and a heat loss model. As a result, the maximum thrust of the adiabatic model was 14.92% lower than that of the internal ballistics model, and the effect of heat loss was insignificant.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.36-40
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• 2008

Minimization of nozzle induces many flow losses in micro-propulsion system. In this study, we studied about thermal transpiration based new conceptual micro propulsion system to overcome these losses. Thermal transpiration device(Knudsen pump) having no moving parts can self-pump the gaseous propellant by temperature gradient only (cold to hot). We designed, fabricated the knudsen pump and analyzed pressure gradient efficiency of membrane according to Knudsen number under vacuum condition. In this paper, we compared mass flow rate of Knudsen pump by using different membrane type ; Polyimide and Hangi, Korean traditional paper.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.6
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• pp.581-586
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• 2008

The MEMS solid propellant thrusters have very low thrust level for applying to the propulsion system of micro/nano satellites or the side jet thruster of smart bombs. In this research, the fabrication possibility of planar type MEMS solid propellant thrusters that have enlarged burning surface area was examined and the safety of the structure of thruster during the firing test was confirmed. The performance of a micro igniter which is the key component of the MEMS solid propellant thruster was estimated by the ANSYS Icepak and evaluated by the experiment. Finally, the thrust was measured by the micro force sensor. The levels of thrust were 300, 600 mN in the case of K=15, 20.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.4
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• pp.53-60
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• 2004

Optimal design of the hybrid motor has been performed for the first stage of nanosat air launch vehicle using F-4E Phantom as mother plane. Selected design variables are number of ports, the initial oxidizer flux, the combustion chamber pressure, and the nozzle expansion ratio. GBM(Gradient Based Method) and GA(Genetic Algorithm) are simultaneously used to compare the versatility of each algorithm for optimal design in this problem. Also, two objective functions of motor weight, and length are treated separatedly in the optimization to study how the objective function can affect the optimal design. The design results show that the optimal design can be successfully achieved either using GBM or GA regardless of the choice of the objective function; motor weight or length. And nanosat air launch vehicle which has total mass of 704.74kg, and length of first stage 3.74m is designed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.105-105
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• 2006

IT 산업 및 반도체 산업이 발전함에 따라 초소형, 고집적화 시스템의 요구에 대응하기 위해서 고해상도 및 고정밀의 패턴 구현에 관한 많은 연구가 진행되고 있다. 이러한 연구는 각종 산업제품의 PCB(Printed Circuit Board) 및 디스플레이 장치인 PDP(Plasma Display Panel), LCD(Liquid Crystal Display) 등에 적용되어 널리 응용되고 있다. 현재 널리 사용되는 인쇄 회로 기판은 마스킹 후 선택적 에칭 방식을 적용하여 금속 배선을 형성하는 방식을 적용하고 있다. 이러한 방식은 설계가 변경될 경우 마스크를 다시 제작해야 하는 번거로움이 있어 설계 변경이 용이하지 않고 더욱 길어진 생산시간의 증가로 인하여 생산성 및 집적도가 떨어지게 된다. 따라서 최근에는 이러한 한계를 극복하기 위한 방안이 여러 가지 측면에서 시도되고 있으며, 그 중에서도 Inkjet Printing 기술에 대한 관심이 증가하고 있다. 본 연구에서는 Inkjet Printing 방식을 적용하여 금속 배선을 형성하고 선폭과 두께의 오차를 줄여 배선의 Tolerance 를 개선할 수 있는 방안을 제안하였다. Inkjet Printing 방식을 이용한 기존의 금속 배선 형성은 고해상도의 DPI(Dot Per Inch)에서 잉크 액적이 뭉치는 Bulge 현상이 발생되어 원하는 형상 및 배선의 폭을 구현하는데 어려움이 있었다. Bulge 현상은 배선의 불균일성을 야기할 뿐만 아니라 근접한 배선의 간섭에도 영향을 미처 금속 배선의 기능을 할 수 없는 단점을 발생시킨다. 따라서 본 연구에서는 이러한 Bulge 현상을 줄이고 배선간의 간섭을 방지하여 원하는 배선을 용이하게 형성할 수 있는 순차적 인쇄 방식을 적용하였다. 본 연구에서는 노즐직경 35um 의 Inkjet Head 와 나노 Ag 입자 잉크를 사용하여 Glass 표면 위에 배선을 형성하고 배선의 폭과 두께를 측정하였다. 또한 순차적 인쇄 방식을 적용하여 700DPI 이상의 고해상도에서 나타날 수 있는 Bulge 현상이 감소하였음을 관찰하였으며 금속 배선의 Tolerance를 10%내외로 유지할 수 있음을 확인하였다.