• Journal of the Korean Society of Propulsion Engineers
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• v.7 no.4
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• pp.46-52
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• 2003

This paper presents the numerical thermal analysis for regeneratively cooled rocket thrust chambers. An integrated numerical model incorporates computational fluid dynamics for the hot-gas thermal environment, and thermal analysis for the liner and coolant channels. The flow and temperature fields in rocket thrust chambers is assumed to be axisymmetric steady state which is presumed to the combustion liner. The heat flux computed from nozzle flow is used to predict the temperature distribution of the combustion liner As a result, we present the wall temperature of combustion liner and the temperature change of coolant.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.130-130
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• 2010

마이크로웨이브를 소스로 사용하는 상압 공정 장치는 비교적 저렴한 비용과 구동의 용이성 때문에 널리 사용되고 있다. 이러한 상압 마이크로웨이브 장치는 에너지 전달 방식에 따라 도파관을 사용하는 TIA (Torch Inject Axial)방식과 동축선을 사용하는 MPT (Microwave plasma torch)로 구분할 수 있다. 이 중 TIA 방식은 동축선에 비해 에너지 전달 용량이 큰 도파관을 사용하기 때문에 대용량 처리가 가능하다. TIA 방식에서 형성된 플라즈마의 조절과 처리 효율의 증가는 형성되는 각각의 스트리머 채널의 조절에 의해 결정된다. 방전기 내부에서 스트리머 채널은 인가된 전기장의 방향으로 성장하게 되며 전기장 현상을 조절함으로써 스트리머 채널의 조절이 가능하다. 내부에 인가되는 전기장은 마그네트론에 의해 인가되는 전기장, 스트리머 채널간의 유도 전기장, 열적 팽창효과에 의한 스트리머 헤드 형상 변화에 의한 전기장으로 구분될 수 있다. 이 때 각각의 항들의 조절을 위해 생성된 플라즈마의 온도, 밀도 등의 범위를 측정할 필요가 있으며 광학적인 방법을 통해 플라즈마의 온도, 밀도를 측정하였다. 이 결과를 토대로 도파관의 형상, 방전 기체의 유량, 방전 기체의 조성을 통해 각각 전기장의 조절이 가능하였다. 각 변수의 조절을 통해 방전기 내부에서 플라즈마 헤드 성장에 대해 알 수 있었고 끝이 열린 TIA 구조에서 발생하는 플라즈마 수렴 현상을 설명할 수 있었다.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.1888-1893
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• 2007

In this study, the microchannel plated heat exchanger were numerically studied for the enhancement of heat transfer in the channel configuration. Unit cold and hot fluid region with the microchannel were modeled and periodic boundary condition at the side wall was applied to continuously repeating geometry. The material of micro-structured plate is STS304 and working fluid is water. Triangular obstacles were placed in micro channel to enhance heat transfer. The performance of microchannel plated heat exchangers were numerically investigated with various obstacle configuration and Reynolds number under the parallel and counter flows. Heat transfer rate has increased about 18% compared with straight channel, but pressure drop also increased about 3.5 times. The main factor of increasing of pressure drop and heat transfer rate is considered that the momentum was lost to collide against obstacles, generation of secondary flow and boundary layer separation, wake and vortex forming phenomena.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.1
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• pp.1-8
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• 2011

An analytical study on the flow resistance of tree-shaped channel-flow architectures was carried out based on the principle of the constructal law; the evolutionary increase in the access to currents that flow through the channels with improvements in the flow configurations were studied in a square domain using two diameters. Two types of tree-shaped configurations were optimized. The minimized global flow resistance decreased steadily as the system size $N^2$ increased. From the two channel configurations, the one that resulted in better pressure drop was selected. Further, it was shown that the system performance can be enhanced by adopting the second tree-shaped configurations when the system size is greater than $18^2$.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.36S no.3
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• pp.1-7
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• 1999

일대다 형상을 갖는 통신시스템에서 많이 고려되는 예약 알로하 방식 매체접속제어 프로토콜의 성능은 예약 채널과 데이터 채널의 분배 양식에 의해 달라진다. 본 논문에서는 이 프로토콜을 직렬 2단 대기열 모델로 근사화하고, 데이터의 지연을 성능 척도로 하여 이를 줄이는 세가지 채널 할당 방식을 제시하였다. 그리고 이들에 대한 모의실험을 통해 그 동작 특성을 규명하고 성능을 평가하였다. 그 결과 이들의 성능은 트래픽의 특성, 특히 데이터 길이의 분산에 크게 의존하며, 일반적으로는 데이터에 우선권을 주는 방식이 우수하나, 데이터 길이의 분산이 큰 경우에는 비례배분 할당 방식이 우수한 것으로 평가되었다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.724-724
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• 2004

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.11
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• pp.65-73
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• 2005

The compressible flow of reactive fluid is investigated by using the transonic small-disturbance (TSD) model and the one-step first-order Arrhenuis chemical reaction. The fluid flow is restricted to dilute premixed reactions with small heat release. The effects of channel shape and Mach number on transonic combustion are studied by numerical analysis. The results show that the channel divergence increases the chemical reaction within the given channel length whereas the channel convergence inhibits the chemical reaction near the outlet and that increasing the inlet flow Mach number at a fixed reaction rate causes the flow acceleration in a diverging channel and the appearance of weak shock waves which do not show in the inert flow case. It also helps to increase the pressure and temperature near the diverging channel outlet and to consume the reactant within the given channel length.

• Journal of Energy Engineering
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• v.9 no.2
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• pp.89-94
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• 2000

양흡입 펌프 회전차 내부 유동특성을 수치적으로 고찰하였다. 수치계산은 설계점과 2개의 탈설계점에서 이루어졌으며, Patankar에 의해 제시된 SIMPLE 알고리즘을 이용하였다. 설계점에서는 양 회전차 채널 내부에서 대칭 형상을 갖는 이차유동 특성을 발견하였지만, 탈설계점에서는 비대칭 유동특성을 발견하였다. 수치해석 결과로는 유량감소에 따라 양흡입 펌프 회전차 채널내부의 이차유동 특성이 달라진다는 사실을 고찰하였다. 또한 양흡입 펌프 회전차 단면에는 모퉁이 와류가 존재함을 알 수 있었다.

• Science of Emotion and Sensibility
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• v.21 no.2
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• pp.137-144
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• 2018

The study figured out the operational conditions of a two-way movement actuator made of one-way shape memory alloy (OWSMA) for versatile ventilation intelligent garments. To develop a low-power actuator that consumes energy only when a garment changes its form such as opening and closing, multiple channels of OWSMA were used, and optimum diameter of the wires was examined. For the switch device, optimum voltage application unit time was determined. Optimum diameter of OWSMA wire was determined by applying 3.7V to the pre-determined candidate diameters, which demonstrated two-way operation in previous studies. In order to evaluate the optimum voltage application time, the internal diameter of the actuator was measured while increasing and decreasing by 50 ms from the unit time of voltage application. Delay time under two-way operation of the actuator was measured to minimize interference caused by heat between channels. Power of 3.7V was applied to OWSMA for assessment of optimal time, and the whole process from heating to cooling was video-recorded with a thermal image camera to determine the point of time at which the temperature of OWSMA wire dropped below the phase transformation temperature. The results showed that $0.4{\Phi}$ was the most suitable diameter, and the optimum unit time of voltage applied to open and close the actuator was 4100ms. It was also shown that the delay time should be more than 1.8 seconds between two-way operations of the actuator.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.8
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• pp.761-769
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• 2009

In this paper, we report on the channel capacity and diversity gain of the vehicle on-glass antenna for FM radio reception. The correlation coefficient and channel capacity were obtained using the simulated 3D radiation pattern of each antenna and the Rayleigh channel model for urban environment. To examine the channel capacity we used two antennas which are a simple straight antenna and L-type antenna. Then we observed the available channel capacity by varying the position of feeds and the shape of the L-type antenna. The sample antenna, which has a maximum feed distance with different polarizations, was built and the receiving performance was measured in the weak FM field area. From the results we confirmed that the distance between the feeds should be placed as far as possible for the high channel capacity. If the distance between the feeds are greater than a certain threshold value than the polarizations of the two antennas are getting more important for determining the channel capacity.