• 한국연소학회지
• /
• 제5권1호
• /
• pp.19-30
• /
• 2000

The characteristics of NOx emissions in pure hydrogen nonpremixed flames with coaxial air are analyzed numerically for the three model cases of coaxial air flames classified by varying coaxial air velocity and/or fuel velocity. In coaxial air flames, the flame length is reduced by coaxial air and can be represented as a function of the ratio of coaxial air to fuel velocity. Coaxial air decreases flame reaction zone, resulting in reducing flame residence time significantly. Finally, the large reduction of EINOx is achieved by the decrease of the flame residence time. It is found that because coaxial air can break down the flame self-similarity law, appropriate scaling parameters, which are different from those in the simple jet flames, are recommended. In coaxial air flames, the flame residence time based on the flame volume produces better results than that based on a cube of the flame length. And some portion of deviations from the 1/2 scaling law by coaxial air may be due to the violation of the linear relationship between the flame volume and the flame reaction zone.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 춘계학술대회논문집E
• /
• pp.323-328
• /
• 2001

Supersonic coaxial, axisymmetric, jets issuing from various kinds of dual coaxial nozzles were experimentally investigated. Four different kinds of coaxial, dual nozzles were employed to characterize the major features of the supersonic, coaxial, dual jets. Two convergent-divergent supersonic nozzles with an impinging angle in the jet axis of the annular jets were designed to have the Mach number 2.0 and used to compare the coaxial jet flows with those discharging from two sonic nozzles. The primary pressure ratio was changed in the range from 4.0 to 10.0 and the assistant jet ratio from 1.0 to 4.0. The results obtained show that the assistant jets from the annular nozzle affect the coaxial jet flows and an increase of both the primary jet pressure ratio and assistant jet pressure ratio produces longer supersonic length of the dual, coaxial jet.

• Journal of Multimedia Information System
• /
• 제5권2호
• /
• pp.143-146
• /
• 2018

The eigen value problem of a coaxial cavity and a modified pill box cavity is investigated using the mode matching technique. The coaxial cavity has a cylindrical cavity with beam ports and center conductor. The pill box cavity is the same as a coaxial cavity without center conductor. The electric field and magnetic field are formulated in propagation region and resonance region. The boundary and orthogonal conditions are applied to the electric and magnetic fields. We derived the eigen value equation by the proposed procedure in a coaxial cavity and a modified pill box cavity. The electromagnetic field of the real structure is disturbed by the coaxial wire. The effect of the coaxial wire in pill box cavity with beam ports increase the dominant resonant frequency. The coaxial line method of the coupling impedance is not adequate for a cylindrical cavity. The results of the mode matching technique and simulation agree well. The results confirm the proposed formulation is valid.

• Journal of Power Electronics
• /
• 제13권2호
• /
• pp.214-222
• /
• 2013

This paper proposes a high efficiency step-down flyback converter using a coaxial-cable coupled-inductor which has a higher primary-secondary flux linkage than sandwich winding transformers. The structure of the two-winding coaxial cable transformer is described, and the coupling coefficient of the coaxial cable transformer and that of a sandwich winding transformer are compared. A circuit model of the proposed transformer is also obtained from the frequency-response curves of the secondary short-circuit and of the secondary open-circuit. Finally, the performance of the proposed transformer is validated by the experimental results from a 35W single-output flyback converter prototype. In addition, the proposed two-winding coaxial transformer is extended to a multiple winding coaxial application. For the performance evaluation of the extended version, 35W multi-output hardware prototype of the DC-DC flyback converter was tested.

• International Journal of Naval Architecture and Ocean Engineering
• /
• 제3권4호
• /
• pp.286-292
• /
• 2011

In order to design a shear coaxial injector of solid particles for underwater propulsion system, basic experiments on gas-liquid shear coaxial injector are necessary. In the gas-liquid coaxial injector self-pulsation usually occurs with an intense scream. When self-pulsation occurs, mass flow rate oscillation and intense scream are detected by the interactions between the liquid and gas phase. Self-pulsation must be suppressed since this oscillation may cause combustion instabilities. Considerable research has been conducted on self-pulsation characteristics, but these researches are conducted in swirl coaxial injector. The main objective of this research is to understand the characteristics of self-pulsation in shear coaxial injector and reveal the mechanism of the phenomenon. Toward this object, self-pulsation frequency and spray patterns are measured by laser diagnostics and indirect photography. The self-pulsation characteristics of shear coaxial injector are studied with various injection conditions, such as the pressure drop of liquid and gas phase, and recess ratio. It was found that the frequency of the self-pulsation is proportional to the liquid and gas Reynolds number, and proportional to the L/d.

• 한국분무공학회지
• /
• 제17권1호
• /
• pp.35-44
• /
• 2012

To improve the mixing and atomizing performance at the center region of the conventional coaxial shear injector spray, the concept of a coaxial porous injector was invented. This novel injection concept for liquid rocket engines utilizes the Taylor-Culick flow in the cylindrical porous tube. The 2-dimensional injector, which can be converted in three injection configurations, was fabricated, and several cold flow tests using water-air simulant propellant was performed. The hydraulic characteristics and the effects of a gas flow condition on the spray pattern and the Sauter mean diameter (SMD) was analyzed for each configuration. The atomizing mechanism of coaxial porous injector was different with the coaxial shear injector, and it was explained by the momentum of the gas jet, which is injected normally against the center liquid column, and by the secondary disintegration at the wavy interface of liquid jet, which was generated at the recessed region. The SMD of 2D coaxial porous injector, which has higher gas momentum, was measured and it shows better atomizing performance at the center and outer side of spray than the 2D coaxial shear injector.

• 한국정보통신학회:학술대회논문집
• /
• 한국정보통신학회 2017년도 추계학술대회
• /
• pp.238-240
• /
• 2017

동축 선로를 이용한 발룬은 쉬운 제작, 높은 동작 전력, 안정적인 동작으로 초고주파 회로에서 자주 이용된다. 하지만, 동축 선로 발룬은 동축 선로와 기판에 존재하는 마이크로스트립 선로와의 연결할 때에 발생하는 기생 리액턴스 성분과 동축 선로 자체가 가지는 인덕턴스와 케패시턴스 성분에 의해 정확한 발룬 동작 특성을 예상하기 어렵다. 본 논문에서는 역위상 특성을 가지는 동축 선로 발룬 두 출력 단자에서의 위상 특성을 측정하였다. 이를 바탕으로 보다 개선된 동축 선로 발룬 제작 가능성에 대해 살펴보려 한다.

• 한국정보통신학회논문지
• /
• 제21권12호
• /
• pp.2241-2248
• /
• 2017

동축 선로 임피던스 변환기는 동일 길이의 두 개 또는 그 이상의 동축 선로 결합을 이용하여 임피던스 변환을 만드는 회로로서 높은 동작 전력, 광대역 동작 특성, 쉬운 제작 등 다양한 장점에 의해 상대적으로 낮은 주파수 영역의 임피던스 정합을 위해 자주 사용된다. 본 논문에서는 두 개의 100mm 동축 선로를 이용한 4:1 임피던스 변환기를 사용하여 동축 선로의 위상 및 세기 특성을 측정하였다. 이를 통해 보조 동축 선로의 길이가 주 동축 선로보다 약 5mm 짧게 하는 것이 보다 저손실의 동축 선로 임피던스 변환기 구현에 효과적임을 알 수 있었다. 또한 4:1 임피던스 변환기와 1:4 임피던스 변환기를 직접 연결하여 측정한 동축 선로 임피던스 변환기의 전달 특성 실험을 통해 접지면과 주 동축선로 외곽 도체 입력부에 약 1pF 캐페시터를 연결하는 것이 보다 광대역 동작 범위 및 대역 내 특성 개선에 도움이 됨을 알 수 있었다.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2007년도 추계학술대회 논문집
• /
• pp.113-116
• /
• 2007

Performance of a steam reformer can be improved by using a coaxial cylindrical reactor, because the design can enhance the heat transfer for the steam reforming reaction, which is the one of main rate-determining steps of overall reactions. The objective of this study is to investigate the coaxial cylindrical reactor numerically. Pseudo-homogeneous model and one medium approach are incorporated for the chemical reactions, and models are validated with experimental results. The catalyst of the coaxial cylindrical reactor is 67% for one of the cylindrical reactor, but fuel conversion of the coaxial cylindrical reactor is increased by 10%. Heat flux profiles are investigated by modified Nusselt number and heat flux which is transported from the product gas to the catalyst bed affecting performance of the steam reformer.

• 산업기술연구
• /
• 제26권B호
• /
• pp.35-41
• /
• 2006

Recently, as ultrasonic medical devices are gradually developed, many of those requires smaller and more precision coaxial cables in probe. So, the use of micro coaxial cable becomes an efficient solution for ultrasonic machine. However, there are many difficulties in stripping micro coaxial cable by traditional mechanical process. In this paper, we use the Nd-YAG laser for the efficient stripping of conduct wire of cable. We propose a new method to strip the shield wire of micro coaxial cable. Through some experiments, we found that there is a new possibility in the proposed method. Also, in order to enhance the performance, we propose a preprocess of the cable before stripping.