• Journal of Advanced Marine Engineering and Technology
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• 제11권3호
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• pp.53-60
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• 1987

Steam ejector is a equipment which compresses the gases to desired discharge pressure. It is widely used for the evacuation systems because of its high working confidence. And recently it is used as the thermo-compressors in the various energy saving systems. Steam ejector is constructed of three basic parts; a suction chamber, a motive nozzle and a diffuser. The high velocity stream jet of steam emitted by the motive nozzle creats suction chamber, which draws the low pressure gases. The diffuser converts the kinetic energy of high velocity flow to pressure energy. It is not easy to determine the dimensions of a steam ejector met to the desired design condition, because that the expected suction rates must be obtained by reapeating the complicate calculation. And also such a calculation is concomitant with geometrical analysis for suction part and diffuser based on the stability of steam flow. Therefore, it is considered that the Computer-Aided Design (CAD) of steam ejector is a powerful design method. In this paper, computer program for steam ejector design is developed based on the theoretical research and the previous experimental results. And the determinating method of diffuser inlet angle and the velocity development profile of suction gas along to the diffuser are suggested. The validity of the development profile of suction gas along to the diffuser are suggested. The validity of the developed computer results with other's for the practical design calculation of a manufactured steam ejector.

• 대한기계학회논문집B
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• 제30권9호
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• pp.842-849
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• 2006

An experimental study has been conducted to investigate the effects of a multi air-staged burner on NOx formation and heat transfer in a 15kW large-scale laboratory furnace adopted the reburning process. The reburn fuel as well as burnout air was injected from each nozzle attached at the wall of the cylindrical furnace. Fuel in both main burner and reburn nozzle was LPG (Liquefied Petroleum Gas). The paper reports the influences on NOx reduction of reburn fuel fraction in reburning zone. Temperature distribution inside the overall region as well as total heat flux at the wall of the furnace has been measured to examine the heat transfer characteristics due to the reburning process. For comparison, the reburning effects were examined for a combustor with two types of burner; a regular single staged burner and a multi-air staged burner. A gas analysis was also performed to evaluate an appropriate condition for NOx emission in a primary zone for the excess air ratio of 1.1. As a result, combustion efficiency expected to become more efficient due to the reduction of heat loss in burnout zone decrease when multi air-staged burner in furnace adopted reburning technology was used.

• 한국분무공학회지
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• 제22권4호
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• pp.175-184
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• 2017

The numerical investigation on the effects of water-mist characteristics has been carried out for the fire suppression mechanism. The FDS are used to simulate the interaction of fire plume and water mists, and program describes the fire-driven flows using LES turbulence model, the mixture fraction combustion model, the finite volume method of radiation transport for a non-scattering gray gas, and conjugate heat transfer between wall and gas flow. The numerical model is consisted of a rectangular enclosure of $L{\times}W{\times}H=1.5{\times}1.5{\times}2.0m^3$ and a water mist nozzle that be installed 1.8 m from fire pool. In the present study, the parameters of nozzle for simulation are the droplet size and the spray velocity. The droplet size influences to fire flume on fire suppression more than the spray velocity because of the effect of the terminal velocity. The optimal condition for fire suppression is that the droplet size and the spray velocity are $100{\mu}m$ and 20 m/s respectively.

• 대한기계학회논문집B
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• 제23권7호
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• pp.831-840
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• 1999

In this work, an aerothermodynamic calculation model for cooled axial flow turbine blades with trailing edge ejection is suggested and a mean line performance analysis of a turbine stage with nozzle cooling is carried out. A unique model regarding the interaction between coolant and main gas is proposed, while existing correlations are adopted to predict viscous loss and blade outflow angle. The interactions considered are the heat transfer from main gas to coolant and the temperature and pressure losses by the mixing of two streams due to the trailing edge coolant ejection. For a stator blade without ejection, trailing edge loss calculated by the trailing edge analysis is compared with that calculated by loss correlation. The effect of heat transfer effectiveness of coolant passage on the mixing loss is analyzed. For a model turbine stage with nozzle cooling, parametric analyses are carried out to investigate the effect of main design variables(coolant mass flow ratio, temperature and ejection area) on the stage performance.

• 한국표면공학회지
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• 제36권1호
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• pp.69-73
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• 2003

The atmospheric pressure plasma is regarded as an effective method for surface treatments because it can reduce the period of process and doesn't need expensive vacuum apparatus. The performance of non-transferred plasma torches is significantly depended on jet flow characteristics out of the nozzle. In order to produce the high performance of a torch, the maximum discharge velocity near an annular gap in the torch should be maintained. Also, the compulsory swirl is being produced to gain the shape that can concentrate the plasma at the center of gas flow. In this work, the distribution of gas flow that goes out to atmosphere through a plenum chamber and nozzle is analyzed to evaluate the performance of atmospheric pressure plasma torch which can present the optimum design of the torch. Numerical analysis is carried out with various angles of an inlet flow velocity. Especially, three-dimensional model of the torch is investigated to estimate swirl effect. We also investigate the stabilization of plasma distribution. For analyzing the swirl in the plenum chamber and the flow distribution, FVM (finite volume method) and SIMPLE algorithm are used for solving the governing equations. The standard k-model is used for simulating the turbulence.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 B
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• pp.972-974
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• 2005

The present work deals with the theoretical study of the effects of copper vapours resulting from the erosion of the electrodes on the properties of a SF6 arc in a Laval nozzle. Computations have been done for a DC arc of 1000A with upstream gas pressure of 3.75MPa. The arc plasma is assumed to be in local thermodynamic equilibrium(LTE). The sheath and non-equilibrium region around the electrodes are not considered in this model. However, its effects on the energy flux into the electrodes are estimated from some experimental and theoretical data. The turbulence effects are calculated using the Prandtl mixing length model. A conservation equation for the copper vapour concentration is solved together with the governing equations for mass, momentum and energy of the gas mixture. Comparisons were made between the results with and without electrodes erosion. It has been found that the presence of copper vapours cools down the arc temperature due to the combined effects of increased radiation and increased electrical conductivity. The copper vapour distribution is very sensitive to the turbulent parameter. The erosion of upstream electrode(cathode) has larger effects on the arc compared to the downstream electrode(anode) as the copper vapour eroded from the anode cannot diffuse against the high-speed axial flow.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년도 제31회 추계학술대회논문집
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• pp.153-156
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• 2008

고공 환경에서의 점화 연소 특성을 확인하기 위해 선행되어야 할 저압/저온 환경 모사 및 연료 유량 제어 실험을 수행하였다. 저압 환경을 모사하기 위하여 초음속 디퓨저를 이용하였고, 공기 유량 공급 및 디퓨저 1차 전단 노즐 압력에 따라 다양한 고도의 저압 환경을 조성할 수 있음을 확인하였다. 또한 저온 환경을 모사하기 위해 액체 질소를 이용한 열교환기를 활용하였고, 혼합 탱크로 유입되는 극저온/상온 공기 온도 조건을 일정하게 유지할 경우 다양한 공기 유량 조건에서 혼합 공기의 온도는 극저온/상온 공기의 혼합비에 의해 결정됨을 알 수 있었다. 이에 따라 본 연구에서 구축한 고고도 환경 모사 시스템을 활용하여 다양한 고도 조건에서의 점화 및 연소 특성 실험 수행이 가능함을 입증하였다.

• 한국가스학회지
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• 제12권4호
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• pp.21-28
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• 2008

삼지화염과 포와젤(Poiseuille) 및 균일분포 연료출구 속도에 따른 부상화염의 부상거동 그리고 화염면 부근에서의 연소 유동 특성에 대하여 수치적 해석을 수행하였다. 부상화염에 대한 수치해석으로 기존 연구 결과를 검정하고 화염대 부근에서 구조적 특성을 살펴보며 포와젤 및 균일분포 연료출구속도 조건에서 운동량 유속으로 부상높이를 일반화하여 비교하였다. 또한 화염면 부근에서 속도, 압력, 온도, 화학반응속도 등으로 연소 유동 특성을 분석하고 규명하였다. 특히 중심선을 따른 속도 변화의 경우 노즐에서 화염대 부근까지는 전형적인 비반응제트 유동에 따른 속도 분포를 형성하지만 화염대 직전에서 속도가 급격히 감소하다가 화염대를 지나면서 급격히 증가한 후에 다시 감소하는 현상을 규명하였다. 화염대 전의 유동영역에서는 화염대가 장애물역할을 하다가 화염대를 지나고 나면 유동을 가속시켜주는 역할을 하고 있기 때문이다. 이러한 현상은 기존의 비반응 제트 유동으로 규명하지 못하였던 것이다.

• 한국추진공학회지
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• 제4권3호
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• pp.11-18
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• 2000

초음속 노즐 뒤에서 형성되는 과소팽창 제트(Underexpanded jet)가 분사될 때 베럴 충격파(Barrel shock), 팽창과(Expansion fan), 마하 디스크(Mach disc), 제트 경계면(Exhaust-gas jet boundary), 그리고 반사 충격파(Reflected shocks)와 같은 구조의 풍격파 셀(Shock cell)이 연속적으로 나타난다. 이러한 충격파 셀은 난류 소산에 의해 희미해지며 거리가 멀어지면 사라진다. 과소팽창 제트가 수직 평판에 충돌하게 되면 챔버 압력 및 출구 마하수 등 여러 인자들에 따라 달라지는 복잡한 유동장을 형성하게 된다. 본 논문에서는 평판에 충돌하는 과소팽창 제트가 형성하는 유동장을 압축성 Navier-Stokes 방정식에 유한체적법을 적용하여 수치적으로 구한 해존 실험 데이터와 비교 검증하였다. 실험 데이터와 계산 결과의 압력구배 및 유동가시화 사진 비교 견과 노즐과 평판이 가까운 경우에 충돌제트유동을 잘 예측할 수 있었으며, 과소팽창비가 작을 때 과소팽창비에 따른 충돌제트 유동분포의 영향은 자게 나타남을 알 수 있었다.

• 한국추진공학회지
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• 제23권1호
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• pp.124-131
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• 2019

가스터빈엔진 고도시험설비 운용특성탐색 및 설비튜닝 연구와 유량/추력 측정방안 검증을 위한 엔진 시뮬레이션덕트 설계 연구를 수행하였다. 설비 운용특성 검증은 배압/추력 제어가 필요하므로 Spikecone type의 가변노즐을 적용하였으며, 유량검증용 ISO 쵸킹노즐의 추가장착이 가능토록 설계하였다. 시뮬레이션덕트 주유로 면적은 1D Sizing으로 결정하고, 노즐면적변화에 따른 시뮬레이션덕트 내부 유동특성은 1D/CFD 해석으로 조사하였으며, 해석결과로부터 설비운용특성 탐색 및 유량/추력 검증시험을 위한 공기공급부 시험조건을 도출하였다. Spike 노즐 구동부는 시험 전운용 구간에서 공력하중조건을 견디도록 모터, 리니어 볼스크류 등의 부품모델을 선정하였으며, 시험 시 10 mm/s의 이송속도가 가능하도록 설계하였다.