• 한국연소학회지
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• 제11권4호
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• pp.27-35
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• 2006

The impacts of equivalence ratio on flow structure and flame dynamic in a model gas turbine combustor are investigated using large eddy simulation(LES). Dynamic k-equation model and G-equation flamelet model are employed as LES subgrid model for flow and combustion, respectively. As a result of mean flow field for each equivalence ratio, the increase of equivalence ratio brings about the decrease of swirl intensity through the modification of thermal effect and viscosity, although the same swirl intensity is imposed at inlet. The changes of vortical structure and turbulent intensity etc. near flame surface are occurred consequently. That is, the decrease of equivalence ratio can leads to the increase of heat release fluctuation by the more increased turbulent intensity and fluctuation of recirculation flow. In addition, the effect of inner vortex generated from vortex breakdown on the heat release fluctuation is increased gradually with the decrease of equivalence ratio. Finally, it can be identified that the variations of vortical structure play an important role in combustion instability, even though the small change of equivalence ratio is occurred.

• 대한기계학회논문집
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• 제13권3호
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• pp.528-537
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• 1989

The objective of this paper is to investigate effects of the specific heat and the diameter of suspending particles on the heat transfer coefficient of two phase turbulent flow with suspension of solid particles in a circular tube with constant heat flux. Heat transfer coefficients of two phase turbulent flow in pipe with suspension of graphite powder were measured with variations of particle sizes and solid-gas loading ratio. Measured data were compared with predictions by numerical analysis in which the turbulece models are closed on the first order level. Results show that heat transfer coefficient increases with increasing the solid-gas loading ratio and the specific heat of suspending material, however, it decreases as the average diameter of particles decreases below $24{\mu}m$.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.3003-3008
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• 2007

Critical nozzle has been frequently employed to measure the flow rate of various gases, but hydrogen gas, especially being at high-pressure condition, was not nearly dealt with the critical nozzle due to treatment danger. According to a few experimental data obtained recently, it was reported that the discharge coefficient of hydrogen gas through the critical nozzle exceeds unity in a specific range of Reynolds number. No detailed explanation on such an unreasonable value was made, but it was vaguely inferred as real gas effects. For the purpose of practical use of high-pressure hydrogen gas, systematic research is required to clarify the critical nozzle flow of high-pressure hydrogen gas. In the present study, a computational fluid dynamics(CFD) method has been applied to predict the critical nozzle flow of high-pressure hydrogen gas. Redlich-Kwong equation of state that take account for the forces and volume of molecules of hydrogen gas were incorporated into the axisymmetric, compressible Navier-Stokes equations. A fully implicit finite volume scheme was used to numerically solve the governing equations. The computational results were validated with some experimental data available. The results show that the coefficient of discharge coefficient is mainly influenced by the compressibility factor and the specific heat ratio, which appear more remarkable as the inlet total pressure of hydrogen gas increases.

• 공업화학
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• 제9권6호
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• pp.901-906
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• 1998

기체분산기로 단일노즐을 사용한 내부순환 공기리프트 반응기에서 기체 및 액체의 유동특성을 해석하였다. 실험은 공기-물계에서 하강관의 직경과 상승관의 높이가 다른 세 가지 반응기를 사용하여 기체속도와 반응기의 높이를 변화시키면서 각 유동지역의 기체체류량과 추적자의 충격-응답곡선을 측정하였다. 실험결과, 기포의 유동양상은 상승관에서 강한 기포합체를 일으키는 슬러그흐름을, 그리고 하강관에서는 직경의 크기에 따라 전이흐름 또는 균일상 기포흐름을 나타내었다. 그리고 동일한 반응기 상부지역의 높이비에서 각 유동지역과 반응기 전체의 평균 기체체류량은 하강관의 직경이 작을수록 상당히 증가하였다. 또한 혼합시간은 기체속도보다 반응기 상부지역의 높이에 크게 영향을 받으며 동일한 반응기 상부지역의 높이비에서는 하강관의 직경과 상승관의 길이가 클수록 상당히 큰 값을 나타내었다. 액체의 유동특성은 하강관에서 기포의 유동양상과 반응기 상부지역의 크기에 따라 크게 변화하였으며 상승관에서 액체의 순환속도는 기체속도와 반응기 상부지역의 크기가 증가할수록 증가하였고 동일한 반응기 상부지역의 높이비에서는 하강관의 직경과 상승관의 길이가 증가할수록 증가하였다.

• 산업기술연구
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• 제32권A호
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• pp.65-70
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• 2012

Carboxy-guns are used for rapid and precise injection of $CO_2$ gas to the target skin area using external power source. In the design of carboxy-gun, the most important thing is how to precisely control injection volume of $CO_2$ gas. This paper deals with the control scheme of injection volume of carboxy-gun using solenoid valve. First the amount of volume that passes through the solenoid valve under on-off time ratio control is estimated based on the assumption of compressible gas flow. The flow rate of gas is experimentally measured under the varying pressure of the gas reservoir. Two results showed good correlation to each other, thus demonstrating the validity of the volume control strategy.

• 대한기계학회논문집B
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• 제25권6호
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• pp.837-844
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• 2001

Jet cutting technology currently makes use of a generic supersonic gas jet to improve the cutting speed and performance. In order to get a better understanding of the flow characteristics involved in the supersonic jet cutting technology, the axisymmetric Navier-Stokes equations have been solved using a fully implicit finite volume method. Computations have been conducted to investigate some major characteristics of supersonic coaxial turbulent jets. An assistant gas jet has been imposed on the primary gas jet to simulate realistic jet cutting circumstance. The pressure and the temperature ratios of the primary and assistant gas jets are altered to investigate the major characteristics of the coaxial jets. The total pressure and Mach number distributions, shock wave systems, and the jet core length which characterize the coaxial jet flows are strongly affected by the pressure ratio, but not significantly dependent on the total temperature ratio. The assistant gas jet greatly affects the basic flow characteristics of the shock system and the core length of under and over-expanded jets.

• 한국전기전자재료학회논문지
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• 제13권2호
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• pp.114-119
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• 2000

Etch characteristics of SF6/CI2 electron cyclotron resonance (ECR) plasmas have been investigated. Surface reaction of gas plasma with polysilicon was also analysed using X-ray photoelectron spectroscopy (XPS). At the same time, the relationship between surface reaction and the etched profile of polysilicon was examined using XPS. The etch rate of polysilicon and oxide increases with increasing flow rate of SF6 in the SF6/CI2 gas mixture, and tis selectivity also increase also increase. It was also found that as increasing flow rate of SF6 in the SF6/CI2 gas mixture, the atomic% of chlorine detected at surface region decrease, but F and S contents increase. At the same time, when the mixing ratio of SF6 gas increases, the anisotropy of etched polysilicon is sharply decreased in the 0%~10% range of the SF6 mixing ratio, but is rarely varied in the range over 10%, in spite of the large variations in flow rates. It can be explained that the bonding of S-Si due to SiSx(x$\leq$2) compound formed on the etched surface suppress the formation of Si-Cl and 'or Si-F bonding in the silicon etching.

• Journal of Welding and Joining
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• 제27권1호
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• pp.71-78
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• 2009

In the circumferential welding of pipe, welding phenomenon changes with the position of pipe. Especially in the overhead position, back bead of vertical-up position would be sunk. To investigate the size of back bead and keyhole with the change of the flow rate of pilot and shield gas at each position, bead-on plate welds were conducted on 6mm thickness SS400 with inclined-up position. When the rest of welding conditions remained constant, the width of back bead was increased as the flow rate of pilot gas was increased. And back bead tended to convex as the flow rate of shield gas was increased.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 학술대회 논문집
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• pp.21-27
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• 2003

This paper proposes a new model of the pressure drop for more accurate description of oscillating flow through regenerator under pulsating pressure conditions in contrast to an existing model based on steady flow. For the universal uses of the oscillating flow model, non-dimensional parameters, which consist of Reynolds number, Valensi number gas domain length ratio, oscillating flow friction factor and phase angle of pressure drop, are derived from the capillary tube model of the regenerator. Two correlation equations of the model are obtained from the experiments for the twill square screen regenerators under various operating frequencies and inlet mass flow rates. The oscillating friction factor is a function of only the Reynolds number and the phase angle of pressure drop is a function of the Valensi number and the gas domain length ratio. Experiment is also performed to examine the effects of the shape of screens.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.131-135
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• 2001

The atomization characteristics of an annular liquid (water) sheet of small radius with a core gas (air) flow were studied. Different sizes of annular gaps (0.2, 0.4 and 0.8 mm) were tested to find the effect of liquid sheet thickness on SMD. The inner diameter of the gas port for the core gas flow was 4 mm. Cross-section averaged SMD was measured for various liquid and gas velocities. Regions of the SMD decrease with the increase of the liquid velocity always existed regardless of the liquid sheet thickness. This attributes to the transition of the flow patterns of spray and also to the aerodynamic interaction between the atomizing gas and the ripples on the liquid sheet surface.