• Journal of Energy Engineering
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• v.4 no.3
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• pp.394-401
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• 1995

본 연구는 중심부에 액체, 외주부에 산화제가 흐르는 기액 동축분류의 유동장에 대한 것이다. 기액 동축 분사기는 연료의 분사량이 적은 소형 연소시스템을 고려하여, 실험은 연공비(W1/Wa)가 0.6 이하를 대상으로, 물과 공기를 사용하여 분사조건에 따른 분무특성과 기액 2상 분무류의 기본구조를 조사하여 액적의 확산, 기액혼합특성에 대하여 검토하여 다음과 같은 결론을 얻었다. 반경방향 기상속도분포 및 액적유속분포는 분구직경 및 분사조건에 관계없이 정규분포에 가까운 형태를 취하고 있으며, 각각 식 (2) 및 (3)으로 나타낼 수 있다. 기상속도는 반치폭은 축방향에 따라 일정한 구배 (≒4.6)로서 증가하며, 기상만의 단상분류의 구배(≒6)에 비해서 완만하다. 액적유속 반치폭은 축방향에 따라 더욱 완만한 구배(≒3.1)로서 증가한다. 무차원 액적유속분포는 축방향에 따라 일정한 구배(n≒1.5)로서 감소한다. 액적의 확산은 상대적으로 기액유량비가 클수록 효과적으라고는 말할 수 없고, 최대 확산을 이루는 최적의 기액유량비가 존재한다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.93-99
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• 2005

Performed were 2-phase numerical studies on two types of fuel atomizers, plain orifice and pressure swirl atomizer. In case of plain orifice, cavitation model was applied so that discharge coefficient, cavitation size, and magnitude of cavitation region characterized and compared with experimental results for several different pressure enforced to the orifice. In case of swirl atomizer, VOF model was applied to analyze air core size, spray angle, and wall pressure distributions with comparison of experimental results.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1998.10a
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• pp.32-32
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• 1998

고체 추진제 로켓의 연소시에 발생되는 산화 알루미늄(A1$_2$O$_3$) 입자는 로켓 추진 노즐에서 팽창과정의 효율을 저하시키는 요소가 되며, 이러한 비효율성은 연소 가스와 입자간의 비평형 상태 효과와 기본적인 속도와 열적 차이에 의해서 발생된다고 보고되었다. 또한 연소시 발생된 산화 알루미늄 입자는 높은 열과 큰 운동량을 가지고 로켓 노즐 내부를 유동하게 되며, 매우 많은 량이 짧은 시간에 고온 고속으로 노즐 벽면이나 기타 구조물에 충돌 및 점착하기 때문에 로켓 노즐내의 표면이 손상을 입게 되고, 로켓의 방향 제어 및 조정 안정성이 저하되며, 구조적인 강도가 약화 될 수 있다. 또한 산화 알루미늄 액적들의 경우 노즐 벽면에 고착되게 되면 로켓의 중량 증가로 인해서 추력의 손실을 초래할 수 있다. 따라서 이러한 연소 부산물들의 운동 경로와 충돌 위치 및 표면에서의 충돌량과 그리고 충돌에 따른 마모량 및 점착 그리고 열전달 특성을 예측하는 것이 필수적이다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.2
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• pp.185-197
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• 1999

Heat transfer and solidification of liquid silicon in von-$K{\acute{a}}rm{\acute{a}}n$ swirling flow is investigated. The moving boundary is fixed for all times by a coordinate transformation, and finite difference method Is used to obtain the instantaneous location of the solid-liquid Interface and the heat transfer from the surfaces of solid and liquid. For small Stefan number or low wall temperature, the transient heat transfer from the surface of solid(QS(t)) is much larger than that from the liquid side of solid-liquid interface(QL(t)) and QL(t) reaches its quasi-steady-state value much faster than QS(t).

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.2
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• pp.305-311
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• 2003

This Paper Presents an information about the heat transfer characteristics of a separate type thermosyphon in electronic equipments. The heat removal problem of electronic equipments is regarded as an important factor and a separate type heatpipes can be utilized as a cooling device of electronic equipments (such as CPU of a Personal computer or notebook). In this study. heat source ($50\times50\times2 mm $aluminum Pseudo CPU) was used for the experiment. The device can transfer heat from the evaporator to the condenser through natural circulation (without any external driving forces) and the results indicate that the device is capable of dissipating over 60W of thermal energy and keeping the heating plate surface temperature under $50^{\circ}C$.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.434-440
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• 2011

Oscillating airfoil haw been challenged for the dynamic stalls of airfoil am wind turbines at high angle of attach. Especially, the pressure oscillation has a huge effect on noise generation, structure damage, aerodynamic performance am safety, because the flow has strong unsteadiness at high angle of attack. In this paper, the unsteady aerodynamics coefficients were analyzed for the oscillating airfoil at high angle of attack around two dimensional NACA0012 airfoil. The two dimensional unsteady compressible Navier-Stokes equation with a LES turbulent model was calculated by OHOC (Optimized High-Order Compact) scheme. The flow conditions are Mach number of 0.2 and Reynolds number of $1.2{\times}10^4$. The lift, drag, pressure distribution, etc. are analyzed according to the pitching oscillation. Unsteady velocity field, periodic vortex shedding, the unsteady pressure distribution, and the acoustic fields are analyzed. The effects of these unsteady characteristics in the aerodynamic coefficients are analyzed.

• Proceeding of EDISON Challenge
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• 2014.03a
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• pp.625-630
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• 2014

연료전지의 성능을 결정짓는 가장 중요한 변수 중의 하나는 각 스택의 채널에 얼마나 균일하게 연료를 공급할 수 있느냐이다. 본 연구에서는 네 가지의 모델을 사용하여 연료전지 매니폴드 형상에 따른 최적 설계를 수행하였다. 위 네 가지 모델은 각기 다른 기하학적 형상을 가지며 Edison CFD를 이용하여 형상 내의 유동을 비교하였다. 초기 모델에서는, 입구부에서 매니폴드로 유입되는 유동의 확산이 잘 일어나지 않아 각 채널의 질량유량이 불균일한 분포를 보였으며 특히 속도가 빠른 중심 영역의 채널에 많은 연료가 유입되었다. 이를 위한 디퓨져 모델링이 제안되었으며 실속이 최소한도로 발생할 때 채널당 질량유량이 가장 균일하다고 가정하였다. 이를 위해 다양한 디퓨져 각을 가진 모델을 사용했고, 이론상으로 실속이 발생하지 않는 형상에서 가장 균일한 분포를 보임을 확인하였다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.6
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• pp.441-446
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• 2007

An experimental study on the countercurrent two-phase flow in narrow rectangular channels has been peformed. Countercurrent flow limitation (CCFL) was investigated using air and water in 760mm long, 100mm wide, vertical test sections with 1 and 3mm channel gaps. Tests were systematically performed with downward liquid superficial velocities and upward gas velocities covering 0 to 0.125 and 0 to 3.5m/s ranges, respectively. As the gap width of rectangular channel increased the CCFL water superficial velocity decreased for the given air superficial velocity. Slight increase of the air superficial velocity resulted in the abrupt decrease of water velocity when $j_g=2{\sim}4m/s$. The critical superficial velocity of air, at which the downward flow of water was no longer allowed, also decreased with the increase of gap width. The experimental results were compared with the previous correlations, which were mainly for round tubes, and the qualitative trends were found to be partially acceptable. However the quantitative discrepancies were hardly neglected. New correlation of CCFL was developed and showed good agreement with the experimental data.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.12
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• pp.1763-1773
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• 1998

In the present experimental study, the flow behavior in a semi-closed two-phase natural circulation loop was examined. Water was used as the working fluid. Heat flux, heater-inlet subcooling, and flow restrictions at the heater-inlet and at the expansion-tank-line were taken as the controlling parameters Six circulation modes were identified by changing heat flux and inlet subcooling conditions ; single-phase continuous circulation, periodic circulation (A), two-phase continuous circulation, and periodic circulations (B), (C), and (D). Among these, the single-phase and two-phase continuous-circulation modes exhibit no significant oscillations and are considered to be stable. Periodic circulation (A) is characterized by the large amplitude two-phase f10w oscillations with the temporal single-phase circulation between them, while periodic circulation (B) featured by the flow oscillations with continuous boiling inside the heater section. Periodic circulation (C) appears to be the manometric oscillation with continuous boiling. Periodic circulation (D) has the longer period than periodic circulation (B) and a substantial amount of liquid flow back and forth through the expansion-tank-line periodically ; this mode is considered the pressure drop oscillation. Parametric study shows that the increases of the inlet- and expansion-tank-line- restrictions and the decrease of inlet subcooling broaden the range of the stable two-phase(continuous circulation) mode.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.21 no.2
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• pp.137-141
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• 1985

In this paper, the author investigate viscous effects on the characteristics of TP620 hydrofoil. The pressure distribution on the foil section in non-cavitating flow should be considered its characteristics of displacement thickness due to viscous effects. Theoretical potential theory, which neglects viscous effects do not agree with this analysis, especially at leading edge region of the foil. And, the efficiency of TP620 hydrofoil considering viscous effects is a little lower than that of the foil, which neglected viscous effects.