• 한국항공우주학회지
• /
• 제33권4호
• /
• pp.71-78
• /
• 2005

초임계 상태의 질소 유동 환경에서 헵탄 액적의 기화 특성을 수치적으로 연구하였다. 더불어 실기체 효과와 액적 내부 순환, 다양한 열역학적 물성치 및 고압 효과를 고려하였다. 또한 헵탄 액적 바로 근처에서의 저속 유동 문제를 풀기 위하여 예조건화 스킴을 적용한 시간 전진법을 수치 코드에 적용하였다. 주위 유동 속도와 주위 압력을 변화 시켜가면서 액적의 거동을 살펴보았다. 유동 속도 증가로 인한 레이놀즈수의 증가에 따라 액적의 변형이 활발히 이루어졌고, 동일한 레이놀즈수에 대해서는 압력이 높아질수록 액적의 변형이 약화되었다.

• 대한기계학회논문집
• /
• 제19권10호
• /
• pp.2699-2709
• /
• 1995

This investigation reports on the study of the ambient turbulent effects on the droplet vaporization in the fuel spray combustion. For tractability, this discussion considers a single droplet in an infinite turbulent flow. In this numerical study, the low-Reynolds-number version of k-.epsilon. turbulence model was used to represent the turbulence effects. The set of two-dimensional conservation equations which describe the transport phenomena in turbulent flow using the mean flow quantities including the droplet internal laminar motion, are solved numerically with the finite difference procedure of Patankar(SIMPLER). The evaluation of the computational model is provided by two limiting cases: turbulent flow over the solid sphere and the laminar flow over a liquid drop. The results show that the turbulence effects are noticeable for the vaporization at high turbulence intensity (10-50%) which is encountered in a typical spray. The magnitude of turbulence effects mainly depends on the turbulent intensity. These effects are not sensitive to the Reynolds number in the range of 50 to 200, ambient temperature in the range of 700 to 1000.deg. K and the volatility.

• 대한기계학회논문집B
• /
• 제20권5호
• /
• pp.1700-1716
• /
• 1996

The two-dimensional, unsteady, laminar conservation equations for mass, momentum, energy and species transport in the gas phase and mass, momentum and energy in the liquid phase are solved simultaneously in spherical coordinates in order to study heating and vaporization of a droplet entrained in the oscillating flow. The numerical solution gives the velocity and temperature distribution in both gas and liquid phase as a function of time. When the gas flow oscillates around an vaporizing droplet, the liquid flow circulates in the clockwise or counterclockwise direction and the temperature distribution in the liquid phase changes its shapes, depending on the gas fow direction. When the gas flow changes its direction of circulating liquid flow is opposite to the gas flow, forming two vortex circulating in the opposite direction. During the heating period, the difference in the maximum and minimum temperature is large, followed by the almost uniform temperature slightly below the boiling temperature. The mass and heat transfer from the droplet depend on the droplet temperature, droplet diameter and the magnitude of relative velocity, giving the droplet lifetime different from the d$^{2}$-law.

• 한국화재소방학회논문지
• /
• 제23권5호
• /
• pp.17-23
• /
• 2009

콘크리트가 화재에 노출되면 콘크리트 표면에서의 수분뿐만 아니라 콘크리트 내부에서의 수분도 수분의 평형 및 전달조건에 의하여 증발이 발생된다. 수분의 평형조건은 재료의 자기이력거동으로 표현되는 물의 증발에 대한 수착등온선 관계로 설명된다. 본 논문은 화재시 콘크리트 부재 내부의 수분변화를 예측하고자 하는 것으로 부재 내부의 임의의 위치에서의 상대함수율을 산정하기 위하여 유한요소방식을 적용하였다. 또한 고온에서 콘크리트의 수분확산 특성치에 대해서도 모델식을 제시하였다. 이러한 해석기법의 정확성을 검증하기 위하여 실험데이터와 비교하였으며, 그 결과 수분증발로 인하여 수분이 감소되는 효과를 포함한 전반적인 부재 내부의 수분이동현상이 실제 실험데이터와 거의 유사하게 나타나는 것으로 확인되었다.

• 설비공학논문집
• /
• 제10권4호
• /
• pp.449-455
• /
• 1998

A header' is the device that makes uniform flow distribution in all branches from header of heat exchangers, pipe burner or chemical equipments. In this study, experimental tests have been performed in order to investigate the flow distribution characteristics in a straight header and tapered header which have 6 and 11 glass pipe branches. The experimental equipment consists of a water circulation system where the fluid velocity in each glass pipe is measured by Ar-ion LDV system. From the experiments and the theoretical equation, it could be recommended that tapered header should be determined so that its internal velocities inside the header become uniform according to taper of the header and number of attached branches for uniform flow distribution in energy systems.

• 한국연소학회지
• /
• 제4권1호
• /
• pp.17-26
• /
• 1999

Vaporization, ignition and combustion of fuel droplets in tandem array are theoretically investigated to understand the droplet interactions in combustors. Including the effects of density variation in gas-phase, internal circulation and transient liquid heating, a numerical studies are performed by changing parameters such as initial droplet temperatures, initial droplet spacings, initial Reynolds numbers, surrounding gas temperatures, and activation energies of fuel vapors. Combustion regime maps classify the droplet combustion phenomena according to the configuration and location of the flame with respect to injection Reynolds numbers and surrounding gas temperatures. In addition, it is shown that the dynamic histories of droplets and ignition delay times are dependent on droplet size ratios and initial spacings of tandem droplets.

• 한국군사과학기술학회지
• /
• 제14권3호
• /
• pp.524-531
• /
• 2011

The cryogenic vessel, storing a liquified solutions as LOX and $LN_2$, consists of a external vessel, internal vessel, thermal insulator and internal support. The internal support should be satisfied with mechanical strength not only to support weight of internal tank but also to maintain uniform space between external and internal tank in spite of external mechanical shock. However, excessive structure design of internal supports is able to increase the amount of heat conduction and the rate of vaporization. The thermal insulator, filled with space between a external and internal vessel, reduces the rate of heat transfer and guarantees the standing time of cryogenic vessel. Especially powder type of insulator has low thermal conductivity and reduce the specification of structure design. In order to evaluate the effect of insulator on structure design, the experiment set-up simulated cryogenic vessel was tested in shock environment according to thermal insulator. As a result, the behavior of internal support under external shock was understood and the design criteria was able to be suggested.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2008년도 제31회 추계학술대회논문집
• /
• pp.221-226
• /
• 2008

본 연구에서는 연소실내 유동으로 인해 발생하는 연소실 축방향 압력변화를 고려한 비정상 내탄도 해석모델을 개발하고 이를 바탕으로 침식연소를 해석하였다. 개발 모델은 선행 연구와 비교하였으며 해석결과가 일치함을 확인하였다. 연소실 압력, 그레인 길이, 그레인 초기온도, 추진제 기화온도가 침식연소에 미치는 영향을 조사하였다.

• 한국추진공학회지
• /
• 제13권2호
• /
• pp.17-25
• /
• 2009

본 연구에서는 연소실의 축방향 압력과 속도변화를 고려한 비정상 내탄도 해석모델을 제안하고 이를 바탕으로 침식연소에 미치는 인자를 해석하였다. 개발 모델의 검증을 위하여 침식연소가 없는 경우와 침식연소가 있는 경우에 대하여 선행연구 결과와 비교하였으며 해석결과가 일치함을 확인하였다. 연소실 압력, 그레인 길이, 그레인 초기온도, 추진제 기화온도가 침식연소에 미치는 영향을 조사하였다.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
• /
• pp.353-356
• /
• 2006

In this paper, the prediction method of internal temperature for reinforced concrete columns under high temperature is presented. Finite element method is employed to facilitate thermal analysis for any position of column. And the effect of the heat of vaporization is applied. To demonstrate the validity of this numerical procedure, the prediction by the proposed algorithm is compared with the test results from this study. The proposed algorithm is in good agreement with experimental results.