• Journal of Advanced Marine Engineering and Technology
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• 제20권3호
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• pp.11-18
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• 1996

Liquid droplets of water and argon surrounded by their vapor have been simulated by the milecular dynamics method. To explore the surface phenomena of clusters, each molecule is classified into 'liquid', 'surface', or 'vapor' with respect to the number of neighbor molecules. The contribution of a 'surface' molecule of the water cluster to the far infrared spectrum is almist the same as that of the 'liquid' molecule. Hence, the liquid-vapor interface is viewed as geometrically and temporally varying boundary of 'liquid' molecules with only a single layer of 'surface' molecules that might have different characteristics from the 'liquid' molecules. The time scale of the 'phase change' of each molecule is estimated for the argon cluster by observing the instantancous kinetic and potential energies of each molecule. To compare the feature of clusters with macroscopic droplets, the temperature dependence of the surface tension of the argon cluster is estimated.

• 대한기계학회논문집B
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• 제28권8호
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• pp.996-1003
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• 2004

The bubble motion during nucleate boiling in a microchannel is investigated by numerically solving the equations governing conservation of mass, momentum and energy in the liquid and vapor phases. The liquid-vapor interface is tracked by a level set method which is modified to include the effects of phase change at the interface and contact angle at the wall. Also, the evaporative heat flux from the thin liquid film that forms underneath a growing bubble attached to the wall is incorporated in the analysis. Based on the numerical results, the effects of channel size, contact angle, wall superheat and waiting period on the bubble growth and heat transfer in a microchannel are quantified.

• 대한기계학회논문집B
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• 제34권12호
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• pp.1079-1085
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• 2010

평판형 증발부를 갖는 루프히트파이프(LHP)에 대한 정상상태 해석모델을 제시하였다. 관련문헌의 고찰에 기초하여 LHP 의 주요 부분인 증발부, 액체저장조(보상챔버), 증기이송관, 액체이송관 및 응축부에서 온도와 압력을 예측할 수 있도록 계산과정을 제시하였으며, LHP 에서 유일하게 모세관 구조물을 가지는 증발부의 해석에 중점을 두었다. 증발부에서 액체 -기체 경계면 부근에서 압력과 온도의 영향을 고려하기 위해 박막이론을 사용하였으며, 수정된 기체분자운동이론에서 응축경계면 온도를 산정하는데 있어서 독특한 방법을 도입하였다. 응축부에서는 상변화 경계면을 단순화하여 처리함으로써 응축부 형상 변화에 상대적인 융통성을 구비하도록 하였다. 본 연구의 LHP 정상상태 해석 모델은 문헌 상의 실험결과에 의해 타당성이 증명되었다. 해석모델에 의한 예측치는 실험치와 비교할 때 절대온도를 기준으로 최대 상대오차 3% 이내로서 합리적으로 잘 일치하였다.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.142-147
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• 2008

This paper reports an analysis of self-pressurization in a closed cryogenic liquid storage system and its comparison with experimental data using liquid nitrogen. Partial equilibrium model(PEM), revised thermodynamic analysis of homogeneous model, has been applied for the pressurization in a closed tank. The vapor and liquid bulk temperature and the liquid-vapor interface temperature are separately calculated as their own representative values in this analysis. The analysis results of the partial equilibrium model are compared with the experimental data and other preceding homogeneous temperature models for validation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1891-1896
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• 2003

The bubble motion during nucleate boiling in a microchannel is investigated numerically. The liquid-vapor interface is tracked by a level set method which is modified to include the effects of phase change at the interface and contact angle at the wall. The computations are made for various channel sizes, liquid flow rates, and contact angles. Based on the numerical results, the bubble growth pattern and its effect on the flow and heat transfer are discussed.

• 대한기계학회논문집B
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• 제32권2호
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• pp.125-132
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• 2008

The bubble dynamics and heat transfer associated with nucleate boiling in parallel microchannels is studied numerically by solving the equations governing conservation of mass, momentum and energy in the liquid and vapor phases. The liquid-vapor interface is tracked by a level set method which is modified to include the effects of phase change at the interface and contact angle at the wall. Also, the reversible flow observed during flow boiling in parallel microchannels has been investigated. Based on the numerical results, the effects of contact angle, wall superheat and the number of channels on the bubble growth and reversible flow are quantified.

• International Journal of Air-Conditioning and Refrigeration
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• 제14권2호
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• pp.41-48
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• 2006

Absorption performance at the vertical interface between refrigerant vapor and liquid solution of $LiBr-H_{2}O$ solution was enhanced by the waves formed due to the interfacial shear stress. The present study investigated experimentally and analytically the improvements of absorption performance in a falling film by wavy film flow. The dynamic parameter was the film Reynolds numbers ranged from 50 to 150. The energy and diffusion equations were solved simultaneously to find the temperature and concentration profiles at the interface of liquid solution and refrigerant vapor. Absorption characteristics due to heat and mass transfer were analyzed for the falling film of the LiBr aqueous solution contacted by refrigerant vapor in the absorber. Absorption performance showed a peak value at the solution flow rate of $Re_{f}>100$. Absorption performance for the wavy film flow was found to be greater by approximately 10% than that for uniform film flow. Based on numerical and experimental results, the maximum absorption rate was obtained for the wavy flow caused by spring insert. The difference between the measured and the predicted results were ranged from 5.8 to 12%.

• Tribology and Lubricants
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• 제18권2호
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• pp.109-116
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• 2002

phase lubrication can be used as an alterative lubrication method to overcome the demerits of liquid and solid lubrications. In this work, the tribological characteristics of metals are investigated under vapor phase lubrication. It was found that the friction coefficient and wear volume can be controlled efficiently by the amount of vapor phase lubricant delivered to the sliding interface. The friction coefficient could be reduced to about 0.1 under vapor lubrication. Also, depending on the amount of vapor lubrication delivered to the system, the width of the wear track could be varied between 50 to 250 Um. It is shown that vapor phase lubrication mechanism is very effective to control the friction and wear phenomena without the use of excessive oil.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.252-259
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• 2001

It is derived for the temperature profile in a cylindrical and planar shape capillary pumped loop evaporators subject to a uniform heat flux prior to the initiation of boiling using the finite difference method. The results of the analysis allow for the determination of applied power levels for which nucleation is likely to occur only within the vapor grooves of the evaporator while maintaining subcooling in the liquid core, thereby increasing the likelihood of a successful startup. Also, limits are found for which additional increases in the applied heat flux do not increase the temperature difference between the vapor grooves and the wick-liquid core interface. Several advantages of larger diameter evaporators observed experimentally in startup are explained and quantified by the model. This analysis is appropriate for standard capillary pumped loop evaporators during a fully-flooded startup as well as starter pump designs and loop heat pipes.

• 설비공학논문집
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• 제13권4호
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• pp.262-270
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• 2001

This paper deals with a prediction method for the condensation of ternary refrigerant mixture inside a horizontal smooth tube. Based on some reliable assumptions, the governing equations for the local heat and mass transfer characteristics are derived, and the prediction for the condensation of ternary zeotropic refrigerant mixtures composed of HFC32/HFC125/HFC134a, including R407C, is carried out. The local values of vapor quality, thermodynamic states at bulk vapor, vapor-liquid interface and bulk liquid, mass flux etc. are obtained for a constant wall temperature and a constant wall heat flux conditions, and the effects of the composition of HFC32/HFC125/HFC134a on heat transfer characteristics are examined. The prediction result is also compared with experimental data for condensation of ternary refrigerant mixtures. The predicted wall temperature distribution has a similar trend with experimental data but the predicted local heat transfer coefficients are 20-30% higher than the experimental data.