• 한국가시화정보학회지
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• 제22권1호
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• pp.6-17
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• 2024

This study examined the natural convection heat flow characteristics of the melting process of PCM (palm oil) inside a liquid flexitank(bag) for a cargo container. A film heating element was installed on the bottom of the container, and numerical analysis was performed under heat flux conditions of 1,000 to 4,000 W/m². As a result, the melt interface of the PCM rises to a nearly horizontal state over time. In the initial stage, conduction heat transfer dominates, but gradually waves at the cell flow and melt interfaces are formed due to natural convection heat transfer. As melting progresses, the Ra number increases parabolically, and the Nu number increases linearly and has a constant value. The Nu number rises slowly under low heat flux conditions, whereas under high heat flux conditions, the Nu number rises rapidly. As the heat flux increases, the internal temperature oscillation of the liquid phase after melting increases. However, under high heat flux conditions, excess heat exceeding the latent heat is generated, and the temperature of the molten liquid is raised, so the increase in melting rate decreases. Therefore, the appropriate heating element specification applied to a 20-ton palm oil container is 2,000 W/m².

• 대한기계학회논문집B
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• 제39권12호
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• pp.953-963
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• 2015

산업적으로 얇은 사각유로에서의 임계열유속을 포함한 열수력 현상을 이해하고 이를 시스템 설계에 반영해야 될 필요성이 증대되고 있다. 포화비등조건에서 임계열유속이 발생하는 주요기구는 일반적으로 환상유동 영역에서 액막이 건조되는 것이다. 이러한 임계열유속을 예측하기 위하여 원형관에 대한 대표적인 액막건조모델을 고찰하고 환상유동 시작 경계조건을 상수로 가정하는 기존 모델의 한계를 살펴보았다. 균일한 열유속으로 가열되는 얇은 수직사각유로 상향유동에서의 임계열유속을 예측하기 위하여 환상유동을 단순 모델링하고, 새로운 액막건조모델을 적용하였다. 284 개 실험데이타에 대한 예측성능을 확인한 결과 MAE 18.1%, RMSE 22.9% 예측오차로 실험데이타를 잘 예측할 수 있음을 확인하였다.

• 설비공학논문집
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• 제9권2호
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• pp.144-152
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• 1997

Film absorption involves simultaneous heat and mass transfer in the vapor-liquid system. In the present work, the absorption process of water vapor by an aqueous soluton of LiBr flowing inside of the vertical tube was investigated. The continuity, momentum, energy and diffusion equations for the solution film and vapor were formulated in integral forms and solved numerically. The model could predict the film thickness, the pressure gradient, and the heat and mass transfer rate. Particularly the effects of vapor flow conditions on the absorption process were investigated in terms of the vapor Reynolds number. As the vapor Reynolds number increased, the shear stress at the vapor-solution interface also increased. Consequently solution film became thinner at higher vapor flowrate under the co-currentflow condition. Thinner film was capable of higher heat transfer to the wall and leaded to higher absorption rate of the water vapor into the solution film.

• 한국인쇄학회지
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• 제23권2호
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• pp.129-141
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• 2005

The liquid film behavior between two rotating rollers has been analyzed for many years. Their contributions were, however, limited almost within the areas of polymer laminar flow in there. When the slip contact of two rotating rollers is used as a role of vehicle to distribute the liquid discharged on to each roller after splitting from the nip, there was few available relationship to control the roller speed and to design system. On this work it was possible to get out a certain relationship between the discharged film thickness ratio and the roller surface seeds without any help of pressure limit at the splitting point. The hydrodynamic analyzation of Newtonian liquid behavior around the point was well proved on some manipulative experiment. The thickness ratio increases along with the roll surface speed ratio increases. And the discharged volume flow rate ratio on each roller surface varies with square of the speed ratio. Both of these relationship have a decision factor also made up by the speed ratio.

• 설비공학논문집
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• 제10권4호
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• pp.456-465
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• 1998

Effect of a non-absorbable gas on the absorption process in a vertical tube absorber was investigated numerically. The water vapor mined with air as the non-absorbable gas is absorbed into LiBr/water solution film. The flow is assumed to be laminar and fully developed in both liquid and gas phases. The diffusion and energy equations were solved in both phases to give the temperature and concentrations, from which heat and mass fluxes were determined. It was shown that the local absorption rate decreases as the mass fraction of air in water vapor increases. The vapor pressure of water at the liquid-vapor interface reduces significantly since the non-absorbable gas is accumulated near the interface. The effect of non-absorbable gases on absorption rate becomes larger as the mass flow rate of the vapor decreases. For small amount of non-absorbable gases the total absorption rate of water vapor increases as the mass flow rate of the vapor decreases. Total absorption rate increases as the mass flow rate of the vapor increases for large concentration of non-absorbables at the inlet of an absorber.

• International Journal of Air-Conditioning and Refrigeration
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• 제7권
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• pp.69-78
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• 1999

Effects of a non-absorbable gas on the absorption process in a vertical tube absorber has been investigated numerically. The water vapor mixed with air is absorbed into LiBr/water solution film. The flow is assumed to be laminar and fully developed in both liquid and gas phases. The diffusion and energy equations were solved in both phases to give the temperature and concentrations, from which heat and mass fluxes were determined. The local absorption rate has been shown to decrease as the mass fraction of air in the water vapor increases. The vapor pressure of water at the liquid-vapor is interface reduced significantly since the non-absorbable gas accumulates near the interface. The effects of non-absorbable gases on absorption rate become larger as the mass flow rate of the vapor decreases. For a small amount of non-absorbable gases, the total absorption rate of water vapor increases as the mass flow rate of the vapor decreases. The total absorption rate increases as the mass flow rate of the vapor increases for large concentrations of non-absorbable gases at the inlet of an absorber.

• 설비공학논문집
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• 제16권2호
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• pp.194-201
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• 2004

In the present study, the improvement of absorption characteristics on combined heat and mass transfer process in a falling film of a vertical absorber by change of geometric parameters were studied experimentally and analytically. The energy and diffusion equations are solved simultaneously to give the temperature and concentration variations at the liquid solution-refrigerant vapor interface and at the wall. Absorption behaviors of heat and mass transfer were analyzed through falling film of the LiBr aqueous solution contacted by refrigerant vapor in the absorber. Effects of film Reynolds number, geometric parameters by insert device (spring) and flow pattern on heat and mass transfer performances have been also investigated. Especially, effects of the flow pattern by geometric parameters have been considered to observe the total heat and mass transfer rates through falling film along the absorber. As a numerical and experimental result, maximum absorption rate was shown at the wave-flow by insert device (spring). The error ranges between experiment and analysis were from 5.8 to 12％ at Re$_{f}$ > 100.0.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2005년도 제25회 추계학술대회논문집
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• pp.346-350
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• 2005

연소압 50bar 이상의 연소조건에서 반복 사용이 가능하도록 제작된 물냉각형 칼로리미터에서 막냉각량 및 작동점의 변화 시 열유속의 특성을 알아보았다. 분사기 헤드와 칼로리미터 사이에 12개의 오리피스를 갖는 막냉각 링이 삽입된다. 칼로리미터는 연소실부와 노즐부로 구성되어 있으며, 총 19개의 냉각 채널로 구성되어 있다. 설계점 연소시험 시 막냉각량이 주 연료의 10.5% 유량일 때, 막냉각량이 없는 경우보다 노즐목에서의 최대 열유속은 약 30% 감소되었고, 막냉각량이 없는 경우, 탈설계점(OD3)이 설계점에 비해 노즐목에서의 최대 열유속이 약 31% 증가 하였다.

• Advances in nano research
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• 제15권2호
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• pp.91-104
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• 2023

Development of thin carbon nanotubes (CNTs) nanoliquid film over the rough surface of a horizontal rotating disk is investigated by considering symmetric roughness either along the azimuthal or radial directions. The disk surface is either heated or cooled axisymmetrically from below. The effects of single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs) are analyzed on the film thinning process with different types of base liquids. Closed form solutions for velocity and temperature field are obtained for small values of Reynolds number whereas the numerical solution is derived for moderate values of Reynolds number. It is found that fluid retention / depletion takes place when the roughness is symmetric along the azimuthal / radial directions. It is also seen that the film thinning rate enhances for MWCNTs compare to SWCNTs. Further it is found that two different heat transfer regions exits within the flow domain depending on the fact that heat is transferred from disk to liquid film and vice-versa.

• 한국분무공학회지
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• 제6권4호
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• pp.14-21
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• 2001

Rotary atomizer is widely used in practical application ranging from combustion, cooling, spray drying, agriculture, chemical system. Rotary cup atomizer has some advantages such as extreme versatility and liquid atomization successfully varying widely in viscosity. In rotary atomization, the feed liquid is centrifugally accelerated to high velocity and the liquid extends over the rotating surface as a thin film before being discharged into an atmosphere. The degree of rotary atomization depends upon peripheral speed, feed rate, liquid properties and atomizer design. An important asset is that thickness and uniformity of the liquid sheet can readily be controlled by regulating the liquid flow rate and the rotational speed. LDPA(Laser Diffraction Particle Analyser) and image aquisition system are used to measure drop size distribution and spray pattern. The atomization characteristics of the rotary cup atomizer is investigated experimentally by varing the liquid feed rate, rotary cup speed and air velocity for atomization. As a results, the effect of air velocity on the atomization characteristics such as drop size and spray uniformity is considerably greater than variation of those with liquid feed rate.