• 한국분무공학회지
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• 제21권2호
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• pp.78-87
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• 2016

This study experimentally investigated the effects of droplet temperature on the heat transfer characteristics during collision of a single droplet on a heated wall above the Leidenfrost temperature. Experiments were performed by varying temperature from 40 to $100^{\circ}C$ while the collision velocity and wall temperature were maintained constant at 0.7 m/s at $500^{\circ}C$, respectively. Evolution of temperature distribution at the droplet-wall interface as well as collision dynamics of the droplet were simultaneously recorded using synchronized high-speed video and infrared cameras. The local heat flux distribution at the collision surface was deduced using the measured temperature distribution data. Various physical parameters, including residence time, local heat flux distribution, heat transfer rate, heat transfer effectiveness and vapor film thickness, were measured from the visualization data. The results showed that increase in droplet temperature reduces the residence time and increases the vapor film thickness. This ultimately results in reduction in the total heat transfer by conduction through the vapor film during droplet-wall collision.

• International Journal of Air-Conditioning and Refrigeration
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• 제6권
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• pp.56-66
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• 1998

The absorption process of water vapor in a liquid film is an important process in LiBr-Water absorption system. The composition of the gas phase, in which a non-absorbable gas is combined with the absorbate, influences the transport characteristics. In the present work, the absorption processes of water vapor into aqueous solutions of lithium bromide in the presence of non-absorbable gas are investigated. The continuity, momentum, energy and diffusion equations for the solution film and gas are formulated in integral forms and solved numerically. It is found that the mass transfer resistance in gas phase increases with the concentration of non-absorbable gas. However the primary resistance to mass transfer is in the liquid phase. As the concentration of non-absorbable gas in the absorbate increases, the interfacial temperature and concentration of absorbate in solution decrease, which results in the reduction of absorption rate. The reduction of mass transfer rate is found to be significant for the addition of a small amount of non-absorbable gas to the pure vapor, especially at the outlet of tube where the non-absorbable gas accumulates. At higher non-absorbable gas concentration, the decrease of absorption rate seems to be linear to the concentration of non-absorbable gas.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제34회 춘계학술대회논문집
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• pp.433-436
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• 2010

본 논문에서는 막냉각홀이 설치된 동익 표면에서의 열/물질전달 특성을 나프탈렌 승화법들 이용해 고찰하였다. 실험에는 저속 환형풍동이 이용되었으며, 풍동 내에는 16개의 동익으로 구성된 터빈단이 설치되어 있다. 동익의 선단부에는 막냉각을 위한 홀이 3열로 배치되어 있으며, 막냉각유체의 분사비를 1.0에서 2.0으로 조절하며 국소 열/물질전달계수를 측정하였다. 전반적인 열/물질전달 계수는 분사비가 높아짐에 따라 증가하며, 박리기포에 의해 압력면에 형성된 낮은 열/물질전달 계수를 갖는 영역은 분사비의 증가와 함께 사라진다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 춘계학술대회논문집
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• pp.315-320
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• 2009

A computational investigation is conducted on free convection from a thin plate having a surface heat source. The thermal configuration simulates the recently-proposed transparent film heater made of a single-walled carbon nanotube film on a glass substrate. The Navier-Stokes computations are carried out to study laminar free convection from the heater. Parallel numerical experiments are performed by using a simplified design analysis model which solve the conduction equation with the boundary conditions utilizing several existing correlations for convective heat transfer coefficient. Comparison leads to the most suitable boundary condition for the thermal model to evaluate the performance evaluation of a transparent thin-film heater.

• 설비공학논문집
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• 제13권10호
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• pp.960-965
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• 2001

The minimum heat flux conditions are experimentally investigated for the subcooled liquid film flow on the horizontal plate. The experimental results show that the minimum heat flux point temperature becomes higher with the increase of the velocity and the subcooling of the liquid film flow. However, the effect of distance from the leading edge of the heat transfer plate on the minimum heat flux is almost negligible. Also, the experimental results show that the propagation velocity of wetting front increases with increasing the velocity and the subcooling of the liquid film flow.

• 설비공학논문집
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• 제7권3호
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• pp.512-520
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• 1995

This study investigates the simultanceous heat and mass transfer between a falling desiccant film and air in cross flow at the interface. The application of this work is the optimization of falling film evaporators for use in potential hybrid air conditioning systems. The specific geometry considered is liquid TEG films falling along the vertical cooled surfaces of a channel with air in cross flow. The equations to describe the coupled heat and mass transfer between a falling desiccant film and air in cross flow for a falling film evaporator have been presented and solved numerically. The effects of important design and operating variables on the evaporator performance predicted by the parametric numerical analysis and suggestions for performance improvements of the evaporator are presented.

• 반도체디스플레이기술학회지
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• 제2권4호
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• pp.31-35
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• 2003

We present a formation technique of thin film heater for heat transfer components. Thin film structures of Cr-Si have been prepared on top of alumina substrates by magnetron sputtering. More samples of Mo thin films were prepared on silicon oxide and silicon nitride substrates by electron beam evaporation technology. The electrical properties of the thin film structures were measured up to the temperature of $500^{\circ}C$. The thickness of the thin films was ranged to about 1 um, and a post annealing up to $900^{\circ}C$ was carried out to achieve more reliable film structures. In measurements of temperature coefficient of resistance (TCR), chrome-rich films show the metallic properties; whereas silicon-rich films do the semiconductor properties. Optimal composition between Cr and Si was obtained as 1 : 2, and there is 20% change or less of surface resistance from room temperature to $500^{\circ}C$. Scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) were used for the material analysis of the thin films.

• 대한기계학회논문집B
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• 제22권9호
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• pp.1267-1276
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• 1998

Falling-film evaporation experiments with aqueous lithium bromide (LiBr) solution were performed to investigate the heat transfer characteristics of enhanced copper tubes. Enhanced tubes (a knurled tube, a spirally grooved tube, and a tube coated with $20{\mu}m$ aluminum particles) and a bare tube were selected as test specimens. Averaged evaporation fluxes of water were obtained from horizontal tubes with various film Reynolds numbers, system pressures, LiBr concentrations and degrees of wall superheat. The enhanced performance of steam generation was compared between tubes with varying parameters. The knurled tube geometry showed the most excellent performance among the tubes tested. The specified enhanced tubes were more useful for generating steam on a low grade heat source such as waste heat.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2000년도 제31회 춘계학술대회
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• pp.166-172
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• 2000

Friction characteristics of phenolic resin-based friction composites containing threedifferent relative amounts of graphite and zirconium silicate were investigated by using a pad-on-disk type friction tester. Constant temperature test and constant interval test at three different initial temperatures(100. 200, 300$^{\circ}C$) were performed to examine the effects of friction heat on friction characteristics at elevated temperature. The friction composite(FMO.7) with higher content of ZrSiO$_4$showed unstable friction force at higher temperature and resulted in larger fluctuations of vibration during friction test. The abrasive action of ZrSiO$_4$in friction composite impeded stable transfer film and induced higher friction heat at friction interface. Friction oscillations according to the temperature were associated with the formation of transfer film(i'd body layer) on the friction composite and the counter part.

• 설비공학논문집
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• 제6권4호
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• pp.453-462
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• 1994

An unsteady quasi one-dimensional model of momentum, heat and mass transfer in a falling film of a vertical plate absorber which is cooled by air was developed using the integral method. Energy conservation of the absorber wall is considered in the model. The model can predict absorption rate, film thickness and mean velocity as well as concentration and temperature profiles. Predictions of steady state temperature and concentration profiles for LiBr/water system for constant wall temperature condition are in good agreement with the two-dimensional finite difference method solutions. Effects of operating conditions, such as convective heat transfer coefficient between the cooling air and the absorber wall, cooling air temperature and film thickness at inlet, on absorption rate of water vapor into LiBr/water solution were shown.