• 대한기계학회논문집
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• 제12권3호
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• pp.551-560
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• 1988

본 연구에서는 해석하려는 시스템의 유동 및 열전달 현상의 개념도를 Fig.1 에 나타내었다. 고체 입자는 윗부분 홈으로부터 분사되어, 선택적 투과면을 통해서 입사되는 복사열을 흡수 하며, 기체는 아래 또는 위의 홈 부분으로부터 들어와서 고체 입자와의 대류열전달로 가열이 된다. 기차게 아래 홈에서부터 분사되는 경우 대류에 의해 가열된 기체가 역성층화로 인해 부력을 받게 되어, 고체 입자의 하강 속도가 감 소할 때 입자의 체류 시간의 증가에 따른 복사열의 흡수효과에 대하여 고찰하였으며 입자의 크기, 투사 복사량, 분사속도, 입자의 질량유량 등을 파라미터로 하여 이들의 변화에 따른 영향을 규명하였다. 2-방연계를 고려한 2-방정식 모델을 구성하고 고체 입자에 대하여는 Lagrangian 방법으로 기술하였으며 수치해석에 있어 유한차분법을 도 입하고 두 상간의 상호연계는 PSI-Cell 방법을 이용하였고 복사 열유속은 2-유속 모델 (two-flux model)을 도입하여 계산하였다.

• 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.

• 태양에너지
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• 제6권2호
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• pp.43-53
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• 1986

The objective of this study is to report on the characterics of convective flow and heat transfer during metling process in order to provide design information for thermal energy storage systems which use phase change material. In present study, flow and heat transfer characteristics of the Phase Change Material in the Open Top Model (O.T.M) and in the Closed Top Model (C.T.M) were studied numerically by the control volume formulation using the algebraic non-orthogonal coordinate transformation. For the calculation procedure, the physical properties of fluid are assumed to be constant except density which is linely dependent on temperature in the bouyancy term of momentum equations. At start of melting process, the thickness of melting layer is assumed from the Stefan Problem assumption. The heat transfer results of Open Top Model and Closed Top Model are compared with the parameters of Grashof number and aspect ratio. It was found that heat transfer phenomena in melted region was greatly affected by buoyancy-driven natural convection and the melting distance of Open Top Model at the upper region is greater than that of Closed Top Model.

• 한국전기전자재료학회논문지
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• 제26권3호
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• pp.221-226
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• 2013

The water soluble quantum dots (QDs) are synthesized by the phase transfer and silica coating reaction. The photoluminescence intensity of silica-coated QDs are mainly affected by the amount of phase transfer agent, SDS (sodium dodecyl sulfate), and the maximum value is obtained at the cmc (critical micell concentration) concentration of SDS in the phase transfer reaction. Based on fluorescence spectra and field emission transmission electron microscope (FETEM), the energy transfer rate by forster resonance energy transfer (FRET) is increasing with the thickness of the silica shell coated on CdSe/ZnS QDs.

• 설비공학논문집
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• 제13권3호
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• pp.145-152
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• 2001

Low Rayleigh number thermal convection in a fluid layer confined between two-infinite horizontal walls kept at spatially sinusoidal temperature distributions, T_L=T_m+\Delta T\sin \kappax,\;T_U=T_m+\Delta T\sin(\kappax-\beta)$, is theoretically investigated by a regular perturbation expansion method. For small wave numbers, an upright cell is formed between the two walls at $\beta$=0. The cell is tilted, as the phase difference increases, and a flow with tow counter-rotating eddies occurs at $\beta=\pi$. when the wave number is large, isolated eddies are formed near the lower and upper walls, for all the phase differences. There exists a wave number at which maximum heat transfer rate at the walls occurs, at each of the phase differences. And the wave number increases with increase of the phase difference. for a fixed wave number, the heat transfer rate decrease with increase of the phase difference.

• 전기학회논문지
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• 제67권5호
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• pp.626-634
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• 2018

These days, widespread use of sensitive loads and distributed generators makes static transfer switch (STS) an essential component in power circuits to achieve a good power quality for AC Grids. In case of a short-circuit fault, previous STS cannot break the fault current. However, the proposed STS has the capability of breaking it quickly as a circuit breaker. Also if there are power quality problems such as Sag/Swell, the proposed STS can quickly transfers the load to the good quality source. Furthermore it is proved that the transfer time of the proposed STS is within one half of period of 3-phase source frequency regardless of the type of load. It is anticipated that the proposed STS may be utilized to realize many stable and reliable AC grid systems.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2003년도 추계학술발표회
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• pp.144-147
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• 2003

In this study, the mass transfer behaviors of phenanthrene, anthracene, and pyrene in soil slurry reactor (SSR) using two-liquid phase (TLP) system were investigated. The mass transfer ratio and rate of PAH in the TLP system using light paraffine oil, which has the highest solubility of PAH, were influenced by the amount of light paraffine oil and mixing speed. When the amount of light paraffine oil decreased from 15 % to 2.5 % (v/v), the mass transfer ratio of anthracene decreased significantly compared with that of phenanthrene and pyrene. As mixing speed increased, the initial mass transfer rate of PAH within 1 day was enhanced. However, each final mass transfer ratio of three PAHs after 5 day was similar irrespective of mixing speed.

• 수산해양교육연구
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• 제28권5호
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• pp.1388-1394
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• 2016

This paper presents a experimental study of two-phase flow boiling of FC-72 in multi channels. Flow boiling heat transfer coefficients are obtained with mass flux ranging from 152.9 to $353.9kg/m^2s$ and heat flux from 5.6 to $46.1kW/m^2$. The experimental results show that the heat transfer is governed by nucleate boiling mechanism in the low heat flux region. However, it is found that the effects of nucleate boiling and forced convection boiling are combined as the heat flux increases. A new correlation to predict the heat transfer coefficient is developed by using the dimensionless number such as Reynolds number, Weber number, boiling number. This correlation shows good predictive accuracy against the measured data.

• 태양에너지
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• 제19권1호
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• pp.9-17
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• 1999

An Experimental study on the boiling and condensation heat transfer performance of thermosyphons with low intergral-fins was performed to investigate its heat transfer characteristics. A plain thermo syphon having the same inner and outer diameter as the finned thermosyphons was also tested for comparison. Water and CFC-30 was used as working fluids. The experimental results have been assessed and compared with same existing theories. Good agreement with the theories of Imura and Nusselt was obtained. The vertical closed-type thermosyphons with low integral-fins gave significant increases in the overall heat transfer coefficient compared to plain thermosyphon. In addition, the overall heat transfer coefficients and the operating characteristics was obtained as a function vof operating temperature for the practical applications. Also, the closed two-phase thermosyphons with low integral-fins would be highly recommended to achieve some inexpensive and compact heat exchangers in the range of low temperatures.

• 태양에너지
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• 제9권1호
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• pp.53-61
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• 1989

In the present investigation, experiments on the melting of a phase change material were performed to research heat transfer phenomena generated by means of conduction and natural convection in the vertical tube at inward melting. The phase change material used in the experiments is 99 percent pure n-Docosane paraffin which is measured melting temperature of $42.5^{\circ}C$, latent heat of 37.5 cal/g, heat conductivity of $0.1505W/m^{\circ}C$. Experiments were performed both in the no-subcooling which is initiating it at melting temperature of phase change material, and in the subcooling which means to initiate it under melting temperature of phase change material, in order to compare and investigate the horizontal temperature history, vertical temperature history, ratio of melting and melted mass, figure of the melting front in the vertical tube. In the experimental results, heat transfer from tube wall to phase change material were due to conduction at early stage and due to natural convection with the passage of time, and then occurred melting downward from surface by volumetric expansion. Natural convection affects temperature distribution in the tube, ratio of melting and melted mass, figure of the melting front and then progress rapidly in case of nosubcooling compared to subcooling.