• 대한기계학회논문집B
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• 제22권7호
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• pp.946-955
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• 1998

Local condensation heat transfer coefficients in tubes were calculated by solving momentum and energy equations for annular film with liquid entrainment. The turbulent eddy distribution across the liquid film has been proposed and the calculated heat transfer coefficients were presented. Also turbulent Prandtl number effects on condensation heat transfer were discussed from three Pr$\_$t/ models. Finally, the calculated condensation heat transfer coefficients of R22 were compared with some correlations frequency referred to in open literature. This calculation model considering liquid entrainment predicted well the in-tube condensation heat transfer coefficient of R22 than the model not considering liquid entrainment. The effect of entrainment on heat transfer was predominant for high quality and high mass flux when the liquid film was turbulent.

• Nuclear Engineering and Technology
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• 제34권4호
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• pp.269-285
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• 2002

Water heat transfer experiments were carried out in a uniformly heated annulus with a wide range of pressure conditions. The local heat transfer coefficients for saturated water (low boiling have been measured just before the occurrence of the critical heat flux (CHF) along the length of the heated section. The trends of the measured heat transfer coefficients were quite different from the conventional understanding for the heat transfer of saturated flow boiling. This discrepancy was explained from the nucleate boiling in the liquid film of annular flow under high heat flux conditions. The well-known correlations were compared with the measured heat transfer coefficients. The Shah and Kandlikar correlations gave better prediction than the Chen correlation. However, the modified Chen correlation proposed in the present work showed the best agreement with the present data among correlations examined .

• 대한안전경영과학회지
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• 제20권3호
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• pp.37-46
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• 2018

According to enhancement of roles and functions of enterprises' distribution centers, recent trend of distribution centers are specialization and diversification which have generated lots of new distribution center building or expansion of the existing ones and led attention on stock transfer importance in case of distribution center relocation. This thesis is a study for how to reduce stock transfer leadtime in order to minimize business risk and how to increase inventory accuracy when stock ownership is transferred in case of distribution center relocation, and to provide inventory accuracy management methods and inventory in/out management types, detailed definition to evaluate level for inventory accuracy management and pros/cons by inventory in/out management type assuming 'the higher inventory accuracy before stock transfer, the shorter stock transfer leadtime when distribution center is relocated'. This thesis provides detailed procedure to secure an absolute stock transfer leadtime and process to confirm hugh inventory accuracy by stakeholders which should be sloved by Task Force Team for stock transfer in case of distribution center relocation.

• Journal of Advanced Marine Engineering and Technology
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• 제32권4호
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• pp.534-541
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• 2008

This paper deals with the heat transfer characteristics of R-290 (Propane), R-600a (Iso-butane) and R-1270 (Propylene) as an environment friendly refrigerant and R-22 as a HCFC's refrigerant for evaporating. The experimental apparatus has been set-up as conventional vapor compression type refrigeration and air-conditioning system. The test section is a horizontal double pipe heat exchanger. Evaporating heat transfer measurements were performed for smooth tube with the outer diameters of 12.70, 9.52 and 6.35 mm and micro-fin tube 12.70 mm, respectively. For the smooth and micro-fin tubes measured in this study, the evaporating heat transfer coefficient was enhanced according to the increase of the mass flux and decrease of the tube diameter. The local evaporating heat transfer coefficients of hydrocarbon refrigerants were superior to those of R-22 and the maximum increasing rate of heat transfer coefficient was found in R-1270. The average evaporating heat transfer coefficients in hydrocarbon refrigerants showed 20 to 28% higher values than those of R-22. Also, the evaporating heat transfer coefficients of R-22 in the tube diameter of the 12.70 mm smooth and micro-fin tube were compared. Generally, the local heat transfer coefficients for both types of tubes increased with an increase of the mass flux. The heat transfer enhancement factor (EF) between smooth and micro-fin tube varied from 1.9 to 2.7 in all experimental conditions.

• 설비공학논문집
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• 제17권12호
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• pp.1113-1122
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• 2005

The experimental heat transfer coefficients have been measured for two-phase convective boiling in two circular microtubes with inner diameters of $430{\mu}m\;and\;792{\mu}m$. While the heat transfer was greatly affected by the heat flux in the low quality region, the mass flux played a role in the high quality region. The smaller microtube had greater heat transfer coefficients. When the heat flux is varied from $20kW/m^2\;to\;30kW/m^2\;at\;G=240kg/m^2s$, the difference between the average heat transfer coefficients of the test tube $A(D_i=430{\mu}m)$ and the test tube $B(D_i=792{\mu}m)$ changes from $32.5\%\;to\;52.1\%$. At $G=370kg/m2^s$, the difference between the average heat transfer coefficients changes from $47.0\%\;to\;53.8\%$. A new correlation for the evaporative heat transfer coefficients in microtubes was developed by considering the following factors; the laminar flow heat transfer coefficient of liquid-phase flow, the enhancement factor of the convective heat transfer, and the nucleate boiling correction factor. The correlation developed in this study predicts the experimental heat transfer coefficients within an absolute average deviation of $8.4\%$.

• 대한기계학회논문집
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• 제19권6호
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• pp.1501-1509
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• 1995

It is known that the heat and mass transfer characteristics in the absorber are most sensitive of the temperature boost of all the heat exchangers and the development of a more efficient absorber should be highly important. This paper describes absorption experiments made with different inside tube diameters, tube length and tube shapes. The purpose of this study is to acquire basic knowledge about heat and mass transfer in a falling film type absorber with vertical inner tubes. Heat and mass transfer were measured for water vapor absorption into a Lithium Bromide-water solution flowing down an absorber of vertical inner tubes. As a result, insert spring tube compares bare tube and heat transfer improved by order of insert spring tube P2(pitch 20 mm) and P1(pitch 10 mm).

• 한국자동차공학회논문집
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• 제5권1호
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• pp.49-58
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• 1997

In this paper, a transfer function was obtained for a PWM high speed solenoid valve controlled metal belt CVT system. The transfer function was defined as the ratio of speed ratio to PWM duty ratio and derived in time domain by linear regression analysis from the experimental results. The transfer function obtained showed different dynamic characteristics for the up and down shift. Also, LQG/LTR controller was designed for the CVT system using the transfer function. It is seen from the experimental results that LQG/LTR control showed good performance for the speed ratio tracking and disturbance rejection. The phase difference and relatively slow response are considered due to the inaccuracy os the transfer functions, which resulted from the inherent nonlinearities of the transmission characteristics of the metal belt CVT.

• 한국광학회지
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• 제9권6호
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• pp.396-402
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• 1998

광학계의 결상성능평가는 optical transfer function(OTF)을 측정하는 것이 표준적인 방법으로 사용되고 있다. 그러나, 대량 생산되는 광학계의 경우에서는 측정의 편리함 때문에 test pattern을 투영하여 contrast를 검사하는 방법도 많이 사용되고 있다. 본 연구에서는 회절결상이론을 사용하여 주기적 line-space pattern에 대한 contrast transfer function(CTF)을 계산하는 프로그램을 개발하고, C­계수와 Zernike 다항식으로 표현되는 3차 파면수차에 의한 광학계의 modulation transfer function (MTF)과 CTF 변화를 비교, 분석하였다.

• Journal of information and communication convergence engineering
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• 제2권2호
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• pp.119-122
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• 2004

In this paper, we examine the necessity and the role of technology transfer/diffusion in the frame of national technology innovation system. On the base of this, we present a construction plan of technology transfer/diffusion system to make the national electric industry for 21st century to possess the competitive power. To achieve above purpose, we examine the relations between theory of technology transfer/diffusion structure and policy. Furthermore, we try to find the necessity for construction of technology transfer ＆ diffusion system and a driving plan. Then, it is analyzed that expected design requirements for the construction of electric technology transfer ＆ diffusion system. Finally, construction and activation plan for electric technology transfer ＆ diffusion system are presented, which would strengthen the national technology competitiveness.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.232-239
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• 2001

The present study is an experimental investigation of nucleate boiling heat transfer mechanism in pool boiling from wire heaters immersed in saturated FC-72 coolant and water. The vapor volume flow rate departing from a wire during nucleate boiling was determined by measuring the volume of bubbles, varying $25{\mu}m,\;75{\mu}m,\;and\;390{\mu}m$, from a wire utilizing the consecutive-photo method. The effects of the wire size on heat transfer mechanism during a nucleate boiling were investigated by measuring vapor volume flow rate and the frequency of bubbles departing from a wire immersed in saturated FC-72. One wire diameter of $390{\mu}m$ was selected and tested in saturated water to investigate the fluid effect on the nucleate boiling heat transfer mechanism. Results of the study showed that an increase in nucleate boiling heat transfer coefficients with reductions in wire diameter was related to the decreased latent heat contribution. The latent heat contribution of boiling heat transfer for the water test was found to be higher than that of FC-72. The frequency of departing bubbles was correlated as a function of bubble diameters.