• 설비공학논문집
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• 제7권2호
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• pp.266-275
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• 1995

A numerical investigation on the conduction-natural convection-surface radiation conjugate heat transfer in the enclosure having substrate and chips has been performed. A 2-dimensional simulation model is developed by considering heat transfer by conduction, convection and radiation. The solutions to the equation of radiative transfer are obtained by the discrete ordinates method using S-4 quadrature. The effects of Rayleigh number and the substrate-fluid thermal conductivity ratio on the cooling of chip are analyzed. The result shows that radiation is the dominant heat transfer mode in the enclosure.

• 오토저널
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• 제11권1호
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• pp.20-30
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• 1989

The unsteady conjugate forced convection-conduction heat transfer from a plate fin is numerically studied. The external forced flow is steady but the temperature of the fin base is an exponential change with time. Therefore, the unsteady energy equations of the fluid and the fin are solved simultaneously under the conditions of equality in heat flux and temperature at the fluid-fin interface at every instant of time. Numerical results are given for various quantities of interest including the local heat transfer coefficient, the local heat flux, the total heat transfer rate and the temperature distribution of fin under the effects of the convection-conduction parameter and the ratio of thermal diffusivities. The results of the present numerical solution have been compared with those of the conventional fin theory.

• 태양에너지
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• 제4권2호
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• pp.43-49
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• 1984

Experiments were performed to study freezing on a finned vertical tube when either conduction in the solid or natural convection in a liquid controls the heat transfer. Conduction is the controlling mode when the liquid is at its fusion temperature, whereas natural convection controls when the liquid temperature is above the fusion value. The liquid was housed in a cylinderical containment vessel whose surface was maintained at a uniform, time-invariment temperature during a data run, and the freezing occurred on a finned vertical tube positioned along the axis of the vessel. The phase change medium was n-octacosan, a paraffin which freezes at about $61^{\circ}C$. For conduction-controlled freezing, the enhancement of the frozen mass due to finning is greatest when the frozen layer is thin and decrease as the layer grows thicker. The degree of enhancement is generally less than the surface area ratio of the finned and unfinned tube.

• 한국정밀공학회지
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• 제16권8호
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• pp.162-169
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• 1999

Fourier heat conduction law becomes invalid for the situations involving extremely short time heating, very low temperatures and fast moving heat source(or crack), since the wave nature of heat propagation becomes dominant. For these conditions, the modified heat conduction equation with the finite propagation speed of heat in the medium could be applied to predict heat flux and temperature distributions. In this study, temperature distributions at the vicinity of a very fast moving heat source are investigated numerically. Thermal fields are characterized by thermal Mach numbers(M) defined as the ratio of moving heat source speed to heat propagation speed in the solid. In the transonic and supersonic ranges($M{\ge}1$), thermal shocks are shown, which separate the heat affected zone from the thermally undisturbed zone.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 하계종합학술대회 논문집(5)
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• pp.103-106
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• 2001

In this paper, a soft switching half-bridge converter using secondary switches for output control and conduction loss reduction is proposed. The conventional half-bridge converter must be fixed on duty cycle for soft switching. The proposed converter was consisted of two added switches in series of the secondary rectifier diodes. The main switches with constant duty cycle are operated ZVS. The secondary switches are operated ZV-ZCS. Especially, the primary switches were fixed duty cycle for maximum voltage conversion ratio. Output of converter is controlled by duty cycle or phase-shifted time of secondary switches. The conduction loss of the proposed converter can be reduced by the secondary switches. The operation characteristic, analysis, simulation and experimental results of the proposed converter are presented.

• Bulletin of the Korean Chemical Society
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• 제11권5호
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• pp.371-376
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• 1990

Polyaniline perchlorate (PAP) was synthesized by the chemical oxidation of aniline using ferric perchlorate as a strong oxidant. The electrical conductivity of PAP was measured at temperatures from - 170 to 25$^{\circ}C$. It is suggested from the conductivity measurements that the conduction mechanism for PAP is a polaron hopping conduction. From the dependence of resistivity on the reciprocal temperature, the activation energy was computed to be 0.072 eV. From the comparison of the ESR parameterks and conductivity at 25$^{\circ}C$ for the polyaniline-based conducting polymers, the conductivities of PAP, PATFB and PATS increase with increasing ${\Delta}H_{pp}$, decreasing A/B ratio and decreasing g-value, respectively. It is shown by TGA results for PAP, PATFB and PATS that the maximum weight loss rates (Pr) are 0.185 (at 269$^{\circ}C$ ), 0.366 (at 324$^{\circ}C$) and 0.23 mg/min (at 338$^{\circ}C$), respectively.

• 반도체디스플레이기술학회지
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• 제11권2호
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• pp.23-26
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• 2012

The monodispersed polystyrene spheres were prepared by emulsion polymerization in aqueous alcohol system. They coated with silver by reduction of silver ion percolated on the surface of them. The spherical hollow type silver has been prepared by dissolving polystyrene with toluene. Epoxy resin compositions with spherical hollow type silver were manufactured, which were composed of a bisphenol F type epoxy resin (RE-304S), amine type hardener (Kayahard AA), and 1-benzyl 2-methyl imidazole (1B2MI) as catalyst. The electrical conductivity with silver content ratio were investigated after cure, the percolation threshold weight ratio for conductance in this epoxy resin system was obtained above the 70 wt% of silver.

• 대한기계학회논문집
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• 제13권4호
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• pp.739-752
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• 1989

본 해석의 목적은 실린더헤드의 3차원 열전도해석을 격자망구성이 편리한 경계요소법을 이용하여 수행함으로써 연소실의 벽면온도를 구하여 연소 실내의 열전달과정 해석을 위한 사이클 시뮬레이션에 사용하는데 있다.

• 한국해양공학회지
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• 제15권3호
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• pp.1-8
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• 2001

With uniform heat generation within the wall of the cylinder placed in a cross flow, heat flows by conduction in the circumferential direction due to the asymmetric nature of the fluid flow around the perimeter of the cylinder. The circumferential heat flow affects the wall temperature distribution to such an extent that in some cases significantly different results may be obtained for geometrically similar surfaces. In the present investigation, the effects of circumferential wall heat conduction on local convective heat transfer is investigated for the case of forced convection around horizontal cylinder in cross flow of air. Two-dimensional temperature distribution $T_w$/(${\gamma}$,${\theta}$) is presented through the numerical analysis. The one-dimensional and two-dimensional solutions are in good agreement with experimental results of local heat transfer coefficients.

• 태양에너지
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• 제12권3호
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• pp.60-69
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• 1992

본 연구에서는 고-액 상변화 시의 잠열을 이용한 축열방법 중에서 고상파라핀을 충전한 수직원관의 관벽을 가열하여 축열하는 경우에 대하여 관 내에서 일어나는 열전달 특성과 축열속도를 이론적으로 해석하였다. 액상에서는 자연대류를 고려하였고 고상에서는 순수 열전도 모델을 사용하였다. 고상파라핀의 초기온도와 관벽의 가열온도 그리고 관의 형상비가 축열속도에 미치는 영향을 알아보았으며, 전체 열전달과정을 순수열전도 모델로 해석하여 자연대류가 축열에 미치는 영향을 고찰하였다. 용융초기에는 관벽과 고액경계면의 영향으로 자연대류에 의한 유동은 장애를 받으나, 40% 정도의 용융이 진행된 후 부터는 내부 액상에서의 자연대류가 활발히 일어나고, 용융중기로 갈수록 관의 상부에 뜨거운 액상층이 축적되므로 자연대류는 소멸하게 된다. 전체적인 융용속도는 순수열전도에 의한 용융속도보다 빨라지게 된다. 관벽의 가열온도와 형상비가 증가할수록 관 내에서의 자연대류가 활발하게 일어나므로 용융속도는 빨라지며, 형상비가 클수록 상하부 간에 불균등한 용융이 일어난다. 고상의 초기온도는 초기의 용융속도에 큰 영향을 미치고 용융이 진행될수록 그 효과는 줄어든다.