• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2005년도 하계학술발표대회
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• pp.232-232
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• 2005

• 태양에너지
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• 제10권2호
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• pp.44-58
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• 1990

본 연구에서는 파라핀을 채운 수평 원관의 관벽을 가열하여 축열할 때에 관내에서 일어나는 열전달현상을 다루었다. 용융이 진행됨에 따라 고액 밀도차에 의해서 고상이 아래로 가라앉는 침강형을 대상으로 하여 고상 윗부분의 액상에서는 자연대류를 고려한 열전달모델을 세우고, 고상의 하부와 관벽 사이의 액막에서는 중력과 부력 그리고 액막 내의 압력에 의한 힘간의 평형관계를 이용하여 액막 내에서의 열전도모델을 세워 이를 수치모사하여 이론적으로 해석하였다. 그리고 실제 실험에 의하여 시간에 따른 용융형태를 사진으로 기록하여 이를 분석함으로써 용융량을 구하였고 유동장을 가시화하여 이론적 결과와 비교하였다. 실험에서 얻은 전체 용융량을 상부액상과 하부액막에서 녹은 양으로 구분하여 용융이 진행됨에 따른 각 부분에서의 용융속도 변화를 알아보았다.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.746-751
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• 2002

In order to make clear the physical relation among the arc plasma, the anode heat transfer and the weld penetration, the results of experimental measurements of temperatures of arc plasma, the distributions of heat input and current on the anode and the weld penetration were presented The experimental results showed that the electron temperature above the anode and current and heat input density on the anode was dominated by the position of the cathode. Furthermore, it was showed that electron temperature of arc plasma was dominated by the cathode shape. These results were related with the results of the welded penetration measurements. As a result, it was showed that the electron temperature above the anode and current density distribution on the anode decided the heat input density distribution on the anode and that the heat input density on the anode remarkably dominated the size of the weld penetration in argon GTA welding process. Furthermore, it was suggested that the cathode played the important role in the determination of the weld penetration in argon GTA welding process.

• 대한기계학회논문집
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• 제17권10호
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• pp.2601-2610
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• 1993

A numerical study on the melting process inside an isothermal spherical capsule is made. It is assumed that the phase change medium of its solid phase is heavier than the liquid phase and therefore the unmelted solid core is continuously moving downward on account of gravity forces. Such a gravity-assisted melting is commonly characterized by the existence of a thin liquid film below the solid core. The present study is motivated to present a full-equation-based analysis of the influences of the initial subcooling and the natural convection on the fluid flow and heat transfer characteristics associated with the gravity-assisted melting. In the light of the solution strategy, the present study is substantially distinguished from the existing works in that the complete set of governing equations in both the melted and unmelted regions are resolved without subdivision of the solution domains. For example, the liquid film region and the upper melted region are treated here as one domain and thus obviating laborious efforts to couple them. Numerical results are obtained by varying the Rayleigh numbers and the degree of subcooling. For the range of parameters examined, the presence of subcooling was found to impede the melting rate. The dropping velocity of the unmelted solid core was observed to affect the natural convection in the liquid significantly. When compared with the available experimental data, much improved prediction was achieved.

• 대한조선학회논문집
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• 제39권1호
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• pp.49-60
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• 2002

용접법은 선박 생산 공정에 있어서 금속 접합을 위해 가장 많이 사용되고 있다. 용접은 금속 접합을 위해 유용한 방법이지만 국부적 가열, 용융, 냉각으로 이어지는 열하중에 의하여 잔류응력과 잔류변형을 발생시킨다. 잔류응력은 구조물의 강도에 부정적인 영향을 끼치고, 잔류변형은 조립 작업에 부정적인 영향을 끼치게 된다. 그러므로 역학적 방법에 의한 잔류응력과 잔류변형의 예측은 이들을 제어할 수 있는 방법을 작업 전에 제시할 수 있도록 하므로, 선체 강도 확보와 선박 생산성 향상을 위하여 매우 중요한 문제라고 볼 수 있다. 본 논문에서는 이러한 배경에서 용접 현상을 가장 잘 시뮬레이션할 수 있는 방법인 유한요소법을 이용한 3차원 열탄소성 해석을 이용하였다. 열탄소성 해석을 위하여 온도분포를 계산한 후 계산된 온도분포를 이용하여 용접변형 및 응력을 순차적으로 계산하였다. 온도분포 계산을 위하여 용융과정을 엔탈피 방법을 이용하여 구현하였으며, 용접비드의 용입은 요소생성법을 이용하여 구현하였다. 본 연구에서 제안된 해석과정은 기존 연구에서 제시한 실험결과와 정성적으로 일치하는 결과를 주는 것을 확인하였다.

• 설비공학논문집
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• 제1권4호
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• pp.319-329
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• 1989

Heat transfer phenomena during inward melting and solidification process of the phase change material were studied expertimentally. The phase change medium was 99% pure n-docosane paraffin ($C_{22}H_{46}$). The solid-liquid interface motion during phase change was recorded photographically. Measurements were made on the temperature, the solid-liquid interface, the melted or frozen mass and the various energy components stored or extracted from the cylinder wall. For melting, the experimental results reaffirmed the dominant role played by the conduction at an early stage, by the natural convection at longer time. For solidification, natural convection effects in the superheated liquid were modest and were confined to short freezing time. Although the latent energy is the largest contributor to the total stored or extracted energy, the aggregate sensible energies can make a significant contribution, especially at large cylinder wall superheating or subcooling, large initial phase change material subcooling or superheating.

• 태양에너지
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• 제9권1호
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• pp.70-77
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• 1989

Sodium pyrophosphate that melting point is $79-80^{\circ}C$ have been Studied on heat storage and heat discharge. In heat storage process, sodium pyrophosphate was kept up initial temperature $50^{\circ}C,\;60^{\circ}C,\;70^{\circ}C$ which melt by heated water at temperature $85^{\circ}C,\;90^{\circ}C,\;95^{\circ}C$. In heat discharge process, initial temperature of sodium pyrophosphate was maintained at temperature $85^{\circ}C,\;90^{\circ}C,\;95^{\circ}C$ which varied cooling temperature $50^{\circ}C,\;60^{\circ}C,\;70^{\circ}C$. The experiment has been reached conclusions as follows. 1) Heat transfer properties of phase change material is controlled by conduction during heating and cooling process. 2) The temperature increased rapidly at initial stage and transient region increase slowly because of characteristic of latent heat. 3) The lower cooling water temperature is the less the time that get to thermal equivalent state take during discharge process. 4) The higher cooling water temperature is the less temperature difference between top and bottom in P.C.M during discharge process.

• 태양에너지
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• 제16권2호
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• pp.113-122
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• 1996

본 연구는 수직원통형 빙축열조 내에 상변화물질로서 순수한 물을 $-10^{\circ}C$의 초기 과냉온도로 응고시킨 후, 작동유체의 입구온도를 $7^{\circ}C,\;4^{\circ}C,\;1^{\circ}C$로, 작동유체의 유입방향을 상향과 하향으로 각각 변화시키면서 외향용융시켰을 경우, 시간경과에 따른 축열매질의 온도분포, 상경계면의 형상, 용융율, 용융에너지를 실험적으로 구하여 이를 비교 검토한 것이다. 작동유체의 입구온도가 $7^{\circ}C,\;4^{\circ}C$의 경우에는 작동유체의 유입방향이 상 하향 모두 물의 최대 밀도점인 $4^{\circ}C$ 부근에서 일시적으로 온도가 상승하지 않고 일정 시간동안 정체하는 온도정체구간이 나타났다. 또한, 용융이 진행됨에 따라 물이 축열조의 하부에 적체되고, 이에 따라 하부에서의 용융이 활발히 진행됨으로써 상경계면 형상은 전체적으로 종모양 형태의 곡선을 나타낸다. 작동 유체의 입구온도가 $7^{\circ}C$인 경우, 용융율(Vl/Vtot)과 용융에너지는 작동유체의 유입방향이 상향인 경우가 하향인 경우에서보다 크게 나타난 반면, 작동유체의 입구온도가 $4^{\circ}C,\;1^{\circ}C$인 경우는 $7^{\circ}C$의 경우와는 달리 하향인 경우가 상향인 경우에서보다 큰 것으로 나타났다.

• 한국자동차공학회논문집
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• 제22권5호
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• pp.13-19
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• 2014

Urea-SCR system is the selective catalytic reduction to reduce nitrogen oxides ($NO_x$) emitted from diesel vehicles. The objective of this study is numerical analysis of 3-dimensional unsteady melting problems of frozen urea by using an electric heater. It can be applied to determine capacity of power with respect to time and the location of the urea suction pipe in urea storage tank. The study includes the change of liquid volume fraction, temperature profiles and a influence of natural convection by using the commercial software STAR-CCM+(v7.06). The accuracy of the numerical analysis is estimated by comparisons with experimental data. After validation, a numerical analysis for freezing urea is conducted with four different heating power. From the results, it was found that relation of velocity of phase interface and amount of melting urea by increasing heating power in a container. There is also a difference in trend between velocity of phase interface and amounts of melting urea because of effect of natural convection.

• 전기학회논문지
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• 제65권1호
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• pp.73-80
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• 2016

The preliminary test for the dual mode plasma torch system was carried out to explore the operation properties in advance. The dual mode plasma torch system that is able to operate in transferred, non-transferred, or dual mode is very adequate for melting the mixed wastes including nonconductive materials such as concrete, asbestos, etc. since it exploits both the high efficiency of heat transfer to the melt in transferred mode and stable operation in non-transferred mode. Also, system operation including restarting is reliable and very easy. A stationary melter with a refractory structure was designed and manufactured considering the melting behavior of slags to minimize the refractory erosion. The power supply for the dual mode plasma torch system built with high power insulated gate bipolar transistor (IGBT) modules has functions for both current control and voltage control and is sufficient to suppress the harmonics during the operation of the plasma torch. The power supply provides two different voltages for transferred operation and non-transferred. It is confirmed that the operation voltage in transferred is always higher than non-transferred. The dual mode plasma torch system was successfully developed and is under operation for a melting experiment to optimize operation data.