• Journal of Biosystems Engineering
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• v.14 no.1
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• pp.24-32
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• 1989

고밀도(高密度)의 열(熱)에너지를 저장(貯藏)하기 위(爲)한 잠열축열장치를 설계(設計), 제작(製作), 작동(作動)하는 경우 잠열축열장치의 사용목적(使用目的)에 적합(適合)한 최적설계(最適設計)와 그 효율적(效率的)인 이용(利用)을 위(爲)해서는 그 부열특성(傅熱特性)이 규명(糾明)되어야 한다. 본(本) 연구(硏究)에서는 실용화(實用化)에 필요(必要)한 이중관형(二重管形) 잠열축열장치의 방열과정(放熱過程)에서의 부열특성(傅熱特性)을 이차원적(二次元的)으로 실험(實驗) 분석(分析)하였으며, 시간변화(時間變化)에 따른 잠열재의 온도변화(溫度變化)와 응고율(凝固率)이 실험분석치(實驗分析値)와 이론분석치(理論分析値)에 있어서 잘 일치하였다. 한편 응고율(凝固率), 방열율(放熱率), 물의 온도변화(溫度變化)에 대(對)한 분석(分析)을 하였다.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2011.06a
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• pp.207-207
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• 2011

본 논문은 공장 등에서 버려지는 중온온도영역($100{\sim}250^{\circ}C$)에서의 패열을 잠열축열 시스템에서 유용하게 사용을 목적으로 잠열축열재인 에리스리톨와 만니톨 그리고 이것들을 혼합한 혼합물에 대한 조사에 관한 것이다. 또한, 만니톨에 에리스리톨을 첨가하는 것에 의해 융해 응고온도가 조정의 가능성에 대해서도 조사한다. 이때 에리스리톨과 만니톨 그리고 이것들의 혼합물의 융점과 잠열량은 시차주사열량계(DSC)를 이용하여 측정되며, 시험관안에 상변화물질을 충전하여 융해 응고거동을 디지털 카메라를 이용하여 관찰 된다. DSC측정결과에서는 만니톨의 함유량이 50~60mass%에서는 3개의 융점, 70~90mass%에서는 2개의 융점을 나타내는 것을 확인할 수 있었다. 또한 시험관을 이용한 실험결과에서는 만니톨의 함유량에 따라서 각 각 다른 융해 응고거동이 일어나는 것을 확인할 수 있었다.

• Solar Energy
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• v.12 no.1
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• pp.59-71
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• 1992

The purposes of the present study are to investigate the characteristics of heat storage and emission of the PCM($CalCl_2{\cdot}6H_2O$) panel, and to analyze the distribution of indoor air temperature in a floor heating space with PCM panels for the heating system. Two identical unit test cells sized $1.8m^W{\times}1.8m^L{\times}1.8m^H$ were built and installed with specially designed aluminium Ondol-panels. It held 1.2kg of calcium chloride hexahydrate(CCH). It was found that PCM panels could reduce the indoor air temperature fluctuations and maintain the phase changing temperature for considerably long duration, $2{\sim}3$ times longer in heating hour over no-CCH one. When the elapsed time was 6 hours, the average temperature difference between PCM panel and Ondol panel was $7.7^{\circ}C$.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.1
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• pp.126-141
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• 1997

The purpose of this research is to develope a FEM program for analyzing solidification processes of axisymmetric casting, considering phase changes and the contact between the metal and mold. Tempera- ture recovery method is employed fro considering the phase changes releasing the latent heat and the coin- cident node method is used for calculating the amount of heat transfer between the metal and mold. Tan- gent modulus algorithm is adopted for calculating flow stress and a gap element is employed for modeling the interface between the mold and metal in finding deformed shapes. In order to verify the developed program, axisymmetric aluminum and steel casting processes are simulated. Temperature distribution, phase front position, and shrinkage and porosity creation are compared with measurements, FIDAP results, and good agreements are examined.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.1 no.1
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• pp.74-81
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• 1991

The temperature profile of Czochralski single crystal growth system was simulated considering the fluid flow and surface radiation heat transfer. View factors of surface elements were calculated for radiation heat transfer. Two phases(solid and liquid) were treated as a continuous phase by assigning artificial large viscosity to the solid phase and latent heat was accounted by iterative heat revolution method. The solidification model was applied to solid front of the pure Ga during the melting to verify the model. The whole simulation model of CZ system was applied to the growth Al single crystal.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.1
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• pp.189-205
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• 1996

The twin-roll type strip continuous casting process(or direct rolling process) of steel materials is characterized by two rotating water cooled rolls receiving a steady supply of molten metal which solidifies onto the rolls. A solidification analysis of molten metal considering phase transformation and thermofluid is performed using finite diffefence method with curvilinear coordinate to reduce computing time and molten region analysis with arbitrary shape. An enthalpy-specific heat method is used to determine the temperatures inthe roll and the steel. The temperature distribution of cooling roll is calculated using two dimensional finite element method, because of complex roll shape due to cooling hole in rolls and improvemnt accuracy of calculation result. The energy equaiton of cooling roll is solved simultanuously with the conservation equaiton of molten metal in order to consider heat transfer through the cooling roll. The calculated roll temperature is compared to experimental results and the heat transfer coefficient between cooling roll surface and rolling material(steel) is also determined from comparison of measured roll temperature and calculated temperature.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.10
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• pp.887-894
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• 2016

The thermal control device using solid-liquid phase change material (PCM) is designed, manufactured, and experimented in thermal environment chamber. The n-Hexadecane is selected as a PCM and its melting point is placed within the component working temperature range. The PCM container is made of Al6061 and has the thermal spreading fins inside. To simulate the working condition for on-orbit satellite the heat pipes are used to connect the heater and radiator and the PCM thermal control device (PCMTD) is installed at the middle portion of heat pipes. The thermal buffer mass (TBM), which is same configuration and volume with PCMTD, is also manufactured to compare the thermal control performance. As a result, the PCMTD is not only more efficient than TBM in their temperature control features but both mass and power of compensation heater are reduced.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.10
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• pp.1213-1222
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• 1999

A finite element method is developed for calculating the temperature and enthalpy distribution and accordingly the solid, liquid and mushy zone in a three-dimensional body subjected to any heat boundary conditions. The method concurrently consider both temperature and enthalpy for consideration of the latent heat effect, differently from other methods of using a special energy balance equation for solving a mushy zone. The developed brick element has eight nodes with one degree of freedom at each node. The numerical method and procedure are verified using the results of one and two dimensional analytic solutions and by other researchers. It is shown that the present method presents a consistent and stable results in either abrupt or ranged phase change problems. Moreover, the numerical results by the present method are hardly effected by the calculation time steps which otherwise are difficult to determine in most phase change problems. Finally, as a three-dimensional application, a T-shaped body of a phase change is presented and the temperature and enthalpy variation along the time are solved.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.7 s.238
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• pp.814-819
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• 2005

The phase change heat transfer has been applied to the processes of machines as well as of manufacturing. The cycle in a heat exchanger includes the phase change phenomena of coolant for air conditioning, the solidification in casting process makes use of the characteristics of phase change of metal, and the welding also proceeds with melting and solidification. To predict the phase change processes, the experimental and numerical approaches are available. In the case of numerical analysis, the Enthalpy method is most widely applied to the phase change problem, comparing to the other numerical methods, i.e. the Equivalent Specific Heat method and the Temperature Recovery method. It's because that the Enthalpy method is accurate and straightforward. The Enthalpy method does not include any correction step while the correction of final temperature field is inevitable in the Equivalent Specific Heat method and the Temperature Recovery method. When the temperature field is to be used in the calculation, however, there must be converting process from enthalpy to temperature in the calculation scheme of Enthalpy method. In this study, an improved method for the Equivalent Specific Heat method is introduced whose method dose not include the correction steps and takes temperature as an independent variable so that the converting between enthalpy and temperature does not need any more. The improved method is applied to the solidification process of pure metal to see the differences of conventional and improved methods.

• Journal of Korea Foundry Society
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• v.13 no.4
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• pp.323-332
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• 1993

An implicit finite difference formulation with three methods of latent heat treatment, such as equivalent specific heat method, temperature recovery method and enthalpy method, was applied to solidification analysis. The Neumann problem was solved to compare the numerical results with the exact solution. The implicit solutions with the equivalent specific heat method and the temperature recovery method were comparatively consistent with the Neumann exact solution for smaller time steps, but its error increased with increasing time step, especially in predicting the solidification beginning time. Although the computing time to solve energy equation using temperature recovery method was shorter than using enthalpy method, the method of releasing latent heat is not realistic and causes error. The implicit formulation of phase change problem requires enthalpy method to treat the release of latent heat reasonably. We have modified the enthalpy formulation in such a way that the enthalpy gradient term is not needed, and as a result of this modification, the computation stability and the computing time were improved.