• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.5
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• pp.299-308
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• 2022

This study was conducted to predict the tendency for heat exchange and boil-off gas (BOG) in a liquefied hydrogen tank under sloshing excitation. First, athe fluid domain excited by sloshing was modeled using a multiphase-thermal flow domain in which liquid hydrogen and hydrogen gas are in the saturated state. Both the the volume of fluid (VOF) and Eulerian-based multi-phase flow methods were applied to validate the accuracy of the pressure prediction. Second, it was indirectly shown that the fluid velocity prediction could be accurate by comparing the free surface and impact pressure from the computational fluid dynamics with those from the experimental results. Thereafter, the heat ingress from the external convective heat flux was reflected on the outer surfaces of the hydrogen tank. Eulerian-based multiphase-heat flow analysis was performed for a two-dimensional Type-C cylindrical hydrogen tank under rotational sloshing motion, and an inflation technique was applied to transform the fluid domain into a computational grid model. The heat exchange and heat flux in the hydrogen liquid-gas mixture were calculated throughout the analysis,, whereas the mass transfer and vaporization models were excluded to account for the pure heat exchange between the liquid and gas in the saturated state. In addition, forced convective heat transfer by sloshing on the inner wall of the tank was not reflected so that the heat exchange in the multiphase flow of liquid and gas could only be considered. Finally, the effect of sloshing on the amount of heat exchange between liquid and gas hydrogen was discussed. Considering the heat ingress into liquid hydrogen according to the presence/absence of a sloshing excitation, the amount of heat flux and BOG were discussed for each filling ratio.

• Journal of the Korea Concrete Institute
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• v.17 no.6 s.90
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• pp.871-878
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• 2005

Reinforced concrete columns exposed to fire experience severe deterioration in material properties and subsequent structural capacities. Degree of losses in structural capacity of a column due to fire-damage mainly depends on the amount of heat transferred into the column during the fire. A reasonable heat transfer model of fire-damaged reinforced concrete column needs to take into account the heat-dependent nonlinear properties of heat conductivity and heat capacity of concrete as well as the evaporation of moistures in a section during the fire. Compared to the previously suggested models, the developed model in this study has included all these parameters in its numerical expressions based on explicit finite difference method. The developed model could predict the temperature changes with a reasonable accuracy for the columns exposed to fire.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.4
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• pp.80-86
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• 2012

This study is for figuring out a possibility of realization of the thermal protection system(TPS) for temporary use under high temperature condition and improving a design of the future TPS. On this purpose, environmental condition of the system has been simplified: the boundary conditions consist of a internally heating surface and a externally heated surface which is simulating the external high temperature condition. Configuration of the system is simplified as a hexahedon. Melting characteristics of the phase change material(PCM) and air temperature variation of TPS with or without connector have been numerically analyzed and compared. As a result of numerical analysis, the heat from the internally heated surface could not be effectively transferred. Therefore, temperature of inner space has been increased.

• Nuclear Engineering and Technology
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• v.24 no.2
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• pp.130-140
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• 1992

The physical benchmark problem on the direct-contact condensation under the horizontal occurrent stratified flow was analyzed using the RELAP5/MOD2 and /MOD3 one-dimensional model. Analysis was peformed for the Northwestern experiments, which involved condensing steam/water flow in a rectangular channel. The study showed that the RELAP5 interfacial heat transfer model, under the horizontal stratified flow regime, predicted the condensation rate well though the interfacial heat transfer area was underpredicted. However, some discrepancies in water layer thickness and local heat transfer coefficient with experimental results were found especially when there is a wavy interface, and those were satisfied only within the range.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1997.11a
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• pp.10-11
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• 1997

고체 추진제를 사용하는 추진 시스템을 개발하는데 가장 커다란 문제로 인식되고 있는 것은 추진제의 연소 특성을 이해하는 일이다. 그 중에서도 연소실의 압력 진동과 추진제 벽면으로 흡수되는 복사 열전달에 의한 연소율(burning rate)의 변화로 인하여 발생하는 연소 불안정에 대한 이해는 아직도 완전히 규명되지 않고 있다. 고체 추진제의 연소 불안정에 대한 이론적 해석은 준-정상 1차원 해석(Quasi-Steady Homogeneous One-Dimension) 방법에 의하여 단순화된 지배방정식을 해석하는 것이 일반적으로 잘 알려져 있는 방법이다. 이 가정은 고체 추진제가 연수되는 영역을 두께가 매우 얇은 영역의 표면반응영역(surface reaction layer)과 화학반응이 없는 응축상태영역(condensed phase zone) 그리고 기체상태의 연료와 화염이 존재하는 기체상태영역(gas phase zone) 등의 3영역으로 구분하며, 기체상태영역에서 발생하는 교란에 대한 응축상태영역의 반응시간 크기(response time scale)가 매우 크기 때문에 응축상태영역의 반응은 준 정상적으로 일어난다고 가정하는 것이다.그러나, 연소실의 온도가 $3000^{\circ}K$ 정도의 높은 온도이어서 복사 열전달에 의한 고체 추진제의 가열이 중요한 열전달 방법으로 작용하게 되므로 이를 무시한 이론적 해석은 물리적인 중요성이 약하여질 수밖에 없다. 본 연구에서는 기체영역으로부터 전달되는 복사 열전달은 투명(transparent)한 표면반응영역을 통과하여 응축상태영역에서 모두 흡수되며 추진제 표면에서의 복사열방출(emission)을 고려하였다. 또한 연소불안정 현상을 해석하기 위하여 표면반응영역에서의 경계조건은 선형교란량으로 대치하는 Zn(Zeldovich-Novozhilov) 방법을 사용하였다. 이 방법은 기체상태영역에 대한 구체적인 해석없이도 연소불안정 현상을 해석할 수 있는 장점이 잇다. 즉 응축상태영역에서의 연소율과 표면온도는 각각 기체영역으로부터 전달되는 온도구배와 연소압력, 그리고 복사 열전달의 함수관계이므로 선형교란에 의한 추진제표면에서의 교란경계조건을 얻을 수 잇으며, 응축영역의 교란지배방정식과 함께 사용하여 압력교란과 복사 열전달의 교란에 대한 연소율의 교란 증감 여부를 판단하여 연소 불안정 현상을 해석할 수 있다.

• Fire Science and Engineering
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• v.27 no.6
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• pp.15-20
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• 2013

The convective heat transfer coefficient, emissivity, and flame heat flux on the surface of Duglas fir are estimated by using repulsive particle swarm optimization. The surface temperature, mass loss rate, and ignition time are measured for various incident heat fluxes from a cone heater of the cone calorimeter. The calculated surface temperatures obtained by using the optimized convective heat transfer coefficient, emissivity and flame heat flux on the surface in this study match well with those obtained from the test. The maximum error between the predicted and measured surface temperatures for the three different external heat fluxes is within 2% showing reasonable agreements. The methodology proposed in this study can be used to obtain various values related to heat transfer on a flaming surface that are difficult to measure in experiments.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.11
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• pp.1477-1482
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• 2011

Using a one-way clutch has been reported to be very effective in reducing the vibration of gear pairs. However, study on the effect of using a one-way clutch has been based on numerical analysis only, and no experimental study has yet been executed. Hence, in this study, experiments to verify the effectiveness of using a one-way clutch to reduce the torsional vibration have been executed. Dynamic responses over a wide range of speeds have been compared for various numbers and positions of the clutch. The results of the experiments verified that a one-way clutch is effective in reducing the vibration by decreasing the tooth mesh vibration as well as the vibration transmitted from the input shaft.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.6
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• pp.580-585
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• 2009

Thermal analysis and design of FPA(Focal Plane Assembly)-CU(Cooling Unit) for Earth observation camera is performed. FPA-CU is the first cooling device for a spacecraft which is designed and manufactured by its own technology in Korea. FPA-CU has a special feature, TBM(Thermal Buffer Mass) which is discriminated from typical cooling devices using heat pipes and radiator. TBM can be regarded as a thermal energy reservoir and it shows thermally transient characteristics, which make it difficult to design the size and shape of TBM. In current study, a method to determine the volume and the size of TBM is proposed and validated. The transient thermal analysis for FPA-CU for 5 operational scenarios is performed and validates the final design of FPA-CU (Radiator,TBM, Heat pipe I/F). In case of an abnormal operation of a heat pipe among three radiator heat pipes, the temperature of FPA can be increased $3{\sim}4^{\circ}C$ according to the numerical simulation.

• Journal of the KSME
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• v.32 no.8
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• pp.673-684
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• 1992

전광 통신의 시대를 맞이하면서 광섬유의 수요가 급증하고 있어 보다 질 좋고 생산 단가가 절 감된 광섬유의 제조가 중요하며 이것은 기존 기술의 최적화와 새로운 제조기술의 개발에 의하 여만 가능할 것이다. 생산성 및 광섬유의 질이 화학증착을 비롯한 각 공정에 의지하므로 각 공 정의 최적화가 중요하며 광섬유 제조 화학증착과정에서 층착 성능은 thermophoresis로써 결정지 어지는 입자운동 및 부착에 의지하므로 향상된 증착 성능을 얻기 위하여서는 각과정에서의 열 전달, 유체유동 및 입자 부착 해석이 선행되어야 한다. 증착의 균일성, 증착효율 및 증착률의 향상을 위한 노력은 모델링을 포함한 실험적 연구 및 새로운 기술의 개발 및 시도가 필요하다고 할 수 있다.

• Journal of the KSME
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• v.26 no.5
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• pp.398-404
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• 1986

열전달에는 많은 개념과 방법론이 포함되므로 그 범위에 있어서, 적어도 다른 어떤 열과학보다도 광범위하다. 이 제목의 첫 과목을 가르치는데 있어, 교수는 토픽의 내용, 수학의 정도, 컴퓨터 사용 및 실험 등에 있어 많은 선택에 직면하게 된다. 이 선택은 학생개발목표는 물론 기자재 및 시간제한 등에 기반을 두어 이루어져야 한다. 열전달 첫 과목의 주된 목적은 학생이 열시스템 설계와 성능에 관계되는 문제를 합리적으로 취급할 수 있도록 준비시키는 것이어야 한다. 따 라서 전달, 대류 및 복사의 기본원리와 열시스템 해석의 방법론에 중점을 두어야 한다.