• Proceedings of the Korean Institute of Industrial Safety Conference
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• 2000.11a
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• pp.263-268
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• 2000

원자력 압력용기의 건전성 평가 및 안전성 확보에 대한 관심은 1978년 미국 Rancho Seco 발전소에서 발생한 가압열충격 사고로 인해 크게 부각되기 시작하였다. 가압열충격(Pressurized Thermal Shock： PTS)이란 계통의 압력이 높은 상태이거나 증가중인 상태에서 급속한 냉각과 과도한 냉각이 발생하는 것을 의미한다. 이러한 냉각에 의해 원자로용기 외벽보다 내벽이 빨리 냉각되어 상당한 온도구배가 발생하고 이 온도구배에 따라 용기 내벽에 최대인장 열응력이 발생한다.(중략)

• Solar Energy
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• v.12 no.3
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• pp.107-115
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• 1992

An experiment was performed to study solidification of binary mixture with double-diffusive convection in the liquid. A rectangular enclosure was filled with ammonium chloridewater solution. The phase change and convection process were studied through shadowgraph. Becasuse of the double-diffusive convection, the temperature field and concentration filed were stratified very rapidly. Correlation between solidified mass fraction and the dimensionless numbers was found; solidified mass concentration can be expressed as a linear function of $(Ste{\cdot}Ra^{1/4})^{2-Ste}{\cdot}Fo^{1/2}$.

• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.4
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• pp.65-72
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• 2011

Numerical simulation has been performed to investigate the bubbly flow in the liquid with vertical temperature gradient. The objective of this study is to establish an accurate numerical prediction program of gas-liquid two-phase flows in a vertical temperature gradient condition, whose mathematical model is formulated by the Eulerian-Lagrangian model. The present numerical results reveal the temperature mixing mechanism and the fluid dynamical characteristics induced by the bubbly flow in the liquid with stratified temperature. The effects of bubble radius, void fraction, and gas flow rate on bubble-driven convective flow are considered, too.

• International Journal of Highway Engineering
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• v.10 no.2
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• pp.145-157
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• 2008

Load transfer efficiency (LTE) reflects the structural performance of doweled and undoweled joints of Jointed Concrete Pavement (JCP). A 3-dimensional (3-D) model of JCP was built using ABAQUS software in this study. Three concrete slabs were placed on bonded sublayers composed of a base and subgrade. Spring elements were used to connect the adjacent slabs at joints. Different spring constants were input to the model to simulate different joint stiffness of the concrete pavement. The LTE of the joint increased with an increase of the spring constant. The effects of material properties and geometric shape on the behavior of JCP were analyzed using different elastic modulus and thickness of the slab and base in the modeling. The results showed the elastic modulus of the subgrade affected the behavior of the slab and LTE more than that of the base and the thickness of the slab and base. The effects of a negative temperature gradient on the behavior of the slab and LTE were more than that of positive and zero temperature gradients. Joints with low stiffness were more sensitive to the temperature gradient of the slab.

• Journal of Energy Engineering
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• v.10 no.3
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• pp.272-277
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• 2001

An experimental study of jet impinging the non-isothermal heating surface with linear temperature gradient is conducted with the presentation of the turbulent flow characteristics and the heat transfer rate, represented by the Nusselt number. The jet Reynolds number ranges from 15,000 to 30,000, the temperature gradient of the plate is 2~4.2$^{\circ}C$/cm and the dimensionless nozzle to plate distance (H/D) is from 2 to 10. The results show that the peak of heat transfer rate occurs at the stagnation point, and the heat transfer rate decreases as the radial distance from the stagnation point increases. A remarkable feature of the heat transfer rate is the existence of the second peak. This is due to the turbulent development of the wall jet. Maximum heat transfer rate occurs when the axial distance from the nozzle to nozzle diameter (H/D) is 6 or 8. The heat transfer rate can be correlated as a power function of Prandtl number, Reynolds number, the dimensionless nozzle to plate distance (H/D) and temperature gradient (dT/dr). It has been found that the heat transfer rate increases with increasing turbulent intensity. The wall jet is influenced by temperature gradient and the effect becomes more important at higher radii.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.10
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• pp.777-784
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• 2017

Energy harvesting through a thermoelectric module normally makes use of the temperature gradient in the system's operational environment. Therefore, it is difficult to obtain the desired output power when the system is subjected to an environment in which a low temperature gradient is generated across the module, because the power generation efficiency of the thermoelectric device is not optimized. The utilization of solar energy, which is a form of renewable energy abundant in nature, has mostly been limited to photovoltaic solar cells and solar thermal energy generation. However, photovoltaic power generation is capable of utilizing only a narrow wavelength band from the sunlight and, thus, the power generation efficiency might be lowered by light scattering. In the case of solar thermal energy generation, the system usually requires large-scale facilities. In this study, a simple and small size thermoelectric power generation system with a solar concentrator was designed to create a large temperature gradient for enhanced performance. A solar tracking system was used to concentrate the solar thermal energy during the experiments and a liquid circulating chiller was installed to maintain a large temperature gradient in order to avoid heat transfer to the bottom of the thermoelectric module. Then, the setup was tested through a series of experiments and the performance of the system was analyzed for the purpose of evaluating its feasibility and validity.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.5
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• pp.483-490
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• 2008

Minimization of nozzle induces many flow losses in micro-propulsion system. In this study, we studied about thermal transpiration based micro propulsion system to overcome these losses. Thermal transpiration device(Knudsen pump) having no moving parts can self-pump the gaseous propellant by temperature gradient only (cold to hot). We designed, fabricated the Knudsen pump and analyzed pressure gradient efficiency of membrane according to Knudsen number under vacuum condition. Experimental results showed that thick membranes are more effective than thin membranes in transition flow regime, and pressure gradient efficiency according to Knudsen number is increased to maximum 82% apart from membrane thickness in free molecular regime.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.10
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• pp.896-901
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• 2015

The skin-frame type structure is designed to investigate the thermal deformation of the wing skin induced by the temperature gradient. In order to effectively simulate the temperature gradient on the wing specimen, a water cooling system is devised on the frame of the specimen. Out of surface skin deformation of the skin-frame type structure made of SUS304 material with respect to the temperature is successfully measured using the digital image correlation (DIC) technique including quantitative evaluation of the measurement uncertainty.

• Journal of the Korean Ceramic Society
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• v.38 no.2
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• pp.193-198
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• 2001

유한요소법을 이용하여 STS VOD 래들에서 내장 내화물의 재질 및 back filler의 시공 위치에 따른 열응력을 수행하였다. 불소성 내화물의 경우 높은 열전도율에 의해 가동면과 배면(back face)간의 온도구배가 소성품에 비해 감소하였으며 탄성계수도 낮아 발생되는 열응력이 2~4배 낮았다. Back filler는 dolomite 내화물의 열간 팽창을 흡수하기 위해 시공하는 것으로, 상대적으로 낮은 열전도율을 가지고 있기 때문에 back filler의 내부와 외부에 급격한 온도구배가 발생된다. 결과적으로 래들의 내부는 고온을 유지하여 내화물이 팽창이 되고, 외부는 온도가 낮아지므로 수축되어 열응력이 증가하였다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.3
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• pp.347-352
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• 1999

The finite element formulation and simulation of drying process for ceramic electric insulators are investigated. The heat and moisture movements in green ceramics caused by the interaction of temperature gradient, moisture gradient, conduction, convection and evaporation are considered. The variations of temperature and moisture not only change the volume but also induce the hygro-thermal stress. The finite element formulation for solving the temperature and moisture distributions as well as the associated hygro-thermal stresses is derived. Using the computer code developed, the drying process of a ceramic electric insulator is simulated. Temperature distribution, moisture distribution, hygrothermal stress and deformed shape during the drying process are predicted.