• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.4
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• pp.1095-1101
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• 1995

Numerical analysis of vertical solidification process allowing solid-liquid density change is performed by a hybrid method between a winite volume method (FVM) and a finite element method (FEM). The investigation focuses on the influence of solid-liquid density change and cooling rates on the motion of solid-liquid interface, solidified mass fraction, temperatures and thermal stresses in the solid region. Due to the density change of pure aluminium, solid-liquid interface moves more slowly but the solidified mass fraction is larger. The cooling rate of the wall is shown to have a significant influence on the phase change heat transfer and thermal stresses, while the density change has a small influence on the motion of the interface, solidified mass fraction, temperature distributions and thermal stresses. As the cooling rate increases, the thermal stresses become higher at the early stage of a solidification process, but it has small influence on the final stresses as the steady state is reached.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.108-112
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• 2000

This paper presents a mathematical model and simulation of the micro-actuator based on thermally induced liquid-vapor phase-change in a partially-filled closed cavity. The volume expansion by liquid-vapor Phase change can generate considerable forces and displacement $({\sim}50{\mu}m)$ required for commercial use. For optimum operation involving many cycles within the closed chamber, active(thermoelectric) heating and cooling is used. The optimization of the system is conducted according to the parameters such as input power and response time. The optimized performance of micro-actuator is reasonable compared to other actuators.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.12
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• pp.1183-1189
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• 2004

An experimental investigation is conducted to measure phase change temperature and supercooling when acetone is added to TMA 30 wt% clathrate during cooling process in heat source. Also rate of volume change is investigated when acetone is added to TMA 30 wt% clathrate during the cooling process in heat source -8$^{\circ}C$. The results show that phase change temperature is about 4.5～5.5$^{\circ}C$ when acetone is added to TMA 30 wt% clathrate during the cooling process for heat sink temperature of -6, -7$^{\circ}C$ and -8$^{\circ}C$. Supercooling is repressed about 2～1$0^{\circ}C$ when 0.08 wt% acetone is added to it and rate of volume change is decreased about 2.9% when 0.1 wt% acetone is added for the heat sink temperature of -8$^{\circ}C$.

• 한국태양에너지학회:학술대회논문집
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• 2009.04a
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• pp.296-301
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• 2009

The ice storage system uses water for low temperature latent heat storage. However, a refrigerator capacity is increased and COP is decreased due to supercooling of water in the course of phase change from solid to liquid. This study investigates the cooling characteristics of the TMA-water clathrate compound including TMA (Tri-methyl-amine, $(CH_3)_3N)$ of $20{\sim}25wt%$ as a low temperature latent heat storage material. The results showed that the phase change temperature and the specific heat is increased and the supercooling degree is decreased as the weight concentration of TMA increased. Especially, the clathrate compound containing TMA 25wt% has the average phase change temperature of $5.8^{\circ}C$, the supercooling degree of $8.0^{\circ}C$ and the specific heat of 3.499 kJ/kgK in the cooling process. This can lead to reduction of operation time of refrigerator in low temperature latent heat storage system and efficiency improvement of refrigerator COP and overall system. Therefore, energy saving and improvement of utilization efficiency are expected.

• International Journal of Air-Conditioning and Refrigeration
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• v.17 no.1
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• pp.32-36
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• 2009

The ice storage system uses water for low temperature latent heat storage. However, a refrigerator capacity is increased and COP is decreased due to supercooling of water in the course of phase change from solid to liquid. This study investigates the cooling characteristics of the TMA-water clathrate compound including TMA (Tri-methyl-amine, $(CH_3)_3N$) of $20{\sim}25wt%$ as a low temperature latent heat storage material. The results showed that the phase change temperature and the specific heat is increased and the supercooling degree is decreased as the weight concentration of TMA increased. Especially, the clathrate compound containing TMA 25 wt% has the average phase change tempera ture of $5.8^{\circ}C$, the supercooling degree of $8.0^{\circ}C$ and the specific heat of 3.499 kJ/kgK in the cooling process. This can lead to reduction of operation time of refrigerator in low temperature latent heat storage system and efficiency improvement of refrigerator COP and overall system. Therefore, energy saving and improvement of utilization efficiency are expected.

• Journal of Energy Engineering
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• v.14 no.1
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• pp.18-23
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• 2005

This study is investigated the cooling characteristics of the TMA clathrate compound including TMA (Tri-methyl-amine, (CH₃)₃N) of 20～25 wt％ as a low temperature storage material at -5℃ heat source. The results showed that as the concentration of TMA is increased, phase change temperature and specific heat are increased, but the supercooling and retention time of liquid phase are decreased. Especially, low temperature storage material containing TMA 25 wt％ has the average of phase change temperature of 5.8℃, supercooling of 8.0℃, retention time of liquid phase for 10 minutes and specific heat of 4.099 kJ/kg℃ in the cooling process. From the results of this study, TMA clathrate compound showed higher phase change temperature than water md supercooling repression effect.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.12
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• pp.647-653
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• 2013

TABS (Thermally Activated Building System) has recently applied by huge commercial buildings, airports, and convention centers in Europe. TABS provides night-time thermal storage by heating or cooling. The embedded water-based heating and cooling system uses the high thermal inertia of concrete in the building construction, in which a heating or cooling pipe is embedded. The aim of this study is to analyze the thermal storage and thermal output of TABS applied with PCM (Phase Change Material). To achieve this, prototypes of TABS and the thermal properties of various PCMs were investigated. By using the simulation program Physibel Voltra 6.0 W, the thermal storage and thermal output were evaluated according to a heating and cooling operation schedule.

• Computers and Concrete
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• v.23 no.4
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• pp.281-294
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• 2019

The post-fire behavior of structural elements and the cooling process has always been one of the main concerns of the structural engineers. The structures can be cooled at different rates, where they affect the structure's behavior. In the present study, a numerical model has been developed using the Abaqus program to investigate the effect of cooling rate on the post-fire behavior of the CFST column. To verify the model, results of an experimental study performed on CFST columns within a full heating and cooling cycle have been used. In this model, coMParison of the residual strength has been employed in order to examine the behavior of CFST column under different cooling rates. Furthermore, a parametric study was carried out on the strength of steel and concrete, the height of the specimens, the axial load ratio and the cross-sectional shape of the specimen through the proposed model. It was observed that the cooling rate affects the behavior of the column after the fire, and thus the higher the specimen's temperature is, the more effect it has on the behavior. It was also noticed that water cooling had slightly more residual strength than natural cooling. Furthermore, it was recognized from the parametric study, that by increasing the strength of steel and concrete and the load ratio, as well as modifying the cross-sectional shape from circular to square, residual strength of column at the cooling phase was less than that of the heating phase. In addition, with reducing column height, no change was witnessed in the column behavior after the cooling phase.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.9
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• pp.614-619
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• 2010

Recently, a problem related to the thermal management in portable electronic and telecommunication devices is becoming issued. That is due to the trend of a slimness of the devices, so it is not easy to find the optimal thermal management solution for the devices. From now on, a pressed circular type cooling device has been mainly used, however the cooling device with thin thickness is becoming needed by the inner space constraint of the applications. In the present study, the silicon flat plate type cooling device with the separated vapor and liquid flow path was designed and fabricated. The normal isothermal characteristics created by vapor-liquid phase change was confirmed through the experimental study. The cooling device with 70 mm of total length showed 6.8 W of the heat transfer rate within the range of $4{\sim}5^{\circ}C/W$ of thermal resistance. In the future, it will be possible to develop the commercialized cooling device by revising the fabrication process and enhancing the thermal performance of the silicon and glass cooling device.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.5
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• pp.459-465
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• 2013

In the manufacturing process of steel plates, materials at high temperatures above $800^{\circ}C$ are rapidly cooled by using a circular impinging water jet to determine their strength and toughness. In this study, the basic heat and fluid flow is solved by using the existing numerical model for boiling heat transfer. Actually, steel undergoes a phase change from austenite to ferrite or bainite during the cooling process. The phase change induces changes in its thermal properties. Instead of directly solving the phase change and the material cooling together, we solve the heat transfer only by applying the thermal properties that vary with temperature, which is already known from other studies. The effects of the changes in the thermal properties on the cooling of steel and the necessity of calculating the phase change are discussed.