• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.3
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• pp.377-383
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• 1999

In this study, the behavior of frost formation according to surface characteristics in the fin-tube heat exchanger has been examined experimentally. The results show that the thickness of the frost which is attached to the hydrophilic heat exchanger becomes thin and the air pressure drop is smaller than that of bare aluminium heat exchanger However, the frost mass of hydrophilic heat exchanger is more than the bare one. Hence, high density frost is attached to hydrophilic heat exchanger. The sensible and latent heat flux of hydrophilic heat exchanger is bigger than that of bare one, but the increasing amount is very small and the improvement of thermal performance is also very small. The variation of fin-pitch of heat exchanger shows little influence on frost formation and hydrophilic heat exchanger loses its surface characteristics rapidly with increasing relative humidity.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.6
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• pp.646-651
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• 2004

When the water flowing inside of the heat transfer equipments such as heat exchangers, condensers, and boilers is heated, calcium, magnesium sulfate, and other minerals in the water are deposited and built up for scales on the heat transfer surfaces. When those scales accumulate on the heat transfer surfaces, their performance of the heat transfer become progressively reduced due to the increase of the heat transfer resistance. The mechanism of this reduced heat transfer is called fouling. This study investigated the formation of the fouling in a heat exchanger with river and tap water flowed inside of it as a coolant. In order to visualize the formation of the fouling and to measure the fouling coefficients, a lab-scale heat exchanging system was used. Based on the experimental results, it was found that the formation of fouling for river water was quite different with the formation for tap water.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1473-1478
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• 2003

Scale is formed when hard water is heated or cooled in heat transfer equipments such as heat exchangers, condensers, evaporators, cooling towers, boilers, and pipe walls. When scale deposits in a heat exchanger surface, it is traditionally called fouling. The objective of the present study is to investigate the formation of fouling in a heat exchanging system. A lab-scale heat exchanging system is built-up to observe and measure the formation of fouling experimentally. Water analyses are conducted to obtain the properties of HAN river water. In the present study a microscopic observation is conducted to visualize the process of scale formation. Hardness of HAN-river water is higher than that of tap water in Seoul.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.4
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• pp.349-354
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• 2004

Scale is formed when hard water is heated or cooled in heat transfer equipments such as heat exchangers, condensers, evaporators, cooling towers, boilers, and pipe walls. When the scale deposits in a heat exchanger surface, it is conventionally called fouling. The objective of the present study is to analyze the process of the fouling formation in a heat exchanger according to different types of water using visualization techniques. In order to experimentally investigate the formation of the fouling, this study built a lab-scaled heat exchanging system. Using the visualization techniques of Scanning Electron Microscopy (SEM) and X-Ray diffraction method, the three dimensional configurations of the fouling formation could be successfully obtained. Based on the experimental results, it was found that the configurations of the fouling formation were different when using tap water compared to river water.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.1
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• pp.95-101
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• 2000

The effect of surface contact angle on the behavior of frost formation in a fin-tube heat exchanger is investigated experimentally. It is shown that both heat exchangers with hydrophilic and hydrophobic surfaces appear to have a better thermal performance than bare aluminium heat exchanger, but the improvements are very small. There is a little increase in the amount of the frost deposited onto the heat exchanger with both hydrophilic and hydrophobic surface. However, the effect of contact angle on the frost density is observed ; the frost with high density forms on the heat exchanger with hydrophilic surface ; and the frost with low density is deposited onto the heat exchanger with hydrophobic surface when compared with the frost deposited onto the heat exchanger with bare aluminium surface. This may be attributed to the fact that the shape of water droplets which condense on the surface of heat exchanger at the early stage of frosting varies with contact angle, and thus makes a difference on the structure of frost formation. From the experiments with different relative humidity of inlet air, it is shown that the variations of operating parameter make no influence on the effect of surface contact angle on the frosting behavior in the heat exchanger.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.10 no.1
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• pp.30-35
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• 2001

Nickel-based heat resisting alloys are commonly used for high temperature application such as in aircraft engines and gas turbines. In this paper, the machinability of Nickel-based heat resisting alloys was investigated with respect to the wear and the chip formation by tool type and cutting condition. Relationship between three types of tool and chip formation was experimentally investigated. Among the three types of tool tested, coated tools(CVD, PVD) ara available for the difficult-to-cut-materials such as Nickel-based heat resisting alloys and etc.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.04a
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• pp.264-269
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• 2000

Nickel-based heat resisting alloys are commonly used for high temperature applications such as in aircraft engines and gas turbines. In this paper, the machinability of Nickel-based heat resisting alloy was investigated with respect to the wear and the chip formation by tool type and cutting condition. Relationship between three types of tool and chip formation was experimentally investigated. Among the three types of tool tested, coated tools(CVD, PVD) are available for the difficult-to-cut-materials such as Nickel-based heat resisting alloy and etc..

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.7
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• pp.596-602
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• 2006

Ice adhesion and blockage problems have been issued in continuous ice slurry making process. So we composed continuous ice slurry making device using a commercial small plate heat exchanger (PHX), and investigated character of ice formation. An experiment of ice formation was peformed with an aqueous solution of ethylene glycol 7 mass%. In the experiment, the effect of the pressurization on ice slurry formation during the cooling process was investigated. The pressurization test for the aqueous solution was performed by setting valves at the PHX inlet and outlet. At the results, the time of continuous ice formation increased as the pressure of the plate heat exchanger increased for cooling temperature of $-5^{\circ}C$. Also continuous ice formation at the cooling temperature of $-7^{\circ}C$ showed a possibility. It was found that the pressurization may contribute to suppress the dissolution of supercooled aqueous solution in the PHX.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.11
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• pp.643-648
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• 2009

Tests were conducted to obtain heat transfer coefficients during slush formation from 10% sucrose solution. The slush was made by scraping the ice formed on the cylinder. Cold brine was supplied inside of the evaporator cylinder to cool the outer surface. Below a certain brine temperature, which was $-5^{\circ}C$ in this study, the solution was supercooled, and suddenly turned into ice crystals. During slush formation, the heat transfer coefficient oscillated significantly, due to periodic removal of ice chunk form the surface. The average heat transfer coefficient during slush formation was 40~70% higher than that obtained during single phase cooling. The heat transfer coefficient was also affected by the brine temperature with increasing heat transfer coefficient at higher brine temperature.

• 연구논문집
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• s.25
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• pp.155-161
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• 1995

During casting of A390 billet by Hot Top process, bosses were formed on the surface of cast bar. The formation of boss is assumed due to a large amount of latent heat released during the formation of primary Si in A390 alloy. The low melting point elements around primary Si are locally remelted to liquid and interdendrite offers a path by which the liquid can pass through to the surface. Addition of Sr decreases the amount of latent heat by preventing the formation of primary Si near the surface and thus suppresses the formation of boss on the surface of cast bar. Therefore, the formation of boss could be reduced remarkably when the casting condition was selected to extract the latent heat outward easily.