• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.229-230
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• 2002

This paper presents the hot spot behaviors on the rubbing surface of ventilated disk brake by using finite element method. The depth of asperities on the rubbing surface is usually $2-3\;{\mu}m$ so the real contact area is microscopically. Non-uniform contacts between the disk and the pads lead to high local temperatures, which may cause the material degradation, and develops hot spots, thermal cracking, and brake system failures at the end. High contact asperity flash temperatures in rubbing systems, which is strongly related to the hot spot. It was generally known that high temperature over about $700^{\circ}C$ may form martensite on the cast iron which is material for automotive disk brakes. In this paper, the contact stress, temperature distribution and strain have been presented for the specific asperities of real contact area microscopically by using coupled thermal-mechanical analysis technique.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.281-284
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• 2003

The microstructural changes of Al-Zn-Mg-Cu alloy containing Sc during hot extrusion and post heat treatment is investigated. Two kinds of Al-Sc alloys with different alloying elements (B1, B2) are hot extruded to make I-shape bars at 380$^{\circ}C$, then the bars are solution treated at 480$^{\circ}C$ for 2hrs followed by artificial aging at 120$^{\circ}C$ for 24hrs. The interior microstructure of as extruded bar consists of elongated grains, however, fine equiaxed grains are mainly observed around surface. The microstructural gradient suggests that different restoration process can proceed during the hot extrusion. For B1 and B2, different grain growth behaviors are found around the surface during the post heat treatment. Rapid grain growth behavior around the surface is discussed related with the crystallographic orientation of the grain.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2369-2374
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• 2008

In the precision hot plate for wafer processing, the temperature uniformity of upper plate surface is one of the key factors affecting the quality of wafers. Precision hot plates require temperature variations less than ${\pm}1.5%$ during heating to $120^{\circ}C$. In this study, we have manufactured the flat plate heat pipe hot chuck of circle type(300mm) and investigated the operating characteristics of flat plate heat pipe hot chuck experimentally. Various liquids(aceton, FC-40, water) were used as the working fluid and charging ratio was changed($14{\sim}36\;vol.%$). Several cases were tested to improve temperature uniformity. Major working fluid to be investigated was water. Using water, various parameters such as charging ratio, wafer operation on-off time, different working fluids. In case of water, the temperature uniformity was ${\pm}1.5%$, response time of wafer were investigated.

• Journal of Advanced Marine Engineering and Technology
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• v.26 no.3
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• pp.320-327
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• 2002

An experimental study of heat transfer from hot flat surface to water sprays was conducted in high temperature region. Heat transfer measurements for hot flat surface were made by 4 sheathed C-A thermocouples. Droplets volume flux were also measured-independently at a position in spray field. The test conditions included variations in droplets volume flux, subcooling of cooling water of $1.565\times10^{-3} to 14.089\times10^{-3}m^3/m^2s and 80 to $20^{\circ}C$ respectively. The effects of inclination angle on heat transfer were investigated and changes in inclination angle of hot flat surface affected heat transfer coefficients of high temperature region.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.14 no.5
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• pp.68-74
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• 2015

In the present work, a series of numerical calculations have been conducted on the cooling of a hot surface using an air/water mist jet. In some cooling processes, such as in the glass-tempering process, direct contact between the cold water drops and the hot surface should be avoided, because this may cause surface cracks due to the sharp temperature gradients. Thus, the main focus of this study is finding the appropriate operating conditions for maximum cooling without direct contact between the drops and the surface. A series of numerical experiments have been performed, and, at the same time, those results were compared with those of the previous experiments for verification purposes. The effects of droplet impinging velocity, hot plate temperature, and liquid loading ratio for mono-dispersed drops of various sizes were studied in detail.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2013.05a
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• pp.109-110
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• 2013

Medium carbon steel was aluminized by hot dipping into molten Al or Al-1%Si baths. After hot-dipping in these baths, a thin Al-rich topcoat and a thick alloy layer rich in $Al_5Fe_2$ formed on the surface. A small a mount of FeAl and $Al_3Fe$ was incorporated in the alloy layer. Silicon from the Al-1%Si bath was uniformly distributed throughout the entire coating. The hot dipping increased the microhardness of the steel by about 8 times. Heating at $700-1000^{\circ}C$ however decreased the microhardness through interdiffusion between the coating and the substrate. The oxidation at $700-1000^{\circ}C$ in air formed a thin protective ${\alpha}-Al_2O_3$ layer, which provided good oxidation resistance. Silicon was oxidized to amorphous silica, exhibiting a glassy oxide surface.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.738-744
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• 2000

The breakup behaviors of impinging droplet on a hot surface are studied experimentally. The droplets are produced by the dripping method and the breakup behaviors of liquid droplet are recorded by photographs. Experimental conditions are, droplet diameter di : 2.5, 3.2 [mm], weber number : $30{\sim}140$, surface temperature : $28^{\circ}C(room\;temperature){\sim}450^{\circ}C$. Water is used to liquid. As weber number of droplet increases, a liquid sheet, which is formed after the impingement on a hot surface, is disintergrated by the dynamical effect. But at low weber number, it has effected by thermodynamical effect. The breakup behaviors of droplet are divided into three patterns with weber number and surface temperature, non-disintegration, transition and disintegration region. Further, these boundary values are affected by the hot surface temperature and weber number. SMD of breakup droplets are calculated in according to surface temperatures and weber number. The minium SMD of breakup droplets are observed at weber number 65.49, temperature $250^{\circ}C$ and weber number 99.08, temperature $350^{\circ}C$.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.4
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• pp.819-827
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• 1992

Investigations of the fatigue damage of roughing mill roll and experimentally. By the computer simulation for analysing the stresses on the roll surface and experimental hot rolling, the following results were drawn : The crakcs observed on the roll surface were initiated thermally in the initial stage of the rolling and propagated by repeated thermal and bending stresses. The size of the roll surface cracks smaller than 4.87mm could avoid the occurrence of tiny scab, surface defect of hot steel strip. Since the size of surface cracks observed on the roughing mill roll was very small, the fatigue damage of roll surface was found not to be the major factor for the formation of the scab.

• Korean Journal of Materials Research
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• v.9 no.4
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• pp.335-340
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• 1999

The hot cracking phenomena and phase behaviors during hot working process of Cu-Ni bearing hot rolled steels were investigated by a $90^{\circ}$bending tests, BSE image analysis and EDS analysis. For aNi-free 1.2% Cu bearing steel, the surface hot cracking occurred about $1100^{\circ}C$ due to a liquid state Cu-enriched phase formed continuously at the interface between oxide scale and matrix. The liquid Cu-enriched phase penetrated into austenite grain boundaries and caused surface cracking during the hot working. In case of 0.6% Ni containing 1.2% Cu-Ni bearing steel, solid state Cu-Ni-riched phase existed at the scale/matrix interface as a discontinuous type. But the higher addition of 1.2% Ni, solid state Ni-Cu-riched phase was formed dominantly in the oxide scale. It was found that the addition of Ni suppressed the surface cracking of 1.2% Cu bearing steel by eliminating the liquid state Cu-enriched phase.

• Journal of Oral Medicine and Pain
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• v.20 no.2
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• pp.307-315
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• 1995

The purpose of this study was to assess the efficacy of several thermal therapies using ice pack, moist-hot pack and ultrasound, separately and concomitantly and to obtain the background information on the vascular changes after thermophysical therapies. The author had used 15 healthy subjects were examined and the subjects were divide into 5 groups : ice pack, moist-hot pack, ultrasound, ice pack and moist-hot pack, ice pack and ultrasound. Observation were made immediate before and 0,5,10,20,30,45,60,90 minutes after treatment. Thermography was performed in an Agema 870 thermovisio with 0.1$^{\circ}C$ difference of gradual temperature shift. The results were as follows : 1. Using ice pack only, the surface temperature of the masseter region was increased lapse of time, and most remarkably 90 minutes after the treatment. 2. Using moist-hot pack only, the surface temperature of the region was remarkably increased immediately after the treatment, but decreased lapse of time. 3. Using moist-hot pack with ice pack, the surface temperature of the face was remarkably increased immediately after the treatment, and decreased lapse of time, Hyperthermia was maintained for a longer time as compared with the group of moist-hot pack only. 4. Using ultrasound only, the surface temperature of the region was increased gradually, and most remarkably 30 minutes after the treatment, but decreased in the course of time. 5. Using ultrasound combined with ice pack, the surface temperature of the region was gradually decreased until 30 minutes after the treatment, and decrease to some extend at 45 minute. And then a gradual increase observed over the remaining period of the experiment. 6. Hyperthermia were maintained for a long time in the groups using ice pack combined with moist-hot pack and ultrasound as compared with the other groups. Our data suggest that ice pack can promote the efficacy of other thermal therapies.