• 한국전산유체공학회:학술대회논문집
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• 2002.05a
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• pp.109-114
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• 2002

The effect of nose radius on aerodynamic heating are investigated by using the Wavier-Stokes code extended to thermochemical nonequilibrium airflow. A spherical blunt body, whose radius varies from 0.003048 m to 0.6096 m, flying at Mach 25 at an altitude of 53.34 km is considered. Comparison of heat flux at stagnation point with the solution of Viscous Shock Layer and Fay-Riddell are made. Obtained result reveals that the flow chemistry for very small radius is nearly frozen, and therefore the contribution of heat flux due to chemical diffusion is smaller than that of translational energy. As the radius becomes larger, the portion of diffusion heat flux becomes greater than translational heat flux and approaches to a constant value.

• Journal of the Korean Society of Food Culture
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• v.4 no.4
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• pp.405-410
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• 1989

The sensory quality describing terms of Takju were surveyed by questionair and classified according to the sensory characteristics. The effects of thermal treatment for the pasteurization of Takju on the sensory quality were tested and statistically evaluated. The important sensory quality attributes of Takju were white, gray, and yellow for color, acidic and yeasty for smell, sour, astringent, bitter and sweet for taste and gritty, viscous and carbonated for mouthfeel. The organoleptic properties of grayness, yeasty and cooked smell, astringent and bitter taste and thickness increased, while sourness, sweetness, yellowness, grittiness and carbonated feel decreased by the pasteurization treatments, heating $82^{\circ}C$, $93^{\circ}C$ or $135^{\circ}C$ for 9 seconds. These changes coincided with the overall reductions in the preference scores of pasteurized Takju. The degree of sensory quality deterioration appeared to be affected to some extent by the heating temperature.

• Journal of the Korean Society for Heat Treatment
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• v.29 no.2
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• pp.51-55
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• 2016

The P/M processing of titanium aluminide using amorphous TiAl is developed by which it is possible to overcome inherent fabricability problems and to obtain a fine microstructure. A high quality amorphous TiAl powder produced by reaction ball milling shows clear glass transition far below a temperature at the onset of crystallization in differential scanning calorimetry above a heating rate of 0.05 K/s. We obtained a fully dense compact of amorphous TiAl powders, encapsulated in a vacuumed can, via viscous flow by hot isostatic pressing (HIP). Isothermally annealing of HIP'ed amorphous compact under a pressure of 196 MPa shows a progressive growth of ${\gamma}-TiAl$ phase with ${\alpha}2$ ($Ti_3Al$), which is characterized by increasing sharpness of X-ray peaks with temperature. Fully dense HIP'ed compact of titanium aluminide TiAl shows a high hardness of 505 Hv, suggesting strengthening mechanisms by sub-micron sized grain of ${\gamma}-TiAl$ and particle-dispersion by second phase constituent, ${\alpha}2$.

• Tribology and Lubricants
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• v.25 no.2
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• pp.86-95
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• 2009

Adhesion tests were carried out in order to investigate the effect of temperature on the adhesion behavior between a PMMA film and a fused silica lens in the micro scale. For the tests, a microtribometer system was specially designed and constructed. The pull-off forces on the PMMA film were measured under atmospheric condition as the temperature of the PMMA film was increased from 300 K to 443 K and decreased to 300 K. The contact area between the PMMA film and the lens was observed during the test. The adhesion behavior was changed with the change of the PMMA surface state as the temperature increased. In glassy state below 363 K, the pull-off force did not change with the increase of temperature. In rubbery state from 383 K to 413 K, the pull-off force increased greatly as the temperature increased. In addition, the area of contact was enlarged. In viscous state above 423 K, the fingering instability was observed in the area of contact when the PMMA film contacted with the lens. It was also found that the adhesion behavior can be varied with the thermal history of the PMMA film. The residual solvent in the PMMA film could emerge to the PMMA surface due to the heating and reduced the pull-off force.

• Journal of computational fluids engineering
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• v.2 no.2
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• pp.59-72
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• 1997

A numerical model is constructed to simulate the interactions of oblique shock wave / turbulent boundary layer on a strongly heated wall. The heated wall temperature is two times higher than the adiabatic wall temperature and the shock wave is strong enough to induce boundary layer separation. The numerical diffusion in the finite volume method is reduced by the use of a higher order convection scheme(UMIST scheme) which is a TVD version of QUICK scheme. The turbulence model is Chen-Kim two time scale model. The comparison of the wall pressure distribution with the experimental data ensures the validity of this numerical model. The effect of strong wall heating enlarges the separation region upstream and downstream. In order to eliminate the separation, wall suction is applied at the shock foot position. The bleeding slot width is about same as the upstream boundary layer thickness and suction mass flow is 10% of the flow rate in the upstream boundary layer. The final configuration of the shock reflection pattern and the wall pressure distribution approach to the non-viscous value when wall suction is applied.

• Journal of the Korean Society of Combustion
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• v.5 no.1
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• pp.31-41
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• 2000

A numerical study was conducted to investigate the combustion phenomena of regular start and unstart processes based on ISL#s RAMAC 30 experiments with different diluent amounts in a ram accelerator. The initial projectile launching speed was 1800m/s which corresponded to the superdetonative speed of the stoichiometric $H_2/O_2$ mixture diluted with $5CO_2\;or\;4CO_2$. In this study, it was found that neither shock nor viscous heating was sufficient to ignite the mixture at a low speed of 1800m/s, as was found in the experiments using a steel-covered projectile. However, we could succeed in igniting the mixtures by imposing a minimal amount of additional heat to the combustor section and simulate the regular start and unstart processes found in the experiments with an aluminum-covered projectile. The numerical results matched almost exactly to the experimental results. As a result, it was found that the regular start and unstart processes depended on the strength of gas mixture, development of shock-induced combustion wave stabilized by the first separation bubble, and its size and location.

• Journal of Astronomy and Space Sciences
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• v.19 no.3
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• pp.181-186
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• 2002

We study a role of the proto-accretion disk during the formation of the planetary system, which is motivated with recent X-ray observations. There is an observational correlation of the mass of extrasolar planets with their orbital period, which also shows the minimum orbital period. This is insufficiently accounted for by the selection effect alone. Besides, most of planetary formation theories predict the lower limit of semimajor axes of the planetary orbits around 0.01 AU. While the migration theory involving the accretion disk is the most favorable theory, it causes too fast migration and requires the braking mechanism to halt the planet~0.01 AU. The induced gap in the accretion disk due to the planet and/or the truncated disk are desperately required to stop the planet. We explore the planetary evaporation in the accretion disk as another possible scenario to explain the observational lack of massive close-in planets. We calculate the location where the planet is evaporated when the mass and the radius of the planet are given, and find that the evaporation location is approximately proportional to the mass of the planet as ${m_p}^{-1.3}$ and the radius of the planet as ${r_p}^{1.3}$. Therefore, we conclude that even the standard cool accretion disk becomes marginally hot to make the small planet evaporate at~0.01 AU. We discuss other auxiliary mechanisms which may provide the accretion disk with extra heats other than the viscous friction, which may consequently make a larger planet evaporate.

• Tribology and Lubricants
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• v.25 no.4
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• pp.207-216
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• 2009

Friction tests were carried out in order to investigate the effects of temperature on the friction and wear behaviors between a PMMA film and a fused silica lens using a microtribometer. The friction forces on the PMMA film were measured under atmospheric condition as the temperature of the film was increased from 300 K to 443 K. The contact area between the film and the lens was observed. The tribological characteristics of the film were significantly changed as the temperature increased. The changes were discussed with the change of the film state from glassy to viscous flow. In addition, the results showed that the friction behavior can be varied with the thermal history of the PMMA film. Residual solvent in the PMMA film could emerge to the PMMA surface due to an additional heating and the solvent on the film surface decreased the friction force.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.4
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• pp.12-23
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• 2004

The effects of improved rice bran oil on the characteristics of exhaust emissions have been experimentally examined by a single cylinder, four cycle, direct injection, water-cooled agricul-tural diesel engine operating at several loads and speeds. The experiments are conducted with light oil, rice bran oil, and improved rice bran oil as a fuel. The fuel injection timing is fixed to 22$^{\circ}$ BTDC regardless of fuel types, engine loads and speeds. To reduce the viscosity of rice bran oil, it is used with the methods of heating, methyl ester and ultrasonic system in a highly viscous rice bran oil. In this study, it is found that the brake specific fuel consumption rate of light oil is the lowest and that of improved rice bran oils is lower than that of pure rice bran oil, and NO$_{x}$ emissions of light oil are the lowest and those of pure rice bran oil are the high- est, while soot emissions of light oil are the highest and those of pure and improved rice bran oils are lower than that of light oil. However these results are not amply satisfied with the emissions regulation limit using the pure and improved rice bran oil as fuels in diesel engines.s.

• Transactions of Materials Processing
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• v.22 no.6
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• pp.323-327
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• 2013

In this paper, the flow lines as a function of product design as well as the forging process design are explored using typical application examples. The prediction of flow lines using metal forming simulation technology is introduced along with their characterization. Experimental studies have shown that the metal flow lines have a strong influence on the structural rigidity of the final product. In this study we present several typical applications. One example is the case of severely cut metal flow lines during machining, especially in the region where periodic contacting forces are applied. Another example is the case of abnormal distortion of flow lines which can cause too much elongation or hot shortness due to viscous heating in the region of distortion. A third example is the case of a macrosegregation region which needs to be controlled so it is not adjacent to the region where the force is applied in the use of the final component. An example of weight reduction for an automobile component with improved flow lines is also introduced. These typical applications can provide process engineers with the insight in designing automobile or mechanical components as well as in designing the manufacturing methods to produce various parts.