• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.3
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• pp.354-363
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• 1997

The purpose of the present work is to show the best thermal storage material and the sensitivity of the parameters on the thermal performance by experimentally investigating the effects of the parameters on the thermal performance of the spherical capsule system using paraffins superior to the commercial one. The paraffins were n-Tetradecane and the mixture of n-Tetradecane 40% and n-Hexadecane 60%. The experimental parameters were the Reynolds number of 8, 12, and 16 and the inlet temperature of-7, -4, -1, and $2^{\circ}C$. The charging and the discharing time, the dimensionless thermal storage amount, and the averge heat transfer coefficient in the tank were obtained by utilizing the local temperature variation in the tank. The local charging and discharging time in the tank was axially and radially different a lot. The effects of the inlet temperature on the charging and the discharging time were larger during the charging process than during the discharging process, but the effects of the Reynolds number on the charging and the discharging time were in reverse order. The paraffins were better by 11~72% than the water with the inorganic material in the charging time aspect, but no difference in the discharging time aspect. The effects of the Reynolds number on the dimensionless thermal storage amount were smaller than the effects of the inlet temperature during the charging process, but in reverse order during the discharging process within the working range of the experimental parameters. The effects of the inlet temperature and the Reynolds number on the average heat transfer coefficient were larger during the discharging process than during the charging process. The average heat transfer coefficient for the paraffins was larger by 40% maximum than that for the commercial material during the charing and the discharging process.

• Proceedings of the Korean Magnestics Society Conference
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• 2007.05a
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• pp.183.1-183.1
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• 2007

• Tribology and Lubricants
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• v.9 no.1
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• pp.62-69
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• 1993

Friction and wear behavior of a carbon/carbon composite material for aircraft brake material was experimentally investigated. Friction and wear test setup was designed and built for the experiment. Friction and wear tests were conducted under various sliding conditions. Friction coefficients were measured and processed by a data acquisition system and amount of wear measured by a balance. Stainless steel disk was used as the counterface material. Temperature was also measured by inserting thermocouple 2.5 mm beneath the sliding surface of the carbon/carbon composite specimen. Wear surfaces were observed by SEM, and analyzed by EDAX. The experimental results showed that sliding speed and normal force did not have significant effects on friction coefficient and wear factor of the composite. Temperature increase just below the surface was not large enough to cause any thermal degradation or oxidation which occurred at higher temperature when tested by TGA. Wear film was generated both on the specimen and on the counterface at relatively low sliding speed but cracks, grooves, and wear debris were observed at high sliding speed. Friction coefficient remained almost constant when the sliding speed or normal load was varied. It is believed that the adhesive and abrasive components contributed mainly to the friction coefficient. Wear behavior at low sliding speed was governed by wear film formation and adhesive wear mechanism. At high speed, fiber orientation, ploughing by counterface asperities, and fiber breakage dominated wear of the carbon/carbon composite.

• Composites Research
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• v.16 no.6
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• pp.33-40
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• 2003

The initial thermal degradation of polymer matrix composite is not observed easily. At the beginning of thermal degradation of polymer matrix composites, phase transformation such as chain scission, oxidation occur, and then micro delamination is produced in matrix and interface between matrix and fiber before blistering. Initial heat damage deteriorate mechanical properties of composites. We presented the detection method of the initial heat damage of composites conveniently using ultrasonic technique. Absorption coefficient and material velocity was measured with thermal degradation and degree of cure. The more thermal degradation was progressed, the more absorption coefficient was increased. When the cure temperature is more high, the absorption coefficient of cured composite is increased and material velocity is decreased. We concluded that cure temperature is more high, the defects such as void is increased and molecular structure cured at high temperature has cross-linking structure which is more absorb the ultrasonic waves.

• Structural Engineering and Mechanics
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• v.64 no.5
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• pp.527-541
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• 2017

In this work, a new hyperbolic shear deformation beam theory is proposed based on a modified couple stress theory (MCST) to investigate the bending and free vibration responses of functionally graded (FG) micro beam made of porous material. This non-classical micro-beam model introduces the material length scale coefficient which can capture the size influence. The non-classical beam model reduces to the classical beam model when the material length scale coefficient is set to zero. The mechanical material properties of the FG micro-beam are assumed to vary in the thickness direction and are estimated through the classical rule of mixture which is modified to approximate the porous material properties with even and uneven distributions of porosities phases. Effects of several important parameters such as power-law exponents, porosity distributions, porosity volume fractions, the material length scale parameter and slenderness ratios on bending and dynamic responses of FG micro-beams are investigated and discussed in detail. It is concluded that these effects play significant role in the mechanical behavior of porous FG micro-beams.

• Food Engineering Progress
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• v.14 no.4
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• pp.354-358
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• 2010

The methods for determining the diffusion parameters for the diffusion of d-limonene, a major volatile compound of orange juice, through a multi-layered food packaging material and predicting its absorption into the packaging material have been investigated. The packaging material used was the 1.5-mm thick multi-layered packaging material composed of high impact polystyrene (HIPS), polyvinylidene chloride (PVDC), and low density polyethylene (LDPE). Orange juice was placed in a cell where volatiles were absorbed in the sample package and kept at $23{\pm}2^{\circ}C$ for 72 hr. The d-limonene absorbed in a 1.5-mm thick multi-layered food packaging material was analyzed by a solid phase micro-extraction (SPME). The absorption parameters for the absorption of d-limonene in the packaging material were determined and absorption of d-limonene into the packaging material was predicted using absorption storage data. The SPME desorption at $60^{\circ}C$ for 1 hr resulted in the most sensitive and reproducible results. The diffusion coefficients of d-limonene in the packaging material and the partition coefficient at $23{\pm}2^{\circ}C$ were approximately $1-2{\times}10^{12}m^2$/s and 0.03, respectively. The absorption profile no earlier than 30 hr was fit well by a model derived from the Fick's law.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.221-226
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• 2001

Chloride diffusion effect of cement paste, freezing and thawing test, carbonation of concrete specimen were carried out using inorganic coating material. According to the chloride ions diffusion test, it is elucidated that permeability and diffusion coefficient of Cl￣ ions and apparent coefficient of coated cement paste is smaller than plain cement paste. A durability of coated concrete specimen was enhanced by the experiment result of concrete carbonation and freezing thawing test.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.11a
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• pp.343-346
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• 1997

This paper presents the basic characteristics of Cr thin-film, which were deposited on glass by DC magnetron sputtering. The optimized deposition condition of Cr thin-film strain gauges were input power 7w/cm$^2$and the Ar working pressure was 9mtorr. GF(Gauge Factor), TCR(Temperature Coefficient of Resistance) and TCS(Temperature Coefficient of Sensitivity) of Cr thin-film strain gauges were 5.86, 400 ppm/$^{\circ}C$ and 0 ppm/$^{\circ}C$, respectively.

• Journal of the Microelectronics and Packaging Society
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• v.27 no.1
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• pp.67-73
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• 2020

In this paper, we used FEM technique to perform warpage and von Mises stress analysis on PCB according to the cavity structures of embedded PCB for FCCSP and the types of prepreg material. One-half substrate model and static analysis are applied to the FEM. According to the analysis results of the warpage, as the gap between the cavity and the chip increased, warpage increased and warpage increased when prepreg material with higher modularity and thermal expansion coefficient was applied. The analysis results of the von Mises stress show that the effect of the gap between the cavity and the chip varies depending on prepreg material. In other words, when material whose coefficient of thermal expansion is significantly higher than that of core material, the stress increased as the gap between the cavity and the chip increased. When the prepreg with the coefficient of thermal expansion lower than the core material is applied, the result of stress is opposite. These results indicate that from a reliability perspective, there is a correlation between the structure of the cavity where embedded chips are loaded and prepreg material.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.136-138
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• 2003

Strain states of clad sheets consisted of AL3003 and SUS430 were studied by FEM simulation. Main simulation parameters include roll size, reduction, material properties, material temperature, and friction between roll and material (or friction between materials). To investigate the effect of friction on the evolution of strain states, the friction coefficient between roll and material (or fraction coefficients between materials) was varied. Components of strain rate, strain were compared according to the variation of friction coefficients. And strain states during cladding were compared with those induced by simple rolling process.