• Journal of the Korean Ceramic Society
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• v.41 no.4
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• pp.297-301
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• 2004

Nano-sized mullite (3Al$_2$O$_3$$.$2SiO$_2$) colloids were prepared by use of the spray combustion method. For combustion reaction, Al(NO$_3$)$_3$$.$9$H_2O$, and CH$_{6}$N$_4$O were used as an oxidizer and a fuel respectively, and then colloidal silica was also added as 2SiO$_2$source for mullite. The temperature of the reaction chamber was kept at 80$0^{\circ}C$ to initiate the ignition of droplets of the mixed precursors. For preventing droplet coagulation, the droplet number concentration was reduced using the metal screen filter, and the residence time of aerosol was kept at 2.5 seconds for laminar flow. The synthesized colloidal particles had an uniform spherical shape with 130 nanometer size and the crystalline phase showed the mullite with stoichiometry in the observations of XRD and TEM.

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.335-342
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• 2003

In order to analyze the deformational behavior accurately, the in-situ testing technique which provides the reliable deformational characteristics at whole strain ranges, needs to be developed. The pressuremeter is a unique method for assessing directly the in-situ shear modulus of soils with strain amplitude. This paper introduces a new alternative, the cavity strain measuring system in pressuremeter designed for whole strain ranges of $10^{-5}$%∼20%. Not only in the synthetic calibration chamber but also in the field, the pressuremeter tests were performed to determine the compliance of the new developed pressuremeter system. The variation in shear modulus with strain amplitude above $5\times 10^{-2}$% was reliably determined by the developed pressuremeter. It is concluded that the major cause of error in small cavity strain measuring is not from the cavity strain measuring system but from the friction between measuring arm and membrane during unloading-reloading loops.

• KIEAE Journal
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• v.17 no.1
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• pp.83-89
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• 2017

Purpose: Thermal sensation or thermal comfort was randomly used in many studies which focused on combined effects of thermal and acoustic environments on human perception. However, thermal sensation and thermal comfort are not synonyms. Thermal comfort is more complex human perception on thermal environment than thermal sensation. This study aims to investigate effects of noise on thermal sensation and thermal comfort separately, and also to investigate effects of temperature on acoustic sensation and comfort. Method: Combined thermal and acoustic configurations were simulated in an indoor environmental chamber. Twenty four participants were exposed to two types of noise (fan and babble) with two noise levels (45 dBA and 60 dBA) for an hour in each thermal condition of PMV-1.53, 0.03, 1.53, 1.83, respectively. Temperature sensation, temperature preference, thermal comfort, noisiness, loudness, annoyance, acoustic comfort, indoor environmental comfort were evaluated in each combined environmental condition. Result: Noise did not affected thermal sensation, but thermal comfort significantly. Temperature had an effect on acoustic comfort significantly, but no effect on noisiness and loudness in overall data analysis. More explicit interactions between thermal condition and noise perception showed only with the noise level of 60 dBA. Impacts of both thermal comfort and acoustic comfort on the indoor environmental comfort were analyzed. In adverse thermal environments, thermal comfort had more impact than acoustic comfort on indoor environmental comfort, and in neutral thermal environments, acoustic comfort had more important than thermal comfort.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.44-44
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• 2008

GdBCO coated conductor have been fabricated using reactive co-evaporation. The batch type co-deposition system was specially designed and was named EDDC (evaporation using drum in dual chamber) that is possible to deposit superconducting layer with optimum composition ratio of materials at temperature over $700^{\circ}C$ and several mTorr of oxygen. The IBAD-MgO substrate with the architecture of LaMnO3(LMO)/IBAD-MgO/Hastelloy was used for coated conductor. In this study, GdBCO superconducting layer was deposited on IBAD-MgO substrate at optimal oxygen partial pressure (pO2) and deposition temperature. After fabrication of GdBCO coated conductor, critical current density was measured by 4-probe method. Surface morphology and texture of GdBCO coated conductors were analyzed by the SEM and XRD, respectively.

• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.6
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• pp.1-6
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• 2011

An experimental study has been conducted to scrutinize into the influence of ultrasonic standing wave field on the variation of methane/air premixed flame structure. Visualization technique utilizing the Schlieren method is employed for the observation of premixed flame propagation. The shape of flame front and local flame velocity are measured according to the variation of reactants pressure and chamber opening/closing condition. The flame fronts affected by the standing wave are clearly distorted but the vertical locations of frontal dents do not undergo any appreciable change. The influence of standing wave on the flame front becomes more prominent as the flame propagates downward. It is found that the propagation velocity of flame front with excitation of standing wave is greater than the case without the excitation. It is eventually revealed that the flame is deformed to lotus-shaped one by the vivid interaction of ultrasonic standing-wave with the reflected wave coming from the right side.

• Korean Journal of Optics and Photonics
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• v.5 no.3
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• pp.386-393
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• 1994

We have investigated output characteristics of XeCI excimer laser excited by transeverse electronbeam. We used e-beam output of 880 kV, 21 kA (70 ns, FWHM) and controlled current density of e-beam by pulsed magnetic coil (4.7 kG) which was fabricated around an e-beam diode (A-K gap is 21 mm) and laser chamber. We have obtained 35 J (4 atm) of e-beam deposition energy injected into laser media. The deposition energy was converted from an exposure area of Radcolor film and rising pressure of gas media which is measured by pressure jump method. The excited volume of $320cm^{3}$ was calculated. The maximum efficiency of 1.7% was obtained with the mixing ratio of HCllXe/Ar==0.2/ 6.3/93.5% and total pressure of 3 atm. Also laser output energy and specific energy were obtained 0.52 J and 1.7 J/I, respectively. For the analysis of experimental results we have developed computer simulation code. From the good agreements with the results of experiment and simulation we could theoretically explain the XeCI* formation channel. relaxation channel, and absorption channel of 308 nm.308 nm.

• Journal of Energy Engineering
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• v.23 no.4
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• pp.247-255
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• 2014

The present study was conducted to elucidate the characteristics of temperature at the inlet and outlet pipes of a refrigerator drain condenser and suggest the method to predict the temperature of the refrigerant at the inlet and outlet pipes of the drain condenser. For this purpose, a built in style refrigerator was installed in a constant temperature chamber to measure temperatures at the inlet and outlet pipes of the drain condenser. From the results of the present analysis, it could be seen that the measured temperatures changed from $37^{\circ}C$ to $46^{\circ}C$ and the actual refrigerant temperatures were higher than the measured temperatures with the difference magnitude of $8^{\circ}C$ to $22^{\circ}C$. The present study suggested that the temperatures of the refrigerator could be calculated with the measured temperatures by introducing curve fitting of the measured temperature. The predicted refrigerant temperatures by the present study had the accuracy within 6% error of the actual refrigerant temperatures.

• Journal of Sensor Science and Technology
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• v.29 no.1
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• pp.27-32
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• 2020

This study proposes a pixel-patterning method for organic light-emitting diodes (OLEDs) based on thermal transfer. An infrared lamp was introduced as a heat source, and glass type donor element, which absorbs infrared and generates heat and then transfers the organic layer to the substrate, was designed to selectively sublimate the organic material. A 200 nm-thick layer of molybdenum (Mo) was used as the lightto-heat conversion (LTHC) layer, and a 300 nm-thick layer of patterned silicon dioxide (SiO₂), featuring a low heat-transfer coefficient, was formed on top of the LTHC layer to selectively block heat transfer. To prevent the thermal oxidation and diffusion of the LTHC material, a 100 nm-thick layer of silicon nitride (SiN_x) was coated on the material. The fabricated donor glass exhibited appropriate temperature-increment property until 249 ℃, which is enough to evaporate the organic materials. The alpha-step thickness profiler and X-ray reflection (XRR) analysis revealed that the thickness of the transferred film decreased with increase in film density. In the patterning test, we achieved a 100 ㎛-long line and dot pattern with a high transfer accuracy and a mean deviation of ± 4.49 ㎛. By using the thermal-transfer process, we also fabricated a red phosphorescent device to confirm that the emissive layer was transferred well without the separation of the host and the dopant owing to a difference in their evaporation temperatures. Consequently, its efficiency suffered a minor decline owing to the oxidation of the material caused by the poor vacuum pressure of the process chamber; however, it exhibited an identical color property.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.763-768
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• 2012

Active window system which can reduce the environmental noises, such as traffic noise and construction noise, from an open window into a room was proposed in the previous works. The key idea of the proposed active window system was that the control sources are approximately collocated with the primary noise source in terms of the acoustic power for global noise reduction throughout the interior room. Moreover, because it is important not to intrude into the living space in the building environment, no error sensors were used and an open-loop control method using control sources at the window frame and the reference sensors outside the room was used for the proposed system. The open-loop control gain was calculated by the interior room model assumed as the semi-infinite space, and the interior sound field was estimated by Rayleigh integral equation under the baffled window model assumption. However, windows with a finite thickness should were considered for the calculation of the open-loop control gain of the active window system since these are representative of most window cases. Therefore, the finite thickness window model based on the Sgard's model was derived and the open-loop control gain using the interior sound field estimated by that model was calculated for active window system. To compare the performance of these two models, a scale-model experiment was performed in an anechoic chamber according to noise source directions. Experimental results showed that the performance for the thickness window model is better than the baffled window model as the angle with respect to the perpendicular direction is larger.

• Journal of the Korean Ceramic Society
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• v.35 no.2
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• pp.172-179
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• 1998

Valve lifter namely tappet is supported by lifter hole which is located upper side of camshaft in cylinder block transforms rotatic mvement of camshaft into linear movement and helps to open and shut the en-gine valve as an engine parts. The face of valve lifter which is continuously contacting with camshaft brings about abnormal wears such as unfair wear and early wear because it is severely loaded in the valve train system. These wears act as a defect like over-clearance and cause imperfect combustion of fuel during the valve lifting in the combustion chamber. Consequently this imperfect combustion makes the engine out-put decrease and has cause on air pollution. To prevent these wears therefore The valve lifter cast in me-tal developed into SiC ceramics valve lifter which has an excellence in wear and impact resistance As a results the optimum process conditions like injection condition mixture ratio and debonding process could be established. After sintering fine-sinered dual microstructure in which prior ${\alpha}$-SiC matches well with new SiC(${\beta}$-SiC) produced by reaction among the ${\alpha}$-SiC carbon and silicon was obtained. Based on the study it is verified that mechanical properties of SiC valve lifter are excellent in Vickers hardness 1100-1200 bending strength (300-350 Pa) fracture toughness(1.5-1.7 Mpa$.$m1/2) Through engine dynamo test-ing SiC valve lifter and metal valve lifter are examined and compared into abnormal phenomena such as early fracture unfair and early wear. It is hoped that this research will serve as an important springboard for the future study of heavy duty diesel engine parts developed by ceramics which has a good wear resis-tance relaibility and lightability.