• Solar Energy
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• v.15 no.1
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• pp.13-28
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• 1995

In this study, the history of Korean traditional Ondol was investigated and the latent heat materials and bioceramics were selected to develop the latent heat storage-bioceramics Ondol system based on the Korean traditional Ondol(sensible heat storage type), and the thermal characteristics of Ondol were analyzed experimentally The results could be summarized as follows; 1. Korean traditional Ondol has been originated in "Whaduk" which had been utilized continuously for about $2{\times}10^6$ years from the Old Stone Age to the Bronze Age, and Korean traditional Ondol using in these days has been utilized for about 976 years from the Koryu Dynasty to the Modern Ages. 2. $Na_2SO_4{\cdot}10H_2O(SSD)$ was selected as latent heat material for the latent heat storage Ondol. 3. Ondol unit was filled with the latent heat material of 0.63 kg and the dimension of Ondol unit was $400mm{\times}400mm{\times}27mm(width{\t\imes}depth{\times}height)$. 4. The comfortable surface temperature($23{\sim}29^{\circ}C$) of the latent heat storage Ondol was lasted 5 hours at the room temperature of $16{\sim}18^{\circ}C$, whereas that of sensible heat storage Ondol was lasted only 1.0 hours in the same conditions. 5. For the thermal effect of bioceramics, the Ondol air temperature i.n case of bioceramics treatment on the pannel was higher than that of without bioceramics treatment.

• Korean Journal of Optics and Photonics
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• v.19 no.5
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• pp.381-385
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• 2008

We have analyzed the effect of the substrate removal and packaging schemes on light output characteristics in InGaN/Sapphire LEDs. The removal of the sapphire substrate helps to dissipate the heat generated in the junction, but the advantage comes only with the detrimental effect of degrading the photon extraction efficiency. If the substrate-removed chip is attached to a metallic mount with good thermal conductivity, the maximum driving current is increased drastically, producing significantly increased light output and therefore compensating the photon extraction efficiency degradation. On a dielectric mount with a relatively poor thermal conductivity, however, it produces smaller light output, over most input current range, than the regular type of chips with the sapphire substrate remaining. Thus, for low power applications, the regular chips may be preferred over the substrate-removed chips, regardless of the chip mounts employed.

• Composites Research
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• v.35 no.2
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• pp.69-74
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• 2022

In this study, the conductive paste used in a wide range such as wiring in the electronic packaging field, the automobile industry, and electronic products is manufactured under various process conditions due to the simplicity of the process, and then the thermal, mechanical, and electrical characteristics are analyzed and simulation studies are conducted to optimize the process. to establish the conditions of the conductive paste manufacturing process. First, a conductive paste was prepared by setting various types of binder resin, an essential component of the conductive paste, and characteristics such as thermal conductivity, tensile strength, and elongation were analyzed. Among the binder resins, the conductive paste applied with a flexible epoxy material had the best physical properties, and a simulation study was conducted based on the physical property data base of the conductive face. As a result of the simulation, the best physical properties were exhibited when the Ag flake volume fraction was 60%.

• Tribology and Lubricants
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• v.38 no.2
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• pp.41-52
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• 2022

Mineral electrical insulating oil, which is widely used in transformers, exhibits excellent cooling performance and transformer efficiency. However, given that it is composed of petroleum-based components, it is weak in terms of biodegradability. This causes environmental problems in case of leakage and a low flash point, which is a factor that would cause great damage in the event of a fire in a substation. In this context, the use of eco-friendly electric insulating oil composed of bio-based vegetable oil and synthetic ester, which has excellent biodegradability and flame retardancy performance, has recently been expanded to the field of electric power, and various research and development (R&D) studies are in progress. According to different research results, vegetable oil and synthetic ester manufacturing technology, thermal stability, oxidation stability, property change, and quality control, which are characteristics of eco-friendly electrical insulating oils, are major factors affecting the maintenance of insulating oil properties. In addition, power companies have established and operated quality control standards according to the use of eco-friendly electrical insulating oil as they expand the exploitatoin of renewable energy in electricity production. In particular, deterioration and oxidation characteristics were jointly identified in R&D as an important influencing factor according to the content of saturated and unsaturated fatty acids present in vegetable oils and synthetic esters in power transformer applications.

• Journal of the Korean Society of Propulsion Engineers
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• v.26 no.4
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• pp.21-27
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• 2022

In this paper, the combustion characteristics of solid propellant embedded with metal wires were analyzed by the ground tests of motors. The propellant grains were made of thermoplastic propellants with Al and Cu as metal wires for the enhancement of burning area and designed with cone shape for better ignition. These metals were used to confirm the enhancement of burning rate on thermal diffusivity properties. The internal ballistics analysis and ground test were performed to investigate the effect of burning rate for each metal wire. We obtained the results of burning rate on a difference of thermal diffusivity of each metal wire with well-made propellant grains.

• Smart Structures and Systems
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• v.20 no.3
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• pp.369-383
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• 2017

In this work, the effects of moisture and temperature on free vibration characteristics of functionally graded (FG) nanobeams resting on elastic foundation is studied by proposing a novel simple trigonometric shear deformation theory. The main advantage of this theory is that, in addition to including the shear deformation influence, the displacement field is modeled with only 2 unknowns as the case of the classical beam theory (CBT) and which is even less than the Timoshenko beam theory (TBT). Three types of environmental condition namely uniform, linear, and sinusoidal hygrothermal loading are studied. Material properties of FG beams are assumed to vary according to a power law distribution of the volume fraction of the constituents. Equations of motion are derived from Hamilton's principle. Numerical examples are presented to show the validity and accuracy of present shear deformation theories. The effects of hygro-thermal environments, power law index, nonlocality and elastic foundation on the free vibration responses of FG beams under hygro-thermal effect are investigated.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.9
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• pp.916-922
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• 2008

Structures being used in space environment, should be designed to have minimum CTE(coefficient of thermal expansion) for the dimensional stability. Accurate CTE data of the materials are required to design the space structures consisting of various materials. There are uncertainties in the characteristics of materials even though the same manufacturing processes are applied. Therefore, it is needed to measure the thermal deformation of not only the material specimen but also substructures in simulated space environment, such as high vacuum condition. In this research, therefore, precise CTE measurement system using displacement measuring interferometer and vacuum chamber has been designed with uncertainty analysis of the measurements. This system can be used to measure the CTE of the specimen or thermal expansion of the substructure with varying size up to 50cm in length. To measure the low CTE material, overall uncertainty of this system is expected under 0.01ppm/K.

• Journal of Powder Materials
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• v.16 no.2
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• pp.115-121
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• 2009

The effects of thermal treatment conditions on ADU (ammonium diuranate) prepared by SOL-GEL method, so-called GSP (Gel supported precipitation) process, were investigated for $UO_2$ kernel preparation. In this study, ADU compound particles were calcined to $UO_3$ particles in air and Ar atmospheres, and these $UO_3$ particles were reduced and sintered in 4%-$H_2$/Ar. During the thermal calcining treatment in air, ADU compound was slightly decomposed, and then converted to $UO_3$ phases at $500^{\circ}C$. At $600^{\circ}C$, the $U_3O_8$ phase appeared together with $UO_3$. After sintering of theses particles, the uranium oxide phases were reduced to a stoichiometric $UO_2$. As a result of the calcining treatment in Ar, more reduced-form of uranium oxide was observed than that treated in air atmosphere by XRD analysis. The final phases of these particles were estimated as a mixture of $U_3O_7$ and $U_4O_9$.

• Journal of the Korean Society of Safety
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• v.30 no.5
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• pp.1-7
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• 2015

This paper is aimed to analyze the electrical and thermal signal such as ignition possibility, ignition time, thermal characteristics and arc fault power that are associated with electrical fire in case of the occurrence of series arc at IV wiring used for interior wiring at commercial power source. In order to analyze the signal, series arc was induced by generating the constant vibration through vibrating device in the one phase (R phase) and ignition possibility was analyzed along the condition of current value by adding cotton material to the contact point of wiring. The ignition time is shortened as the electric current value increased, burning time is not associated with current value and the temperature rose up to $740^{\circ}C$ though it was not ignited. It was checked out that the temperature was the energy source enough that can generate the fire related with insulation aging of wiring and the inflammable. The possibility of electrical fire by series arc was shown as more than 12% at 5A, more than 42% at 20A and arc showed 27W at 5A, 180W at 20A. It was confirmed that the possibility of electrical fire exists at the condition as above and the circuit breaker did not operate. This data can be used as the reference value for the investigation of electrical fire or development of the circuit breaker.

• ETRI Journal
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• v.26 no.4
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• pp.315-320
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• 2004

This paper proposes a 10-${\mu}m$ thick oxide layer structure that can be used as a substrate for RF circuits. The structure has been fabricated using an anodic reaction and complex oxidation, which is a combined process of low-temperature thermal oxidation (500 $^{\circ}C$ for 1 hr at $H_2O/O_2$) and a rapid thermal oxidation (RTO) process (1050 ${\circ}C$, for 1 min). The electrical characteristics of the oxidized porous silicon layer (OPSL) were almost the same as those of standard thermal silicon dioxide. The leakage current density through the OPSL of 10 ${\mu}m$ was about 10 to 50 $nA/cm^2$ in the range of 0 to 50 V. The average value of the breakdown field was about 3.9 MV/cm. From the X-ray photo-electron spectroscopy (XPS) analysis, surface and internal oxide films of OPSL prepared by a complex process were confirmed to be completely oxidized. The role of the RTO process was also important for the densification of the porous silicon layer (PSL) oxidized at a lower temperature. The measured working frequency of the coplanar waveguide (CPW) type short stub on an OPSL prepared by the complex oxidation process was 27.5 GHz, and the return loss was 4.2 dB, similar to that of the CPW-type short stub on an OPSL prepared at a temperature of 1050 $^{\circ}C$ (1 hr at $H_2O/O_2$). Also, the measured working frequency of the CPW-type open stub on an OPSL prepared by the complex oxidation process was 30.5 GHz, and the return was 15 dB at midband, similar to that of the CPW-type open stub on an OPSL prepared at a temperature of $1050^{\circ}C$ (1 hr at $H_2O/O_2$).