• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.7
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• pp.992-997
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• 2012

In this paper, we were analyzed the vibration characteristics of the three-phase cast resin transformer using less than 50% of load in the field. Most of the cast resin transformer is less than 50% in the domestic field is used for load conditions. Consisting of a solid insulator cast resin transformer is generating lots of noise and vibration. In addition, because it is affected by Joule 's heat is used in light load conditions. As a results, the transformer vibrations at frequencies below about from 200Hz to 500Hz were detected. Vibration velocity depends on the load variations were found. Load up to approximately 20-30% in most cases the vibration velocity was found at 4,000 ${\mu}m/s$ or less, 8,000 ${\mu}m/s$ or more. Vibration frequency at light load conditions were generated at the 120Hz, 240Hz, 360Hz and 480Hz. At the load condition of from 10% to 20%, vibration velocity is higher than another. Most of the vibration velocity were identified at the 1,000 ${\mu}m/s$ or less. Using the vibration frequency and velocity measurements data, the load on the cast resin transformer analyzed the correlation of the burden. Therefore, this data could be found in the vibration characteristics of the light-load conditions. If the field measurements using the data perform diagnostics on the transformer, it's expected to be very effective.

• Journal of Institute of Convergence Technology
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• v.8 no.1
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• pp.21-25
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• 2018

We developed nano-porous $TiO_2-SiO_2$ composites (commercial name : PTI, porous titania insulator) with low thermal conductivity as thermal insulating material as well as function of photocatalyst. The objectives of this paper are, firstly, to evaluate of the thermal conductivity of the PTI powder in the temperature range from -160 to $250^{\circ}C$, secondly to evaluate of thermal conductivities of insulation materials that is applied PTI powder. The structure of the PTI powder that has the pores size of 20-30 nm and the particle diameter of 2-10 nm. The PTI had a high surface area of $400m^2/g$ and a mean pore size of $45{\AA}$, which was fairly uniform. The thermal conductivity was measured by GHP(guarded hot plate) method and HFM(heat flux method). The PTI structure is a three-dimensional network nano-structures composed by a pearl-necklace that involved a precious stone in the center of the necklace. The thermal conductivities of PTI-PX powder by the GHP and HFM were 0.0366 W/m.K, 0.0314 W/m.K at $20^{\circ}C$, respectively. This is similar to values that are proportional to the square of the absolute temperature of the thermal conductivity of static air. The thermal conductivities of insulating sheets coated with PTI powder were similar results with that of the PTI powder.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.6
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• pp.604-608
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• 2015

In this paper, we study the characteristics of heat transfer for an insulated multi-core tube using glass wool as an insulator for the multi-core tube. By performing experiments and modeling, we examine the variations in the temperature characteristics of hydraulic oil inside the multi-core tube with atmosphere temperature, inlet temperature, and the flow rate of hydraulic oil for the insulated multi-core tube that we developed. When the minimum inlet flow rate of hydraulic oil employed within the scope of the research is 0.29 l/min, the temperature difference obtained in the experiments and numerical analysis was a maximum of $3^{\circ}C$. For a constant atmospheric temperature, as the inlet temperature of the hydraulic oil increases, the outlet temperature of the hydraulic oil will also increase, regardless of its inlet flow rate. Further, when the inlet flow rate of the hydraulic oil is more than 1.01 l/min, the effect of the atmospheric temperature on the temperature drop of the hydraulic oil is low.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.6
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• pp.262-266
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• 2010

The Calcium-aluminate electride thin films on the quartz substrates was coated by sol-gel process. The crystallization of the C12A7 thin film was observed at $800^{\circ}C$ and high density C12A7 thin film was achieved on heat treatment at $1,200^{\circ}C$ for 1 hour. The reduction heat treatment of C12A7 thin film could be converted from insulator to conductor and the electrical conductivity was 120 S/cm in the C12A7 thin film heat treated at $1,200^{\circ}C$ with $H_2$ gas for 48 hours.

• Journal of the Korean Institute of Gas
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• v.16 no.2
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• pp.9-13
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• 2012

The present study has been carried out to diagnose the temperature safety of a boiler desuperheater which decreases abnormally higher temperature of superheated steam in a reheater of a power plant. The liquid water in the desuperheater stays in a closed space. It becomes heated by the high temperature superheated steam and boiling could occur. Boiling might increase internal pressure and it could destroy the desuperheater if the internal pressure exceeds the allowable pressure of the desuperheater. The present study modeled reasonably the desuperheater and four cases of heat transfer analysis are executed with the consideration of insulator and natural convective fluid flow of the inside cooling water. For the case excluded the natural convective fluid flow, the temperature exceeds the allowable temperature and pressure. On the other hand, for the real case included natural convective fluid flow and insulator, the active heat transfer from higher temperature region to lower temperature region occurs and it makes the temperature in the cooling water below the allowable temperature and pressure. From this fact, it could be thought that the desuperheater in the reheater is safe from destroy or back flow.

• Composites Research
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• v.19 no.1
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• pp.9-14
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• 2006

Experimental investigation on heat transfer ratio was firstly performed with three types of sandwich panels such as the Carbon/Epoxy Skin-Aluminum Honeycomb and Balsa Core Sandwich Panel of 37mm thickness, the Carbon/Epoxy Aluminum Skin-Honeycomb Core Sandwich Panel of 57mm thickness (including insulator) and the Carbon/Epoxy Skin-Aluminum Honeycomb Core Sandwich Panel of 37mm thickness based on the KS F 2278:2003(Insulation test method of windows). In additional to this investigation, experimental tests were also done for evaluation of heat transportation ratio with the Aluminum Skin- Aluminium Honeycomb Sandwich Panels of 27mm and 35mm thickness, and Aluminum Skin-Foaming Aluminum Sandwich Panel of 27mm thickness by the KS F2277:2002 (Insulation measuring method of construction component-Calibration heat box method or protective heat box method). In this study, it was found that the larger net heat transfer cross sectional area between the skin and the sandwich core is given, the higher heat transportation ratio occurs. It was also found that the hybrid type insulation had better insulation characteristics compared to the non-hybrid type insulation.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.5
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• pp.943-951
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• 1992

The objectives of this study are to analyse the thermal response behavior occurring in the charring ablative material more realistically by considering ablation and char phenomena occurring in several material layers, and to increase the reliability of thermal analysis by being able to get stable solutions through using the finite analytic method. A program has been developed to predict the temperature distribution, ablation thickness, char thickness, ablation velocity and char velocity by solving non-linear one-dimensional heat conduction equation. Results of calculation were compared with results of published papers. From this compariosn this program was proved to be a very good tool for thermal design and analysis of charring ablative materials used in the rocket propulsion system.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.21 no.2
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• pp.64-70
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• 2007

A voltage drop in the electrical circuit must be unavoidable. The voltage drop in the electrical circuit means a loss of heat. The heat lost would change the characteristics of the insulator and thus, the insulating performance would be towered resulting in electric leakage, electric shock, power failure, fire and other accidents. Hence, an optimized design against the voltage drop in the electrical circuit must be an important factor determining safety and economy of electrical facilities. This study analyzed the effects of voltage drop on the electrical circuit for such low-voltage electrical facilities requiring the public safety foremost and subject to multi-distributed random loads as street lamps, buildings and subway stations, and thereupon, developed an optimized voltage drop computation program to enhance safety and economy of those electrical facilities.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.4
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• pp.625-628
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• 2008

Ba-Zn ferrite powders for electromagnetic insulator were synthesized by self-propagating high-temperature synthesis(SHS) with a reaction of $xBaO_2+(1-x)ZnO+0.5Fe_2O_3+Fe{\rightarrow}Ba_xZn_{1-x}Fe_2O_4$. In this study, phase indentification of SHS products was carried out by using x-ray diffractometry and quasi-nano sized Ba-Zn powders were prepared by a pulverizing process. SHS mechanism was studied by thermodynamical analysis about oxidation reaction among $BaO_2,\;ZnO,\;Fe_2O_3$, and Fe. As oxygen pressure increases from 0.25 MPa to 1.0 MPa, the SHS reactions occur well and make clearly the SHS products. X-ray analysis shows that final SHS products formed with the ratio of $BaO_2/ZnO$ of 0.25, 1.0 and 4.0, are mainly $Ba_xZn_{1-x}Fe_2O_4$. Based on thermodynamical evaluation, the heat of formation increases in the order of $ZnFe_2O_4,\;BaFe_2O_4$, and $Ba_xZn_{1-x}Fe_2O_4$. This supports that $Ba_xZn_{1-x}Fe_2O_4$ phase is predominately formed during SHS reaction. The SHS reactions to form $Ba_xZn_{1-x}Fe_2O_4$ depends on oxygen partial pressure, and the heat of formation during the SHS reaction. The SHS reactions tends to occur well with increasing the oxygen partial pressure and BaO2/ZnO ratio in the reactants This means that the SHS reaction for the formation of Ba-Zn ferrite includes the reduction of BaO2/ZnO and the oxidation of Fe. $Ba_xZn_{1-x}Fe_2O_4$ powders after pulverizing is agglomeratedwith a size of about $50{\mu}m$, in which quasi-nano sized particles with about 300nm are present.

• Asian Journal of Turfgrass Science
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• v.4 no.1
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• pp.49-55
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• 1990

Experiments were conducted to investigate the relationships between the soil freezing depth and the accumulated degree-day of temperature below $0^{\circ}C$ at 17 locations during 1989-1990 winter season in kangwon province. The observed results are as follows : 1.When accumulated degree-day of temperature below at was 141t at late January soil freezing depth of sunny place was 46.5cm, that of shaded lot was 59 cm, and that of marginal place sunny or shaded area was 55cm, in Chun cheon. 2.Accumulated degree-day of temperature below at of Dae gwangryong area was more than that of Un-du, whereas soil freezing depth of Dae gwangryong was lower that of Un-du. It was considered that snow covering worked as heat insulator. 3.Soil freezing depth of vinyl mulching on Zoysia turf was less by around 2Ocm than that of non-vinyl mulching. Rice hulls covering of 4Ocm showed the great heat insulation effects with the soil freezing depth of 1.5cm at sunny place and 6.5cm at shaded lot compared to that of 47cm at sunny and 59.5 cm at shaded place bare ground. 4.Among investingated areas, Dunae, Honeg seong gun was the deepest soil freezing, 89cm with $569^{\circ}C$ of accumulated degree-day of temperature below $0^{\circ}C$ at late February. 5.dehydration of Juniperus C. var. Kaizuca, Euonymus japonica, and Chamaecyparis pisifira at winter season was around 5 %, however dehydration of Vinca minor was more than 10 %. A Studies on the Soil Freezing Depth and Change of Moisture contents in evergreen Plants upon subzero Temperature in Kangwon area.(2)