• 대한기계학회논문집B
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• 제29권9호
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• pp.1065-1073
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• 2005

The thermal conductivity of water- and ethylene glycol-based nanofluids containing alumina $(Al_2O_3)$, zinc oxide (ZnO) and titanium dioxide $(TiO_2)$ nanoparticles is measured by varying the particle diameter and volume fraction. The transient hot-wire method using an anodized tantalum wire for electrical insulation is employed for the measurement. The experimental results show that nanofluids have substantially higher thermal conductivities than those of the base fluid and the ratio of thermal conductivity enhancement increases linearly with the volume fraction. It has been found that the ratio of thermal conductivity enhancement increases with decreasing particle size but no empirical or theoretical correlation can explain the particle-size dependence of the thermal conductivity. This work provides, for the first time to our knowledge, a set of consistent experimental data over a wide range of nanofluid conditions and can therefore serve as a basis for developing theoretical models to predict thermal conduction phenomena in nanofluids.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.372-378
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• 2005

Finite element analysis of concrete slab system in apartment building was executed using the tables of orthogonal arrays, and optimal design process was proposed. At first, experimental results show that sound peak components to influence the overall level and the rating of floor impact sound insulation were coincident with natural frequencies of the reinforced concrete slab. Finite element model of concrete slab was compared with experimental results, and well corresponded with an error of less than 10%. The tables of orthogonal arrays were used for finite element analysis with 8 factors. 3 related to material properties and 5 related to slab shape parameters and its results were analyzed by statistical method, ANOVA. The most effective factor among them was slab thickness, and main effect factor from slab shape parameters was different from each natural frequency. The interaction was found in the higher mode over $3^{rd}$ natural frequency. From main effect plot and interaction plot, the optimal design factor to increase the natural frequency was determined.

• Transactions on Electrical and Electronic Materials
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• 제14권1호
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• pp.20-23
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• 2013

When applying superconducting wire to power machines, an investigation needs to be carried out on the characteristics of wire phase changes in connection with the insulating layer. This study examined trends in the increase of the wire's resistance and the characteristics of its recovery from quenching by a current-applied cycle at temperatures of 90 K, 180 K, and 250 K. The procedure was conducted based on the thickness and presence (or absence) of the insulating wire layers. To achieve this, YBCO thin-film wires with the same critical temperatures were prepared with copper and stainless steel stabilizing layers. At levels (-one, three, and five-), with superior performance, polyimide pressure-sensitive adhesive tape was attached to the wires at a very low temperature. The eight prepared test samples were wound around the linear frames. The wire's voltage and current created from the phase change characteristics were measured at the wire's prescribed temperature, using the four-point probe method. The wire's resistance and recovery characteristics were examined for each cycle at temperatures of 90 K, 180 K, and 250 K.

• 조명전기설비학회논문지
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• 제28권9호
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• pp.73-82
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• 2014

This research proposes a new type of flyback converter topology based on magnetic circuit sharing. The proposed flyback topology uses a transformer involving shared magnetic flux, and its characteristic is magnetic flux cancelation by cross magnetic flux in the magnetic flux-sharing part of the core. The new topology aims to reduce the volume of transformer by reducing the cross section of the core. Compared to conventional converters using only 1 transformer, its circuit configuration involving the serial input and parallel output of 2 flyback coils allowed increased converter insulation strength. In addition, the adoption of interleaved switching method achieved the improvement of output voltage ripple, while magnetic circuit sharing reduced by 50% the cross section of core where magnetic circuit was shared.

• 한국안전학회지
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• 제29권6호
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• pp.137-143
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• 2014

Asbestos is given to a variety of six naturally occurring silicate minerals. These minerals possess high tensile strength, flexibility, resistance to chemical and thermal degradation, and electrical resistance. These minerals have been used for decades in thousands of commercial products, such as insulation and fireproofing materials, automotive brakes, textile products, cement and wallboard materials. When handled, asbestos can separate into microscopic-size particles that remain in the air and are easily inhaled. It is now known that prolonged inhalation of asbestos fibers can cause serious and fatal illnesses including malignant lung cancer, mesothelioma, and asbestosis. Therefore the use of asbestos and asbestos products has dramatically decreased in recent years. Also all constructions including asbestos should be removed under strictly controlled conditions and very tightly implemented health & safety management systems. In this study, the process of the removal work of the asbestos cement slate was analyzed by IDEF-0 modeling and evaluated by 4M risk assessment method. The results show that removal work of the asbestos cement slate was classified five process and eighteen detail process. The risk of safety side the higher than the risk of health side in 4M risk assessment.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 추계학술대회 논문집 학회본부 B
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• pp.585-587
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• 1999

The rotorbody and rotor winding of generator are isolated by an insulator and the output characteristic of the generator is maintained in the best states. Only when an insulation resistance between them is over a certain extent. The aim of this research is to develop the simulator for rotor earth fault detection circuits. It is composed of the power resource which is to control the virtual field voltage, stepping motor which is to give virtual ground. It is possible to inspect with the device and program developed in this study in the same as real operating condition and evaluate the integrity of generator rotor through the function of data acquisition and graphic output. If these technologies will be applied to the inspection, prevent a damage of the generator and contribute to improve maintenance reliance.

• 전기학회논문지
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• 제59권9호
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• pp.1644-1651
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• 2010

VLF $tan{\delta}$ diagnosis technology is introduced in IEEE Std 400 and proposed as evaluation criterion in an effective way of detecting water tree which mainly causes the failure of XLPE insulated cables. In order to inspect the accuracy of the VLF $tan{\delta}$ method for XLPE insulated power cables in Korean distribution system, diagnosis for 41 cables which were being serviced in the fields has been carried out and they were removed for AC breakdown voltage test after. Regarding the 41 cables, it was hard to confirm any relation between the VLF $tan{\delta}$ values and AC breakdown voltages and also water tree in the insulation was not detected. However, the other cables were failed several days after the diagnosis of the 41 cables. Water trees were found and their VLF $tan{\delta}$ values were also much higher than the criterion of IEEE standard. It has been ascertained that we need to change the IEEE criteria in order to improve the accuracy of detecting water trees by additional analyzing of field examples of failure and case studies from overseas countries and therefore amended VLF $tan{\delta}$ test voltage and evaluation criteria have been proposed.

• 한국농업기계학회:학술대회논문집
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• 한국농업기계학회 1993년도 Proceedings of International Conference for Agricultural Machinery and Process Engineering
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• pp.433-442
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• 1993

Coolstore air relative humidity (RH) is an important factor affecting the quality of horticultural products, particularly via product moisture loss. RH also has an important effect on the performance of the refrigeration evaporators and can affect the strength of paper-based packaging materials. In a large New Zealand apple coolstore, RH increased from about 75% early in season to 90% at the end, as activities in the coolstore and external conditions changed. A steady-state analysis of sensible and latent heat entry and heat removal during four typical operational periods over the season was carried out. Predicted RH was in good agreement with measured dat. For the coolstore studied, evaporator surface area and the occurrence of pre-cooling within the coolstore were the design and operational factors having greatest effect on RH. Door protection and management, and floor insulation were the next more significant factors. The method of analysis has more general application and ould be used in a variety of situations so that design for optimum RH can be performed systematically.

• KIEAE Journal
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• 제15권3호
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• pp.21-28
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• 2015

Purpose: In this study, we analyzed the energy performance levels and high-performance technology trends through the case studies of foreign high-performance buildings. Method: Buildings built within 10 years were selected for the analysis of recent trends. we analyzed the buildings of U.S.A, Germany and Japan using LEED certified buildings, Passive House certified buildings and CASBEE certified buildings database for the case study of foreign high-performance buildings. A total of 20 high-performance buildings including 14 cases in U.S.A, 4 cases in Germany and 4 cases in Japan were selected. Annual energy consumption levels for 20 high-performance buildings were collected with the actual energy consumption data or data from simulation programs officially recognized by DOE. Annual energy consumption were compared with the energy performance standard of the office buildings in the CBECS database, ASHRAE Standard 90.1-2004 and Building Energy Efficiency Rating System in Korea. Result: The order of the green strategies applied in the main categories are Renewable Energy(63%), Indoor Environment Control(51%), Envelope Improvement(44%) and HVAC System & Control(28%). Specified strategies most widely used in the sub-categories are high-performance Insulation (70%), High Efficiency Heating, Cooling Source Equipment(85%), Photovoltaic&Solar Thermal(80%) and Daylighting(80%).

• KIEAE Journal
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• 제14권4호
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• pp.133-138
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• 2014

The present study was carried out to assess the basic material properties and thermal behavior of light-weight foamed concrete panel mixed with PCM (Phase Changing Material). To do so, this study fabricated light-weight foamed concrete (1.0kg/m3) in pre-foaming method and mixed it with PCM micro capsule of 1-dodecanol and melamine to examine its physical and thermal properties. The results confirmed strength reinforcement effect by proper replacement ratio of fly-ash, which is an industrial by-product, and PCM. In addition, it found out that PCM-mixed light-weight foamed concrete had time delay and temperature reduction effect within the range of PCM phase transition according to the rise of outdoor temperature. It was also observed that the insulation performance of PCM-mixed light-weight foamed concrete was more dependent upon thickness than PCM replacement ratio.