• Proceedings of the KIEE Conference
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• 1998.07d
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• pp.1282-1284
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• 1998

ZnO Varistor is an electronic ceramic device for controlling the surge voltage from low level to high. In this study, the puncture mechanism occurring in ZnO varistor is investigated, and the simulation for restraining the puncture by formulating the relation between the applied voltage and the increase of the inside temperature of grain is applied. In order to simulate the cause of the current localization which is the primary factor causing the puncture, the localization phenomenon and the temperature distribution induced by the localized current, the Voronoi network is applied, which can realize the structure of the practical varistor better than the established simple network. Using the current through each grain and the voltage applied to the grain boundary obtained from that simulation, the Joule heating energy is calculated and the phenomenon that the puncture occurs can be analyzed quantitatively by simulating the electric and thermal characteristics according to the externally applied pulsed voltage.

• Journal of the Korean Society of Visualization
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• v.7 no.1
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• pp.3-8
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• 2009

Most vehicles have a heating, ventilating and air conditioning (HVAC) device to control the thermal condition and to make comfortable environment in the passenger compartment. The improvement of ventilation flow inside the passenger compartment is crucial for providing comfortable environment. For this, better understanding on the variation of flow characteristics of ventilation air inside the passenger compartment with respect to various ventilation modes is strongly required. Most previous studies on the ventilation flow in a car cabin were carried out using computational fluid dynamics (CFD) analysis or scale-down water-model experiments. In this study, whole ventilation flow discharged from the air vent of a real passenger car was measured using a special PIV (particle image velocimetry) system for large-size FOV (field of view). Under real recirculation ventilation condition, the spatial distributions of stream-wise turbulence intensity and mean velocity were measured in the vortical panel-duct center plane under the panel ventilation mode. These experimental data would be useful for understanding the detailed flow structure of real ventilation flow and validating numerical predictions.

• Journal of Mechanical Science and Technology
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• v.19 no.4
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• pp.1036-1043
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• 2005

Concentric annular heat pipes (CAHP) were fabricated and tested to investigate their thermal characteristics. The CAHPs were 25.4 mm in outer diameter and 200 mm in length. The inner surface of the heat pipes was covered with screen mesh wicks and they were connected by four bridge wicks to provide liquid return path. Three different heat pipes were fabricated to observe the effect of change in diameter ratios between 2.31 and 4.23 while using the same outer tube dimensions. The major concern of this study was the transient response as well as isothermal characteristics of the heat pipe outer surface, considering the application as uniform heating device. A better performance was achieved as the diameter ratio increased. For the thermal load of 180 W, the maximum temperature difference on the outer surface in the axial direction of CAHP was $2.3^{\circ}C$ while that of the copper block of the same outer dimension was $5.9^{\circ}C.$ The minimum thermal resistance of the CAHP was measured to be $0.004^{\circ}C/W.$ In regard to the transient response during start-up, the heat pipe showed almost no time lag to the heat source, while the copper block of the same outer dimensions exhibited about 25 min time lag.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.58-63
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• 2009

A ground-loop heat exchanger for the ground source heat pump system is the core equipment determining the thermal performance and initial cost of the system. The size and performance of the heat exchanger is highly dependent on the ground thermal properties - the ground effective thermal conductivity, the borehole thermal resistance and the undisturbed ground temperature. Nowadays, precast concrete piles using steel reinforced precast concrete piles - energy piles - are used to reduce the installing cost of the ground-loop heat exchanger. We were carried out some tests to investigate the effects of some parameters such as borehole length, grouting materials and U-tube configuration of the energy piles. 4 concrete piles, each measuring $250mm{\sim}400mm$ in diameter and approx. 10m in length, and rigged with single spiral and 3 U-tube loop of $16mm{\times}2.3mm$ PB piping. The thermal response tests were conducted using a testing device for 4-different ground-loop heat exchangers. During the heating period, the energy piles absorb the heat of 0.89kW to 1.37kW.

• Journal of Sensor Science and Technology
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• v.17 no.1
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• pp.9-14
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• 2008

In this paper, the gas responses of tungsten oxide films prepared by anodic reaction was discussed. Sensing electrodes and heating electrodes were patterned by photolithography method on quartz substrate. Porous tungsten oxide was fabricated in electrolyte solutions of 5 % HF (HF :$C_2H_6OH:H_2O$=3 : 2 : 20) by anodic reaction. The anodic reaction with metal (platinum wire) as a cathode and the sensing device as an anode was conducted under the various reaction times (1-10 min) at 10 mA/$cm^2$ The surface structure and morphology of the fabricated sensor have been analysed by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). All the peaks of XRD results were well indexed to the pure phase pattern. The average diameter of the porous tungsten oxide surface were ranged about 100 nm. The fabricaed sensor showed good sensitivity to 200 ppm toluene at operating temperature of $250^{\circ}C$.

• Proceedings of the Korean Society of Organic Agriculture Conference
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• 1999.11a
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• pp.5-24
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• 1999

There are severl types of Eco-village developed in abvanced countries including urban, suburban and rural style. For the establishment of Eco-village in Korea, it was focussed to introduce the rural style which has been developed inyersively in European countries such as Denmark, England and Germany. As a key cencept for Eco-villge it was explained briefly and discussed on the renewable energy(wind power park, bio-mass and solar energy collector and heating system), eco-architure, methane gas device, living machine (wastewater treatment facility) and organic farming. It was also discussed how important the basic standard and guidelines for organic agriculture to run essential for the system. For this reason major principles of international applicable standard(draft) for organically grown foods by FAO/WHO Codex alimentarius was shortly desidered. as one of very suitable type for Environmental Agriculture Districts Program which Korean govenment is going to establish in the near future. In conculusion it was also suggested that positive participation of organic famers, enthusiastic eneagement of inhabitans and support strategy of govemment /NGO groups might play very important role for successful managment of Eco-village ecologically sustainable after establishment.

• Journal of the Korean housing association
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• v.19 no.3
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• pp.21-29
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• 2008

To investigate the actual conditions on the living environment of group-homes for the elderly and their living environment, 4 group-homes were surveyed. As the results, conditions of location for the group-home of the elderly looked positive, on the other hand, safety for criminal prevention, accessability and convenient facilities were not on level satisfied. The average area of each space in the group-home indicated that the bed room was $11.21\;m^2$, the living room $28.13\;m^2$, the kitchen $23.59\;m^2$, and the bath room had an integrated type of bath room and toilet $7.63\;m^2$. The physical environments of each space in the group-home were investigated, In bed room, door, windows and illumination were relatively good but safety was extremely inferior. Living room mostly looked good except the doorsill which needs refurbishment. In kitchen, cooking table, windows, illumination, ventilator were somewhat satisfactory but gas-warning device should have been installed. In addition, in bath room and toilet, location, door, window, illumination and finished material were satisfactory. But the stepped difference between the bath room and other space, safety-bar, emergency bell and floor heating system were seriously deteriorated and must be improved for the safety of the elderly. Conclusively, living environment of group-home for the elderly is mainly satisfactory but it was necessary to take a consideration for their safety.

• Journal of computational fluids engineering
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• v.10 no.2
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• pp.48-53
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• 2005

This work discusses the numerical analysis, the design and experimental test of the SMA actuator along with its capabilities and limitations. Convective heating and cooling using water actuate the SMA(Shape memory alloy) element of the actuator. The fuel such as propane, having a high energy density, is used as the energy source for the SMA actuator in order to increase power and energy density of the system, and thus in order to obviate the need for electrical power supplies such as batteries. The system is composed of a pump, valves, bellows, a heater(burner), control unit and a displacement amplification device. The experimental test of the SMA actuator system results in 150 MPa stress(force : 1560 N) with $3\%$ strain and 0.5 Hz. actuation frequency. The actuation frequency is compared with the prediction obtained from numerical analysis. For the designed SMA actuator system, the results of numerical analysis were utilized in determining design parameters and operating conditions.

• Korean Journal of Organic Agriculture
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• v.9 no.2
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• pp.39-54
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• 2001

For the development of Eco-village in Korean rural area, it was focussed to introduce the rural style which has been developed intensively in European countries such as Denmark, England and Germany. As the main concept for Eco-village it was explained briefly in the paper on the renewable energy(wind power park, bio-mass and solar energy collector and heating system), eco-architecture, methane gas device, living machine(wastewater treatment facility) and organic farming. It was also discussed how important the basic standard and guidelines for organic agriculture to run Eco-village environmentally soundly as a whole system and why it is so much essential for the system. For this reason major principles of international applicable standard for organically grown foods by FAO/WHO Codex alimentarius was also shortly described. In the paper the Eco-village concept was considered as a suitable model for Environmental Agriculture Districts Project which Korean government is going to establish at rural area in the near future. In conclusion it was suggested that the positive participation of organic farmers, enthusiastic engagement of inhabitants and support strategy of government/NGO groups might play very important role for successful management of Eco-village ecologically benign and economically sustainable after establishment.

• Analytical Science and Technology
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• v.8 no.4
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• pp.487-492
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• 1995

The chemical compositions and pyrolysis characteristics of oil shales and source rocks distributed in the southwestern and southeastern parts of the Korean peninsular have been investigated. In order to compare the results of Korean samples with those of shales giving high oil yields, two Colorado oil shale samples and one Paris source rock samples were also investigated. Chemical compositions of the samples were analysed by means of gravimetry, CHN analysis, X-ray diffraction method, inductively coupled plasma atomic emission spectrometry and atomic absorption spectrometry. A custom made pyrolyser and a Rock-Eval system were used for the pyrolysis studies. Pyrolyses of the samples were carried out by means of a temperature controlling device to $600^{\circ}C$ at a heating rate of $5^{\circ}C/min$ with a helium flow rate of $1200m{\ell}/min$. The results of pyrolysis study indicated that Colorado shale samples belong to type I and all the other samples belong to type II.