• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 춘계학술대회 논문집
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• pp.704-707
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• 1999

Partial discharge(PD) in air insulated electric power systems is responsible for considerable power lossesfrom high voltage transmission lines. PD in air often leads to deterioration of insulation by the combined action of the discharge ions bombarding the surface and the action of chemical compounds that are formed by the discharge and may give rise to interference in ommunication systems. PD can indicate incipient failure. Thus understanding and classification of PD in air is very important to discern source of PD. In this paper, we investigated PD in air by using statical method. We classified air discharge with corona, surface discharge and cavity discharge by source of discharge. we used the mean pulse-height phase distribution $H_{qmean}(\psi)$, the max pulse-height phase distribution $H_{qmax}(\psi)$ , the pulse count phase distribution $H_n(\psi)$ and the max pulse height vs. repetition rate $H_{q}(n)$ for analysis PD pattern. We used statistical operators, such as skewness(S+. S-1, kurtosis(K+, K-), mean phase(AP+. AP-), cross-correlation factor(CC) and asymmetry from the distribution.

• 대한조선학회논문집
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• 제56권4호
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• pp.361-372
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• 2019

The flow pattern of air layers and skin-friction drag reduction by air injection are investigated to find the suitable multiphase flow model using unstructured finite-volume CFD solver for the Reynolds-averaged Navier-Stokes equations. In the present computations, two different multiphase flow modeling approaches, such as the Volume of Fluid (VOF) and the Eulerian Multi-Phase (EMP), are adopted to investigate their performances in resolving the two-phase flow pattern and in estimating the frictional drag reduction. First of all, the formation pattern of air layers generated by air injection through a circular opening on the bottom of a flat plate are investigated. These results are then compared with those of MMkiharju's experimental results. Subsequently, the quantitative ratios of skin-friction drag reduction including the behavior of air layers, within turbulent boundary layers in large scale and at high Reynolds number conditions, are investigated under the same conditions as the model test that has been conducted in the US Navy's William B. Morgan Large Cavitation Channel (LCC). From these results, it is found that both VOF and EMP models have similar capability and accuracy in capturing the topology of ventilated air cavities so called'air pockets and branches'. However, EMP model is more favorable in predicting quantitatively the percentage of frictional drag reduction by air injection.

• 설비공학논문집
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• 제16권10호
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• pp.932-941
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• 2004

The objective of this study is to detect the multi-fault of HVAC system using a new pattern classification technique. To classify the effect of single-fault in determining the pattern, supply air temperature, OA-damper, supply fan, and air flowrate were chosen as experimental parameters. The combination of supply temperature, flow rate, supply fan and OA-damper were chosen as multi-fault conditions. Three kinds of patterns were introduced in the analysis of multi-fault problem. To solve multi-fault problem, the new pattern classification technique using residual ratio analysis was introduced to detect the multi-fault as well as single-fault. The residual ratio could diagnose single-fault or multi-fault into several patterns.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 Proceedings ICPE 01 2001 International Conference on Power Electronics
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• pp.687-691
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• 2001

With today's global environmental and energy problems, high expectations exist for solar power generation to reduce carbon dioxide generated by the consumption of fossil fuels. On the other hand, power consumption in residential homes is increasing every year. Among the many household appliances, the power demand for air conditioners increases dramatically during the summer, particularly in the afternoons. As this pattern closely matches the output pattern of solar cells, it should be possible to combine a photovoltaic array with an air conditioner to decrease the energy consumption within the home. We have developed a residential solar-powered air conditioner that operates through a combination of photovoltaic array and commercial power. In this paper, the configuration and specification of the residential solar-powered system are described to a novel high efficiency inverter using a ZVCS boost converter. And the performance evaluations of the solar-powered air conditioner are examined by the analysis of a new tracking controller with a maximum power $P_{max}$ detection of solar cell.

• 한국산업보건학회지
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• 제5권2호
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• pp.226-240
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• 1995

This research has a purpose to achieve experimental data used for design of ventilation systems necessary for indoor air quality control and their operation and management. For the study, spatial concentration distribution of indoor air quality according to pollutant site in a simplified model chamber. In low flow ventilation, flow pattern of indoor air was mainly influenced by diffusion and additionally, spatial distribution was formed by convection. Distribution of ventilation efficiency according to each pattern of model chamber was evaluated. It was confirmed that diffusion patterns of a pollutant among sites were formed, centering around main stream areas of supply and exhaust outlets.

• 한국연소학회지
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• 제4권1호
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• pp.141-153
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• 1999

Numerical analysis for the combustion flow in the combustion chamber of incineration system has been carried out in order to acquire the basic design capability of incineration system. Established mathematical model was applied to the performance prediction of the pre-designed combustion chamber of commercial plant. Especially, combustion characteristics and the variation of flow pattern have been deeply discussed in accordance with secondary air injection. Secondary air injection was effective for the turbulent mixing between air and carbon monoxide/volatile matter resulting in considerably reduced CO content at the exit. Secondary air injection was found to be one of the key design parameters because the size of recirculation zone could be changed with the variation of injection characteristics.

• 한국생산제조학회지
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• 제21권3호
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• pp.473-478
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• 2012

In this paper, the air bubble formation mechanism in the rectangular and triangular line-and-space pattern during dispensing UV Nanoimprint Lithography (UV-NIL) at an atmospheric condition is studied. To investigate the air bubble formation, an analytic model based on geometric approach and a numerical model based on CFD(computational fluid dynamics) were used in the analysis. It was found in the numerical analysis that every time the flow front passed through a corner of the pattern, it proceeded with a newly formed shape, occurring due to interface reconfiguration, since the flow fronts were formed such that they minimized the surface energy. Moreover, the conditions for the air bubble formation were investigated by applying the analytic analysis based on geometric approach and the numerical analysis. Good overall agreement was found between the analytic and numerical analysis.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2004년도 유체기계 연구개발 발표회 논문집
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• pp.43-48
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• 2004

A screw-type centrifugal pump was manufactured to carry solids primarily and its impeller has a wide flow passage. However, the effect of flow passage shape on delay of the choke due to entrained air has not been clarified yet. Moreover, because its impeller has a particular shape, only few studies have tried to clarify the pump performance and details of internal flow pattern of that pump. For that reason, we carried out the pump performance experiment under air-water two-phase flow condition with different impeller tip clearances, pump rotational speeds and void fractions by using a small screw-type centrifugal pump designed to acquire basic data. In a general centrifugal pump, it was reported that loss of pump head from single-phase flow to the choke due to air entrainment new the best efficiency point was large. However, the loss near the best efficient point in a screw-type centrifugal pump became less than that in a general centrifugal pump.

• 한국항공운항학회지
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• 제28권4호
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• pp.117-124
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• 2020

This study empirically analyzed air transport trade patterns using data for 30 years between Korea and its trading partners in order to identify specific factors that determine the size of Korea's air transport trade. Independent variables were GDP per capita, capital distance between countries, country area data and number of airports. In addition, it reflected whether it is a landlocked country and whether it has joined the OECD, APEC and ASEAN+3. According to the results of the analysis, it was found that the air cargo trade pattern in Korea is proportional to GDP per capita, and the scale increases as the distance is closer. In addition, the national area and the airport capital acted as a factor in increasing air transport trade. However, whether a country is a landlocked country did not show significant results in terms of trade, exports, and imports. The OECD, APEC, and ASEAN+3 variables were found to generally increase air transport trade.

• 한국환경과학회지
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• 제22권1호
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• pp.47-57
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• 2013

Studies evaluating the health effects of hazardous air pollutants assume that people's exposure to typical pollutant level is the same as specific regional pollutant level. However, depending on social and demographic factors, time-activity pattern of people can vary widely. Since most people live in indoor environments over 88% of the day, evaluating exposure to hazardous air pollutants is hard to characterize. Objective of this study was to estimate the exposure levels of university students of $NO_2$, VOCs(BTEX) and $PM_{10}$ using the scenarios with time-activity pattern and indoor concentrations. Using data from time-use survey of National Statistical Office in 2009, we investigated time-activity pattern of university students and hourly major action. A total of 1,057 university students on weekday and 640 on weekend spent their times at indoor house 13.04 hr(54.32%), other indoors 7.70 hr(32.06%), and transportation 2.36 hr(9.83%). Indoor environments in which university students spent their times were mainly house and school. Air pollutants concentrations of other indoor environments except house and school such as bar, internet cafe and billiard hall were higher than outdoors, indicating that indoor to outdoor ratios were above 1. According to three types of exposure scenarios, exposure to air pollutants could be reduced by going home after school.