• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• 제17권2호
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• pp.131-139
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• 1988

The thermoacoustic oscillation induced in an air column with variable cross section area is investigated theoretically and experimentally. The onset condition of the oscillation is derived by equating the acoustic power production to the power dissipation. The power production at the heater is predicted by using the efficiency factor obtained by heat transfer analysis for a single wire in a uniform cross flow and considering the interference between heater wires. The power dissipation is estimated by measuring the attenuating coefficient from the pressure decay curve. The theoretical prediction to the onset condition of the oscillation is confirmed experimentally. The effect of the variation of the column cross section area on the onset condition is presented.

• Journal of the Korean Institute of Rural Architecture
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• 제12권2호
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• pp.23-29
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• 2010

Vinyl house is a simple agricultural structure that is installed economically and easily. In contrast, every year the farmers have spent a lot of money because of the collapse of this structure caused by the external forces such as strong wind and heavy snow. To prevent this damage due to frequent heavy snow and strong wind, it would be necessary to design it again. But getting rid of former vinyl house and reconstructing is unreasonable. It would be very economic if the former vinyl house is strengthened simply. This paper covers the investigation of the effect of the bracing systems that are additionally inserted inside the ordinary single frames as well as unbraced multiple frames that resisting only the strong wind load.

• Journal of the Korean Chemical Society
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• 제6권1호
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• pp.54-60
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• 1962

The water gas shift conversion catalyst prepared by the American Cyanamide Co. was subjected to fluidization in a 2-in. Pyrex glass tube to obtain the basic fluidization characteristic data. The size of the catalyst charged ranged from 70 to 120 meshes and it was supported on a single layer 300-mesh wire gauze through which the fluidizing medium, the air, was passed. Following are some data and facts found by the authors: (1) The catalyst particles were porous, and their surfaces were trough and irregular. (2) The average effective particle density and the average shape factor of these particles were 152.2 lb/$ft^3$ and 0.865 respectively. (3) As the particle diameter of the catalyst increased, the minimum fluid voidage of the bed decreased slightly. (4) Just before the incipient fluidization, pressure drop suddenly fell and the bed expanded simultaneously. (5) After fluidization set in, the expansion characteristics of the catalyst bed were similar to those of sand and glass beads except intense bubbling in the catalyst bed.

• Journal of electromagnetic engineering and science
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• 제1권1호
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• pp.88-94
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• 2001

In this paper, the lightning-induced voltages on shielded twisted-pair wires with multipoint grounding on cable sheath are calculated by using finite-difference time domain (FDTD) method. The equivalent single-wire line that represents a bundle of twisted-pair wires is adopted for computational efficiency. A finitely conducting ground is also taken into account in both lightning electromagnetic field calculations and surge propagation along the shielded cable for a practical simulation. It is found that multipoint additional grounding on cable sheath provides more shielding effectiveness especially in the early time response of the lightning-induced voltages. From this study, the requirements for lighting surge protection devices in a telecommunication subscriber cab1e can be established.

• The Transactions of the Korean Institute of Electrical Engineers P
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• 제59권3호
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• pp.325-329
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• 2010

Capacitor has been used principally for the power factor compensation long ago. However now it does as passive filter to reduce harmonics of nonlinear load with reactor. Most of the customer's low-voltage feeder has been designed with approximately balanced and connected at the 3 phase four wire system. But voltage and current unbalance is appeared by the mixing operation of single or three phase load etc. The addition of reactor at the condenser may rise its terminal voltage. Voltage and current values above rating can act on electrical stress on the condenser. In this paper, we calculated and measured that voltage, current and capacity of condenser are changed under the voltage balance. We conclude that magnitude and deviation of phase voltage act on major point of electrical stress.

• The Transactions of the Korean Institute of Electrical Engineers P
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• 제57권1호
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• pp.36-40
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• 2008

Most of the low-voltage feeder are designed with approximately balanced and connected at the three phase four wire systems. However, Most of the power distribution systems' load which is composed of single or three phase are unbalanced by generating load unbalance. Unbalanced current will draw a highly unbalanced voltage. The power factor of an induction motor at rated operation is between 25 and 90%, depending on the size and speed of the motor. However, many induction motors operate below the nominal rating, resulting in poor power factor. This condition needs power factor improvement. Addition of power capacitor at the motor terminal may draw to stress due to voltage unbalance. This paper presents operation characteristics on steady states of a three-phase induction motor under unbalanced voltages with power capacitor. The existence of voltage unbalance have an effect on stress of power capacitor.

• IE interfaces
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• 제8권1호
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• pp.5-13
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• 1995

Automated vision inspection has become a vital part of computer related industries. Most of the existing inspection systems mainly utilize black and white images. In this paper, we consider an application of automated vision inspection in which cable color has to be recognized in order to detect the quality status of assembled wire harness. A back-propagation neural network is proposed to classify seven different cable colors. To represent a single point in image space, we use the ($L^*,\;a^*,\;b^*$) model which is one of commonly used color-coordinate systems in image processing. After training the neural network with ($L^*,\;a^*,\;b^*$) data obtained from color image, we tested its performance. The results show that the neural network is able to classify cable colors with high performance.

• Proceedings of the KIPE Conference
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• 전력전자학회 2019년도 추계학술대회
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• pp.43-45
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• 2019

펄스폭 변조 기법 (Pulse width modulation)을 사용하는 단상 인버터의 출력은 기본주파수 성분만이 아니라 고조파의 성분을 포함하고 있기 때문에 고조파 저감을 위한 필터의 사용이 필연적이다. LCL 필터는 기존의 L이나 LC 필터에 비해 시스템의 크기와 부피를 줄이며 동시에 전류 리플 감쇠 효율 등의 필터 성능이 뛰어나 최근 사용이 증가하는 추세이다. 본 논문에서는 LCL-필터의 인덕터에 알루미늄 권선을 적용하기위해 커패시터의 직렬 댐핑 저항과 더불어 인덕터의 권선 저항 또한 추가하여 필터의 전달함수를 고려하였다. 알루미늄은 구리 보다 전도율이 낮아 저항이 크지만, 구리에 비해 가볍고 가격이 저렴한 장점이 있다. 이를 계통 연계형 인버터에 적용하기 위해, 인덕터의 저항 성분 차이에 따른 댐핑(damping) 효과를 시뮬레이션을 통해 분석하였고 구리 권선과 알루미늄 권선을 사용한 인덕터를 각 제작하여 500 W 급 하드웨어 실험을 통해 전력변환장치에서의 알루미늄 권선 인덕터 적용 가능성을 확인하였다.

• Proceedings of the KSME Conference
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2292-2297
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• 2008

Recently, a study on condensers for refrigerators has focused on new model which will cost less and will be more efficient. Some widely used condensers for domestic refrigerators are wire-and-tube type condenser, hot-wall type condenser, and spiral type condenser. Some companies which use the spiral type condenser at the moment try to develop a new type condenser which will cost less and will be as efficient as the spiral type. The new type condenser consists of a steel tube, steel plates and louver fins attached to the tube. The tube and the plate are bent into a single-passage serpentine shape.

• Journal of the Korean Society for Precision Engineering
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• 제25권1호
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• pp.115-121
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• 2008

In this paper, a three-dimensional computational fluid dynamic model of a proton exchange membrane fuel cell(PEMFC) with serpentine flow channel is presented. A steady state, single phase and isothermal numerical model has been established to investigate the influence of the GDL (Gas Diffusion Layer) parameters. The GDL is made of a porous material such as carbon cloth, carbon paper or metal wire mesh. For the simplicity, the GDL is modeled as a block of material having numerous pathways through which gaseous reactants and liquid water can pass. The porosity, permeability and thickness of the GDL, which are employed in the model parameters significantly affect the PEMFC performance at the high current region.