• Transactions on Electrical and Electronic Materials
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• 제17권4호
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• pp.231-234
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• 2016

The AC insulation breakdown voltage was investigated for seven types of winding coils made of polyamideimide (PAI), flexural PAI (nanosilica 5 wt%) and anti-corona PAI (nanosilica 15 wt%) wires with various winding coil diameters of φ5, φ15 and φ25 mm. The winding coil was made of enameled wire with an enamel thickness of 30~50 μm, and the rectangular copper wire had a thickness of 0.77~ to 0.83 mm and width of 1.17~ to 1.23 mm, respectively. The insulation breakdown voltages of the original PAI coils with diameters of φ5, φ15 and φ25 mm were 7.30, 6.58, and 5.95 kV, respectively, and those values decreased as the winding coil diameter increased, regardless of the wire types.

• 전기학회논문지
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• 제56권6호
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• pp.1035-1038
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• 2007

We designed and manufactured a 1.8T high temperature superconducting(HTS) insert coil for a NMR magnet operated at 4.2 K. Suitable HTS superconductor and HTS coil were carefully designed and developed. We have selected multi-filamentary Bi2223 conductor fabricated by American Superconductor Corporation(AMSC). The selected conductor consists of Bi2223 filaments of 55, silver stabilizer and stainless steel reinforcement tapes. Therefore, it shows good hoop strength as well as compression tolerance. The conductor has a tape cross-section of 0.31mm x 4.8mm. the Bi2223 conductor shows large anisotropy of critical current. The critical current of conductor in magnetic field parallel to the flat surface are much higher than that in magnetic field perpendicular. The HTS coil has an inner diameter of 78 mm, an outer diameter of 127 mm and a coil length of 600 mm. In this paper, the detailed design, fabrication and test results on the HTS insert coil are presented.

• 한국안전학회지
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• 제33권1호
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• pp.7-15
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• 2018

The friction factors according to the flow regimes in helical coil tubes depend on the coil diameter, the tube diameter, and the coil pitch. In previous studies, correlations for the laminar flow regime in helical coil tubes have been proposed. However, studies on the transition flow regime and the turbulent flow regime are insufficient and further researches are necessary. In this study, characteristics of the friction factors for the laminar, transition and turbulent flow regimes in helical coil tubes were experimentally investigated. The helical coil tubes used in the experiments were made of copper. The curvature ratios of the helical coil tubes, which means the ratio of helical coil diameter to inner diameter of the helical coil tube are 24.5 and 90.9. Experiments were carried out in the range of $529{\leq}Re{\leq}39,406$ to observe the flows from the laminar to the turbulent regime. The friction factors were obtained by measuring the differential pressures according to the flow rates in the helical coil tubes while varying the curvature ratios of the helical coil tubes. Experimental data show that the friction factors for the helical coil tube with 24.5 in the curvature ratio of the helical coil tube were larger than those in the straight tube in all flow regimes. As the curvature ratio of the helical coil tube increases, the friction factor in turbulent flow regime tends to be equal to that of the straight tube. In addition, it was confirmed that the transition flow regimes in the helical coil tubes were much wider than those in the straight tube, also the critical Reynolds numbers were larger than those in the straight tube. The results obtained in this experimental study can be used as basic data for studies on the water hammer phenomenon in helical coil tubes.

• 대한치과교정학회지
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• 제22권1호
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• pp.135-146
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• 1992

It was the purpose of this study to analyze and compare the mechanical properties of ortho dontic open coil springs. Four variable factors were presented - wire diameter (.008", .009", .010"), lumen size (.030", .032", .036"), arch wire size and shape (.016" round, $ .016^{{\prime}{\prime}}{\times}.022^{{\prime}{\prime}}$ rect.) and alloy type (HiT II, Elgiloy, Sentalloy). The total 104 specimens were divided into 13 groups, and compression test was performed on an Instron test machine. The load deflection curve of each open coil spring was obtained, from which, the load-deflection relations, stiffnesses, percent recoveries were computed statistically. The results were obtained as follows: 1. When the lumen size of the coil spring remained constant, stiffness and percent recovery increased as the wire diameter increased. 2. When the wire diameter of the coil spring remained constant, stiffness and percent recovery decreased as the lumen size increased. 3. The effect of size and shape of arch wire on the coil spring was not statistically significant. 4. In alloy types, stiffness was the greatest in HiT II (55.21), Elgiloy (42.61) and Sentalloy (7.74) in that order. Sentalloy exhibited superior percent recovery and long range of action.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 제3회 압연심포지엄 논문집 압연기술의 미래개척 (Exploitation of Future Rolling Technologies)
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• pp.119-125
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• 1999

At Wire Rod Mill Plant, wire is made of the billet produced at continuous casting machine, or rolled bloom produced at billeting mill, and the product can be classified of wire of 5.5${\Phi}$ and bar in coil of 14∼42${\Phi}$ in diameter(bar in coil will be referred to as coil as below). At present, wire is produced at POSCO No.1, 2, 3 WRM, coil at garret line of No. 2 WRM. Head and tail of coil are properly cut and treated to scrap to fulfill the customer's satisfaction. This above cutting is done off line, and small size coil can be cut manually with clipper, large size coil with hydraulic cutter. Nowadays, it is being investigated to cut automatically in line with trimming shear after passing mill stand. At the moment, Because the coil produced at the garret line of No.2 WRM is hot 400∼600$^{\circ}C$ and trimming is done manually with cutter, there are always interference from manual operation or safety problem of bad working condition. Not only because of the diversity of the coil size 14∼42${\Phi}$ in diameter, but because of the rolling speed 2.5∼22m/sec, it is required to be equipped with several trimming shear. But this can be accomplished with only one shear installed proper place at this paper.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제53권8호
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• pp.477-487
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• 2004

Helical magneto-cumulative generators(MCGs) are devices which convert explosive energy into electromagnetic energy. The electromagnetic energy supplied from an external circuit is amplified by an explosively driven metal conductor mounted at the center of a helical coil compressing magnetic flux between the conductor and the coil. To optimize the coil design, output properties of small-size helical MCGs were measured while varying design parameters; the number of coil sections, length of the sections, pitch in the sections, and type of copper wire. Dimensions of the coil were kept constant, 50 mm in diameter and 200 mm in length. The coil was fabricated by using enamel-coated copper wire of 1 mm in diameter. The highest energy amplification ratio and figure of merit were 52.5 and 0.81, respectively. from an helical MCG with initial inductance of 63.7 $\mu$H at initial energy of 0.152 kJ Based on the experimental and calculated results, empirical formulas capable of optimizing coil designs were derived. By using these formulas, pitch in each coil section can be obtained at an arbitrary inductive load for high energy amplification ratio and figure of merit.

• 한국초전도ㆍ저온공학회논문지
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• 제9권1호
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• pp.43-46
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• 2007

Solenoid coil is one of the commonly used one in superconducting power machines because it can produce uniform magnetic field at the center of the coil. Most of the AC loss in a solenoid coil is magnetization loss which is generated by the perpendicular magnetic field. This paper compares the electrical characteristics of two solenoid coils made of YBCO wire and BSCCO wire. We made and tested the BSCCO solenoid coil and YBCO solenoid coil which had the same number of turns and inner diameter. Number of turns and inner diameter of both coils were 30 turns and 10cm, respectively. AC loss of both coils were calculated by using the finite element method. Result shows that AC loss of YBCO coil was about 1/7 of that of the BSCCO coil when the current was 40A.

• 한국전자파학회논문지
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• 제29권12호
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• pp.907-914
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• 2018

무선충전은 전선 없이 전자기기를 충전할 수 있다는 사용자의 편의적인 측면에 장점이 커 활발히 연구개발되고 널리 보급되었다. 하지만 무선충전패드에서 수신기의 중심이 어긋날 경우에 충전이 되지 않아 수신기의 중심을 잘 맞춰야 한다는 점은 사용자의 편의성이라는 무선충전의 효용성을 크게 저감시킨다. 본 논문은 이러한 무선충전의 한계를 극복하고자 수신기의 위치 자유도를 향상시키기 위한 코일 설계를 진행하였다. Tx 코일이 Rx 코일과 사이즈가 비슷할 때보다 외경 크기가 클 때 중심에서 효율은 다소 저하되었지만, 중심이 어긋날 경우의 효율이 개선되어 Rx 코일의 위치 자유도가 향상됨을 알 수 있었다. 이 때, Tx 코일에 내측 코일이 추가로 구성된 이중코일 구조를 제안하여 효율을 추가적으로 향상시킬 수 있었다. 자유도 개선 결과를 시뮬레이션과 측정을 통해 효율을 확인하였고, 경향성이 일치함을 볼 수 있었다. 측정 결과, 105~210 kHz 동작 주파수에서 송수신 코일의 전송거리 3 mm, 오정렬 15 mm일 때, 수신 코일에 전류가 1A 흐를 때 기준으로 기존 Tx 코일의 전송 효율은 37 %, 외경 크기를 키운 코일의 효율은 45 %, 내측 코일을 추가한 이중 코일은 47 %로 효율이 향상되었다.

• Journal of Advanced Marine Engineering and Technology
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• 제31권5호
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• pp.552-557
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• 2007

This paper has dealt with the effect of non ionized surfactant and water mixture on drag reduction and heat transfer enhancement in a circular pipe flow with experimentally. The test section was consisted of stainless steel pipe with inside diameter of 16mm. The wire coil was used to increase heat transfer in a pipe and the on ionized surfactant(Oleyl Dihydroxyethyl Amino Oxide, ODEAO) was used to reduce the drag force of water mixture with surfactant. The main parameters of this experiment were diameter and pitch of wire coil and the ratio of test section length and horizontal wire coil length. In this experiment, the acquired results were 1) Drag reduction effect existed in this ODEAO-water mixture, 2) Friction factor and heat transfer were increased with insertion the heat transfer enhancement coil, 3) With increasing of pitch ratio, heat transfer was decreased, and 4) Heat transfer was decreased by the decreasing of inserting coil diameter.

• Journal of Mechanical Science and Technology
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• 제20권2호
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• pp.212-226
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• 2006

This paper is a continuation of the authors' previous work on spiral coil heat exchangers. In the present study, the heat transfer characteristics and the performance of a spirally coiled finned tube heat exchanger under wet-surface conditions are theoretically and experimentally investigated. The test section is a spiral-coil heat exchanger which consists of a steel shell and a spirally coiled tube unit. The spiral-coil unit consists of six layers of concentric spirally coiled finned tubes. Each tube is fabricated by bending a 9.6 mm diameter straight copper tube into a spiral-coil of four turns. The innermost and outermost diameters of each spiral-coil are 145.0 and 350.4 mm, respectively. Aluminium crimped spiral fins with thickness of 0.6 mm and outer diameter of 28.4 mm are placed around the tube. The edge of fin at the inner diameter is corrugated. Air and water are used as working fluids in shell side and tube side, respectively. The experiments are done under dehumidifying conditions. A mathematical model based on the conservation of mass and energy is developed to simulate the flow and heat transfer characteristics of working fluids flowing through the heat exchanger. The results obtained from the present model show reasonable agreement with the experimental data.