• Title/Summary/Keyword: Non-uniform Field

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Numerical Study of Land/Channel Flow-field Optimization in Polymer Electrolyte Fuel Cells (PEFCs) (I) -The Effects of Land/Channel Flow-field on Current Density and HFR Distributions- (고분자전해질형연료전지의 가스 채널 최적화를 위한수치적연구(I) -가스 채널 치수가 전류밀도와 HFR 분포에 미치는영향성-)

  • Ju, Hyun-Chul
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.32 no.9
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    • pp.683-694
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    • 2008
  • The performance and durability of Polymer Electrolyte Fuel Cells (PEFCs) are strongly influenced by the uniformity of current density, temperature, species distributions inside a cell In order to obtain uniform distributions in them, the optimal design of flowfield must be a key factor. In this paper, the numerical study of land/channel flowfield optimizations is performed, using a multi-dimensional, multi-phase, non-isothermal PEFC model. Numerical simulations reveal more uniform current density and HFR(High Frequency Resistance) distributions and thus better PEFC performance with narrower land/channel width where the less severe oxygen depletion effect near the land region and more uniform contact resistance variation along the in-plane direction are achieved. The present study elucidates detailed effects of land/channel width and assist in identifying optimal flow-field design strategies for the operation of PEFCs.

Study on the Breakdown of the Transformer Insulating Oil in Nonuniform Electric Field (불평등 전계에서 변압기 절연유 절연파괴 연구)

  • Ha-Young Cho;Soon-Hyung Lee;Mi-Yong Hwang;Yong-Sung Choi
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.36 no.3
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    • pp.280-285
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    • 2023
  • A breakdown voltage and breakdown electric field of the transformer insulating oil of liquid dielectric were studied in uniform electric field and non-uniform electric field and the transformer insulating oil was observed by the process reached breakdown. Insulation performance evaluation of the liquid dielectric was evaluated at the electrode spacing of 2.5 mm under the conditions of domestic and international standards (KS C IEC 60156), so a comparative review was conducted at the electrode spacing of 2.5 mm. When the electrode spacing is 2.5 mm, the average breakdown voltage is 38.5 kV for sphere-sphere electrodes, 26.6 kV for plate-plate electrodes, 22.9 kV for needle-needle electrodes, and 24.3 kV for sphere-needle electrodes. 23.7 kV for the sphere-plate electrode, and 20.7 kV for the needle-plate electrode. From these results, it can be seen that the average value of the breakdown voltage at the electrode spacing of 2.5 mm, in ascending order, is sphere-sphere, plate-plate, sphere-needle, sphere-plate, needle-needle and needle-plate. It was found that the breakdown voltage of the unequal field was lower than that of the equal field.

Quench Characteristics of YBCO Film for Current Limiting Using Magnetic Field

  • 박권배;최효상;김혜림;현옥배;황시돌
    • Progress in Superconductivity
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    • v.3 no.2
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    • pp.252-256
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    • 2002
  • We studied YBCO films for current limiting of the resistive type which utilizes a transition from superconducting to normal state caused by exceeding critical current. The films were deposited on sapphire substrates and covered by gold top layer. The current limiting element consists of 2 mm wide YBCO stripes connected in series. A serious problem in using YBCO films for current limiting is inhomogeneities caused by imperfect manufacturing. Therefore simultaneous quench is a difficult problem when elements for current limiting are connected in series. So some researchers have recently proposed using magnetic field and heating for simultaneous quench. We have measured extended exec trim field-current density(E-J) characteristics for current limiting elements of YBCO films in applied magnetic field of 0 - 130 mT. And we have investigated quench characteristics in current limiting elements and between elements of YBCO films in applied magnetic field. The result of the experiments show that the presence of applied magnetic fields induces uniform quench distribution fur the stripes in element at $50V_{rms}$, otherwise non-uniform quenches were observed. And simultaneous quenches between elements were investigated at $150V_{rms}$. We suggest that suppressing the critical current by increased fields due to fault current effectively forced the stripes of higher $J_{c}$(0) to quench, resulting in equalizing quench times.s.s.s.

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Prebreakdown Phenomena of $SF_{6}$ Gas in a Non-uniform Field Disturbed by a Metallic Protrusion

  • Lee, Kyoung-Ok;Lee, Bok-Hee;Jeon, Duk-Kyu
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 1996.05a
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    • pp.137-141
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    • 1996
  • This paper deals with the prebreakdown phenomena of $SF_{6}$ gap stressed by non-oscillating and oscillating impulse voltages in a strong inhomogeneous field disturbed by a fred needle shaped-protrusion on the earth-side electrode. The breakdown voltage-time characteristics were measured for both positive and negative polarities and over the gas pressure range of 0.1∼0.5 MPa, and the temporal developments of the 77breakdown were observed by a shunt of 50 n. The dependence of the leader stopping time on the gas pressure were obtained. The local field enhancement due to the space charges, which is produced by the streamer corona, has influence with the electrical breakdown of the test gap. The test streamer corona is oxy a necessary condition for the electrical breakdown and the subsequent ionization activities launch the leader at the local field region.

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Thermal-fluid-structure coupling analysis for plate-type fuel assembly under irradiation. Part-I numerical methodology

  • Li, Yuanming;Yuan, Pan;Ren, Quan-yao;Su, Guanghui;Yu, Hongxing;Wang, Haoyu;Zheng, Meiyin;Wu, Yingwei;Ding, Shurong
    • Nuclear Engineering and Technology
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    • v.53 no.5
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    • pp.1540-1555
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    • 2021
  • The plate-type fuel assembly adopted in nuclear research reactor suffers from complicated effect induced by non-uniform irradiation, which might affect its stress conditions, mechanical behavior and thermal-hydraulic performance. A reliable numerical method is of great importance to reveal the complex evolution of mechanical deformation, flow redistribution and temperature field for the plate-type fuel assembly under non-uniform irradiation. This paper is the first part of a two-part study developing the numerical methodology for the thermal-fluid-structure coupling behaviors of plate-type fuel assembly under irradiation. In this paper, the thermal-fluid-structure coupling methodology has been developed for plate-type fuel assembly under non-uniform irradiation condition by exchanging thermal-hydraulic and mechanical deformation parameters between Finite Element Model (FEM) software and Computational Fluid Dynamic (CFD) software with Mesh-based parallel Code Coupling Interface (MpCCI), which has been validated with experimental results. Based on the established methodology, the effects of non-uniform irradiation and fluid were discussed, which demonstrated that the maximum mechanical deformation with irradiation was dozens of times larger than that without irradiation and the hydraulic load on fuel plates due to differential pressure played a dominant role in the mechanical deformation.

Deterministic manipulation and visualization of near field with ultra-smooth, super-spherical gold nanoparticles by atomic force microscopy

  • KIM, MINWOO;LEE, JOOHYUN;YI, GI-RA;LEE, SEUNGWOO;SONG, YOUNG JAE
    • Proceedings of the Korean Vacuum Society Conference
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    • 2015.08a
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    • pp.111.1-111.1
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    • 2015
  • As an alternative way to get sophisticated nanostructures, atomic force microscopy (AFM) has been used to directly manipulate building primitives. In particular, assembly of metallic nanoparticles(NPs) can provide various structures for making various metamolecules. As far, conventionally made polygonal shaped metallic NPs showed non-uniform distribution in size and shape which limit its study of fundamental properties and practical applications. In here, we optimized conditions for deterministic manipulation of ultra-smooth and super-spherical gold nanoparticles (AuNPs) by AFM. [1] Lowered adhesion force by using platinum-iridium coated AFM tips enabled us to push super-spherical AuNPs in linear motion to pre-programmed position. As a result, uniform and reliable electric/magnetic behaviors of assembled metamolecules were achieved which showed a good agreement with simulation data. Furthermore, visualization of near field for super-spherical AuNPs was also addressed using photosensitive azo-dye polymers. Since the photosensitive azo-dye polymers can directly record the intensity of electric field, optical near field can be mapped without complicated instrumental setup. [2] By controlling embedding depth of AuNPs, we studied electric field of AuNPs in different configuration.

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Effect by Temperature Distribution of Target Surface during Sputtering by Bipolar Pulsed Dc and Continuous Dc (직류와 양극성 펄스직류에 의한 스퍼터링시 타겟 표면의 온도 분포와 그 영향)

  • Yang, Won-Kyun;Joo, Jung-Hoon;Kim, Young-Woo;Lee, Bong-Ju
    • Journal of the Korean Vacuum Society
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    • v.19 no.1
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    • pp.45-51
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    • 2010
  • We measured the temperature of target surface inducing by various physical phenomenon on magnetron sputtering target and confirmed the possibilities if the temperature distribution could affect plasma and deposited thin film. The target of magnetron sputtering has two types: round type and rectangular type. In a rectangular target, the concentrated discharge area by corner effect by magnetic field and non-uniform erosion of target are generated. And we found the generation of non-uniform temperature distribution on the target surface from this. This area was $10{\sim}20^{\circ}C$ higher than non-sputtering area. And if particles are generated during sputtering process, they were $20^{\circ}C$ higher than the area where is higher than non-sputtering area. These effects result in non-uniformity of thin films, crack of ceramic target, and shortening target life by non-uniform erosion.

CFD prediction of vortex induced vibrations and fatigue assessment for deepwater marine risers

  • Kamble, Chetna;Chen, Hamn-Ching
    • Ocean Systems Engineering
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    • v.6 no.4
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    • pp.325-344
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    • 2016
  • Using 3D computational fluid dynamics techniques in recent years have shed significant light on the Vortex Induced Vibrations (VIV) encountered by deep-water marine risers. The fatigue damage accumulated due to these vibrations has posed a great concern to the offshore industry. This paper aims to present an algorithm to predict the crossflow and inline fatigue damage for very long (L/D > $10^3$) marine risers using a Finite-Analytical Navier-Stokes (FANS) technique coupled with a tensioned beam motion solver and rainflow counting fatigue module. Large Eddy Simulation (LES) method has been used to simulate the turbulence in the flow. An overset grid system is employed to mesh the riser geometry and the wake field around the riser. Risers from NDP (2003) and Miami (2006) experiments are used for simulation with uniform, linearly sheared and non-uniform (non-linearly sheared) current profiles. The simulation results including inline and crossflow motion, modal decomposition, spectral densities and fatigue damage rate are compared to the experimental data and useful conclusions are drawn.

Influence of non-uniform current distribution on transport ac loss in Bi-2223/Ag tapes (불균일 전류분포가 Bi-2223/Ag 초전도선재의 통전손실에 미치는 영향)

  • Choi, S.;Nah, W.;Joo, J.;Kim, J.H.;Ryu, K.W.;Sohn, M.H.;Kwon, Y.K.
    • Proceedings of the KIEE Conference
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    • 2005.07b
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    • pp.1240-1242
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    • 2005
  • In this study, we estimate the transport current loss of Bi-2223/Ag tapes with non-uniform current distribution. The conductor was consisted of three Bi-2223/Ag tapes and the each tapes were attached in parallel. The loss of conductor was investigated both numerical and experimental methods. The numerical code to predict ac loss was developed, and finite element method was introduced. It contained intrinsic properties of superconducting tape, which was obtained from nonlinear current voltage relation with external magnetic field and its orientation. Two results were compared and discussed. They showed good agreements with each other.

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Bending Strain Dependence of the Transport Property in Jointed BSCCO Tapes

  • Dedicatoria, Marlon J.;Shin, Hyung-Seop
    • Progress in Superconductivity and Cryogenics
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    • v.12 no.2
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    • pp.5-8
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    • 2010
  • In this study, the effect of bending strain on the transport property and critical current of lap and butt-jointed (non-laminated) BSCCO tapes has been investigated. The samples were joined using a mechanically controlled jointing procedure. To achieve a uniform thickness at the joint a single point loading contact has been devised. GFRP mandrels with different bending radii which support the sample during bending have been used. $I_c$ have been measured at 77 K and self field. In the case of easy bending test for jointed BSCCO tapes, sudden degradation of $I_c$ is caused by the local strain concentration due to non uniform deformation at the edge parts of the joint. In the case of hard bending test of jointed BSCCO tapes transverse macroscopic crack at specific subsection caused a large $I_c$ degradation. The transport property of jointed BSCCO tapes in each bending mode was discussed with the damage morphology occurred.