• Title/Summary/Keyword: Annular region

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Theoretical and Numerical Study of Cylindrical-vector-mode Radiation Characteristics in Periodic Metallic Annular Slits and Their Applications

  • Kim, Hyuntai;Jeong, Yoonchan
    • Current Optics and Photonics
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    • v.2 no.5
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    • pp.482-487
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    • 2018
  • We investigate the radiation characteristics of radially polarized light and azimuthally polarized light through plasmonic subwavelength-scale annular slit (PSAS) structures, by means of both theoretical and numerical methods. Effective-medium theory was utilized to analyze the characteristics of PSAS structures, and the corresponding results showed that PSAS structures can function as a metallic medium for azimuthally polarized light, or as a low-loss dielectric medium for radially polarized light. Numerical calculations based on the finite-element method were also performed, to verify the theoretical analyses. It turned out that the numerical results supported the theoretical results. Moreover, we exploited the PSAS structures in novel nanophotonic elements with dual functionalities that could selectively focus or pass/block incident light, depending on its polarization state. For example, if PSAS structures were implemented in the dielectric region of a metallic Fresnel zone plate, the modified zone plate could function as a blocking element to azimuthally polarized light, yet as a focusing element to radially polarized light. On the contrary, if PSAS structures were implemented in the metallic region of a metallic Fresnel zone plate (i.e. the inverted form of the former), it could function as a focusing element to azimuthally polarized light, yet as a simple transparent element to radially polarized light.

Flow Patterns of Gas-Liquid Two-phase Flow under Microgravity (미소중력하의 기액이상류의 유동양식)

  • 최부홍
    • Journal of Advanced Marine Engineering and Technology
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    • v.27 no.3
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    • pp.460-465
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    • 2003
  • Microgravity experiments were conducted to determine the effect of liquid and gas superficial velocities on flow behaviors. Flow behaviors observed under microgravity conditions can be classified into five flow patterns: bubble. Taylor bubble, slug, semi-annular and annular flows. Transition boundary between four flow patterns could be determined by drift-flux model. It was also found that the effect of gravity and pipe inclination on flow pattern transition was not significant in the inertia dominant region.

NUMERICAL INVESTIGATION OF TURBULENT FLOW FROM AN ANNULAR JET (환형제트 난류유동에 대한 수치해석 연구)

  • Kim, Jungwoo
    • Journal of computational fluids engineering
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    • v.18 no.4
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    • pp.47-52
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    • 2013
  • In the present study, the turbulent flow from an annular jet is investigated by using large eddy simulation. Particularly, the effect of the ratio of the inner and outer diameters is one of the main interests of this study. The instantaneous fields presented in this paper showed that behind the jet exit the backflow region, as well known in literatures, exists, and its detailed behavior depends on the ratio of the inner and outer diameters ($D_1/D_2$). The dependence on $D_1/D_2$ is attributed to the different shear layer development according to $D_1/D_2$. At small $D_1/D_2$, the development of the outer shear layer is similar to that from the circular jet. However, with increasing $D_1/D_2$, the interaction between the outer and inner shear layers becomes strong, resulting in fast transition to turbulence.

Wideband Slow Light in a Line-defect Annular Photonic-crystal Waveguide

  • Kuang, Feng;Li, Feng;Yang, Zhihong;Wu, Hong
    • Current Optics and Photonics
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    • v.3 no.5
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    • pp.438-444
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    • 2019
  • In this theoretical study, a line-defect photonic-crystal waveguide hosted in an annular photonic crystal was demonstrated to provide high-performance slow light with a wide band, low group-velocity dispersion, and a large normalized delay-bandwidth product. Combined with structural-parameter optimization and selective optofluid injection, the normalized delay-bandwidth product could be enhanced to a large value of 0.502 with a wide bandwidth of 58.4 nm in the optical-communication window, for a silicon-on-insulator structure. In addition, the group-velocity dispersion is on the order of $10^5$ ($ps^2/km$) in the slow-light region, which could be neglected while keeping the signal transmission unchanged.

Calculation for the pattern degradation of the parabolic reflector caused by both the surface roughness of the reflector and the structural misalignment (반사판의 표면거칠기와 구조의 오정렬에 의한 파라볼라 반사판 안테나 패턴 일그러짐 계산)

  • 김주완;김병성;남상욱;이충웅
    • Journal of the Korean Institute of Telematics and Electronics A
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    • v.32A no.1
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    • pp.36-44
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    • 1995
  • For a parabolic reflector antenna, a simple method is presented for computing efficiently the average power pattern degradations caused by the surface roughness of the reflector and misalignments between the reflector and the feed. In this procedure, both nonuniform surface errors and nonuniform illuminations are employed. The assumptions to derive the expressions are that in each annular region of the antenna, the rms value of the surface roughness is known, and in a zone in a annular region, the phase error by misalignments is constant, and can be taken to its value at the center of the zone. Detailed parametric studies are performed with derived expressions to determine the effects of those errors and illumination tapers on parameters such as gain and sidelobe levels.

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Correlation of Convective Boiling Heat Transfer in a Horizontal Tube for Pure Refrigerants and Refrigerant Mixtures (순수 및 혼합냉매의 유동증발 열전달 상관식)

  • Shin, J.Y.;Kim, M.S.;Ro, S.T.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.8 no.2
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    • pp.254-266
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    • 1996
  • Boiling heat transfer coefficients of pure refrigerants(R22, R32, R125, R134a, R290, and R600a) and refrigerant mixtures(R32/R134a and R290/R600a) are measured experimentally and compared with several correlations. Convective boiling term of Chen's correlation predicts experimental data for pure refrigerants fairly well(root-mean-square error of 12.1% for the quality range over 0.2). An analysis of convective boiling heat transfer of refrigerant mixtures is performed for an annular flow to study degradation of heat transfer. Annular flow is the subject of this analysis because a great portion of the evaporator in refrigeration or air conditioning system is known to be in the annular flow regime. Mass transfer effect due to composition difference between liquid and vapor phases, which is considered as a driving force for mass transfer at interface, is included in this analysis. Correction factor $C_F$ is introduced to the correlation for the pure substances through annular flow analysis to apply the correlation to the mixtures. The flow boiling heat transfer coefficients are calculated using the correlation considering nucleate boilling effect in the low quality region and mass transfer effect for nonzazeotropic refrigerant mixtures.

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대칭 및 비대칭 binary filter가 수차를 포함한 광학계의 축상 GAIN에 미치는 영향

  • 최기준;정창섭;심상현
    • Korean Journal of Optics and Photonics
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    • v.12 no.3
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    • pp.165-171
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    • 2001
  • We discuss the influence of annular binary filters on the axial PSF of imaging systems which are apodized by a radiallysymmetric filter and have spherical aberration and coma. In this paper we consider a whole family of annular binary fIlters in two cases. First, the binary filters are composed of two transparent annuli of the same area. Second, the binary filters are composed of a central clear circle and a concentric annular aperture with area bigger than that of the inner circle. In order to investigate the influence of the proposed filters on the axial PSF, we may use the axial resolution gains, which evaluate in terms of the FWHM of the intensity in the focal region of an apodized imaging system in comparison with that corresponding to a nonapodized one. We evaluate the PSF for the conventional and confocal systems having an aberration. ation.

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Estimation of Secondary Flow Pressure of an Annular Injection Type Supersonic Ejector Using Fabri-Choking (패브리-초킹을 이용한 환형분사 초음속 이젝터 부유동 압력 예측)

  • Kim Sehoon;Jin Jungkun;Kwon Sejin
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • v.y2005m4
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    • pp.405-408
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    • 2005
  • A theoretical analysis is developed for an annular injection type supersonic ejector having a second-throat downstream under the assumption that the Fabri-chocking is placed in mixing chamber. Non-mixing theory is applied to formulate secondary flow pressure in the region between inlet of the mixing chamber and Fabri-chocking. To describe the shock standing at the inlet of the mixing chamber, two dimensional oblique shock relations are used and it is assumed that the shock affects only primary flow at Fabri-chocking plane. In conclusion, it agrees well with experiments in case of small contracting angle of mixing chamber, under 4degrees.

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A Fundamental Study of the Subsonic Spiral Jet (아음속 스파이럴 제트 유동에 관한 기초적 연구)

  • Cho, Wee-Bun;Kim, Heuy-Dong
    • Proceedings of the KSME Conference
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    • 2003.11a
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    • pp.502-507
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    • 2003
  • Spiral jet is characterized by a wide region of the free vortex flow with a steep axial velocity gradient, while swirl jet is largely governed by the forced vortex flow and has a very low axial velocity at the jet axis. However, detailed generation mechanism of spiral flow components is not well understood, although the spiral jet is extensively applied in a variety of industrial field. In general, it is known that spiral jet is generated by the radial flow injection through an annular slit which is installed at the inlet of convergent nozzle. The objective of the present study is to understand the flow characteristics of the spiral jet, using a computational method. A finite volume scheme is used to solve 3-dimensional Navier-Stokes equations with RNG ${\kappa}-{\varepsilon}$ turbulent model. The computational results are validated by the previous experimental data. It is found that the spiral jet is generated by coanda effect at the inlet of the convergent nozzle and its fundamental features are dependent the pressure ratio of the radial flow through the annular slit and the coanda wall curvature.

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A study on the development of the velocity and temperature fields in a laminar flow through an eccentric annular ducts (偏心된 二重圓管의 環狀部를 지니는 層流流動에서의 連度場 및 溫度場의 確立에 대한 硏究)

  • 이택식;이상산
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.10 no.6
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    • pp.861-869
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    • 1986
  • A numerical study has been conducted on the development of the velocity and temperature fields in a laminar flow through an eccentric annular duct. A bipolar coordinates system is adopted, and a numerical program is developed to analyze 3-dimensional parabolic flow problems. In the analysis of the velocity field, the entrance length has been defined as the distance where the axial pressure gradient is greater than that of the developed velocity field by 5%. The dimensionless hydrodynamic entry length increases with increasing eccentricity. In the transverse flow fields, the reverse flow region along the wall due to the developing axial velocity near the entrance of the duct is found. In the analysis of the temperature field, the thermal entry length has been defined as the axial distance where the mean fluid temperature is 5% less than that of the developed temperature field. The dimensionless thermal entry length increases as eccentricity or Prandtl number increases. The overshoot of the mean Nusselt number over the developed value at the zero-temperature wall is encountered, and the rate of the overshoot increases with the increase of the eccentricity and Prandtl number.