• Title/Summary/Keyword: Boundary Layer

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A Study of Conjugate Laminar Film Condensation on a Flat Plate (수평평판에서 복합 층류 막응축에 대한 연구)

  • Lee Euk-Soo
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.17 no.4
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    • pp.303-311
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    • 2005
  • The problem of conjugate laminar film condensation of the pure saturated vapor in forced flow over a flat plate has been investigated as boundary layer solutions. A simple and efficient numerical method is proposed for its solution. The interfacial temperature is obtained as a root of 3rd order polynomial for laminar film condensation, and it is presented as a function of the conjugate parameter. The momentum and energy balance equations are reduced to a nonlinear system of ordinary differential equations with four parameters: the Prandtl number, Pr, Jacob number, $Ja^{\ast}$, defined by an overall temperature difference, a property ratio R and the conjugate parameter ${\zeta}$. The approximate solutions thus obtained reveal the effects of the conjugate parameter.

A Study on the Heat Transfer Characteristics on Flat Plate Surface by Two-dimensional Impinging Air Jet (평판전열면(平板傳熱面)에 충돌(衝突)하는 2차원충돌분류계(二次元衝突噴流系)의 열전달특성(熱傳達特性)에 관(關)한 연구(硏究))

  • Lee, Y.H.;Kim, S.P.;Seo, J.Y.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.3 no.1
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    • pp.61-68
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    • 1991
  • The purpose of this study is to investigate the heat transfer characteristics and the flow structure in the case of rectangular air jet impinging vertically on the flat heating surface. The maximum value of Nusselt number at stagnation point is observed at H/B=10. It is found that this trend has been caused by the effect of stretching of large scale vortex in the stagnation region. For potential core region the Nusselt number distribution in the downstream of the stagnation point decreases gradually and begins to increase at about X/B=3. From the flow visualization it could be seen that small eddy produced from the nozzle edge grows in large scale and that large scale eddy disturbed the thermal boundary layer on the heating plate. The local average Nusselt number becomes maximum at X/B=0.5 regardless of H/B variation.

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Analysis on the Coldness Release Process of Ice Storage Tank (빙축열조의 방냉과정에 대한 해석)

  • Yoo, H.S.;Kim, Y.I.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.1 no.1
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    • pp.9-20
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    • 1989
  • This paper presents an analysis to predict thermal behaviors of water in ice storage tank during the coldness release process. To deal with complicated transient phenomena due to ice-water phase change and the density inversion, a theoretical model which consists of initial perfectly mixed, stratified and thermal diffusion state was introduced and a criterion on the growth of thermal boundary layer was developed. The analysis includes considerations on the type of ice-making heat exchanger, refrigerator on/off and tank arrangement. Also, discussions on the various parameters and operating conditions which have influence on the performance of the system were made. Finally, simulated results were shown, which agreed with experiments in trends reasonably.

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A Study on Improvement of Performance for Perforated Type Total HEX Element (다공형 유로를 적용한 전열교환기 소자의 성능향상에 관한 연구)

  • Kwak, Kyung-Min;Bai, Cheol-Ho;Kim, Jee-Yong;Chu, Euy-Sun
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.19 no.7
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    • pp.529-536
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    • 2007
  • The perforated type element for a heat recovery ventilation system has been studied to improve the performance. Four holes of diameter of 6mm are punched out for each flow channel to break the boundary layer development and increase the turbulence. KS cooling and heating conditions and test procedures are applied for study. The efficiencies are compared to those of the typical element with smooth surface. For cooling operations, the temperature, latent and enthalpy efficiencies increase 2.5%, 18% and 8%, respectively. For heating operations, the temperature, latent and enthalpy efficiencies increase 3%, 5% and 3.2%, respectively.

Buckling Stability of Timoshenko Beams on Two-Parameter Elastic Foundations under an Axial Force (축력을 받고 두 파라메타 탄성기초 위에 놓인 티모센코 보의 좌굴 안정성)

  • 정승호
    • Journal of the Korea Society for Simulation
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    • v.8 no.2
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    • pp.111-122
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    • 1999
  • The paper presents a stability analysis of uniform Timoshenko beams resting on two-parameter elastic foundations. The two-parameter elastic foundations were considered as a shearing layer and Winkler springs in soil models. Governing equations of motion were derived using the Hamilton's principle and finite element analysis was performed and the eigenvalues were obtained for the stability analysis. The numerical results for the buckling stability of beams under axial forces are demonstrated and compared with the exact or available confirmed solutions. Finally, several examples were given for Euler-Bernoulli and Timoshenko beams with various boundary conditions.

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Soil-Structure Interaction Analysis in the Time Domain Using Explicit Frequency-Dependent Two Dimensional Infinite Elements (명시적 주파수종속 2차원 무한요소를 사용한 지반-구조물 상호작용의 시간영역해석)

  • 윤정방;김두기
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 1997.10a
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    • pp.42-49
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    • 1997
  • In this paper, the method for soil-structure interaction analyses in the time domain is proposed. The far field soil region which is the outside of the artificial boundary is modeled by using explicit frequency-dependent two dimensional infinite elements which can include multiple wave components propagating into the unbounded medium. Since the dynamic stiffness matrix of the far field soil region using the proposed infinite elements is obtained explicitly in terms of exciting frequencies and constants in the frequency domain, the matrix can be easily transformed into the displacement unit-impulse response matrix, which corresponds to a convolution integral of it in the time domain. To verify the proposed method for soil-structure interaction analyses in the time domain, the displacement responses due to an impulse load on the surface of a soil layer with the rigid bed rock are compared with those obtained by the method in the frequency domain and those by models with extend finite element meshes. Good agreements have been found between them.

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Non Darcy Mixed Convection Flow of Magnetic Fluid over a Permeable Stretching Sheet with Ohmic Dissipation

  • Zeeshan, A.;Majeed, A.
    • Journal of Magnetics
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    • v.21 no.1
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    • pp.153-158
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    • 2016
  • This paper aims to discuss the Non Darcy boundary layer flow of non-conducting viscous fluid with magnetic ferroparticles over a permeable linearly stretching surface with ohmic dissipation and mixed convective heat transfer. A magnetic dipole is applied "a" distance below the surface of stretching sheet. The governing equations are modeled. Similarity transformation is used to convert the system of partial differential equations to a system of non-linear but ordinary differential equations. The ODEs are solved numerically. The effects of sundry parameters on the flow properties like velocity, pressure, skin-friction coefficient and Nusselt number are presented. It is deduced the frictional resistance of Lorentz force decreases with stronger electric field and the trend reverses for temperature. Skin friction coefficient increase with increase in ferromagnetic interaction parameter. Whereas, Nusselt number decrease.

An Experimental Investigation of the Heat Transfer Characteristics on the Endwall Surface Within the Plane Turbine Cascade (선형 터빈케스케이드 끝벽의 열전달 특성에 관한 연구)

  • 양장식;나종문;이기백
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.9
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    • pp.2386-2398
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    • 1995
  • The paper describes the results of an experimental investigation of the heat transfer rate on the endwall surface within the plane turbine cascade passage and includes the effect of the heat transfer for the two different boundary layer thicknesses and Reynolds numbers. The limiting streamlines on the endwall surface have been visualized by the oil film method in order to compare with the endwall heat transfer. The hue-capturing method using the termochromatic liquid crystals with great spatial resolution has been used to provide the local distribution of the endwall heat transfer coefficients. Because the detailed contours of the local heat transfer coefficients over the entire endwall can be obtained from the hue-capturing method, it has been possible to obtain information on the endwall heat transfer within the plane turbine cascade passage from these heat transfer contours.

An Experimental Study on Wake Cavity Flow Characteristics of Two-dimensional Wedge Shaped Control Fins (2차원 쐐기형 제어핀 후류의 공동유동 특성에 대한 실험연구)

  • Jeong, So-Won;Ahn, Byoung-Kwon
    • Journal of the Society of Naval Architects of Korea
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    • v.53 no.3
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    • pp.180-187
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    • 2016
  • As distinct from a slender body, the separation of the boundary layer on a bluff body give rise to complex wakes in which various kinds of vortices form, develop and interact with each other. In this paper, we investigate cavitation wake field behind wedge shaped two-dimensional fin models. Eight different models are tested at the Chungnam National University Cavitation Tunnel (CNU-CT). First, we measure wake cavity shapes and compare with numerical results, which shows the good agreement with each other. In addition, we demonstrate that wake flow characteristics of the control fin are clearly identified by the correlation analysis of high-speed camera images and pressure fluctuation measurements.

DSP-based Robust Nonlinear Speed Control of PM Synchronous Motor Using Adaptive and Sliding Mode Control Techniques

  • Baik, In-Cheol;Kyeong-Hwa;Kwan-Yuhl;Youn, Myung-Joong
    • Journal of Electrical Engineering and information Science
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    • v.3 no.2
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    • pp.251-260
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    • 1998
  • A DSP-based robust nonlinear speed control of a permanent magnet synchronous motor(PMSM) which is robust to unknown parameter variations and speed measurement error is presented. The model reference adaptive system(MRAS) based adaptation mechanisms for the estimation of slowly varying parameters are derived using the Lyapunov stability theory. For the disturbances or quickly varying parameters. a quasi-linearized and decoupled model including the influence of parameter variations and speed measurement error on the nonlinear speed control of a PMSM is derived. Based on this model, a boundary layer integral sliding mode controller to improve the robustness and performance of the nonlinear speed control of a PMSM is designed and compared with the conventional controller. To show the validity of the proposed control scheme, simulations and experimental works are carried out and compared with the conventional control scheme.

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