• Title/Summary/Keyword: 혼합대류

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Three-Dimensional Numerical Study on Mixed Convective Vortex Flow in Rectangular Channels at High Prandtl Number (사각채널 내 고 Pr 수의 혼합대류 볼텍스 유동에 관한 3차원 수치적 연구)

  • Piao, Ri-Long;Bae, Dae-Seok
    • Proceedings of the Korean Society of Marine Engineers Conference
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    • 2005.11a
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    • pp.29-30
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    • 2005
  • A three-dimensional numerical calculation has been performed to investigate mixed convective vortex flow in rectangular channels(width/height=4) with the upper part cooled and the lower part heated uniformly. In this study, the Prandtl number was 909, the Reynolds number was varied from 0 to $9.6{\times}10^{-2}$ and the Rayleigh number from $10^3$ to $5{\times}10^4$. The governing equations were discretized using the finite volume method. From a parametric study, velocity and temperature distributions were obtained and discussed. It is found that vortex flow of mixed convection in rectangular channels can be classified into three flow patterns which depend on Reynolds and Rayleigh numbers, and the regular vortex structure disappears around Rayleigh number $5{\times}10^4$.

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The study of mixed convection in a rectangular enclosure for indoor air control (실내공기 제어를 위한 사각공간내의 혼합대류에 관한 연구)

  • 이철재;정한식;권순석
    • Journal of Ocean Engineering and Technology
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    • v.10 no.4
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    • pp.109-117
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    • 1996
  • The numerical and experimental studies on the mixed convection of a rectangular enclosure for indoor air control has been studied numerically using the finite volume method and experimentally with holographic interferometry and Laser apparatus. The parameters studied here are Pr= 0.71, $30{\leq}Re{\leq}600$, $700{\leq}Gr{\leq}100000$ and the positions of an outlet. The results show streamlines, isothrems, velocity distributions and photograph of holographic interferometry and streamlines. It is found that the minimum cell occurs at Re=100, Gr=10000. The mean Nusselt numbers can be expressed by the correlation equation $Nu=C{\cdot}Gr^a$ $Re^b.$ The comparison of numerical and experimental results shows a good agreement.

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3-D Numerical Analysis on a low Reynolds Number Mixed Convection in a Horizontal Rectangular Channel (수평 사각채널 내 저 레놀즈수 혼합대류 유동의 3차원 수치해석)

  • Piao, Ri-Long;Bae, Dae-Seok
    • Proceedings of the Korean Society of Marine Engineers Conference
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    • 2005.06a
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    • pp.210-215
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    • 2005
  • A three-dimensional numerical simulation is performed to investigate on a low Reynolds number mixed convection in a horizontal rectangular channel with the upper part cooled and the lower part heated uniformly. The three-dimensional governing equations are solved using a finite volume method. For convective term, the central differencing scheme is used and for the pressure correction, the PISO algorithm is used. Solutions are obtained for A=4, Pr=0.72, 10, 909, the Reynolds number ranging from $2.1{\times}10^{-2}$ to $1.2{\times}10^{-1}$, the Rayleigh number is $3.5{\times}10^4$. It is found that vortex roll structures of mixed convection in horizontal rectangular channel can be classified into three roll structures which affected by Prandtl number and Reynolds number.

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Characteristics of the Mixed Convection Flow and Heat Transfer in a Channel with Open Cavity (개방된 캐비티를 가진 채널 내에서의 혼합대류 유동과 열전달 특성)

  • Ko, Y.C.;Bae, D.S.;Kim, N.S.
    • Journal of Power System Engineering
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    • v.11 no.4
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    • pp.56-64
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    • 2007
  • A numerical simulation is carried out mixed convection in horizontal channel with a heat source from below of rectangular cavity. Finite volume method was employed for the discretization and PISO algorithm was used for calculating pressure term. The parameters governing the problem are the Reynolds number ($10^{-2}{\leq}Re{\leq}50$), the Rayleigh number ($10^3{\leq}Ra{\leq}2.06{\times}10^5$), the Prandtl number ($0.72{\leq}Pr{\leq}909$), the aspect ratio ($0.5{\leq}AR=W/H{\leq}2$) and the angle of inclination ($0^{\circ}{\theta}60^{\circ}$). Mean Nusselt number distributions were obtained and effect of Reynolds number, Rayleigh number and Prandtl number on mixed convection in the horizontal channel with rectangular cavity were investigated.

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Analysis of Mixed Convection Heat Transfer in Arbitrarily Shaped Flat Tubes (임의형상을 갖는 납작관에서의 혼합대류 열전달 해석)

  • 박희용;박경우;이상철
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.13 no.5
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    • pp.398-410
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    • 2001
  • The flow and heat transfer characteristics for three-dimensional mixed convection flows in a radiator flat tube with U--shaped grooves are analyzed numerically. The flow and temperature fields are calculated by using the modified SIMPLE algorithm for irregular geometry. One tube specification among the various flat tube exchangers is recommended by considering the heat transfer and pressure drop. The effects of variation of coolant flow conditions and external air conditions on the flow and the thermal characteristics for the selected tube are investigated. the results show that inlet velocity of coolant flow is the very important factor in heat transfer and pressure drop, and top side is better position than the others as fin cleave to tube.

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Heat transfer of Mixed convection in rectangular space with constant heat flux (일정 열유속의 열원을 갖는 사각공간의 혼합대류 열전달)

  • 조대환
    • Journal of Advanced Marine Engineering and Technology
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    • v.23 no.4
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    • pp.552-558
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    • 1999
  • Ventilation of the marine engine room is very important for the health of the workers as well as the normal operation of machines. To find proper ventilation conditions of this engine room numerical simulation with a standard k-$\varepsilon$model was carried out. In the present study the marine engine room is considered as a closed space with a heat source and forced ventilation ducts. The injection angle of air supply is found to be important. Injection with a downward angle depresses recirculation flow causing a strong stream in the wider space of the room Ventilation and removal of the released heat are promoted with this pattern, There is a possibility of local extreme heating at the upper surface of the engine when supply and exhaust ports of air are in bilateral symmetry.

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An Experiment and Numerical Analysis of Mixed Convection in a Rectangular Space with Variable Partition (가변 격판을 갖는 사각공간 내의 혼합대류에 대한 실험과 수치해석)

  • 이광성;신재호;이중섭;정한식;정효민
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.13 no.12
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    • pp.1230-1235
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    • 2001
  • The laminar convection heat transfer in a ventilated space with various horizontal partitions was studied numerically and experimentally. The experimental results by holographic interferometer showed good agreements with the numerical results. For the numerical study, the governing equations were solved by using a finite volume method for $46.6\leqRe\leq1332,\;1460\leqGr\leql1585$, Pr=0.71 and the variations of partition lengths. The isotherms and velocity vectors have been represented for various parameters. As the length of partition increases, the convection heat transfer decreases. Based on the numerical data, a correlation was obtained for the dimensionless mean Nusselt number in terms of $Gr/Re^2$. In the region of $Gr/Re^2$<1, the mean Nusselt number was very small, but in the region of $Gr/Re^2\geq1$, the mean Nusselt number was constant.

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Non-gray Radiation with Turbulent Convection in the Entrance Region of a Smooth Tube (매끈한 튜브의 입구 영역에서 난류유동에 의한 대류와 비회복사)

  • Seo, T.B.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.7 no.4
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    • pp.667-680
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    • 1995
  • 튜브 내의 입구영역에서 난류 유동에 의한 대류와 비회복사(non-gray radiation)가 동시에 일어날 때의 열전달특성을 수치해석적으로 연구하였다. 작동유체는 이산화탄소, 수증기, 질소의 혼합가스라고 가정하였다. 지배방정식을 계산하기 위해 유한차분법이 이용되었고, 복사전달방정식을 이차편미분방정식으로 바꾸기 위해 P-1 근사법이 사용되었다. 그리고 혼합가스의 비회흡수계수(non-gray absorption coefficient)는 지수광폭밴드모형(exponential wide band model)을 이용해서 구하였다. 열전달특성에 대한 온도조건의 영향을 조사하기 위해 튜브의 축방향에 대한 평균 온도와 뉴셀트수(Nusselt number)의 변화를 몇 가지 다른 온도조건에 대해 나타내었다. 또한, 가스의 성분조성에 대한 영향을 조사하였으며, 이러한 결과에 기초해서 튜브 내에서 난류유동에 의한 대류와 비화복사가 동시에 일어날 때의 복사 뉴셀트수를 쉽게 예측할 수 있는 방법을 제시하였다.

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A Study of Mixed Convection on a Flat Plate with an Unheated Starting Length (비가열부가 있는 평판에서의 혼합대류에 관한 연구)

  • 김민수;강영규;백병준;박복춘
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.5
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    • pp.1304-1312
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    • 1993
  • The buoyancy effects on mixed convection heat transfer over a flat plate surface with unheated starting length is reported. The governing equations are solved by a finite difference method using Patankar scheme and the solution was numerically obtained for various mixed convection parametr $Gr_{x}/Re_{x}^3$, and Prandtl number of 0.7 Local heat flux was measured by using Schilieren Interferometer. The local heat transfer results show that the presence of the unheated starting length can significantly accentuate the effects of buoyancy. The degree of accentuation of the buoyancy effects is strongly influenced by the magnitude of $Gr_{x}/Re_{x}^3$. When the parameter is larger than the order of $10^{-3}$, the contribution of natural convection to the heat transfer coefficients increased significantly due to the unheated starting length. In contrast, when $Gr_{x}/Re_{x}^3$ is smaller then about $10^{-5}$ , the buoyancy contribution is essentially unaffected by the unheated starting length. The shape of the velocity profile is also found to be highly responsive to the interaction between the buoyancy and the starting length.

Retrieval of Nitrogen Dioxide Column Density from Ground-based Pandora Measurement using the Differential Optical Absorption Spectroscopy Method (차등흡수분광기술을 이용한 지상기반 Pandora 관측으로부터의 대기 중 이산화질소 칼럼농도 산출)

  • Yang, Jiwon;Hong, Hyunkee;Choi, Wonei;Park, Junsung;Kim, Daewon;Kang, Hyeongwoo;Lee, Hanlim;Kim, Joon
    • Korean Journal of Remote Sensing
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    • v.33 no.6_1
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    • pp.981-992
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    • 2017
  • We, for the first time, retrieved tropospheric nitrogen dioxide ($Trop.NO_2$) vertical column density (VCD) from ground-based instrument, Pandora, using the optical density fitting based on Differential Optical Absorption Spectroscopy (DOAS)in Seoul for the period from May 2014 to December 2014. The $Trop.NO_2$ VCDs retrieved from Pandora were compared with those obtained from Ozone Monitoring Instrument (OMI). A correlation coefficient (R) between those retrieved from Pandora and those obtained from OMI is 0.55. To compare with surface $NO_2$ VMRs obtained from in-situ, Trop. $NO_2$ VCDs retrieved from Pandora and those obtained from OMI are converted into $NO_2$ VMRs in boundary layer (BLH $NO_2$ VMRs) using data measured from Atmospheric Infrared Sounder (AIRS). Surface $NO_2$ VMRs obtained from in-situ range from 5.5 ppbv to 61.5 ppbv. BLH $NO_2$ VMRs retrieved from Pandora and OMI range from 2.1 ppbv to 44.2 ppbv and from 0.9 ppbv to 11.6 ppbv, respectively. The range of BLH $NO_2$ VMRs retrieved from OMI is narrower than that of BLH $NO_2$ VMRs retrieved from Pandora and surface $NO_2$ VMRs obtained from in-situ. There is a batter correlation between surface $NO_2$ VMRs obtained from in-situ and BLH $NO_2$ VMRs retrieved from Pandora (R= 0.50)than the correlation between surface $NO_2$ VMRs obtained from in-situ and BLH $NO_2$ VMRs retrieved from OMI (R = 0.36). This poor correlation is thought to be due to the lower near-surface sensitivity of the satellite-based instrument (OMI) than Pandora, the ground-based instrument.