• 제목/요약/키워드: Average Nusselt number

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브로민화 수은(I)(Hg2Br2) 물리적 증착공정의 2차원 밀폐공간에서 이중확산 자연 대류에서의 물질전달 연구: Part II. 물질전달 (Mass transfer study of double diffusive natural convection in a two-dimensional enclosure during the physical vapor transport of mercurous bromide (Hg2Br2): Part II. Mass transfer)

  • 하성호
    • 한국결정성장학회지
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    • 제33권4호
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    • pp.145-152
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    • 2023
  • 2.31 × 104 ≤ Grt ≤ 4.68 × 104의 범위에서 온도 Grashof 수(Grt)의 변화에 대하여, 소스와 결정영역에서의 평균 Nusselt수를 나타내고 있다. 결정영역에서의 평균 Nusselt 수가 소스영역에서의 평균 Nusselt 수 보다 2배 이상 큰 것으로 나타나고 있다. 소스영역에서의 평균 Nusselt 수는 온도 Grashof 수(Grt)에 대하여, 증가하는 경향을 보여주고 있으며, 반면에 결정영역에서의 평균 Nusselt 수는 온도 Grashof 수(Grt)에 대하여, 감소하는 경향을 나타나고 있다. 3.28 × 105 ≤ Grs ≤ 4.43 × 105의 범위에서 농도 Grashof 수(Grs)의 변화에 대하여, 소스와 결정영역에서의 평균 Sherwood 수를 나타내고 있다. 소스영역과 결정영역에서의 평균 Sherwood 수는 농도 Grashof 수(Grs)가 증가함에 따라, 감소하는 경향을 보이고 있다. 결정영역에서의 평균 Sherwood 수는 소스영역에서의 평균 Sherwood 수보다 약 4배 정도 크다.

루우버휜형 열교환기의 열전달특성에 관한 실험적 연구 (Experimental Study of Heat Transfer Characteristics in the Louvered-Fin Type Heat Exchanger)

  • 전창덕;홍주태;이진호
    • 설비공학논문집
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    • 제8권1호
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    • pp.120-139
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    • 1996
  • Experiment was performed to study the heat transfer characteristics in 27 kinds of 15 : 1 scale models of multi-louverred fin heat exchangers with a wide range of variables(R $e_{Lp}$ =100~1, 800, $L_p$/F$p$=0.3~0.9, $\theta$=20$^{\circ}$~40$^{\circ}$). Thermofoil heaters were used to heat the louver fins and the local average Nusselt number for each louver in the louver array was obtained at constant wall temperature conditions. Correlations are developed to predict the heat transfer characteristics and drag coefficients. Generally, the heat transfer characteristics in the multi-louvered fins is shown to be similar to those of the laminar heat transfer on a flat plate. As the Reynolds number, the louver pitch to fin pitch ratio$L_p$/F$p$and the louver angle($\theta$) increase respectively, the average Nusselt number increases, but the variation of average Nusselt number as a function of the louver angle is smaller than that as a function of the louver pitch to fin pitch ratio. In case of$L_p$/F$p$ <0.5, the average Nusselt number of the 3rd louver is especially lower than the others, it is expected that it is due to the flow structure such as a recirculation flow and a flow separation.

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수직평판에서 층류막상 응축열전달에 관한 해석적 고찰 (An analytical study on the heat transfer of the laminar filmwise condensation on a vertical surface)

  • 김형섭
    • 오토저널
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    • 제2권1호
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    • pp.21-31
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    • 1980
  • Two phase boundary layer equations of laminar filmwise condensation are solved by an approximate integral method under the following condition; saturated vapour flows vertically downward over a cooled surface of uniform temperature, the condensate film is so thin that the inertia and convection terms are neglected. The following conclusions are drawn under the above assumptions. 1. free convection In case of the linear temperature profile in a liquid film, numerical results for the average coefficients of heat transfer may be expressed as N $u_{m}$=4/3,(G $r_{l}$ /4.H)$^{1}$4/ and in case of the quadratic profile, numerical results may be expressed as N $u_{m}$=2/1.682,(G $r_{l}$ /H)$^{1}$4/. 2. Forced convection When the temperature profile is assumed to be linear in a liquid film, numerical results fir the average heat transfer coefficients may be expressed as N $u_{m}$=(A, R $e_{l}$ /H)$^{1}$2/. This expression is compared with the experimental results hitherto reported; For theoretical Nusselt number (N $u_{m}$)$_{th}$<2*10$^{4}$, the experimental Nusselt number (N $u_{m}$)$_{exp}$ is on the average larger than theoretical Nusselt number (N $u_{m}$)$_{th}$ by 30%. For (N $u_{m}$)$_{th}$>2*10$^{4}$, experimental Nusselt number (N $u_{m}$)$_{exp}$ is about 1.6 times as large as theoretical Nusselt number (N $u_{m}$)$_{th}$. These large deviation may be caused by the presence of turbulence in the liquid film. In case of the quadratic temperature profile in a liquid film, numerical results for the average coefficients of heat transfer may be expressed as N $u_{m}$'=(2,A,Re/H)$^{1}$2/. This formular shows that theoretical Nusselt number (N $u_{m}$)$_{th}$ is larger than experimental Nusselt number (N $u_{m}$)$_{exp}$ by 60%. It is speculated that when the temperature difference between cooled surface and saturated vapour is small, temperature profile in a liquid film is quadratic.quadratic.. quadratic.quadratic..atic..

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Studies on Nusselt and Sherwood number for diffusion-advective convection during physical vapor transport of Hg2Br2

  • Kim, Geug Tae;Kwon, Moo Hyun
    • 한국결정성장학회지
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    • 제31권3호
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    • pp.127-136
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    • 2021
  • This paper is dedicated to numerical simulation for diffusion-advective convection in a square cavity during physical vapor transport of Hg2Br2. Flow characteristics of the temperature difference between the source and crystal regions, 50℃ (300℃ → 250℃), partial pressures of component argon of 20 Torr and 100 Torr are investigated and presented as velocity vectors and streamlines, isotherms and iso-mass concentrations contours. Moreover, alterations of average Nusselt and average Sherwood numbers with (a) the source and crystal regions, (b) the pressures of component argon of 20 Torr and 100 Torr are analyzed and addressed in details. Both average Nusselt and average Sherwood numbers are seen to decrease with the increasing values of the partial pressures of component argon. Also, it is found that for the two different partial pressures of component argon, average Nusselt numbers at the source region are greater than at the crystal region, and inversely, average Sherwood numbers at the crystal region are greater than the source region by a factor of 3.

딤플과 돌출이 설치된 수평채널의 열전달 및 압력강하 특성에 관한 수치해석적 연구 (Numerical Study on Heat Transfer and Pressure Drop Characteristics in a Horizontal Channel with Dimple and Protrusion Arrays)

  • 김지훈;허주녕;신지영;손영석
    • Journal of Advanced Marine Engineering and Technology
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    • 제36권1호
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    • pp.57-63
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    • 2012
  • 열전달 향상을 위하여 이차유동을 발생시켜 열전달을 증가시키는 방법에는 여러 가지가 있다. 본 연구에서는 수평채널에 딤플과 돌출을 설치하여 각각의 깊이와 높이를 변화시켰을 때의 압력강하 및 열전달 특성을 수치해석을 통하여 연구하였다. 딤플과 돌출은 수평채널의 윗면과 아래면 에 설치되었으며, 깊이 및 높이를 0.125, 0.25, 0.25, 0.3, 0.375로 하였다. 딤플의 경우, 후면부에서 높은 Nusselt 수가 나타났고 깊이가 커질수록 평균 Nusselt 수가 감소하였다. 돌출의 경우, 전면부에서 높은 Nusselt 수가 나타났고 높이가 커질수록 Nusselt 수가 증가하였다. 딤플과 돌출 모두 유속이 증가함에 따라 열전달이 향상되는 경향을 보였지만 성능계수는 감소하였다. 성능계수는 유속이 낮은 영역에서 가장 크게 나타났다.

미세유로를 갖는 납작관의 열·유동 해석 (Thermal and Flow Analysis of the Flat Tube with Micro-Channels)

  • 정길완;이관수;김우승
    • 대한기계학회논문집B
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    • 제23권8호
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    • pp.978-986
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    • 1999
  • In this study, the general thermal and flow characteristics of flat tube with micro-channels has been studied and the correlation of Nusselt number and friction factor is proposed. The optimal flat tube geometry is determined by optimal design process. It is assumed to be a three dimensional laminar flow in the analysis of thermal and flow characteristics. The periodic boundary condition is applied since the geometry of flat tube with micro-channels shows uniform cross-section in primary flow direction. Local Nusselt number is examined for thermal characteristics of each membrane, and module average Nusselt number and friction factor are calculated to determine the characteristics of the heat transfer and pressure drop in overall flat tube with microchannels. The correlations between Nusselt number and friction factor are given by Reynolds number, aspect ratio of membranes, and the width of flat tube. ALM (Augmented Lagrangian Multiplier) method is applied to the correlations to determine an optimal shape of flat tube. It is shown that the optimal aspect ratio of flat tube is approximately 1.0, irrespective of the width of flat tube and Reynolds number.

1열 원형 서브머지드 충돌수분류군에 의한 열전달의 실험적 연구 (Impingement Heat Transfer Within a Row of Submerged Circular Water Jets)

  • 엄기찬
    • 설비공학논문집
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    • 제22권8호
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    • pp.538-544
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    • 2010
  • An experimental investigation is presented to study the effect nozzle spacing, jet to plate spacing and Reynolds number on the local heat transfer to normally upward impinging submerged circular water jets on a flat heated surface. Nozzle arrays are a single jet(nozzle dia. = 8 mm), a row of 3 jets(nozzle dia. = 4.6 mm, nozzle spacing = 37.5 mm) and a row of 5 jets(nozzle dia. = 3.6 mm, nozzle spacing = 25 mm), and jet to plate spacing ranging from 16∼80 mm(H/D = 2∼10) is tested. Reynolds number based on single jet exit condition is varied 30000∼70000($V_o$ = 3∼7 m/s). Except for the condition of H/D = 10, the average Nusselt number of multi-jet is higher than that of single jet. For H/D = 2, average Nusselt number is increased by 50.3∼82.5% for a row of 3 jets and by 52.9∼65.2% on a row of 5 jets when compared to the average Nusselt number on the single jet.

평판 핀 튜브 열교환기의 공기측 강제대류 열전달계수에 대한 실험 및 수치계산 (Experimental Measurement and Numerical Computation on the Air-Side Forced Convective Heat Tranfer Coefficient in Plate Fin-Tube Exchangers)

  • 윤영환;팽진기;윤건식
    • 설비공학논문집
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    • 제18권9호
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    • pp.729-737
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    • 2006
  • Air-side forced convective heat transfer of a plate fin-tube heat exchanger is investigated by experimental measurement and numerical computation. The heat exchanger consists of staggered arrangement of refrigerant pipes of 10.2 m diameter and the pitch of fins is 3.5 m. In the experimental study, the forced convective heat transfer is measured at Reynolds number of 1082, 1397, 1486, 1591 and 1649 based on diameter of refrigerant piping and mean velocity. Average Nusselt number for the convective heat transfer coefficient is also computed for the same Reynolds number by commercial software of STAR-CD with standard $k-{\varepsilon}$ turbulent model. It is found that the relative errors of average Nusselt numbers between experimental and numerical data are less than 6 percentage in Reynolds number of $1082{\sim}1649$. The errors between experiment and other correlations are ranged from 7% to 32.4%. But the correlation of Kim at al is closest to the experimental data within 7% of the relative error.

사각채널에 설치된 배플이 열전달과 마찰계수에 미치는 효과 (Effects of Baffles on Heat Transfer and Friction Factors in a Rectangular Channel)

  • 안수환;강호근;배성택;송민호
    • Journal of Advanced Marine Engineering and Technology
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    • 제30권6호
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    • pp.693-701
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    • 2006
  • The present work investigates the local heat transfer characteristics and the associated frictional loss in a rectangular channel with inclined solid and perforated baffles to obtain the basic design data for gas turbine. Five different geometries of baffles such as 1) solid (without hole), 2) three holes, 3) six holes, 4) nine holes, 5) twelve holes were covered. A combination of two baffles of same overall size is used. The flow Reynolds number is ranged from 28,900 to 70,100. The placement of baffles augments the overall heat transfer greatly by combining both jet impingement and the boundary layer separation. The present results show that the average Nusselt number distribution is strongly dependent on number of holes in the baffle plates, i.e., the average Nusselt number increases with increasing number of holes. The friction factor decreases also with increasing the number of holes. however. its value increases with increasing the Reynolds number.

단일수분류 및 수분류군에 의한 열전달(2)-1열 수분류군- (Heat Transfer from Single and Arrays of Impinging Water Jets(II)-1 Row of Impinging Water Jets-)

  • 엄기찬;이종수;금성민
    • 대한기계학회논문집B
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    • 제21권9호
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    • pp.1115-1125
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    • 1997
  • Experiments have been conducted to obtain local and average heat transfer coefficients associated with impingement of a row of circular, free surface-water jets on a constant heat flux surface. Nozzle arrays are a row of 3 jets (nozzle dia.=4.6 mm) and a row of 5 jets (nozzle dia.=3.6 mm), and the nozzle configuration is Reverse cone type revealed good performance in heat transfer. Nozzle-to-plate spacings ranging from 16 mm to 80 mm were investigated for two jet center to center spacings 25 mm and 37.5 mm in the jet velocity of 3 m/s (R $e_{D}$=27000) to 8 m/s (R $e_{D}$=70000). For a row of 3 jets and a row of 5 jets, the stagnation heat transfer of the central jet is lower than that of adjacent jets. In the wall jet region between jets, for small nozzle-to-plate spacing and large jet velocity, the local maximum in the Nusselt number was observed, however, for small jet velocity or large nozzle-to-plate spacing, the local maximum was not observed. Except for the condition of $V_{O}$=8 m/s and H/D=10, the average Nusselt number reveals the following ranking: a row of 5 jets, a row of 3 jets, single jet. For a row of 3 jet, the maximum average Nusselt number occurs at H/D=8 ~ 10, and for a row of 5 jets, it occurs at H/D=2 ~ 4. Compared with the single jet, enhancement of average heat transfer for a row of 3 jets is approximately 1.52 ~ 2.28 times, and 1.69 ~ 3.75 times for a row of 5 jets.ets.s.