• 설비공학논문집
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• 제16권6호
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• pp.584-588
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• 2004

This work was performed to investigate the heat transfer characteristics of the circular fin-tube heat exchanger. This paper contains the experimental data for the seven kinds of fin geometries. The correlation of Stasiulevicius agreed with the experimental data at high Reynolds number, however not well at low Reynolds number. The Nusselt number was well correlated with Graetz number, and showed a transition near Gz=10. An empirical correlation proposed in the present work agreed well with the experimental data.

• 한국자동차공학회논문집
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• 제12권2호
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• pp.91-100
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• 2004

Plate heat exchangers (PHE) have been widely used in different industrial applications, because of high heat transfer efficiency per unit volume. Basic study is performed for PHE to the application of intercooler in automobile. In order to understand the flow phenomena in the plate heat exchanger, a channel which was formed by the upper and lower plate in single plate was considered as calculation domains. Because chevrons attached on the upper plate are brazed with chevrons attached on the lower plate, the flow channel has very complex configuration. This complex geometry was analyzed by Fluent. In order to validate this methodology the proper experimental and theoretical data are collected and compared with numerical results. Finally, due to the lack of experimental values for PHE to the application of intercooler, various chevron angles and air velocities at inlet were tested in terms of physical phenomena. From this point of view, results of velocity vector, path lines, static pressure, heat flux, heat transfer coefficient, and Nusselt number are physically reasonable and accepted for the solutions. From these results, the correlations for pressure drop and Nusselt number with respect to chevron angle and Reynolds number in specific PHE are obtained for the design purpose. Thus, the methodology of the flow analysis in the full geometry of the channel was established for the predictions of performance in plate heat exchanger.

• 설비공학논문집
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• 제8권4호
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• pp.561-575
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• 1996

The interaction of turbulent mixed convection and surface radiation in a three-dimensional channel with the heated blocks is analyzed numerically. Two blocks are maintained at high temperature and the other bottom and horizontal walls are insulated. S-4 method is employed to calculate the effect of the radiative heat transfer. The low Reynolds number k-$\varepsilon$ model proposed by Launder and Sharma is used to estimate the turbulent influence on the heat transfer enhancement. From above modeling, the effects of various channel specifications on the flow and heat transfer characteristics are investigated. The variables used for the present study are Reynolds number, block spacing, the channel height spacing for block and the emissivity. Average Nusselt numbers along the block surfaces are correlated and presented in terms of Reynolds number, emissivity and dimensionless geometric parameters. For the range of conditions in this study, average Nusselt numbers along the block surfaces are strongly influenced by the Reynolds numbers and channel height spacing for block but weakly influenced by the block spacing and the emissivity of the adiabatic walls.

• 대한기계학회논문집B
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• 제28권10호
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• pp.1139-1146
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• 2004

The effect of triangular tabs attached at the perimeter of jet nozzle on heat transfer enhancement was investigated experimentally. The modified flow structure was visualized using a smoke-wire method. Four different types of jet nozzle having 0, 4, 6 and 8 tabs were tested at jet Reynolds number Re=15,000 to investigate the effect of tabs on the variation of heat transfer rate. The local and average Nusselt numbers are increased with increasing the number of tabs. At nozzle-to-plate distance of L/D=4, the average Nusselt number was increased about 9.9% at Re=15,000 in the impingement region for the case of 8 tabs attachment. As the nozzle-to-plate distance increases, however, the heat transfer enhancement effect of triangular tabs is reduced. For the case of 4 tabs, the heat transfer enhancement is not so distinctive at L/D=8. As the protrusion depth of tabs into the jet flow increases, the heat transfer rate is also enhanced when the nozzle-to-plate distance is smaller than L/D=6.

• 설비공학논문집
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• 제18권9호
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• pp.698-706
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• 2006

Experiment and numerical calculation have been peformed to investigate mixed convection heat transfer between inclined parallel plates. Particle image velocimetry (PIV) with thermo-sensitive liquid crystal (TLC) tracers is used for visualizing and analysis. This method allows simultaneous measurement of velocity and temperature fields at a given instant of time. Quantitative data of the temperature and velocity are obtained by applying the color-image processing to a visualized image, and neural network is applied to the color-to-temperature calibration. The governing equations are discretized using the finite volume method. The results are presented for the Reynolds number ranges from 0.004 to 0.062, the angle of inclination, ${\Theta}$, from 0 to 45 degree and Prandtl number of the high viscosity fluid is 909. The results show velocity, temperature and mean Nusselt numbers distributions. It is found that the periodic flow of mixed convection between inclined parallel plates is shown at $0^{\circ}{\leq}{\Theta}<30^{\circ}$, Re<0.062, and the flow pattern can be classified into three patterns which depend on Reynolds number and the angle of inclination. The minimum Nusselt numbers occur at Re=0.05 regardless of the angle of inclination.

• 설비공학논문집
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• 제18권9호
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• pp.722-728
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• 2006

Natural convection flows in a cubical air-filled slanted cavity that has one pair of opposing faces isothermal at different temperatures, $T_h\;and\;T_c$, respectively, the remaining four faces having a linear variation from $T_c\;toT_h$ are numerically simulated by a solution code (PowerCFD) using unstructured cell-centered method. Special attention is paid to three-dimensional flow and thermal characteristics according to a new orientation (diamond type) for the cubical-cavity benchmark problem in natural convection. Comparisons of the average Nusselt number at the cold face are made with experimental benchmark solutions found in the literature. It is found that the code is capable of producing accurately the nature of the laminar convection in a cubical air-filled slanted cavity with differentially heated walls.

• 에너지공학
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• 제11권4호
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• pp.283-290
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• 2002

동심환형 곡관의 내벽면에서 일정한 열전달이 있는 경우에 대하여 혼합대류의 유동장 및 열전달계수를 수치적으로 구하였다. 유동장은 주흐름방향으로의 압력과 온도구배가 일정한 완전발달흐름으로 가정하였다. 유동장의 특성을 나타내는 물리적 변수인 반경비는 0.2, 0.5, Grashof수는 8000, 80000 그리고 Dean수는 0-900범위에서 계산을 실시하였다. 반경비, Grashof수, Dean수를 변화시키며 2차유동, 열유속, 마찰비, 열전달계수에 대한 수치해를 구하였다. 마찰비와 Nusselt수는 Dear수의 제곱근에 비례하게 증가됨을 볼 수 있다.

• 에너지공학
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• 제15권1호
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• pp.28-34
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• 2006

고온의 연소가스를 교란시키고 열교환 요소와 오랜시간 접촉하도록 원관을 옆으로 서로 맞대어 붙인 후 이 원관의 배열과 수직한 방향으로 연소가스가 흐르도록 설계된 열교환기에 대하여 실험적으로 열전달특성을 조사하기 위해서 유동이 충분히 발달한 영역에서 관 외부 원주방향으로 스테인레스 박판을 부착하고 직류 전원공급기를 통해 열유속을 주어, 관 주위의 대류열전달계수를 측정하였다. 실험 결과 세로피치 0.075 m, 가로피치 0.08 m이고 엇갈림 배열일 때 열전달계수가 15% 정도 차이가 크게 났으며, 레이놀즈수가 증가할수록 열전달계수도 증가함을 알 수 있었다. 또한 전체 평균 누셀트 수도 엇갈림 배열이 정렬배열에 비해 높게 나타났다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 추계 학술대회논문집
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• pp.83-88
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• 2006

Natural convection flows in a cubical air-filled cavity that has one pair of opposing faces isothermal at different temperatures, $T_h\;and\;T_c$ respectively, the remaining four faces having a linear variation from $T_c\;to\;T_h$ are numerically simulated by a solution code(PowerCFD) using unstructured cell-centered method. An extension to a previously published work, special attention of this work is paid to three-dimensional flow and thermal characteristics in nature convection according to new orientation at Ra= $1{\times}105$. Comparisons of the average Nusselt number at the cold face are made with benchmark solutions and experimental results found in the literature. It is demonstrated that the average Nusselt number on the cold face has a maximum value around the diamond-type inclination angle of $43.2^{\circ}\;at\;Ra=1{\times}105$. We also report the effect of new orientation on the type of flow and temperature structure in a cubical-cavity.

• Journal of Advanced Marine Engineering and Technology
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• 제34권2호
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• pp.235-242
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• 2010

본 연구는 열교환기의 가열된 표면위에 부착된 지열수 스케일의 조도 영향을 검증하기 위한 강제 대류 열전달에 관한 실험적 연구이다. 실험은 원형 원관 위에 5종류의 실리카 스케일 입자를 균일하게 부착하여 행하였다. Reynolds수는 13,000에서 50,000의 범위에서 행하였다. 국소와 평균 열전달 특성은 스케일 입자 크기와 레이놀즈수의 함수로서 측정하였으며 평균오염저항을 이들의 결과로부터 평가하고 그들의 특성들을 분석 하였다. 원관의 열전달 특성은 지열수 스케일의 오염에 의해, 특히 입자 크기에 의해 크게 변화하였다. 또한 국소와 평균 Nusselt수는 원관 간격과 Reynolds 수에 의해 크게 의존 되었다.