• Journal of Energy Engineering
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• v.9 no.4
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• pp.328-333
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• 2000

이 연구의 목적은 액정법을 이용하여 주름형상 판형 열 교환기에서의 내부유동과 열 전달 성능의 특성을 파악하는데 있으며 공기를 작동유체로 사용하였다. 과거에는 실험이 주로 판형 열 교환기의 입·출구에서의 열 전달 성능에만 관심이 집중되었다. 그러나 이 실험에서는 액정법을 이용하여 판형열교환기 셀 표면 위에서의 국소 누셀트수의 분포를 연구하였다. 레이놀즈수가 증가할수록 열 전달 성능은 증가하였으나 마찰계수는 감소하였다. 주름각이 증가할수록 열 전달 성능과 마찰계수는 모두 증가하였다. 국소 누셀트수 분포로부터 열 전달이 잘 일어나는 부분은 주름을 타고 넘어 들어온 두 유동이 만나는 곳이며 또한, 셀의 가운데 부분은 셀의 수직단면적이 커서 셀 표면과 유동의 접촉이 약하므로 작은 누셀트수를 가지는 것을 알 수 있다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.8 no.3
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• pp.241-249
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• 1984

두 개의 긴 수직평판핀을 가진 등온수평원통으로 부터의 자연대류 열전달을 2차원 유한차분법에 의한 수치해석으로 연구하였다. 축방향의 두 수직평판핀을 가진 수평원통으로 부터의 열전달은 Ra=$10^{6}$, Pr=5 및 무차원 $K_{f}$t/KD=0.5인 경우에 보통 원통에서의 열전도보다 5.32% 증가되었다. Ra와 Pr가 증가하면 국소핀 누셀트수는 증가하고 무차원핀 온도는 감소된다. 그 러나 무차원핀 변수가 증가하면 국소핀 누셀트수와 무차원핀 온도분포는 증가된다. 최대국소핀 누셀트수는 Ra=$10^{6}$인 경우에 상향핀과 하향핀의 (r-r$_{0}$)=0.1-0.2에서 존재한다. 수 직핀을 가진 원통주위에서 부력 유도된 유동은 보통 원통에서 보다 더욱 활발하였다. 따라서 Ra=$10^{6}$ , Pr=5인 경우에 핀 근방에서의 무차원 무차원반경 방향 속도는 보통원통의 경 우보다 큰 값을 가진다.다.다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.2
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• pp.265-279
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• 1986

Ra=$10^{6}$, Pr=5에서 관열전도율과 두께가 변화할 때의 단일수평관에서의 자연대류 열전달에 관하여 유한차분법을 이용하여 해석적으로 연구하였다. .delta.$_{w}$ /d$_{o}$ =0.1에서 관열전도율이 높을수록 높은 온도와 높은 국소 누셀트 수를 나타 내며, .theta.=20。에서의 원주방향속도는 (r-r$_{o}$ )=0.08에서 최대가 되며 반경방향속 도는 (r-r$_{o}$ )=0.14에서 최대가 된다. 관외벽온도는 관 두께가 증가함에 따라 거의 유사하게 감소한다. $K_{w}$ /K$_{f}$ =75에서 각도변위가 증가함게 따라 국소 누셀트수는 현저히 증가하나 관 두께가 증가함에 따라서는 감소한다. .delta.$_{w}$ / d$_{o}$ =0.1에서 평균 누셀트수와 평균 온도는 무차원 열전도율이 증가함에 따라 $K_{w}$ /K$_{f}$ ＞15에서는 평균 누셀트 수는 서서히 증가하고 평균 온도는 거의 같 은 값을 가지며 지수함수로 표시할 수 있었다. $K_{w}$ /K$_{f}$ =75,50에서 평균 누 셀트수와 온도는 무차원 관 두께가 증가함에 따라 거의 직선적으로 감소되며 선형 함 수로 나타낼 수 있었다.

• Solar Energy
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• v.13 no.1
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• pp.1-10
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• 1993

The purpose of this research is to investigate the characteristics of heat transfer in the downward axisymmetric free water jet system impinged on a flat oblique plate which has the uniform heat flux. Experimental conditions considered were Reynolds number, distance between nozzle and Bat plate, inclination angle of heater surface and nozzle exit velocity. Local Nusselt number was subjected to the influence of Re number, Pr number, oblique angle of heating surface and local position of flat plate. In the wall region of downward surface, The secondary peak point of heat transfer appeared at the local point of X/D=-8 from the stagnation point. The stagnation heat transfer rate of this experimental study augments 2.4 times than that of laminar theorical solution. The stagnation nusselt number is function of Reynolds number, nozzle-plate spacing Prandtl number and oblique angle of impinging plate.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.5
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• pp.490-498
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• 2004

This paper measures the forced convective heat transfer from heated cylinder to air flow in a rectangular duct at Re$_{D}$ =2,337, 4,589, 6,621 and 7,944 through experiments. And the heat transfer is computed by 3-D numerical computation in which various turbulent models are applied. It is shown through the comparison of experimental and computed data that numerical computation with standard k-$\varepsilon$ model predicts the experimental data most accurately. Furthermore, the correlation from the computed heat transfer is almost similar to that from the experiment when Re$_{D}$ is greater than 4,589. In addition, the correlation of McAdams is the closest to that from experimental data among various correlations from literature in the range of Reynolds number.ber.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1902-1907
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• 2008

The current work presents a design and fabrication technique for a microchannel system to measure the local temperature distribution inside microchannel. This micro channel system fabricated by MEMS technique is integrated with a heater and an array of temperature sensors so that detailed heat transfer phenomena inside micro-scale channel can be studied. Materials widely used in semiconductor process were selected to fabricate a heater and temperature sensors on a silicon wafer. On these heater and sensors a channel wall was fabricated with SU-8. The friction constant and the local Nusselt number distribution measured for the deionized water flow in the microchannel is presented.

• Journal of Energy Engineering
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• v.14 no.1
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• pp.30-36
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• 2005

This paper reports the experimental study of the heat transfer characteristics of the wake region behind a cylinder in cross flow. Local heat transfer coefficient was measured from the stagnation point (θ=0°) to 180°, and the variation of Nu in the axial direction along the cylinder was also studied. The results show that the heft transfer rate at the rear (θ=180°) near the duct wall can increase as much as 58% over the 2 dimensional value at the center of the duct. The heat transfer profiles in the wake region also show distinct effects of the aspect ratio and the heat transfer boundary condition.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.12
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• pp.3135-3147
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• 1993

A numerical method is presented which can solve the steady flow and heat transfer from a rotating and heated circular cylinder in a uniform flow for a range of Reynolds number form 5 to 100. The steady response of the flow and heat transfer is simulated for various spin parameter. The effects on the flow field and heat transfer characteristics known as lift, drag and heat transfer coefficient are analyzed and the streamlines, velocity vectors, vorticity, temperature distributions around it were scrutinized numerically. As spin parameter increases the region of separation vortex becomes smaller than upper one and the lower region will vanish. The lift force, a large part is due to the pressure force, increases as the Reynolds number and it increases linearly as spin parameter increases. The pressure coefficient changes rapidly with spin parameter on the lower surface of the cylinder and the vorticity is sensitive to the spin parameter near separation region. As spin parameter increases the maximum heat coefficient and the thin thermal layer on front region are moved to direction of rotation. However, with balance between the local increase and decrease, the overal heat transfer coefficient is almost unaffected by rotation.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1554-1559
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• 2003

The objective of the present study is to reveal thermal characteristic of microcapsulated lauric acid slurry, which have high latent heat during phase change from solid to liquid, in circular pipe. Test were performed with microcapsulated lauric acid slurry in a heating test section with a constant heat flux boundary condition. Local Nusselt number and the effective thermal capacity were measured. As the size of microcapsulated lauric acid were increased, Local Nusselt number of microcapsulated lauric acid slurry were increased. The effective thermal capacity of microcapsulated lauric acid slurry was 0.5 times than it of water

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.11
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• pp.1006-1012
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• 2004

The objective of the present study is to reveal thermal characteristic of micro-capsulated lauric acid slurry, which has high latent heat during phase change from solid to liquid, in circular pipe. Tests were performed with the microcapsulated lauric acid slurry in the heating test section with a constant heat flux boundary condition. Local Nusselt number and the effective thermal capacity were measured. As the sizes of microcapsulated lauric acids were increased, local Nusselt numbers of microcapsulated lauric acid slurries were increased. The effective thermal capacity of microcapsulated lauric acid slurry was 1.43 times larger than that of water.