• 태양에너지
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• 제18권2호
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• pp.123-135
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• 1998

자연대류에서 정사각형 밀폐공간의 중앙에 고립된 전도성 장애물이 들어 있을 때 열전도도의 효과를 수치해석적으로 연구하였다. Pr=0.17, $Ra=1.0{\times}10^4,\;1.0{\times}10^5,\;1.0{\times}10^6$, 유체와 전도체의 열전도율비인 $K^*$=1.0, 6.6, 34.0 그리고 전도성 장애물의 비 ${\zeta}$=0.5,1.0,2.0에서 수치연구를 수행하였다. 그 결과들은 유선, 등온선 그리고 Nusselt수로 나타내었다. Ra and $K^*$ 값이 일정한 상태에서 평균 Nusselt수가 증가함에 따라 ${\zeta}$ 가 증가하였다. ${\zeta}=1.0$(장애물의 형상비)일 경우 Rayleigh수에 관계없이 $K^*$(장애물의 열전도율비)가 증가할수록 평균 Nusselt수는 감소한다. 장애물의 크기와 열전도율비가 동일할 때 대류열전달 효과는 ${\zeta}=0.5$인 경우보다 ${\zeta}=2.0$일 때 더 향상되었다.

• 대한기계학회논문집B
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• 제27권1호
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• pp.1-8
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• 2003

The heat transfer and flow measurements on a cylindrical pedestal mounted on a flat surface with a turbulent impinging jet were made. The experiments were made for the jet Reynolds number of Re = 23,000, the dimensionless nozzle-to-surface distance of L/d = 2~10, the dimensionless pedestal height of H/D = 0~1.5. Measurements of the surface temperature and the Nusselt number distributions on the plate surface were made using liquid crystal and shroud-transient technique. Flow measurements involve smoke flow visualization and the wall pressure coefficient. The results show that the wall pressure coefficient sharply decreases along the upper surface of the pedestal. However, the pressure increases when the fluid escapes from the pedestal and then collides on the plate surface. The secondary maxima in the Nusselt numbers occur in the region of 1.0 $\leq$ r/d $\leq$ 1.9. Their values for the case of H/D = 0.5 are maximum 80% higher than those for other cases. The formation of the secondary maxima may be attributed to the reattachment of flow on the plate surface which was separated at the edge of the pedestal.

• 에너지공학
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• 제15권1호
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• pp.60-66
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• 2006

발포 알루미늄이 삽입된 환형관에서의 유동과 대류 열전달 특성을 실험적 연구를 수행하여 분석하고 heat sink로서의 실현 가능성을 검토하였다. 다른 기공밀도를 갖는 두 종류의 발포 알루미늄을 사용하여 유동과 열전달 특성을 파악하고 마찰계수와 열전달 관련 Nusselt수를 Darcy 수, Reynolds수, Prandtl수의 함수로 상관식을 구하였다. 발포 알루미늄이 없는 경우에 비해 마찰계수는 증가하지만 Nusselt수에서도 6에서 10배의 증가를 나타낸다. 따라서 열교환기의 크기가 제한되는 경우 열교환기에 발포알루미늄을 삽입하면 전열면적을 감소시킬 수 있으므로 열교환기를 소형화할 수 있다.

• 설비공학논문집
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• 제7권1호
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• pp.112-119
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• 1995

Measurements of the local heat transfer coeffcients on a spherically concave surface with a round impinging jet are presented. The liquid crystal transient method was used for these measurements. This method, which is a variation on the transient method, suddenly exposes a preheated wall to an impinging jet while video recording the response of liquid crystals for the measurement of the surface temperature. The Reynolds numbers used were 1,000, 23,000 and 50,000 and the nozzle-to-jet distance was L/d=2, 4, 6, 8, 10. Presented results are compared to previous measurements for flat plate. In the experiment, the local heat transfer Nusselt numbers on a concave surface are higher than those on a flat plate. Maximum Nusselt number at all region occured at L/d=6 and second maximum in the Nusselt number occured at R/d=2 for both Re=50,000 and Re=23,000 in case of L/d=2 and for only Re=50,000 in case of L/d=4. All other cases exhibit monotonically decreasing value of the Nusselt number along the curved surface.

• 대한기계학회논문집B
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• 제38권11호
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• pp.943-950
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• 2014

본 연구는 다양한 위치의 원형 실린더가 존재하는 사각 밀폐계에서 Prandtl 수 변화에 따른 밀폐계 내부의 자연대류 현상에 대한 수치해석을 수행하였다. Rayleigh 수가 $10^3$, $10^4$, $10^5$ 그리고 다양한 위치의 내부 원형 실린더에 대해서 Prandtl 수를 0.1, 0.7, 7 로 변화시키며 Prandtl 수의 영향을 분석하였다. 내부 원형 실린더의 위치는 -0.2 에서 0.2 까지 0.1 간격으로 변화시켰다. Prandtl 수의 변화에 따른 밀폐계 내부의 자연대류 현상은 밀폐계 내부의 온도장과 유동장 및 표면 평균 Nusselt 수의 분포를 바탕으로 분석하였다. Rayleigh 수가 $10^5$ 일 때 내부 실린더의 위치에 상관없이 Prandtl 수가 증가할수록 평균 Nusselt 수는 증가하였다.

• 한국전산유체공학회지
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• 제13권2호
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• pp.20-26
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• 2008

A numerical study is carried out to analyze the steady three-dimensional turbulent flow and convective heat transfer in a staggered pin-fin array with diamond shaped elements at various geometrical configurations. Steady Reynolds-averaged Navier-Stokes equations and energy equation are solved using a finite volume based solver. Shear stress transport (SST) model is used as turbulence closure. The computational domain is composed of one pitch of pin-fin displacement with periodic boundary conditions on the surfaces normal to the streamwise direction and the cross-streamwise direction. The numerical results for Nusselt number and friction factor are validated with experimental results. The effects of pin angle, pin height and pitch on Nusselt number, friction factor and efficiency index are investigated.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.546-552
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• 2001

The heat transfer and flow measurements on a pedestal encountered in chip cooling. A uniform wall temperature boundary condition at the plate surface and on a pedestal was created using shroud method. Liquid crystal was used to measure the plate surface temperature. The jet Reynolds number (Re) ranges from 11,000 to 50,000, the dimensionless nozzle-to-surface distance (L/d) from 2 to 10, and the dimensionless pedestal diameter-to-height (H/D) from 0 to 1.0. The results show that the Nusselt number distributions at the near the pedestal exhibit secondary maxima at $r/d{\cong}1.0\;and\;1.5$. The formation of the secondary maxima is attributed to an create in the vortex by the pedestal.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집B
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• pp.130-135
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• 2000

To enhance heat transfer characteristics of water, fine ice was added to it. The convective heat transfer characteristics of the ice slurry were investigated in a flow loop with a constant heat flux test section. The Nusselt number and Fanning friction coefficient of water flow were found to be similar to the expected curve by Petukhov. The Nusselt number of the ice sin flow was higher than the Nusselt number of water. Effective thermal capacity of the 10.84% ice slurry was found to have 2.39 times of the thermal capacity of water.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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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

• 대한기계학회논문집
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• 제19권7호
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• pp.1758-1769
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• 1995

The heat transfer of oscillating flow in a cylinder with regenerator was investigated by the moving boundary technique. The flow in regenerator was modeled by means of Brinkman Forchheimer-Extended-Darcy equation . Results showed that when piston moved toward right, velocity vectors near cylinder wall at left piston and right side of regenerator inclined to symmetric axis and velocity vectors near cylinder wall at right piston and left side of regenerator inclined to cylinder wall. And the time averaged Nusselt number was increased by 46.73% when the oscillatory frequency became twice and decreased by 31.46% when the oscillatory frequency became half. The time averaged Nusselt number was increased by 18.09% when thickness of the regenerator became twice and decreased by 7.53% when thickness of the regenerator became half. But mesh size of regenerator hardly affected the Nusselt number. And efficiency of regenerator was larger as the oscillatory frequency was smaller, thickness and mesh size of regenerator was larger.