• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2210-2213
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• 2008

In the present study, effects of degree of confinement on heat transfer characteristics of a micro-scale slot jet impinging on a heated flat plate are experimentally investigated. The effects of Reynolds numbers (Re = $1000{\sim}5000$), lateral distances (x/B = $1{\sim}10$), nozzle-to-plate spacings (Z/B = $1{\sim}20$), and degree of confinement ($B_c$/B = 3, 48) on the Nusselt number are considered. The results show that the effects of the degree of confinement on the cooling performance of the micro-scale impinging slot jet are significant at lower nozzle-to-plate spacings and higher Reynolds numbers. In addition, it is shown that the cooling performance of the micro-scale unconfined slot impinging jet is 200% higher than that of the micro-scale confined slot impinging jet.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.540-545
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• 2001

An experimental study was conducted to compare the heat transfer characteristics of an impinging slot jet and three kinds of impinging circular jets. Thermochromic liquid crystal with an image processing system was employed to measure the temperature of impinging wall where constant heat flux condition was applied. The distribution of convective heat transfer coefficients were then evaluated for eight nozzle-to-surface distance settings for each jet cases. The cooling effect was linearly proportional to the number of nozzles for circular jet cases at the same nozzle exit speed. However, the heat transfer under constant volume flow rate was the most at single circular jet. It was concluded that the overall convective heat transfer was better at the circular jets than the slot jet.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.11
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• pp.754-761
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• 2011

The present study numerically investigates two-dimensional flow and heat transfer in the multiple confined impinging slot jet. Numerical simulations are performed for the different Reynolds numbers(Re=100 and 200) in the range of nozzles from 1 to 9 and height ratios(H/D) from 2 to 5, where H/D is the ratio of the channel height to the slot width. The vector plots of velocity profile, stagnation and averaged Nusselt number distributions are presented in this paper. The dependency of thermal fields on the Reynolds number, nozzle number and height ratio can be clarified by observing the Nusselt number as heat transfer characteristic at the stagnation point and impingement surface. The Nusselt number at the stagnation point of the central slot shows unsteadiness at H/D=3 and Re=200. The value of Nusselt number at the stagnation point of the central slot decreases with higher Reynolds number and number of nozzle although overall area averaged Nusselt number increases. Hence careful selection of geometrical parameters and number of nozzle are necessary for optimization of the heat transfer performance of multiple slot impinging jet.

• Journal of the Korean Society of Visualization
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• v.3 no.2
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• pp.57-62
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• 2005

The flow characteristics in a confined slot jet impinging on a flat plate were investigated by using cinematic Particle Image Velocimetry technique. The jet Reynolds number was varied from 250 to 1000 for a fixed jet-to-plate spacing of H/W=5. We found that the vortical structures in the shear layer are developed with increase of Reynolds number and that the jet becomes unsteady by the interaction of vortex pairs between 500 and 750 of Reynolds number. Vortical structures and their temporal evolution are verified by using proper orthogonal decomposition.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.603-608
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• 2000

The characteristics of laminar and turbulent slot impinging jet flows are examined using segregated FEM with SUPG. Turbulent flows are modeled using $Wilcox^{(1)}$ $k-\;{\omega}$ turbulence model. The results are validated by comparing with velocity field of the existing experimental data. The distance of the target plate from the nozzle varies between 2, 4 and 5 times the slot jet width. Present study shows that the $k-\;{\omega}$ model gives results which agree well with the existing experimental data. In turbulence flows, the velocity profile of present calculation is more accurate than the existing numerical calculations. In laminar flows, We found tertiary vortex which was not found in the previous numerical study by M. $chen^{(6)}$ et al due to the numerical difference.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2798-2803
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• 2008

The confined slot air jet impinging normally on a moving flat surface has been investigated numerically by using commercial CFD code Ansys CFX-V11. Turbulent flows are modeled using k-w turbulence model. Two-dimensional turbulent flow is considered. Calculations were conducted for a nozzle-to-plate spacing of eight slot nozzle width, at three Reynolds number(Re=4500, 6700 and 10,000) and four surface-to-velocity ratios i.e. 0, 0.25, 0.5 and 1. Results are compared against corresponding cases for heat transfer from a stationary plate. Local Nusselt number is calculated under constant wall temperature condition. The analysis reveals that the average Nusselt number increases considerably with the jet exit Reynolds number, but decrease with the plate velocity.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.534-539
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• 2001

An experimental investigation of heat transfer characteristics on confined jet impinging plate using multiple slot jets has been performed. The effects of jet Reynolds numbers(Re=2000, 3950, 5900, 7900), dimensionlesss slot-to-plate distances(H/B=2, 4, 6, 8) and jet-to-jet distances(S=16B, 20B, 24B, 30B) on the local and average heat transfer coefficients have been examined. To clarify local heat transfer characteristics, naphthalene sublimation technique were used. From the experimental results, it was found that the local and average heat transfer rates increase with increasing jet Reynolds number. Measurements of local heat transfer coefficients produced by multiple of slot jets have given an indication of the nature of the interaction between jets and of the uniformity of heat transfer obtainable with various arrangements. At S/B=20, Re=7900 and H/B=6, maximum average Nusselt number is obtained.

• 한국가시화정보학회:학술대회논문집
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• 2005.12a
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• pp.23-27
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• 2005

The flow characteristics in a confined slot jet impinging on a flat plate were Investigated by using cinematic Particle Image Velocimetry technique. The jet Reynolds number was varied from 250 to 1000 for a fixed jet-to-plate spacing of H/W=5. We found that the vortical structures in the shear layer are developed with increase of Reynolds number and that the jet becomes unsteady by the interaction of vortex pairs between 500 and 750 of Reynolds number. Vortical structures and their temporal evolution are verified by using cinematic Particle Image Velocimetry technique.

• Journal of the Korean Society of Visualization
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• v.6 no.1
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• pp.34-40
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• 2008

The flow characteristics in a confined slot jet impinging on a flat plate were investigated in low Reynolds number regime (Re$\leq$1,000) by using time-resolved particle image velocimetry technique. The jet Reynolds number was varied from 404 to 1026, where it is presumed that the transient regime exists. It is found that the vortical structures in the shear layer are developed with increasing Reynolds number and that the jet remains steady at the Reynolds number of 404. Vortical structures and their temporal evolution are verified and the results were compared with previous numerical studies.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.79.1-79.1
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• 2005