• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.4
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• pp.527-536
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• 1996

Convective nucleate boiling and burnout heat flux have been studied on a flat, downward facing, constant heat flux surface cooled by an impinging water jet. The tests are progressed from low, nonboiling power to high, burnout heat flux power. The jet velocity and the subcooling do not affect the nucleate boiling curve of $q{\sim}{\Delta}T_{sat}$ diagram, but the supplementary water height affects the curve. For the case of dimensionless height of supplementary water S/D=1, the boiling curve shift to the heigher heat flux than that of S/D=0 or S/D=2. Burnout heat flux is enhanced with increasing jet velocity and subcooling. Also. by using the supplementary water(S/D=1 or S/D=2), burnout heat flux is larger than that of the simple water jet(S/D=0). A generalized correlation for the burnout heat flux data in the present boiling system with an impinging water jet is successfully evolved.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.6
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• pp.846-854
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• 1999

Measurements of the local heat transfer coefficients were made on a hemispherically convex surface with a round oblique impinging jet. 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 crystal for the surface temperature measurements. The Reynolds number used was 23000 and the nozzle-to-surface distance was L/d=2, 4, 6, 8, and 10 and the jet angle was $\alpha$=$0^{\circ}\; 15^{\circ}\;30^{\circ}C\; and \;40^{\circ}C$. In the experiment, the Nusselt number at the stagnation point decreases as the jet angle increases and has the maximum value for L/d=6. The X-axis Nusselt number distributions exhibit Secondary maxima at $0^{\circ}C\re $\alpha$\re 15^{\circ}C, L/d\le6$ for X/d＜0(upstream) and at $0^{\circ}C\re $\alpha$40^{\circ}C,\;L/d\le4\;and\; at\; 30^{\circ}C\re $\alpha$$\leq$40^{\circ}C,\;L/d\le 6 $for X/d＞0(downstream). The secondary maxima occurs at long distance from the stagnation point as the jet angle increases or the nozzle-to-surface distance decreases. The Y-axis Nusselt number distributions exhibit secondary maxima at Y/d=$\pm$2 for $0^{\circ}C\le a\le30^{\circ}C\; and\; L/d\le4, and \;for\;$\alpha$=40^{\circ}C$and L/d=2. The displacement of the maximum Nusselt number from the stagnation point increases as the jet angle increases or the nozzle-to-surface distance decreases and the maximum distance is about 0.67 times of the nozzle diameter. The ratio of the maximum Nusselt number to the stagnation Nusselt number increases as the jet angle increases.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.565-571
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• 2001

The objective of this study was to investigate the characteristics of air flow and heat transfer caused by trapezoid rods array in impinging air jet system. In this study, trapezoid rods have been set up on front of flat plate to act as a turbulence promoter. Local Nusselt numbers were determined as a function of three parameters: (a) the space from rods to heating surface(C=1, 2, 4mm), (b) the pitch between each rods(P=30, 40, 50mm), (c) the distance from nozzle exit to flat plate(H/B=2, 6, 10). And this research compared the above with the experiment without trapezoid rods. As a result, heat transfer performance was best under the condition of C=1mm and as the pitch is 30mm. In this case, maximum rate of heat transfer augmentation is about 1.9 times greater compared to that without trapezoid rods.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.3
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• pp.716-724
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• 1990

Oblique impinging plane jets were investigated experimentally and numerically at Reynolds number 21000. The inclination angle was varied from 90.deg.(normal to the impinging plate) to 60.deg.. The distance H between the nozzle exit and the stagnation point on the impinging plate was fixed at H/D=8. The working fluid was air. The mean velocity components and turbulent quantities were measured by a hot-wire anemometer. And the static pressure distributions on the impinging plate were measured by a Pitot tube. In numerical computation, the governing partial differential equations of elliptic type were solved with conventional k-.epsilon. turbulence model. The measurements show that, after impingement, the jet half width alone the wall increases in both directions, and that similarity for each turbulent quantity such as Reynolds shear stress or turbulent kinetic energy is revealed in the wall jet region. The computed results show some deviation from experimental data in the impingement region, where streamline curvature is significant. However, the computed results agree qualitatively well with measurements.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.15 no.2
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• pp.182-187
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• 1986

Experimental measurements of the heat transfer and heat flux to a jet impinging on a heated surface were obtained in the nucleate boiling regimes. Tes-variables were jet at velocity and aspect ratio ($b/\ell$) of the heated surface. A slope of nucleate boiling curve increased with increasing the aspect ratio of the heated surface, namely approaching a rectangular square, and it is shown that surface tension has an important role for the onset of nucleate boiling heat transfer. A generalized correlation of the jet nucleate boiling heat transfer. A generalized correlation of the jet nucleate boiling heat transfer was found using a pi theorem.

• Journal of Energy Engineering
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• v.20 no.2
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• pp.96-102
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• 2011

This research has been proceeded over the transition region(H/B=10) of two-dimensional impinging air jet system, in which square rods has been set up in front of heating surface in order to increase heat transfer. The objective of this research was to investigate the characteristics of heat transfer and air flow, in cases the clearance from rods to heating surface(C=1, 2, 4, 6 mm) and the width of rods(W=4, 6, 8 mm) changed. And this research compared the above with the experimentation without rods. As result, heat transfer performance was best under the condition of C=1 mm, and as the width is 8 mm, it is largely influenced by eddies and acceleration in case width of rods changed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.8
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• pp.1115-1122
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• 2002

The present experiment investigates the effects of pore density f of aluminum foam heat sinks, the jet-to-jet spacing X and the nozzle plate-to-target surface spacing H of 3$\times$3 square impinging arrays on the averaged Nusselt number. The performance of the aluminum foam heat sinks and the rectangular plate heat sink is evaluated in terms of the enhancement factor. /equation omitted/. The multiple impinging jet with X/d=4.0 displays higher Nusselt numbers than single impinging jet for 12.0$\leq$H/d$\leq$20.0. With the variation of the jet-to-jet spacing, the aluminum foam heat sink of 10 PPI show higher Nusselt numbers than the 20 and 40 PPI aluminum foam heat sinks. Further, the 10 PPI aluminum foam heat sink demonstrates 26% higher enhancement factor than the rectangular plate heat sink in the range of 7000$\leq$Re$\leq$11000.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.11
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• pp.1659-1666
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• 2001

The objective of this study was to investigate the characteristics of air flow and heat transfer caused by trapezoid rods array in impinging air jet system. Trapezoid rods have been set up on front of flat plate to act as a turbulence promoter. Local Nusselt numbers were determined as a function of three parameters : (a) the space from re(Is to heating surface(C=1, 2, 4mm), (b) the pitch between each rods(P=30, 40, 50mm), (c) the distance from nozzle exit to flat plate(H/B=2, 6, 10). The measurements were compared with those of the experiment without trapezoid rods. As a result, when rods are installed in front of the impinging palate, the acceleration of the flow and the eddies due to the rods seem to contribute to the heat transfer enhancement. Heat transfer performance was best under the condition of C=1mm and as the pitch is 30mm. The maximum rate of heat transfer augmentation is about 1.9 times greater compared to that without trapezoid rods.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.267-271
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• 2000

The local heat transfer rate of an axisymmetric submerged air jet impinging on normal to a heated flat plate was investigated experimentally with varying solidity of mesh screen. The mean velocity and turbulent Intensity profiles of streamwise velocity component were measured using a hot-wire anemometry. The temperature distribution on the heated flat surface was measured with thermocouples. The screen installed in front of the nozzle exit(behind of 35mm) modify the jet flow structure and local heat transfer characteristics. For higher solidity screen, turbulence intensity at core lesion is high and increases the local heat transfer rate at nozzle-to-plate spacings(L/D<6). For larger nozzle-to-plate spacings(L/D>6), however, the turbulent Intensities of all screens tested in this study approach to an asymptotic curve, but the small mean velocity at the core region reduces the local heat transfer rate for high solidity screens.

• 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.