• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.9
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• pp.904-913
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• 2001

The objective of this study was to investigate the characteristics of jet flow and heat transfer caused by trapezoid rods array in impinging jet system. In this study, trapezoid rods have been set up in front of flat plate to serve as a turbulence promoter. The bottom width of trapezoid rod was W=4, 8 mm and oblique angle were 80$^{\circ}$. The space from rods to the heating surface was C=1, 2, 4 mm, the pitch between each rods was P=30, 40, 50 mm, and the distance from nozzle exit to flat plate was H=100, 500 mm. This results were compared with the case without trapezoid rods. As a result, when rods are installed in front of the impinging plate, the acceleration of the jet flow and the eddies due to the rods seem to contribute to the heat transfer enhancement. Among test conditions, the heat transfer performance was best for the condition of W=8 mm, C=1 mm, P=30 mm and H/B=10. The maximum heat transfer rate is about 1.9 times larger than that without trapezoid rods.

• Journal of KSNVE
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• v.11 no.2
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• pp.285-291
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• 2001

The impingement of a weak shock wane discharged from the open end of a shock tube upon a flat plate was investigated using shock tube experiments and numerical simulations. Harten-Yee Total Variation Diminishing method was used to solve axisymmetric, unsteady, compressible flow governing equations. Experiments were carried out to validate the present computations. The effects of the flat plate and baffle plate sizes on the impinging flow field over the flat plate were investigated. Shock Mach number was varied in the range from 1.05 to 1.20. The distance between the plate and shock tube was changed to investigate the effect on the peak pressure. From both the results of experiments and computations we obtained a good empirical equation to predict the peak pressure on the flat plate.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.562-567
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• 2000

The Impingement of a weak shock wave discharged from the open end of a shock tube upon a flat plate was investigated using shock tube experiments and numerical simulations. Harten-Yee Total Variation Diminishing method was used to solve axisymmetric, unsteady, compressible flow governing equations. Experiments were carried out to validate the present computations. The effects of the flat plate and baffle plate sizes on the impinging flow field over the flat plate were investigated. Shock Mach number was vaned in the range from 1.05 to 1.20. The distance between the plate and shock tube was changed to investigate the effect on the peak pressure. From both the results of experiments and computations we obtained a good empirical equation to predict the peak pressure on the flat plate.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.1 no.1
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• pp.73-81
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• 1989

The purpose of this study is augmentation of heat transfer without additional power in a rectangular impinging air jet. As a method of passive heat transfer augmentation in a two-dimensional air jet, heat transfer surface of flat plate with rods is used. This study, particularly in the wall jet rigeon, investigates the effect of the clearance between the flat plate and rod. Mechanism of heat transfer enhancement is investigated by measuring the local heat transfer coefficient. It is concluded that the superposition of the effects of flow accelerlation through the clearance between the flat plate and the rod, and reattachment of the flow was the cause of the excellent performance. The overall heat transfer rate of flat plate with rods is about 1.5 times larger than that of flat plate without rods.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.2
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• pp.100-106
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• 2006

The behavior of spray impinging on the inclined constant temperature flat plate was experimentally investigated. To clarify the wall effect of a high pressure DISI injector, a relative angle of the inclined wall to a spray axis was varied. Spray penetration along the wall was observed optically and it was compared with that of a Fan spray type and Swirl type spray. To evaluate various spray motion quantitatively, a spray path penetration which describe the development of a spray tip along the wall was newly introduced. To observe the structure of an impinging spray, it was visualized by a controlled stroboscope light and its visualized image was captured on an CCD camera. Using the digital image of impinging spray $H_x$ and $R_x$ was extracted to clarify the structure of impinging spray. The main parameter of the relative position of the wall was the inclined angle which was defined as the angle was varied from $0^{\circ}$ (vertical impingement) to $60^{\circ}$ at the same condition.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.4
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• pp.452-458
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• 1998

The objective of this study is to obtain the unstable characteristics of the high-speed two-dimensional jet impinging normally onto a flat plate. The study is based on the feedback model and the experiment of the frequency characteristics of the impinging tones. Using the experimental data for the tonal frequencies of the impinging tones the convection speed of the unstable jet is obtained along with all the other features. Three kinds of unstable modes are clarified: asymmetric $A_{1}$ and $A_{2}$ and symmetric S. The condition for the excitation of each mode is found in terms of Strouhal number and Reynolds number. The convection speed is estimated and discussed in comparison with existing theoretical models. It is found that the convection speed increases with frequency when the mode is asymmetric, but decreases when it is symmetric. In addition, the characteristics of the high-speed impinging jet are compared with the low-speed impinging jet.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.593-596
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• 2008

Because of good performance of heat transfer characteristics, impinging jets are widely used in many industries for cooling or heating. And the present num erical studies attempt to show the effects of impinging jet. This paper considers the application of the turbulent models to impinging jet flow with pulsed inlet. It is assumed two-dimensional turbulent flows. The jet Reynolds num ber is set at 23,000 and the distance from the exit of the nozzle to the plate is 3 times larger than the diam eter of the nozzle. The influence of the Strouhal num ber(pulsation frequency) on Nusselt number at the impinging region is investigated. Strouhal numbers are ranged 0.0 to 0.5 and the forcing amplitudes are 1%,5%,9% of mean inlet velocity. In this study, the Nusselt number at the impinging region is sensitive to the pulsation frequency. Heat transfer coefficient strongly increase at Strouhal num ber of 0.4.

• Journal of the Korean Society of Combustion
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• v.16 no.1
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• pp.15-21
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• 2011

An experimental study was conducted to investigate the flame stability of the synthetic gas (syngas) using an impinging premixed jet burner. Since the syngas mainly consisted of $H_2$ and CO, the $H_2$/CO mixture was simulated as the syngas. $H_2$/CO mixture ratios, fuel/air mixture velocities and equivalence ratios were used as major parameters on the flame stabilitym The role of the impinging plate on the flame stability was also examined. In addition, laminar burning velocities of the $H_2$/CO mixture were predicted numerically to understand the characteristics of the flame stability for the syngas. The increase in the H2 concentration into the syngas brings about the extension of the blowout limit and the reduction in the flashback limit in terms of the stable flame region. The impinging jet plate broadened the blowout limit but does not play important role in changing of the flashback limit. Finally, it was found that the stability region of the flame using the syngas, which is expressed in terms of the mixture velocity and the equivalence ratio in this study, significantly differed from that of $CH_4$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.4
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• pp.475-484
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• 2001

The purpose of this study is to investigate the heat transfer augmentation using the perforated plate placed in front of a target plate in an axisymmetric impinging air jet system. The new liquid crystal technique using neural networks with median filtering is used to determine the Nusselt number distributions on the target surface. The experiments were made for the jet Reynolds number (Re) 23,000. The effects of the pitch-to-diameter (p/d1) from 1.5 to 2.5 in the perforated plate, the hole diameter on perforated plate (d1) from 4㎜ to 12㎜, the perforated plate to target surface distance (z/d1) from 1 to 3, and the nozzle-to-target surface distance (L/d) from 2 to 10 on the heat transfer characteristics were experimentally investigated. It was found that when the perforated plate was located between the nozzle exit and the target plate, the average heat transfer rate at the stagnation region corresponding to r/d$\leq$1.0 was increased up to the maximum 2.3 times compared to the case without the perforated plate.

• 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.