• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.2
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• pp.195-203
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• 2000

The local heat/mass transfer coefficients for arrays of impinging circular air jets on a plane surface are determined by means of the naphthalene sublimation method. Fluid from the spent jets is constrained to flow out of the system in one direction. Therefore, the spent fluid makes a crossflow in the confined space. The present study investigates effects of jet-orifice-plate to impingement-surface spacing and jet Reynolds number. The spanwise- and overall-averaged heat/mass transfer coefficients are obtained by numerical integrating the local heat transfer coefficients. The local maximum heat/mass transfer coefficients move further in the downstream direction due to the increase of crossflow velocity. At the mid-way between adjacent jets, the heat/mass transfer coefficients have a small peak owing to the collision of the adjacent wall jets and are affected strongly by the crossflow. The effect of the crossflow occurs strongly at the small orifice-to-impingement surface distance.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.7
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• pp.1675-1683
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• 1995

A numerical study of the fluid flow and heat transfer characteristics of the two-dimensional impingement jet with a confinement plate has been carried out. The fluid flow was calculated by solving the full Navier-Stokes equation. In doing that, the well known SIMPLER algorithm was used and the trouble making convection term was discretized according to QUICKER scheme. The energy equation was simply solved by using the SOR method. For the Reynolds number of 10000, two channel heights, say 1.5 and 3.0 times the jet exit width, and two thermal boundary conditions constant wall temperature and constant wall heat flux were considered. Discrete heat sources were flush mounted along the impingement plate at a distance of 0, 2, 3, 4, 5, 6, 10, 12, times the jet exit width from the stagnation point. The length of each heat source is 4 times the jet exit width long. The Nusselt number averaged over each heat source was compared with experiment. Comparison shows that both calculations and experiment have the secondary peak of Nusselt number at downstream of stagnation point, even though there is a little quantitative difference in between. The difference is believed due to abscure thermal boundary condition in experiment and also accuracy of turbulence model used. The secondary peak is shown to be caused by rigorous turbulent flow motion generated as the wall jet flow is retarded and developes into the channel flow without flow reversal.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.229-232
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• 2002

For the purpose of Thermal Protection Material design problem, a numerical analysis of axisymmetric high temperature supersonic impinging jet flows of exhaust gas from combustor on curved surfaces has been accomplished. A modifed CSCM Upwind Navier-Stokes method which is able to cure the carbuncle Phenomena has been developed to study strong shock wave structure and thermodynamic wall properties such as pressure and heat transfer rate on various curved surfaces. The results show that the maximum heat transfer rate which is the most important parameter affecting thermo-chemical surface ablation on the plate did not occur at the center of jet impingement, but rather on a circle slightly away from the center of impingement and the shear stress distribution alone the wall is similar to the wall heat transfer late distribution.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.3
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• pp.291-301
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• 1994

This paper presents the promotion of heat transfer through the use of wire-mesh screens. To improve heat transfer in an impingement water system, the wire-mesh screens are installed between the nozzle-to-heater surfaces. When the wire-mesh screens are not employed, this report exhibits the maximum heat transfer and the secondary maximum value at the stagnation point. But in case of using the wire-mesh screens, the transfer coefficient value of maximum heat exists at the stagnation point, and the second maximum value doesn't occur. Therefore, the heat transfer is more improved than 4~6 times that of the mean Nusselt numbers of simple water jet system, Also, within the region presented in this study, the heat transfer was promoted by using the wire-mesh screens at the stagnation point ; thus, the heat transfer was more increased than 6-7. 5 times that of simple water jet system.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.2
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• pp.204-213
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• 2000

This study deals with jet impingement, which is extensively used in the process industries to achieve intense heating, cooling or drying rates and also widely employed as a test flow for turbulent models due to its complex flow configuration, on a flat plate by numerical methods. In this calculation, the finite volume method was employed to solve the Navier-stokes equation based on the non-orthogonal coordinate with non-staggered variable arrangement. To get a better understanding for the fluid flow and heat transfer characteristics of the turbulent jet impingements, $k-{\varepsilon}-{\overline{v^{'2}}}$ turbulent model was adapted and compared with the experimental data and the result of standard $k-{\varepsilon}$ turbulent model. Numerical calculations were carried out with various flow rates, nozzle to plate distances. In the case of the axisymmetric jet impingement on a flat plate, $k-{\varepsilon}-{\overline{v^{'2}}}$ turbulent model showed better agreement with the experimental data than the standard $k-{\varepsilon}$ turbulent model in the prediction of the mean velocity profiles, the turbulent velocity profiles. the turbulent shear stress and the heat transfer rate. The highest heat transfer rate can be obtained when the impingement occurs within the potential core..

• 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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.6
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• pp.751-757
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• 2001

An experimental study of impinging jet-flow structure has been carried out for a fully developed single circular jet impingement cooling on a flat plate, and the effect of the wall thickness at nozzle exit edge is investigated. Impinging jet flow structures have been measured by Laser-Doppler Velocimeter to interpret the heat transfer results presented previously by Yoon et al.(sup)(10) The peaks of heat transfer rate are observed near the nozzle edge owing to the radial acceleration of jet flow when the nozzle locates close to the impingement plate. The growth of the velocity fluctuations in the wall jet flow is induced by the vortices which originate in the jet shear layer, and consequently the radial distribution of local Nusselt numbers has a secondary peak at the certain radial position. As a wall of circular pipe nozzle becomes thicker for small nozzle-to-target distance, the entrainment can be inhibited, consequently, the acceleration of wall jet flow is reduced and the heat transfer rate decreases.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.274-279
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• 2001

An experimental investigation of heat transfer characteristics at the surface of two-dimensional protruding heated blocks using confined impinging multiple slot jets has been performed. The effects of jet-to-jet distances(S=16B, 24B), dimensionless nozzle-to-block distances(H/B=2, 6) and jet Reynolds numbers(Re=2000, 3900, 5800, 7800) on the local and average heat transfer coefficients have been examined with five isothermally heated blocks at streamwise block spacing(p/w=1). To clarify local heat transfer characteristics, naphthalene sublimation technique was used. From the results, it was found that the local and average heat transfer of heated blocks increases with decreasing jet-to-jet distance and increasing jet Reynolds number. Measurements of local heat transfer coefficients have given an indication of the nature of the interaction between jets and of the uniformity of heat transfer obtainable with various arrangements. In the case of S/B=16, H/B=6 and Re=7800, maximum average Nusselt number of overall blocks was obtained.

• The KSFM Journal of Fluid Machinery
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• v.15 no.2
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• pp.5-11
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• 2012

In this paper, the heat transfer coefficient measurement techniques using TSP(temperature sensitive paint) were introduced and the results of a comparative study on the heat transfer coefficient measurement by steady state and transient TSP techniques were discussed. The distributions of heat transfer coefficient by a single $60^{\circ}$ inclined impingement jet on a flat surface were measured by both techniques. Tested Reynolds number based on the jet diameter (d) was 30,000 and the distance between jet exit and target plate (L) was fixed at 10d. Results showed that the measured Nusselt number by both techniques indicated significant difference except near the center of impingement jet. Also, the heat transfer coefficients measured by the transient TSP technique were affected by the reference temperature of the jet. Based on the measured data, characteristics of both TSP techniques were analyzed and suggestions for applying them were also given.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.3
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• pp.386-398
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• 1998

The present experiment is conducted to investigate heat transfer characteristics on the impinging surface with secondary flows around circular nozzle jets. The changed vortex pattern around jet affects significantly the flow characteristics and heat transfer coefficients on the impinging surface. The effects of the jet vortex control are also considered with jet nozzle-to-plate distances and main jet velocities. The vortex pattern around a jet is changed from a convective instability to an absolute instability with a velocity suction ratio of the main jet and the secondary counterflow. With the absolute instability condition, the jet potential core length increases and the heat transfer on the impinging surface is increased by small scale eddies. The region of high heat transfer coefficients is enlarged with the high Reynolds number due to increasing secondary peak values. The effect of suction flows is influenced largely with collars attached the exit of the jet nozzle because the attached collar guides well the counterflow around the main jet.