• 한국가시화정보학회지
• /
• 제3권2호
• /
• pp.57-62
• /
• 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.

• 한국기계가공학회지
• /
• 제14권5호
• /
• pp.68-74
• /
• 2015

In the present work, a series of numerical calculations have been conducted on the cooling of a hot surface using an air/water mist jet. In some cooling processes, such as in the glass-tempering process, direct contact between the cold water drops and the hot surface should be avoided, because this may cause surface cracks due to the sharp temperature gradients. Thus, the main focus of this study is finding the appropriate operating conditions for maximum cooling without direct contact between the drops and the surface. A series of numerical experiments have been performed, and, at the same time, those results were compared with those of the previous experiments for verification purposes. The effects of droplet impinging velocity, hot plate temperature, and liquid loading ratio for mono-dispersed drops of various sizes were studied in detail.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2002년도 학술대회지
• /
• pp.237-240
• /
• 2002

In the present study, we perform LES of turbulent flow and temperature fields in a circular impinging jet at Re=5000 for two cases of H/D=2 and 6 (H denotes the distance between the jet exit and flat plate, and D does the diameter of the jet exit). In the case of H/D=2, the regular vortical structures observed in free jet do not exist because of the smaller distance than the potential core. The Nusselt number on the wall is largest at $r/D{\cong}10.67$ where vortex rings Impinge. At $r/D{\cong}1.5{\~}2.0$, the vortex rings induce the secondary vortices, resulting in a secondary peak in the Nusselt number there. In the case of H/D=6, the vortex rings change into three-dimensional vortical structures and the small-scale vortices impinge on the flat plate. The increase of turbulent intensity due to small-scale vortices results in the largest Nusselt number at the stagnation point.

• 한국화재소방학회논문지
• /
• 제15권1호
• /
• pp.41-46
• /
• 2001

수평 평판과 충돌하는 제트에 의해 생성되는 연기유동을 관찰하기 위해 질소가스네 kerosene 연기입자를 띄워 유동장을 가시화하였다. 광원으로는 아르곤-이온 레이져 평면광이 사용되었다. Kerosene smoke의 산란 광에 의한 수직평면 상(image)과 수평평면 상을 고속 CCD 카메라와 비디오 카메라로 녹화하였으며, 얻어진 영상으로부터 연기선단의 순간속도 및 평균속도를 측정하였다.

• 설비공학논문집
• /
• 제9권4호
• /
• pp.427-434
• /
• 1997

Heat transfer characteristics of a two-dimensional oblique impinging jet were experimentally investigated. The local heat transfer coefficients were measured by a thermochromic liquid crystal. The jet Reynolds number studied was varied from 10000 to 35000, the nozzle-to-plate distance(H/B) from 2 to 16, and the oblique angle($\alpha$) from $60^{\circ}$ to $90^{\circ}$. It was observed that the local Nusselt numbers in the minor flow region were larger than those in the major flow region at the same distance along the plate due to the higher levels in the turbulent intensity caused by more active mixing of the jet flow.

• 대한설비공학회지:설비저널
• /
• 제13권1호
• /
• pp.14-21
• /
• 1984

The purpose of this investigation is to study heat transfer characteristics in wall jet region on a flat plate caused by upward impinging water jet. In the wall jet region, heat transfer results by impinging water jet are being compared with the ones with supplementary water. As the radius increases, the heat transfer coefficient in the wall jet region consquently decreases, but decreasing nozzle-heat plate distance, the reduction rate increases. The experimental equation is expressed as follows : $$\frac{N_{ur}}{P_r^{0.4}}{\cdot}\overline{\xi}=m(\overline{\eta}{\codt}Re{\delta})^n,\;m=0.034\~0.056,\;n=1.74\~2.007$$ The optimum height of supplementary water is obtained to improve heat transfer effect of wall jet region.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2008년도 추계학술대회B
• /
• pp.2562-2567
• /
• 2008

Jet impingement on a moving plate, which is applicable to cooling of hot metals in a steel-making process, is investigated numerically by solving the Navier-Stokes equations in the liquid and gas phases. The liquid-gas interface or free surface is tracked by a level-set method which is improved by incorporating the ghost fluid approach based on a sharp-interface representation. The computations are made for multiple jets as well as a single jet to compare their flow characteristics. Also, the effects of the nozzle pitch, moving velocity of plate and jet velocity on the interfacial motion and the associated flow and temperature fields.

• 설비공학논문집
• /
• 제1권2호
• /
• pp.182-189
• /
• 1989

The propose of this study is augmentation of heat transfer without additional external power in 2-dimensional impinging air jet. The passive heat transfer augmentation method tried in this experimental study is placement of rod bundles with the clearance, 2mm, in front of the heat transfer surface. The effects of pitch distance among rods and nozzle-to-target plate distance are investigated. The overall heat transfer rate of flat plate with rods reaches maximum at H/B=10 and P=40mm, and for H/B=2 and P=40mm the augmentation rate of heat transfer becomes maximum to a value which is about 1.57 times that of the flat plate without rods.

• 대한기계학회논문집B
• /
• 제28권8호
• /
• pp.961-967
• /
• 2004

An inclined jet impinging on a pin fin heat sink is proposed and investigated experimentally. To investigate the flow pattern, flow visualization using fluorescence and velocity measurement using particle image velocimetry(PIV) are conducted with water. The jet impinges over a wide span of the heat sink with a large recirculation in the upper free space and occasionally with another smaller one in the upstream corner. Further, thermal experimentation is conducted using air to obtain temperature profiles using a thermocouple rake in the air and using thermal image on the heat sink back plate, with impinging angles of 35, 45 and 55 degrees. The Reynolds number range based on the nozzle slot is varied from 1507 to 6405. The results show that impinging angle of 55 degree shows the largest heat transfer capability. The results of thermal experiment are compared and discussed with those of flow visualization.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 1998년도 제10회 학술강연회논문집
• /
• pp.15-15
• /
• 1998

The problem of the impingement of a sonic or a supersonic jet on a flat surface has not only wide applications but has also interesting and very complex flow phenomena. The main applications of this impinging jet include prediction of solid surface erosion, design of launcher systems, stage separation of multi-stage rocket system, V/STOL operations, thermal spray system, and manufacturing technologies of materials. Much have been learned about the supersonic impinging jet flow field but many fundamental questions have not been answered satisfactorily. The problem encompasses many facets of fluid dynamics which, in combination, present the compressibility effect and the viscous-inviscid interaction, coupled with flow separation and reattachment. What is more, there are many flow parameters that have on the impinging jet flow field, for example, Mach number, Reynolds number, pressure ratio, distance between the nozzle exit and flat plate, jet shock structure, nozzle diameter and etc. Thus the existing data on the supersonic impinging jet flow present considerable disagreement in which quantitative comparison between one result and another is often impossible.