• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.1
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• pp.81-94
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• 1988

A series of experiments was performed in this study to investigate the boiling heat flux between an impinging water jet and a hot surface. Test variables were surface roughness, jet velocity, saturation temperature excess of surface, nozzle diameter and the gap distance between nozzle plate and the hot surface. In order to make the impinged cooling water a forced flow streaming a long the hot surface immediately after the initial impingement, the flat nozzle tip was extended to a circular flat plate having the same diameter as the hot surface. Utilizing the dimensionless parameter study on continuity, momentum and energy equations, 5 groups of variables involved in the nucleate boiling heat transfer were derived so that it is possible to estimate the increased heat flux by impinging water jet in a similar experimental work. For the case of saturated water being impinging onto a high temperature surface, an applicable correlation among dimensionless parameters describing the heat flux was found to be as follow.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.3
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• pp.302-310
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• 2003

Experiments were conducted to show the characteristics of the flow on unventilated parallel plane jets. Measurements of mean velocity components and turbulent intensities were carried out with a particle image velocimetry to investigate the flow field generated by the air issued from two identical plane parallel nozzles and mixed with the ambient air. The measurements range of these experiments were Reynolds number of 5300 based on the nozzle width and the cases of nozzle-to-nozzle distance were four times. six times and eight times the width of the nozzle. Results show that a recirculation zone with a sub-atmospheric static pressure was bounded by the inner shear layers of the individual jets and the nozzles plate. The positions. where maximum value of mean turbulent intensities and mean turbulent kinetic energy show, were at the same position with the merging point. The spread of jets in the merging region increases more rapidly than that of Jets in the converging and the combined region. As nozzle-to-nozzle distances were increased. it was shown that merging and combined lengths were shorter.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.1
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• pp.50-58
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• 2000

Experiments were carried out to obtain the effects of nozzle configuration and jet to jet spacing on the heat transfer characteristics of single line of circular water jets impinging on a constant heat flux plane surface. The nozzle configurations are Cone type, Reverse cone type and Vertical circular type, and the nozzle arrays are single jet(nozzle dia. 8 mm), 1 row of 3 jets and 1 row of 5 jets. Jet velocities ranging from 3m/s to 8m/s were investigated for the nozzle to target plate spacing of 80 mm. For the Cone and Reverse cone type nozzle arrays, the average Nusselt number of 1 row of 5 jets was larger than that of 1 row of 3 jets at Re$_{D}$<45000, but that of 1 row of 3 jets was larger than that of 1 row of 5 jets at $Reo\le45000$. For the Vertical circular type nozzle, however, the average Nusselt number of 1 row of 3 jets was larger than that of 1 row of 5 jets at all jet velocities. In the condition of fixed mass flow rates, the maximum heat transfer augmentation was obtained for 1 row of 5 jets and was over 2 times larger than that of the single jet for all nozzle configurations. The nozzle configurations that produce the maximum average Nusselt number are as follows: For 1 row of 3 jets, the Vertical circular type at $Reo\le45000$ and the Reverse cone type at $Reo\le45000$. But, they are the Reverse cone type at Re$_{D}$<55000 and the Vertical circular type at$Reo\le55000$ for 1 row of 5 jets.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2000.04a
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• pp.227-228
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• 2000

가상 임팩터(virtual impactor)는 가속노즐(acceleration nozzle)아래에 충돌판(impaction plate) 대신 가상의 공간을 가진 수집관(receiving tube)이 설치되어 유선의 방향이 $90^{\circ}$로 바뀔 때, 큰 입자는 유선에서 벗어나 수집노즐에 포집된다(Hounam and Sherwood, 1965). 가상 임팩터에는 관성 임팩터(inertial impactor)와는 다르게, 절단입경(cut-size)보다 큰 입자를 분리할 수 있는 부 유동(minor flow)과 절단입경보다 작은 입자를 분리할 수 있는 주 유동(major flow)으로 나눈다. (중략)

• Proceedings of the Korean Nuclear Society Conference
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• 2001.05a
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• pp.344.2-344
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• 2001

• Proceedings of the Korean Nuclear Society Conference
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• 2001.05a
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• pp.186.1-186
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• 2001

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2002.02a
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• pp.292-307
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• 2002

• Journal of Korean Society for Atmospheric Environment
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• v.19 no.1
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• pp.67-76
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• 2003

Recently consideration of health and interest on bio aerosols have been growing steadily. In this study, inertial impactor, which can be used to collect airborne particles and bio aerosols, was newly devised for real-time observation on the particles collected on impaction plate. and named Visual Impactor. Flow field and particle trajectory in the space between nozzle and impaction plate was analyzed numerically, and the collection effciencies were calculated. Calibration and performance evaluation of the Visual Impactor was conducted with polydisperse aerosols generated from 0.1％ sodium chloride solution. Cut-off diameter from numerical simulation was in good agreement with that from experimental results. Because of particle bounce and particle deposition on nozzle tip due to short jet-to-plate distance, the collection efficiencies from numerical and experimental analyses were different slightly. Visual Impactor was used to collect airborne particles, and the features of collected particles could be seen in real-time. Airborne particles in different weather conditions (fine, cloudy, and rainy) were sampled and compared one another The features of collected airborne particles were dependent strongly upon relative humidity. In addition, with hours elapsing, shapes and colors of collected particles were changed by evaporation and surface tension, etc.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.3
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• pp.373-381
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• 2000

The flow and heat transfer characteristics on the impingement surface can be controlled by the change of vortex with the acoustic excitation, because the flow characteristics of an impinging jet are affected strongly by the vortices formed at the jet exit. To investigate the effects of acoustic excitation, we measured the velocity, turbulent intensity distributions for the free jet and local heat transfer coefficients on a impingement surface. As the acoustic excitation, subharmonic frequency of excited frequency plays an important role to the control of the jet flow. If the vortex pairings are promoted by the acoustic excitation, turbulence intensity of the jet flow is increased quickly. On the other hand if the vortex pairings are suppressed, the jet flow has low turbulence intensity at the center of the jet. Therefore, the low heat transfer rates are obtained on the impingement plate for a small nozzle-to-plate distance. However, it has high heat transfer rates at a large distance between the nozzle and plate due to the increasing of potential-core length.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1196-1200
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• 2004

Micropump is very useful component in micro/nano fluidics and bioMEMS applications. In this study, a bubble-powered micropump was fabricated and tested. The micropump consists of two-parallel micro line heaters, a pair of nozzle-diffuser flow controller and a 1 mm in diameter, 400 ${\mu}m$ in depth pumping chamber. The two-parallel micro line heaters with 20 ${\mu}m-width$ and 200 ${\mu}m-length$ were fabricated to be embedded in the silicon dioxide layer of a wafer which serves as a base plate for the micropump. The pumping chamber, the pair of nozzle-diffuser unit and microchannels including the liquid inlet and outlet port were fabricated by etching through another silicon wafer. A glass wafer (thickness of $525{\pm}15$ ${\mu}m$) having two holes of inlet and outlet ports of liquid serve as upper plate of the pump. Finally the silicon wafer of the base plate, the silicon wafer of pumping chamber and the glass wafer were aligned and bonded (Si-Si bonding and anodic bonding). A sequential photograph of bubble nucleation, growth and collapse was visualized by CCD camera. Clearly liquid flow through the nozzle during the period of bubble growth and slight back flow of liquid at the end of collapsing period can be seen. The mass flow rate was found to be dependent on the duty ratio and the operation frequency. As duty ratio increases, flow rate decreases gradually when the duty ratio exceeds 60%. Also as the operation frequency increases, the flow rate of the micropump decreases slightly.