• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1747-1751
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• 2008

Electrohydrodynamic jet printing (EHDP) technique is widely used for the direct writing. However, in the existing EHDP method, the printing characteristics are affected by the printing substrate used, and the line width of the printed is determined by the geometry of the nozzle. We propose an EHDP method which is capable of (1) removing the effect from the substrate, and (2) controlling the line width through the ON/OFF control of the each nozzle in the nozzle array. Printing characteristics of our EHDP system were examined and successful ON/OFF control of the nozzle array were demonstrated. By using the proposed EHDP, it is expected that stable meniscus regardless of the substrate and different line widths even using the same nozzle can be achieved.

• 한국생산제조학회지
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• 제25권1호
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• pp.42-47
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• 2016

This paper presents the development of a floating outboard type of compact water jet propulsion system. The planning case of the water jet system is developed by performing precision processing after manufacturing FRP (Fiber Reinforced Plastics) from plug mold casting. This system is composed of an intake, impeller, diffuser, reverse bucket, and main shaft. In addition, a rebuilt engine was applied through marine engineering. The water jet propulsion system performance was verified to discharge a maximum $0.29m^3/s$ of flow rate and 37 m/s of flow velocity in a test pool on land. A field test was performed by installing the water jet propulsion device on board a ship that was tested off the coast of Korea. The weight of the hull, engine, and other equipment was approximately 1.2 tons, and the sailing speed was a maximum 22 knots at 3,600 rpm.

• 설비공학논문집
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• 제17권4호
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• pp.333-340
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• 2005

Horizontal air-jet effect has been utilized in some air conditioning systems in order to control the contaminated air indoor. In the present study, the flow and heat transfer of the contaminated air from a range hood system has been investigated with or without horizontal air-jet effect when the hood fan is on or off. For the present numerical experiment, PAT Flow code has been used. From the present numerical simulations, it has been shown that the air jet of a range hood generates coanda effect confining the contaminated air in a certain region. Furthermore, the qualitative relation between the flow rate of the capture air jet and the distribution pattern of the contamination has been discussed.

• 소성∙가공
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• 제22권2호
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• pp.74-79
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• 2013

The ultra-precision polishing method using MR fluid has come into the spotlight for polishing metals and optical materials. The MR fluid jet polishing process can be controlled using a change of viscosity by an imposed magnetic field. The MR fluid used for polishing process is a mixture of CI particles, DI water, $Na_2CO_3$ and glycerin. The efficiency of polishing depends on parameters such as polishing time, magnetic field, stand-off distance, pressure, etc. In this paper, the MR fluid jet polishing was used to polish nickel and brass mold materials, which is used to fabricate backlight units for 3-D optical devices in mobile display industries. In MR jet polishing, ferromagnetic materials like nickel can decrease the polishing efficiency by interaction with the cohesiveness of the MR fluid more than non-ferromagnetic materials like copper. A series of tests with different polishing times showed that the surface roughness of brass (Ra=1.84 nm) was lower than that of nickel (Ra=2.31 nm) after polishing for 20 minutes.

• Journal of Ship and Ocean Technology
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• 제12권1호
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• pp.1-15
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• 2008

An edgetone is the discrete tone or narrow-band sound produced by an oscillating free shear layer, impinging on a rigid surface. In this paper, 2-dimensional edgetone to predict the frequency characteristics of the discrete oscillations of a jet-edge feedback cycle is presented using lattice Boltmznan model with 21 bits, which is introduced a flexible specific heat ratio y to simulate diatomic gases like air. The blown jet is given a parabolic inflow profile for the velocity, and the edges consist of wedges with angle 20 degree (for symmetric wedge) and 23 degree (for inclined wedge), respectively. At a stand-off distance w, the edge is inserted along the centerline of the jet, and a sinuous instability wave with real frequency is assumed to be created in the vicinity of the nozzle exit and to propagate towards the downward. Present results presented have shown in capturing small pressure fluctuating resulting from periodic oscillation of the jet around the edge. The pressure fluctuations propagate with the speed of sound. Their interaction with the wedge produces an irrotational feedback field which, near the nozzle exit, is a periodic transverse flow producing the singularities at the nozzle lips. It is found that, as the numerical example, satisfactory simulation results on the edgetone can be obtained for the complex flow-edge interaction mechanism, demonstrating the capability of the lattice Boltzmann model with flexible specific heat ratio to predict flow-induced noises in the ventilating systems of ship.

• 한국화재소방학회논문지
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• 제22권1호
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• pp.16-23
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• 2008

본 연구에서는 도로터널에서의 화재발생 시 최적의 방재시스템을 구축하기 위하여 실제 터널의 축소모형을 대상으로 제트팬의 위치 및 운전방식에 따른 연기의 유동 및 교란을 가시화함으로서 연기의 전파특성을 고찰하여 제트팬 운전방식의 타당성을 연기의 농도 분포에 의하여 검토하였다. 실험 결과로 화원으로부터 상류방향으로 근접한 제트팬 운전 시에는 연기의 역류를 방지하기위하여 화원과 제트팬의 거리는 최소 50 m이상 이격시켜야 한다. 반면에 화원으로부터 하류방향으로 근접한 제트팬 운전 시에는 모든 조건에 대하여 연기의 편류가 발생하지 않으나 하류방향으로 흐르는 연기의 성층화에 영향을 주기 때문에 사용이 불가능하다.

• 한국항공우주학회지
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• 제38권2호
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• pp.160-168
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• 2010

공명 주파수의 음파로 가진된 비예혼합 분류화염에서 가진 강도에 대한 영향을 실험적으로 조사하였다. 이를 위해 Mie 산란광 단면법, PLIF, PIV 등 광학적 가시화 방법이 사용되었다. 가진된 분류화염의 부상경로는 연료유량 및 가진 강도에 따라 크게 세 가지 영역으로 구분되는데, 비교적 큰 가진 강도에서 부상될 때 화염기저가 마치 난류화염처럼 부상되는 영역I과 작은 가진 강도에서 쉽게 부상되는 영역II 그리고 이 두 영역들 사이에서 부상된 화염기저가 부분 예혼합의 분젠화염과 같은 형태로 과도기적 영역이 존재함을 알았다. 본 연구에서는 영역I과 II로 구분되는 부상경로 차이에 대한 이해를 높이고자 가진 위상에 따른 노즐과 화염기저간의 유동 혼합과 속도 분포 특성을 아세톤 PLIF와 PIV 시스템을 사용하여 조사하였다.

• 대한기계학회논문집B
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• 제21권8호
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• pp.1009-1023
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• 1997

The breakup length of a liquid jet with flowrate, formed by releasing through a nozzle of circular cross-section into the atmosphere, was experimented and studied for 3 liquid nozzles of varying diameters. The experimental result was analyzed using the existing theoretical equation for predicting the breakup length. It was found that the breakup length of liquid jet depends on the velocity, and the breakup length increases with increasing of the liquid nozzle diameter. Also, the variation range of the breakup length for the same flowrate of liquid increased rapidly as velocity was increased for laminar flow, but in the turbulent flow region, it leveled off in the range of approximately 0.55-0.7 of the mean breakup length. Furthermore, when the longest smooth liquid jet was applied to the co-axial flow air blast atomizer, the effect of air flow on the flow pattern and breakup length was studied for 6 glass nozzles of different lengths and diameters. It was found that depending on the diameter of the mixing tube and liquid jet, it was possible to observe a wide range of flow patterns, such as liquid jet through flow, partial annular flow and annular flow. The liquid jet breakup length was more sensitive to the change in the length rather than the diameter of the mixing tube. As the length of the mixing tube shortens, the breakup length also shortens rapidly.

• 한국해양공학회지
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• 제18권5호
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• pp.15-21
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• 2004

An edge tone is the discrete tone or narrow-band sound produced by an oscillating free shear layer, impinging on a rigid surface. In this paper, we present a 2-D edge tone to predict the frequency characteristics of the discrete oscillations of a jet-edge feedback cycle, using the finite difference lattice Boltzmann method (FDLBM). We use a modified version of the lattice BGK compressible fluid model, adding an additional term and allowing for longer time increments, compared to a conventional FDLBM, and also use a boundary fitted coordinates system. The jet is chosen long enough in order to guarantee the parabolic velocity profile of the jet at the outlet, and the edge consists of a wedge with an angle of ${\alpha}$ = 23. At a stand-off distance, the edge is inserted along the centerline of the jet, and a sinuous instability wave, with real frequency, is assumed to be created in the vicinity of the nozzle and propagates towards the downstream. We have succeeded in capturing very small pressure fluctuations, resulting from periodical oscillations of a jet around the edge. The pressure fluctuations propagate with the speed of sound. Its interaction with the wedge produces an non-rotational feedback field, which, near the nozzle exit, is a periodic transverse flow, producing the singularities at the nozzle lips.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1915-1920
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• 2004

An edge tone is the discrete tone or narrow-band sound produced by an oscillating free shear layer impinging on a rigid surface. In this paper we present a two-dimensional edge tone to predict the frequency characteristics of the discrete oscillations of a jet-edge feedback cycle by the finite difference lattice Boltzmann method. We use a new lattice BGK compressible fluid model that has an additional term and allow larger time increment comparing a conventional FDLB model, and also use a boundary fitted coordinates. The jet is chosen long enough in order to guarantee the parabolic velocity profile of the jet at the outlet, and the edge consists of a wedge with an angle of ${\alpha}=23^{\circ}$ . At a stand-off distance ${\omega}$ , the edge is inserted along the centreline of the jet, and a sinuous instability wave with real frequency f is assumed to be created in the vicinity of the nozzle and to propagate towards the downstream. We have succeeded in capturing very small pressure fluctuations result from periodically oscillation of jet around the edge. That pressure fluctuations propagate with the sound speed. Its interaction with the wedge produces an irrotational feedback field which, near the nozzle exit, is a periodic transverse flow producing the singularities at the nozzle lips.