• 설비공학논문집
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• 제10권6호
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• pp.743-752
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• 1998

Experiments were performed to characterize single-phase heat transfer behavior of submerged liquid jet with multiple nozzle normally impinging on the smooth and extended surfaces. Arrays of 9 and 36 nozzles were used, with diameters of 0.5 to 2.0mm providing nozzle area ratio (AR) from 0.05 to 0.2. The square pin fin arrays were chosen as extended surfaces and the effects of geometrical parameters such as fin height, the ratio of fin width to channel width on heat transfer enhancement were examined. Single nozzle characteristics were also evaluated for comparison. The results clearly showed that heat transfer enhancement could be realized by using multiple nozzles at the constant volume flow rate. The average Nusselt number of multiple nozzle impingement on the smooth surface was correlated by the following equation : Nu/$Pr\frac{1}{3}=0.94 Re^{0.56}N^{-0.12}AR^{0.50}$The average heat transfer coefficients of multiple nozzle impingement on the extended surfaces decreased with increasing fin height and the ratio of fin width to channel width. The effectiveness of ex-tended surfaces ranged from 1.5 to 3.5 depending on the fin height, the ratio of fin width to channel width of pin fin arrays, nozzle number and nozzle area ratio.

• 설비공학논문집
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• 제11권5호
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• pp.647-657
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• 1999

An experimental study has been peformed to investigate the heat transfer characteristics of impinging jets with multiple orifice nozzles. Four different shapes of multiple orifice nozzle were tested to improve the heat transfer characteristics of impinging jet. Heat transfer coefficients were obtained by using transient and steady method based on the liquid crystal thermography, and both methods showed very similar results. The effects of multiple orifice nozzles on the heat transfer characteristics of impinging jets were discussed in detail. The results showed that multiple orifice nozzles improved the heat transfer characteristics of impinging jet. Especially, heat transfer coefficients around stagnation region of impinging jets were highly increased.

• 대한기계학회논문집B
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• 제31권3호
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• pp.306-312
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• 2007

This paper describes the flow characteristics of circular multiple jet investigated by hot-wire anemometry. The nozzle arrays were classified into two cases; 6- or 7-nozzle located circumferentially in equal interval without or with a central jet. The flow field was measured according to the number of nozzles when the Reynolds number based on the nozzle exit is about $10^4$. Mean velocity, Reynolds shear stress and turbulent kinetic energy were investigated in the downstream of jets. The Tollmien's theory holds for downstream only when a nozzle locates at the center. Jet interaction is influenced due to with or without a center nozzle. In addition, the two-dimensional numerical computation was conducted for 3-nozzle case to obtain the general flow structure near the nozzle exit, which verifies the formation of the recirculation region with captive vortices, that is, the evidence of the interaction between jets.

• 폴리머
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• 제32권4호
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• pp.334-339
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• 2008

최근 전기방사공정은 다양한 고분자의 마이크로 및 나노 크기 섬유를 만드는 기술로서 널리 사용되어 왔다. 일반적으로 많은 연구자들에 의하면, 다중노즐 전기방사공정은 노즐들 사이의 전기장 간섭효과 때문에 짧은 시간에 높은 생산성을 갖기 어려웠다. 이러한 문제를 극복하기 위하여 본 연구에서는 다양한 보조전극을 이용한 다중노즐 전기방사공정을 개발하였다. 본 연구에서 사용된 물질은 바이오소재로서 많이 사용되고 있는 poly($\varepsilon$-carprolactone)(PCL)을 사용하였다. 다중노즐 시스템의 영향을 확인하기 위하여 전기방사의 안정성, 다중노즐을 사용하였을 때의 생산성 및 제조된 나노섬유의 크기와 안정성을 보조전극을 사용하였을 때와 사용하지 않았을 때를 비교하였다. 결과적으로 보조전극을 사용한 노즐의 안정성이 사용하지 않은 노즐에 비해 전기방사 안정성과 우수한 생산성을 보였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
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• pp.84.2-84.2
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• 2005

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1365-1370
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• 2004

It has been reported that if eight small nozzles are arranged along the circle of 40 $^{\sim}$ 72 times the diameter of single nozzle, the propane non-premixed flames are not extinguished even in 200m/s, In this research, experiments were extended to the methane flame. Nine nozzles were used- eight was evenly located along the perimeter of the imaginary circle and one at the geometric center. The space between nozzles, s, the exit velocity and the role of the jet from the center nozzle were considered. On the contrary to the propane non-premixed case, the maximum blowout velocity for the methane diffusion flame was achieved when small amount of fuel is supplied through the center nozzle and s/d equals around 21. In the laminar region, the flame attached at the center nozzle anchored the outer lifted flames.

• 대한기계학회논문집B
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• 제29권3호
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• pp.349-355
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• 2005

It has been reported that propane non-premixed interacting flames are not extinguished even in 210m/s if eight small nozzles are arranged along the imaginary circle of 40 ~ 72 times the diameter of single nozzle. In this research, experiments were extended to the methane flame. Nine nozzles were used- eight was evenly located along the perimeter of the imaginary circle and one at the geometric center. The space between nozzles, s, the exit velocity and the role of the jet from the center nozzle were considered. On the contrary to the propane non-premixed flame, small amount of fuel fed through the center nozzle makes the methane diffusion flame stable even at the choking conditions. In the laminar region, the flame at the center nozzle anchored the outer lifted flames.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2014년도 추계학술대회 논문집
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• pp.463-463
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• 2014

Multi-packet blade systems usually undergo multiple nozzle excitations during operation. For the design of multi-packet blade systems undergoing multiple nozzle excitations, transient characteristics around an operating frequency and resonance frequencies should be identified. In this study the equations of motion of multi-packet blade systems undergoes multiple nozzle excitations are derived. The reliability of the derived equations is verified by obtaining responses at resonance frequencies. Then, using the model, the effects of system parameters on the transient characteristics of the system are investigated.

• 대한기계학회논문집B
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• 제32권1호
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• pp.7-14
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• 2008

It has been reported that partially premixed interacting flame could be sustained till sonic exit velocities if eight small nozzles are arranged optimally and one nozzle on the center is fed small amount of fuel. But the equivalence ratios in this experiments were 20-60. In this research, experiments were conducted to know the effects of lean-rich staging in multiple jet flames on the blowout velocity. The fuel mole tractions in the fuel-air mixture, the nozzle exit velocity and the diameter between adjacent nozzles were alternatively changed. When the lower mole fraction fuel was fed to the nozzles located near the center and small amount of fuel to the center nozzle, flame was not extinguished even at the nozzle exit velocity of 200m/s. Also the interacting flame could be sustained till that velocity when four small size nozzles for lean mixture were located within the arrangement of four nozzles for rich mixture and configured optimally.

• 한국시뮬레이션학회논문지
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• 제15권4호
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• pp.59-67
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• 2006

본 연구에서는 갠트리타입 기종을 사용한 PCB 조립 생산시 생산시스템의 수행도 향상을 위한 방안을 개발하여 제시한다. 갠트리타입의 기종에서는 헤더나 슬롯의 이동보다는 노즐의 교체가 시스템의 수행도 향상에 주된 걸림돌이 되므로 동시흡착을 최대화할 수 있는 방안을 모색하였다. 본 연구에서 제시된 해법은 피더의 위치와 노즐의 위치를 감안하여 동시흡착을 수행하도록 함으로써 노즐 교체를 최소화하고, 기판당 조립시간의 감소도 이루어지도록 하였다. 제안 해법의 유효성을 입증하기 위해 시뮬레이션 모형을 구축하고 부품의 수를 변화시켜가면서 다음 작업대상피더와 교체노즐의 선정을 다양하게 하여 여러 운영방안들의 수행도와 비교 분석하였다. 시뮬레이션 결과, 동시흡착을 유도하는 노즐교체를 할 경우 전반적인 수행상태가 양호한 것으로 나타났다.