• 에너지공학
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• 제21권2호
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• pp.187-193
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• 2012

본 연구의 목적은 벽면제트영역의 열전달증진을 위해 직삼각형 로드 및 정사각형 로드를 충돌판앞에 배열한 후 로드와 충돌판 사이의 간극을 변화시키면서 열유동 특성을 실험적으로 검토한 것이다. 열전달증진율은 천이영역인 H/B=10보다는 포텐셜코어영역인 H/B=2에서 더 높게 나타났다. 본 실험범위에서 최대 열전달증진율은 직삼각형 로드를 설치할 때(H/B=2, C=1mm인 조건) 로드가 없는 평판과 비교하면 평균 약 46% 높게 나타났다. 그리고 직삼각형 로드와 정사각형 로드의 열전달증진율을 비교하면 간극 변화와 관계없이 직삼각형 로드가 정사각형 로드보다 평균 약 3~8% 정도 높게 나타났다.

• 한국유체기계학회 논문집
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• 제2권2호
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• pp.64-73
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• 1999

The three-dimensional numerical study of a water jet pump was carried out to investigate the relationship between performance and the geometric variables of nozzle space, area ratio, and throat length. Because of the complex geometry, the multiblock technique was adopted for numerical analysis and a special treatment for transferring data from each of the block interfaces was implemented in order to maintain the conserved properties. To validate the present code, flow passing through a square duct with a 90-deg bend was computed, our results show good accordance with other experimental and computational results. The numerical simulation was done with the flow of the water jet pump having a 180-deg bend in order to calculate the performance at different operating conditions. The performance of the water jet pump can be improved by study of parameters which clarify the relations between the geometric variables and the flow characteristics of vortex strength and location.

• 대한기계학회논문집B
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• 제24권10호
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• pp.1409-1416
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• 2000

In this study, turbulent flows in a planar combustor which has a square rib-type flame holder are numerically investigated by Large Eddy Simulation(LES). Firstly, the flow fields with or without jet injection downstream of the flame-holder are examined using uniform inlet velocity. Comparison of the present LES results with experimental one shows a good agreement. Secondly, to investigate mixing of oxidizer(air) and fuel injected behind the flame holder, the scalar-transport equation is introduced and solved. From the instantaneous flow and scalar fields, complex and intense mixing phenomena between fuel and jet are observed. It is shown that the ratio of jet to blocked air velocity is an important factor to determine the flow structure. Especially, when the ratio is large enough, the fuel jet penetrates the main vortices shed from the flame holder, resulting in significant changes in the flow and scalar fields.

• 한국태양에너지학회 논문집
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• 제25권4호
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• pp.101-110
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• 2005

An experimental study of heat transfer of submerged water jet impinging normally on a flat plate is presented. Heat transfer measurements obtained with Reverse cone type nozzle(Rcone) were compared to those obtained with Cone type nozzle(Cone) and Square edged type nozzle(Vert) of the same diameter(D=8mm) for different jet velocities in the range of $3{\sim}7m/s(Re_D=30000{\sim}70000)$ and various nozzle-to target spacings($H/D=2{\sim}10$). The local Nusselt number profiles exhibited a sharp drop for $r/D{\leq}0.5$ and 2nd, 3rd peaks revealed at r/D=2, 3 respectively, followed by a slower decrease there after. The peaks were weakened with increasing the nozzle-to target spacing and decreasing the jet velocity. The stagnation Nusselt number of the Reverse cone type nozzle was larger than those of the other two nozzles for H/D=2. 10, but Cone type nozzle had the highest value for $H/D=4{\sim}8$. Also average Nusselt number of the Reverse cone type nozzle was higher than those of the other two nozzles at $H/D=2{\sim}10$, except for $V_o=7ms$ of H/D=6.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 춘계학술발표대회
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• pp.59.2-59.2
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• 2011

We have demonstrated ink-jet printed indium tin oxide (ITO) and indium tin zinc oxide (IZTO) electrodes for cost-efficient organic solar cells (OSCs). By ink-jetting of crystalline ITO nano-particles and performing a rapid thermal anneal at $450^{\circ}C$, we were able to obtain directly patterned-ITO electrodes with an average transmittance of 84.14% and a sheet resistance of 202.7 Ohm/square without using a conventional photolithography process. The OSCs fabricated on the directly patterned ITO electrodes by ink-jet printing showed an open circuit voltage of 0.57 V, short circuit current of 8.47 mA/cm2, fill factor of 44%, and power conversion efficiency of 2.13%. This indicates that the ITO directly-patterned by ink-jet printing is a viable alternative to sputter-grown ITO electrodes for cost-efficient printing of OSCs due to the absence of a photolithography process for patterning and more efficient ITO material usage.

• Journal of Mechanical Science and Technology
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• 제15권12호
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• pp.1691-1698
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• 2001

In recent years, significant progress has been made in modeling turbulence behavior in plasma and its effect on transport. It has also been made in diagnostics for turbulence measurement; however, there is still a large gap between theoretical model and experimental measurements. Visualization of turbulence can improve the connection to theory and validation of the theoretical model. One method to visualize the flow structures in plasma is a laser Schlieren imaging technique. We have recently applied this technique and investigated the characteristics of a highly underexpanded pulsed plasma jet originating from an electrothermal capillary source. Measurements include temporally resolved laser Schlieren imaging of a precursor blast wave. Analysis on the trajectory of the precursor blast wave shows that it does not follow the scaling expected for a strong shock resulting from the instantaneous deposition of energy at a point. However, the shock velocity does scale as the square root of the deposited energy, in accordance with the point deposition approximation.

• 대한기계학회논문집B
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• 제23권6호
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• pp.753-760
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• 1999

Experiments were conducted to investigate the effect of the initial turbulent intensity on the flow and heat transfer characteristics for a two-dimensional impinging jet. A square rod was installed at the nozzle exit to increase initial turbulent intensity. A hot wire probe and thermochromic liquid crystal technique were used to measure the turbulent intensity and the surface temperature. All measurements were made over a range of nozzle-to-plate distance from 1 to 10 at Re=20,000. When the rod is not installed, the maximum stagnation point Nusselt number is occurred at H/B=9. A higher initial turbulent intensity enhanced the heat transfer on the surface. A correlation between stagnation point Nusselt number and turbulent intensity are presented.

• International Journal of Advanced Culture Technology
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• 제3권2호
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• pp.171-178
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• 2015

In this work, mixing processes of hot and cold fluids of three different jet types are predicted by large-eddy simulation (LES) on FLUENT platform. Temperature at different positions of internal wall and mixing conditions of T-junctions at different times are obtained, then the simulated normalized mean and root-mean square (RMS) temperature, temperature contour and velocity vector of every case are compared. The results indicate that, the mixing regions in the tee junction is related to the jet type, and temperature fluctuations on the pipe wall in the type of the deflecting jet is the least.

• 대한기계학회논문집
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• 제11권2호
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• pp.214-221
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• 1987

본 논문에서는 2차원충돌분류에서 사각리브(rib)를 갖는 요철형전열면에 대한 실험에 관한 것이며, 리브의 높이를 (ｅ=5nm) 일정하게 하고 리브의 피치(ｐ=25,35,50 nm) 변화, 노즐출구와 전열면간 거이(H/B=1~14) 및 노즐출구유속(ｕ$_{e}$=12.30~ 18.07m/s)의 변화에 따른 전열특성을 실험적으로 구명하고 평판전열면의 경우와 비교 검토한다. 또한 스모크와이어(smoke-wire)법으로 평판 및 리브판에서의 유체의 거동 을 가시화하여 전열기구의 정성적 특성을 검토하는데 목적이 있다.

• 한국가시화정보학회지
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• 제9권2호
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• pp.48-53
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• 2011

The shape of nozzle cross-section plays an important role in stabilizing electrospray jet. The angle of contact line is governed based on the famous Young-Laplace equation. Compared to a round nozzle that has a constant curvature along the orifice, the square nozzle has four square corner edges and four straight edges that hold the meniscus in a different manner and is of interest in this study. By utilizing both square and round capillary nozzle, we examine the effect of nozzle shape in electrohydrodynamic jetting. The ejections were recorded with a high speed camera and analyzed to examine the jetting repeatability based on dynamic movement of meniscus. The result suggests that if the corner edges are not sharp, then its effect on repeatability is also limited.