• Journal of Energy Engineering
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• v.8 no.2
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• pp.298-308
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• 1999

Experimental study on characteristics of direct contact condensation of steam discharged into a sub-cooled water pool has been performed using five different sizes of horizontal nozzle over a wide range of steam mass fluxes and pool temperatures. Steam condensation phenomena have been observed visually and by taking pictures of steam jets using a high speed video camera. Two different steam jet shapes such as ellipsoidal shape and conical shape were typically observed for a stable steam jet, depending on the steam mass flux and pool temperature. The steam jet expansion ratio and the steam jet length as well as the condensation heat transfer coefficients were determined. The effect of steam mass flux, pool temperature, and nozzle diameter on these parameters were also discussed. Empirical correlations for the steam jet lengths and the condensation heat transfer coefficients as a function of steam mass flux and condensation driving potential were established. The axial and radial temperature distributions in steam jet and in surrounding water were measured. The effect of steam mass flux, pool temperature, and nozzle diameter were also discussed. The condensation regime map, which consists of six regimes such as chugging, transient chugging, condensation oscillation, stable condensation, bubble condensation oscillation, and intermittent oscillation condensation, were established. In addition, the dynamic pressures at the pool wall were measured. The close relation of dynamic pressure and steam condensation mode, which is also dependent on steam mass flux and pool temperature, was found.

• Journal of Aerospace System Engineering
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• v.13 no.6
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• pp.9-16
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• 2019

The experiment on the liquid jet in crossflow in supersonic BFS (backward-facing step) flow was conducted to investigate the mixing characteristics. The working fluids are nitrogen and water. The shadow graph technique was used to visualize the flow field. Images captured by the high-speed camera were applied to analyze the flow phenomena. The liquid jet was injected at the re-circulation zone created by the supersonic jet flow. Experimental conditions are defined based on the pressure of the nitrogen gas chamber and pressurized liquid tank. In respective cases, the penetration depth of liquid jet and location of the Mach disc were observed to be proportional to the momentum ratio of gas and liquid jets.

• Journal of ILASS-Korea
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• v.16 no.4
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• pp.176-185
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• 2011

The empirical correlations for the prediction of penetration height of liquid jet in crossflow are reviewed and classified in this study. Around thirty different correlations had been proposed by many investigators. It has generally known that the penetration height of a liquid jet in a cross-flow is a function of the liquid to air momentum flux ratio and the normalized downstream distance from the injector. However, several researchers incorporated the Weber number, liquid-to-water or air viscosity ratio, pressure ratio or Reynolds number, temperature ratio in the empirical correlations. The existing correlations can be grouped as correlations in a power-law, logarithmic, and exponential forms, respectively. Correlations in a power-law form can be further classified as three groups such as basic form, Weber number form and other parameters form. It should be pointed out that correlations in a logarithmic form in terms of Weber number or any other parameters could not be found. Universal correlation has still not been established due to the significant discrepancies between various correlations suggested to date. Several of the studies reported the significant discrepancies of predicted values by the existing correlations. The possible reasons for discrepancies will be summarized as measurement technique, assumptions made in defining terms in the liquid to air momentum flux ratio, difficulties in defining the boundaries of the liquid jets, and nozzle/injector geometry. Evaluation of validity for the correlations proposed recently by several investigators is essentially required. Those include eight power-law forms, two logarithmic forms, and one exponential form.

• Journal of the Korean Society of Propulsion Engineers
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• v.12 no.6
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• pp.38-47
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• 2008

The liquid column and spray trajectory have been experimentally studied in liquid jets injected into subsonic crossflow. With water as fuel injection velocity, injection angle were varied to provide of jet operation conditions. The Pulsed Shadowgraph Photography and Planar Liquid Laser Induced Fluorescence technique was used to determine the injection characteristics in a subsonic crossflow of air. And the mainly objectives of this research was to get a empirical formula of liquid column and spray region trajectory with forward and reversed injection of air stream. As the result, This research has been shown that each trajectories were spatially dependent on air-stream velocity, fuel injection velocity, various injection angle, and normalized injector exit diameter. Furthermore, the empirical formula of liquid column trajectories has been some different of drag coefficient results between forward and reversed angled injection.

• Journal of the Korean Wood Science and Technology
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• v.21 no.4
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• pp.7-28
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• 1993

본 총설에서는 새로운 방부제와 방부처리 기술의 현재 발전 동향을 요약, 보고한다. 많은 새로운 방부제들이 약제의 독성 측면에서 환경적인 충격을 완화시킬 수 있는 잠재성을 가지고 있지만, 방부제로서 상업화되기 위해서는 이러한 약제들은 약제의 효능과 환경 안전성 간의 몇 가지 상호 조정 관계가 반드시 해결되어야 한다. Ammoniacal copper 계통의 방부제들이 지접부 사용에 적합한 새로운 수용성 방부제들의 주종을 이루고 있으며, 기존의 유용성 방부제들을 물에 용해한 emulsion 형태도 지접부 사용의 가능성을 보여 준다. 새로운 유용성 방부제 중에서 copper naphthenate, substituted isothiazolones, chlorothalonil, oxine copper가 지접부 사용을 위한 최상의 후보로 평가되고 있다. 유용성 방부제를 emulsion 형태로 사용하는 것은 유용성 방부제에 사용되는 석유 계통 용제의 소비를 감소시키기 때문에 중대한 의미를 가진다. 방부제들의 효능을 개선하고 강화시키기 위해 사용되는 첨가제들도 본 총설에서 거론된다. 재질개량을 위해 사용되는 비통상적인 방법(nonconventional system)들도 생물학적 열화 및 기상열화에 대한 저항성을 부여하여 목재의 사용수명을 증가시킨다. 전처리 공정에서 침상 자상처리(Needle incising)와 레이져 자상처리는 난주입 수종의 처리도를 개선시킬 수 있는 잠재성을 가지고 있다. 처리기술에 있어서 여러 가지 혁신적인 변화들은 기존의 처리 schedule을 조성함에 그 기본을 두고 있다. 난주입 수종의 처리도 개선은 pulsation법이나 고압 약제 분사법 (high energy liquid jets) 같은 고압을 적용하는 처리법에 의해서 달성된다. 미래의 처리공장들은 방부제를 기체상태로 또는 물질의 임계점 이상에서 방부제를 처리할 수도 있다. 이러한 새로운 접근은 외관이 깨끗하고, 처리도도 매우 양호한 처리재를 생산하는데 일조하리라 기대한다. 환경에 대한 대중적인 지대한 관심은 앞으로 목재 방부산업에 큰 영향을 미칠 것으로 보인다. 결과적으로 방부제의 처리목재내 가속 정착에 관한 연구에 상당한 노력이 투자될 것이다. 처리 후 가공에 관한 다른 주요한 연구는 방부제 처리 후 실시되는 재건조가 처리재의 역학적 성질에 미치는 영향에 대한 것이다.

• Journal of the Optical Society of Korea
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• v.13 no.1
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• pp.8-14
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• 2009

In a laser-plasma wakefield accelerator, the ponderomotive force of an ultrashort high intensity laser pulse excites a longitudinal wave or plasma bubble in a way similar to the excitation of a wake wave behind a boat as it propagates on the water surface. Electric fields inside the plasma bubble can be several orders of magnitude higher than those available in conventional RF-based particle accelerator facilities which are limited by material breakdown. Therefore, if an electron bunch is properly phase-locked with the bubble's acceleration field, it can gain relativistic energies within an extremely short distance. Here, in the bubble regime we show the generation of stable and reproducible sub GeV, and GeV-class electron beams. Supported by three-dimensional particle-in-cell simulations, our experimental results show the highest acceleration gradients produced so far. Simulations suggested that the plasma bubble elongation should be minimized in order to achieve higher electron beam energies.