• 지질공학
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• 제31권3호
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• pp.433-445
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• 2021

고전압 아크 방전에 의한 플라즈마 발파의 유체 침투 효율을 검증하기 위해 실험실 규모의 토사 시료에 대하여 발파 시험을 실시하였다. 이 연구를 위해 대용량 축전기가 포함된 플라즈마 발파 장치와 직경 80 cm, 높이 60 cm 크기의 컬럼형 토사 시료를 제작하였다. 토사 시료로는 사질토와 실트를 7:3 비율로 섞은 A 시료 7개와 9:1 비율로 섞은 B 시료 3개가 제작되었다. A 시료에 플라즈마 발파 없이 수압만으로 유체를 주입했을 때는 시추공 주변으로 국소적인 침투만 발생되었고 침투면적비는 5% 이하로 분석되었다. 플라즈마 발파에 의한 유체 침투 시험은 1 kJ, 4 kJ 그리고 9 kJ의 방전 에너지로 실시되었다. A 시료에 대한 플라즈마 발파 시험에서 유체의 침투면적비는 1회만 발파하였을 때는 16~25%이고 5회 연속 발파 시에는 30~48%로 분석되어, 수압만으로 유체를 주입했을 때보다 침투면적이 최대 9.6배까지 넓어졌다. B 시료에 대한 5회 연속 플라즈마 발파 시험에서 유체의 침투면적비는 33~59%로 분석되어 동일 조건의 A 시료 시험에 비해 침투면적이 1.1~1.4배 정도 넓어졌다. 이러한 결과는 플라즈마 발파 시에 방전 에너지가 클수록, 발파 횟수가 증가할 수록 유체의 침투면적이 증가하며, 투수성이 큰 토양에서 플라즈마 발파가 더욱 효과적임을 보여준다. 유체 침투 효과를 삼차원적인 부피로 분석하기 위해 유체 침투반경을 계산하였다. 수압으로만 유체를 주입했을 때의 침투반경은 9 cm인 반면에, 9 kJ의 에너지로 5회 발파 시에는 침투반경이 27~30 cm로 계산되어 유체 침투 효과가 최대 333%까지 증가되었다. 이러한 연구결과는 투수성이 낮은 실제 오염토양에서 원위치 토양 세정을 실시할 때 플라즈마 발파 기술을 적용하면, 세정제의 전달범위가 증가되어 정화효율이 개선될 수 있다는 것을 보여준다.

• Journal of Welding and Joining
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• 제35권2호
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• pp.13-22
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• 2017

In laser full penetration welding process, full penetration hole(FPH) is formed as a result of force balance between the vapor pressure and the surface tension of the surrounding molten metal. In this work, a three-dimensional numerical model based on a conserved-mass level-set method is developed to simulate the transport phenomena during laser full penetration welding process, including full penetration keyhole dynamics. Ray trancing model is applied to simulate multi-reflection phenomena in the keyhole wall. The ghost fluid method and continuum method are used to deal with liquid/vapor interface and solid/liquid interface. The effects of processing parameters including laser power and scanning speed on the resultant full penetration hole diameter, laser energy distribution and energy absorption efficiency are studied. The model is validated against experimental results. The diameter of full penetration hole calculated by the simulation model agrees well with the coaxial images captured during laser welding of thin stainless steel plates. Numerical simulation results show that increase of laser power and decrease of welding speed can enlarge the full penetration hole, which decreases laser energy efficiency.

• 한국주조공학회지
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• 제33권6호
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• pp.248-253
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• 2013

To add alloying elements into a pure copper melt, the wire-feeding efficiency of cored (alloy containing) wire was evaluated using a commercial, computational fluid-dynamics program. The model design was based on an industrial-scale production line. The variables calculated included wire feed rate, melt temperature, wire diameter, melt flow rate and wire temperature. Efficiency was evaluated after a series of calculations based on the penetration depth of the alloy-wire into the molten copper bath. Of the five variables investigated, the wire feed rate and wire diameter were the most influential factors affecting the feeding efficiency of the cored-wire.

• Nuclear Engineering and Technology
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• 제38권7호
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• pp.689-696
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• 2006

For a perforated plate, it is challenging to develop a finite element model due to the necessity of the fine meshing of the plate, especially if it is submerged in fluid. This necessitates the use of a solid plate with equivalent material properties. Unfortunately, the effective elastic constants suggested by the ASME code are deemed not valid for a modal analysis. Therefore, in this study the equivalent material properties of a perforated plate are suggested by performing several finite element analyses with respect to the ligament efficiencies.

• 한국분무공학회지
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• 제7권3호
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• pp.12-17
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• 2002

In this paper, spray and combustion characteristics of a liquid-fueled ramjet engine were experimentally investigated. The spray penetrations were measured to clarify the spray characteristics of a liguid jet injected transversely into the subsonic vitiated airstream, which is maintained a high velocity and temperature. The spray penetrations are increased with decreasing airstream velocity, increasing airstream temperature, and increasing air-fuel momentum ratio. To compensate our results of penetrations, the new experimental equation were modified from Inamura's equation. In the case of insufficient penetration, the combustion phenomenon in ram-combustor were unstable. Therefore, the temperature distribution was slanted to the low wall of the ram-combustor. These trends gradually disappeared as the length and air temperature of the combustor became longer. Combustion efficiency increased when the length of the combustor was long and the air temperature was high. Especially, stable flame region is enlarged when the length of the combustor was long and the air temperature was high. Type Abstract here. Type Abstract here.

• 한국분무공학회지
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• 제9권2호
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• pp.34-40
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• 2004

In a liquid-fueled ramjet engine, the insufficient mixing and evaporation result in the low combustion efficiency and combustion instability. Improving its characteristics and devising a means of fuel droplets with air may compensate these disadvantages of liquid fuel ramjet engine. The jet penetrations of various fuel injectors were measured to investigate the spray characteristics of a liquid-fueled ramjet engine under high pressure air-stream conditions. The penetrations in high pressure conditions are smaller than the values calculated from Inamura's or Lee's equations, and the jet penetrations in the high pressure conditions have a similar tendency. In the dual orifice injectors, the jet penetrations of rare orifice is rapidly increased due to the reduction of the drag, which is created by the jet column of front orifice. The jet penetration of rare orifice is increased because of the drag reduction created by the jet column of the front orifice. Because of the drag reduction formed by the column of jet, the jet penetration in the rear orifice of dual orifice injector is much larger than the jet penetrations of single orifice injector. As the distances of the orifice are increased, the jet penetrations of the rear orifice decrease.

• International Journal of Fluid Machinery and Systems
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• 제10권2호
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• pp.164-175
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• 2017

Francis turbines are often operated over a wide load range due to high flexibility in electricity demand and penetration of other renewable energies. This has raised significant concerns about the existing designing criteria. Hydraulic turbines are not designed to withstand large dynamic pressure loadings on the stationary and rotating parts during such conditions. Previous investigations on transient operating conditions of turbine were mainly focused on the pressure fluctuations due to the rotor-stator interaction. This study characterizes the synchronous and asynchronous pressure and velocity fluctuations due to rotor-stator interaction and rotating vortex rope during load variation, i.e. best efficiency point to part load and vice versa. The measurements were performed on the Francis-99 test case. The repeatability of the measurements was estimated by providing similar movement to guide vanes twenty times for both load rejection and load acceptance operations. Synchronized two dimensional particle image velocimetry and pressure measurements were performed to investigate the dominant frequencies of fluctuations, vortex rope formation, and modes (rotating and plunging) of the rotating vortex rope. The time of appearance and disappearance of rotating and plunging modes of vortex rope was investigated simultaneously in the pressure and velocity data. The asynchronous mode was observed to dominate over the synchronous mode in both velocity and pressure measurements.

• 한국입자에어로졸학회지
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• 제12권3호
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• pp.51-56
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• 2016

Due to recent development in nanotechnology and increasing usage and production of nanomaterials, numerous studies related to environment, sanitation and safety handling of nanoparticle are being conducted. Since nanoparticles can be easily absorbed into human bodies through breathing process, based on their toxic substances and their large specific surface, these particles can cause serious health damage. Therefore, to reduce nanoparticle emissions, nanofiltration technology is becoming a serious issue. Filtration is a separation process during which a fluid passes through a barrier by removing the particles from the stream. Barrier filters can be made of various materials and shapes. One of the most common type of barrier filter is the fibrous filter. Fibrous filters are divided in two types: nonwoven and woven fabrics. Polypropylene is a thermoplastic material, used as a base material for melt blown nonwoven fabric. In this study, we examined filtration property of KCl nanoparticles with a mean particle diameter of 75 nm using multilayer meltblown filter samples. These experiments verify that the penetration of nanoparticle in the filter correlate with pressure drop; the meltblown layer MB1 has the greatest effect on dust collection efficiency of the filter. Among all tested samples, dust collection efficiency of 2-layer filter was best. However, when considering the overall pressure drop and dust collection efficiency, the 4-layer filter has the highest quality factor for particles smaller than 70 nm.

• 지질공학
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• 제30권4호
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• pp.557-575
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• 2020

유류오염 토양의 투수성 및 정화효율을 개선하기 위하여 고전압 아크 방전에 의한 플라즈마 블라스팅을 토양에 적용하였다. 이 연구를 위하여 고전압 발생장치를 새로 제작하였고, 실트질 모래인 토양시료, 토양시료에 소석회를 혼합한 시료와 토양시료에 시멘트를 혼합한 세 종류의 토양시료를 다져서 소형 토조와 대형 토조를 제작한 후 각각의 토조내에서 플라즈마 블라스팅을 시행하여 유체확산의 범위와 투수성의 변화를 측정하였다. 플라즈마 블라스팅이 시행된 토양시료에서는 플라즈마 블라스팅이 시행되지 않은 대조군에 비해 유체의 확산 부피가 약 11~71% 증가하였다. 낮은 전압하에서 플라즈마 블라스팅이 시행되면 토양 내에서는 구조적 취약면(다짐면)을 따라 수평적 확산이 우세하게 나타났으나 높은 전압에 의한 플라즈마 블라스팅은 토양 내에 구형의 입체적인 확산을 발생시켰다. 플라즈마 블라스팅은 투수성 또한 증가시켰으며, 소석회 및 시멘트가 혼합된 토양에서 더욱 뚜렷하게 관찰되어, 플라즈마 블라스팅이 시행된 시료들은 대조군 시료에 비해 투수계수가 450~1,052% 범위로 증가하였다. 플라즈마 블라스팅이 1회만 실시된 토양시료의 투수계수는 방전 전압이 높아질수록 증가하였으나 동일한 전압으로 여러 번의 블라스팅이 시행된 토양시료의 투수계수는 증가하거나 감소하였다. 토양시료에 경유를 이용하여 인위적으로 오염시킨 토양시료에 플라즈마 블라스팅을 실시하여 정화효율을 측정하였다. 플라즈마 블라스팅이 시행되면, 방전지점 근처의 토양에서는 평균 393%, 방전지점으로부터 20 cm 이상 이격된 하부 토양에서는 평균 239% 정도의 정화효율이 개선되었으나 방전 전압과 정화효율은 상관성을 보이지 않았다. 위의 결과는 플라즈마 블라스팅이 토양의 투수성과 정화효율을 상당히 개선하므로, 유류오염 토양의 원위치 정화에 효율적으로 이용될 가능성을 보여주었다.

• 한국환경과학회지
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• 제20권8호
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• pp.929-942
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• 2011

A novel conductivity technique was developed to detect penetration depth of the vessel fluid into the feedpipe. For a given reactor geometry, critical agitator speeds were experimentally determined at the onset of feedpipe backmixing using Rushton 6 bladed disk turbine (6BD) and high efficiency axial flow type 3 bladed (HE-3) impellers. The ratio of the feedpipe velocity to the critical agitator speed ($v_f/v_t$) was constant for either laminar or turbulent feedpipe flow regimes. Compared to the results of fast competitive reaction, feedpipe backmixing had to penetrate at least one feedpipe diameter into the feedpipe to significantly influence the yield of the side product. However, higher $v_f/v_t$ than that for L/d = 0 (position at the feedpipe end) of the conductivity technique is recommended to completely eliminate feedpipe backmixing in conservative design criteria. The conductivity technique was successful in all feedpipe flow conditions of laminar, transitional and turbulent flow regimes.