• International Journal of Aeronautical and Space Sciences
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• 제2권1호
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• pp.12-19
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• 2001

Study of turbulent mixing layers has been a popular subject from the point of view of both practical application and phenomenological importance in engineering field. Turbulent mixing layers can be applied in many fields where rapid transition to turbulence is desirable in order to prevent boundary layer separation or to enhance mixing. The ability to control mixing, structure and growth of the shear flow would obviously have a considerable impact on many engineering applications. In addition to practical applications, free shear flows are one of the simplest flows to understand the fundamental mechanism in the transition process to turbulence. After the discovery of large-scale vortical structure in free shear flows many researchers have investigated the physical mechanism of generation and dissipation processes of the vortical structure. This study investigated the role of the large-scale vortical structures in the turbulent mixing layer using LES(Large-Eddy Simulation). The result shows that the pairing interaction of the vortical structure plays an important role in the growth rate of a mixing layer. It is found that the turbulence quantities depend strongly on the velocity ratio. It is also found that the vorticity in the high-velocity-side can extract energy from the mean flow, while the vorticity in the low-velocity-side lose energy by the viscous dissipation. Finally the results suggest the guideline to obtain the desired flow by control of the velocity ratio.

• 상하수도학회지
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• 제20권2호
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• pp.245-255
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• 2006

Dissolved air flotation is a solid-liquid separation system that uses fine bubbles rising from bottom to remove particles in water. In order to enhance the flotation velocity and removal efficiency of flocs in the flotation process, we tried to obtain pretreatment conditions for the optimum DAF process operation by comparing and evaluating features of actual floc formation and flotation velocity etc, according to coagulant types and conditions for flocculation mixing intensity by using PIA, PDA, and FSA. Accordingly, generating big flocs that have low density at low flocculation mixing intensity may reduce treatment efficiency. In addition, generating small flocs at high flocculation mixing intensity makes floc-bubbles smaller, which reduces flotation velocity, In this study, it was found that high flocculation mixing intensity could not remove the remaining micro-particles after flocculation, which had negative effects on treated water quality, Therefore, in order to enhance treatment efficiency in a flotation process, flocculation mixing intensity around $50sec^{-1}$ is effective.

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 1999년도 추계 학술발표회 논문집
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• pp.171-180
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• 1999

In this study, the burning velocity of LFG and LFG mixing fuels related with flame stabilization have been analyzed numerically using C3 reaction mechanism which consists of 92 species and 621 reaction for using LFG. The results show that the burning velocities of LFG and LFG mixing fuels are obtained as a function of CH$_4$ and LFG percent in stoichiometric conditions. Also, a correlation of the burning velocities LFG and LFG mixing fuels are obtained over a wide range of equivalence ratio. The comparison of burning velocity from correlation with that calculated numerically show good agreements. From these results, the proposed burning velocity correlations for LFG and LFG mixing fuels can be applied for the practice of LFG.

• 한국추진공학회지
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• 제3권4호
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• pp.44-50
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• 1999

Unlike impinging Quadlet injector(OOOF type)에 대한 혼합효율, 혼합특성속도, 혼합특성속도효율을 연소성능을 예측하기 위해 비연소 실험을 통하여 구하였다. 모의 추진제는 물($H_2$O)와 케로신($CH_{1.97}$)을 사용하였고, 혼합상관인자로써 산화제, 연료 분류의 운동량비를 사용하였다. 인젝터 분무특성을 파악하기 위해 오리피스(orifice) 각 hole에 대한 유량계수, 분무형상, 질량분포 획득이 수행되어졌다. 연구 결과, 침투깊이는 혼합효율, 혼합특성속도, 혼합특성속도 효율에 영향을 미침을 알 수 있었다. 또한, 혼합효율 및 혼합특성속도 효율은 MR=1.67(TMR=2.5)에서 87%로 최대값을 가지며 산화제 과잉상태보다 연료 과잉상태에서 더 큰 감소율을 보였다.

• Environmental Engineering Research
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• 제21권4호
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• pp.365-372
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• 2016

The effects of hydrodynamics and alum dose on particle growth were investigated by monitoring particle counts in a rapid mixing process. Experiments were performed to measure the particle growth and breakup under various conditions. The rapid mixing scheme consisted of the following operating parameters: Velocity gradient (G) ($200-300s^{-1}$), alum dose (10-50 mg/L) and mixing time (30-180 s). The Poisson regression model was applied to assess the effects of the doses and velocity gradient with mixing time. The mechanism for the growth and breakup of particles was elucidated. An increase in alum dose was found to accelerate the particle count reduction. The particle count at a G value of $200s^{-1}$ decreased more rapidly than those at $300s^{-1}$. The growth and breakup of larger particles were more clearly observed at higher alum doses. Variations of particles due to aggregation and breakup of micro-flocs in rapid mixing step were interactively affected by G, mixing time and alum dose. Micro-flocculation played an important role in a rapid mixing process.

• 한국물환경학회지
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• 제30권2호
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• pp.166-174
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• 2014

Velocity gradient, G, a measure of the average velocity gradient in the fluid has been applied for complete mixing of chemicals in mechanical mixing devices. G values were calculated by the power input transferred to fluid in turbulent and transient range. Chemical reactions occur so fast that total mass transfer time required for even distribution of the chemicals determine the overall reaction time. The total mass transfer time is composed of the time for complete mixing through the reactor and for diffusion of the chemicals into the eddy. Complete mixing time was calculated by CFD (computer fluid dynamics) and evaluated by tracer tests in 2 liter jars at different rotating speeds. Turbulent range, Reynolds number above 10,000 in regular 2 liter jars occurred at revolution speed above 100 rpm (revolution per minute), while laminar range occurred at revolution speed below 10 rpm. A typical range of rotating speed used in jar tests for water and wastewater treatment was between 10 and 300 rpm, which covered both transient and turbulent range. G values supplied from a commercial jar test apparatus showed big difference from those calculated with power number specially in turbulent range. Diffusion time through eddy decreased 1.5 power-law of rotating speed. Complete mixing time determined by pumping number decreased increases in rotating speed. Total mass transfer time, finally, decreases as rotating speed increases, and it becomes 1 sec at rotating speed of 1,000 rpm. Complete mixing times evaluated from tracer tests showed higher than those calculated by power number at higher rotating speed. Complete mixing times, however, calculated by CFD showed similar to those of experimentally evaluated ones.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제20회 춘계학술대회 논문집
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• pp.225-232
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• 2003

분리 삼중충돌 제트의 액상 혼합에 대한 실험적 연구결과를 통해 분리 삼중충돌 인젝터의 요소설계시 고려해야 할 기하학적 파라메타와 혼합성능을 고려하는 방법을 제시하였다. 실험은 비반응성인 케로신과 물을 사용하여 수행하였으며, 분사공의 기학적 조건과 분사조건(운동량비)에 따른 국소혼합비 분포를 측정하여 혼합효율 및 혼합특성속도를 산출하였다. 분사공의 각종 기하학적 요소와 운동량비에 따른 혼합효율 및 혼합 특성속도를 비교/분석하고 혼합성능과 연소성능과의 상관관계를 규명하였으며, 혼합의 정도를 향상시키는 설계점과 혼합성능 측면에서의 분리 삼중충돌 인젝터의 최적 설계조건에 대하여 고찰하였다.

• 대한화장품학회지
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• 제19권1호
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• pp.85-107
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• 1993

화장품에 사용되는 미분체의 혼합특성을 알기 위하여 화장품용 미분체 혼합기인 ribbon mixer, powder mixer micropulverizer, fine impact mill에 미립자, 구상 및 판상의 형태를 가진 bulk powders를 혼합시간을 변화 시키면서 혼합하는 실험을 하였다. 혼합분체의 혼합정도를 평가하기 위하여 산화철을 tracer로 사용하였으며, 원료 및 혼합물의 particle size distribution, specific surface area, density 및 표면색상을 측정하였다. 미분체 혼합물의 혼합시간과 표면색상변화, 입도분포 및 비표면적과의 사이에 대수적 1차 상관관계가 성립되었고, 색상의 변화로부터 혼합정도를 평가할 수 있는 간단한 식을 도출하였다. 사용된 혼합기에 대해 혼합기구별 modelling과 혼합에 따른 입도 분포 및 비표면적의 변화로부터 혼합기 impellar tip에서의 linear velocity별 혼합기는 대류혼합, 전단혼합 및 확산혼합으로 분류되었다.

• 한국안전학회지
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• 제27권5호
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• pp.35-41
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• 2012

The Numerical simulation was performed on the flow field around the two-dimensional rectangular bluff body in order to complement the previous experimental results of the bluff body stabilized flames [1]. For both fuel ejection configurations against an oxidizer stream, the flame stability was affected mainly by vortex structure and mixing field near bluff body. FDS(Fire Dynamic Simulator) based on the LES(Large Eddy Simulation) was employed to clarify the isothermal mixing characteristic and wake flow pattern around bluff body. The air used atmosphere and the fuel used methane. The result of counter flow configuration shows that the flow field depends on air velocity but the mixing field is influenced on the fuel velocity. At low fuel velocity the fuel mole fraction is below the flammable limit and hence the mixing is insufficient to react. Therefore, as the result, the flame formed at low fuel velocity is characterized by non-premixed flames. For the flow field of co-flow configuration, flame stability was affected by fuel velocity as well as air velocity. the vortex generated by fuel stream has counter rotating direction against the air stream. Therefore, the momentum ratio between air and fuel stream was important to decide the flame blow out limit, which is result in the characteristic of the partially premixed reacting wake near extinction.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1994년도 Proceedings of the Korea Automatic Control Conference, 9th (KACC) ; Taejeon, Korea; 17-20 Oct. 1994
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• pp.494-497
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• 1994

We propose a novel velocity detection method of moving object based on a speckle pattern on the target surface using a self-mixing laser diode (SMLD). By this measurement, it was confirmed that the speckle signal has its waveform independent of the target velocity, and has its averaged frequency directly proportional to the target velocity. So it will be possible to detect the velocity of the target transversely translating against the laser light beam using a compact measuring system.