• 한국생산제조학회지
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• 제22권3호
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• pp.459-464
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• 2013

The purpose of a micro-mixing device is to enhance the mixing by increasing the diffusion effect between different types of flows. There have been many attempts to actively or passively increase mixing. However, those studies were limited to lab-scale experiments because the production of devices requires a series of processes, time, cost, and the mixing quality itself. For this reason, this study attempted to develop a quick and simple process for micro-mixing device fabrication by using conventional machining and bonding processes and applying ultrasonic waves from the outside of the mixing device. The mixing quality was quantified by using the mixing index, and the results showed that the proposed system increases the mixing from ~33% to ~10% with respect to the flow rates.

• International Journal of Aerospace System Engineering
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• 제2권2호
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• pp.79-82
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• 2015

The handicap for investigating the aero-optical effect focuses on the accurate prediction on the index refraction fluctuation or density fluctuation. In recent years, with the development of CFD techniques and optical experimental techniques, the comprehension have developed on the aero-optical transmitting effect in many kinds of complex flow. This study mainly introduces the optical aberration in compressible mixing layer. And then the debates about the mechanism of aero-optical effects and assessment of image blur also present.

• 한국추진공학회지
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• 제17권1호
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• pp.52-60
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• 2013

이젝터-디퓨져 시스템은 두 유동 사이의 순수전단운동을 통해 저압의 2차유동을 동반하여 고압의 주된 유동을 만들어 낸다. 일반적으로, 이젝터-디퓨져 시스템에서 유동장은 난류 혼합, 압축 효과로 인해 매우 복잡하게 되며, 저효율의 큰 문제점을 가지고 있다. 현재까지 이젝터 시스템의 성능을 향상시키기 위한 많은 연구가 수행 되어 왔지만 만족스럽지 않은 실정이다. 본 연구에서는 이젝터 시스템의 성능향상을 위해 2차유동의 입구에 혼합 안내깃을 설치하였으며, CFD는 이젝터-디퓨져 시스템의 초음속 내부 유동을 모사하여 수행하였다. 얻어진 결과는 기존의 실험결과를 입증하였으며, 본 논문에서 혼합 안내깃 효과를 전압 손실, 유인비 및 압력회복에 대해서 논의되었다.

• 정보학연구
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• 제2권2호
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• pp.89-105
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• 1999

본 논문은 컴퓨터를 이용한 문서 화상의 보안 통신에서 요구되는 문서 화상의 보안, 위조, 인증 등의 제반 분쟁에 대처하기 위한 연구이다. 문서 화상의 보안을 위해서 기존에 연구되어온 각종 암호화 방식 및 스크램블 방식과 같이 정보의 보안 여부를 노출시키고 비도에 의지하는 방식과 달리 정보의 보안여부를 제3자가 판독하기 어렵도록 하여 일상의 문서 교환으로 인식하게 함으로써 1차적으로 이의 해독에 따른 위험을 감소시키고 2차적으로는 해독이 가해진다 하여도 알고리즘 자체의 비도에 의해 해독을 용이하지 않도록 하는 방식의 보안 체계를 제안한다.

• Journal of the Optical Society of Korea
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• 제15권1호
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• pp.96-102
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• 2011

Simultaneous measurements using a scanning spectrograph system and transmissometer were performed for the first time over an urban site in Gwangju, Korea, to derive the ambient $NO_2$ volume mixing ratio. The differential slant column densities retrieved from the scanning spectrograph system were converted to volume mixing ratios using the light traveling distance along the scanning line of sight derived from the transmissometer light extinction coefficients. To assess the performance of this system, we compared the derived $NO_2$ volume mixing ratios with those measured by an in situ chemiluminescence monitor under various atmospheric conditions. For a cloudless atmosphere, the linear correlation coefficient (R) between the two data sets (i.e., data derived from the scanning spectrograph and from the in situ monitor) was 0.81; the value for a cloudy atmosphere was 0.69. The two sets of $NO_2$ volume mixing ratios were also compared for various wind speeds. We also consider the measurement errors, as estimated from an error propagation analysis.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.585-588
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• 2008

Thermal mixing phenomena in a Y-type microchannel were investigated using a micro-PIV. Two inlet reservoirs of the microchannel were controlled individually so that the characteristics of thermal mixing in the channel with temperature difference were compared with those without the difference. The velocity field in the mixing process was measured using the micro-PIV system that includes an ICCD (Intensified CCD) camera. The mixing area and uniformity were also analyzed. It is observed that the flow fluctuation in spanwise direction is induced by temperature difference, which enhances mixing process in microchannels.

• 대한기계학회논문집A
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• 제28권1호
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• pp.63-69
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• 2004

It is of great interest to enhance mixing performance in a microchannel in which the flow is usually characterized as a low Reynolds number (Re) so that good mixing is quite difficult to be achieved in this laminar flow regime. In this regard, we present a new chaotic passive micromixer, named Barrier Embedded Micromixer (BEM), of which the mixing mechanism is based on chaotic flows. In BEM, chaotic flow is induced by periodic perturbation of the velocity field due to periodically inserted barriers along the channel wall while a helical type of flow is obtained by slanted grooves on the bottom surface of the channel in the pressure driven flow. To experimentally compare the mixing performance, a T-microchannel and a microchannel with only slanted grooves were also fabricated. All microchannels were made of PDMS (Polydimethylsiloxane) from SU-8 masters that were fabricated by conventional photolithography. Mixing performance was experimentally characterized with respect to an average mixing intensity by means of color change of phenolphthalein as pH indicator. It was found that mixing efficiency decreases as Re increases for all three micromixers. Experimental results obviously indicate that BEM has better mixing performance than the other two. Chaotic mixing mechanism, suggested in this study, can be easily applied to integrated microfluidic systems , such as Micro-Total-Analysis-System, Lab-on-a-chip and so on.

• 한국압력기기공학회 논문집
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• 제7권4호
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• pp.44-50
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• 2011

Turbulent mixing of hot and cold coolants is one of the possible causes of high cycle thermal fatigue in piping systems of nuclear power plants. A typical situation for such mixing appears in turbulent flow through a T-junction. Since the high cycle thermal fatigue caused by thermal striping was not considered in the piping fatigue design in several nuclear power plants, it is very important to evaluate the effect of thermal striping on the integrity of mixing tees. In the present work, before conducting detailed evaluation, three thermal striping evaluation methodology suggested by EPRI, JSME and NESC are analyzed. Then, a by-pass pipe connected to the shutdown cooling system heat exchanger is investigated by using these evaluation methodology. Consequently, the resulting thermal stresses and the fatigue life of the mixing tee are reviewed and compared to each other. Futhermore, the limitation of each methodology are also presented in this paper.

• 한국해양공학회지
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• 제35권2호
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• pp.121-130
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• 2021

In this study, a computational fluid dynamics (CFD) simulation based on an Eulerian-Eulerian approach was used to evaluate the mixing performance of a mud agitator through the distribution of bulk particles. Firstly, the commercial CFD software Star-CCM+ was verified by performing numerical simulations of single-phase water mixing problems in an agitator with various turbulence models, and the simulation results were compared with an experiment. The standard model was selected as an appropriate turbulence model, and a grid convergence test was performed. Then, a simulation of the liquid-solid multi-phase mixing in an agitator was simulated with different multi-phase interaction models, and lift and drag models were selected. In the case of the lift model, the results were not significantly affected, but Syamlal and O'Brien's drag model showed more reasonable results with respect to the experiment. Finally, with the properly determined simulation conditions, a multi-phase flow simulation of a mud agitator was performed to predict the mixing time and spatial distribution of solid particles. The applicability of the CFD multi-phase simulation for the practical design of a mud agitator was confirmed.

• 한국전자통신학회논문지
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• 제2권3호
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• pp.150-156
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• 2007

본 논문에서는 정보화 사회와 더불어 네트워크 환경에서 사용하는 여러 시스템들의 정보보안을 위한 보안 시스템을 연구하였다. 이에 따라 복잡성 및 낮은 처리 속도 등의 문제를 해결하기 위하여 블록 및 스트림 방식을 적용한 대칭형 기반 혼합형 암호 시스템을 설계하였다. 인증 기능을 포함한 대칭형 기반 혼합형 암호 시스템은 처리 속도와 계산량이 비대칭형보다 우수한 성능을 가지고 있다. Synopsys 1999.10과 ALTERA MaxPlus 10.1로 시스템을 설계하여 시뮬레이션을 한 결과 제안된 혼합형 암호 시스템은 네트워크 환경에서 정보보안이 필요한 분야에 매우 효율적인 지원과 성능을 제공할 것이다.