• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.309-312
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• 2006

Effective mixing is an important problem in microfluidics for chemical and biomechanical applications. In this study, the influences of the Reynolds number and the oscillating frequency on mixing characteristics of micro-stirrer are studied in a microchannel with single stirrer. The influence of fluid inertial effects in an active mixer is first discussed. It is found that the stirring effects by stirrer oscillation are promptly attenuated at low Reynolds number, which makes greatly difficult the rapid mixing. As the inertial effects are increased, the chaotic advection is generated and then developed. The mixing phase is finally developed some mushroom shaped structure. And the mixing efficiency is also studied as a function of the oscillating frequency. We found that the mixing efficiency does not always increase with higher oscillating frequency of stirrer. Consequently, we found the functional relation between the optimal frequency of a stirrer and the Reynolds number.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.8 s.251
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• pp.796-805
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• 2006

In this study, the problem of using the mixing index as a measure of the mixing performance for a certain flow field has been discussed. The flow model subjected to this study is the two-dimensional unsteady lid-driven cavity flow. The transport equation for the concentration within the cavity was solved by using the finite volume method where the convective terms are discretized with the central difference scheme. It was shown that both the concentration dispersion and the mixing index depend highly on the initial distribution of the concentration, and therefore the mixing index obtained from the concentration dispersion equation loses its universal applicability.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.268-269
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• 2003

The Boltzmann kinetic equation is solved directly by means of the conservative splitting method. Underexpanded supersonic free jet flows with small Knudsen numbers are studied. In this numerical simulation features intrinsic to appropriate experiments are observed. Streamwise vortices in a mixing layer and chaotic downstream temporal-spatial fluctuations of microscopic quantities with large amplitude are obtained.

• Journal of computational fluids engineering
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• v.11 no.4 s.35
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• pp.101-106
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• 2006

In the microfluidic devices the most important thing is mixing efficiency ol various fluids. In this study a newly designed miler is proposed to enhance the mixing effect with the purpose to apply it to microchannel mixing in a short future. This design is composed of a channel with cross baffles periodically arranged on the both bottom and top surfaces ol the channel. To obtain the yow patterns, the numerical computation was performed by using a commercial code, ANSYS CFX 10.0. To evaluate the mixing performance, we computed Lyapunov exponent and obtained Poincare sections. it was shown that our design provides the excellent mixing effect.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2460-2464
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• 2008

The present paper suggests new method to know the effects of molecular diffusion and the helicity of microchannel flows on mixing in passive micromixers, which are essential components of a microfluidic chip. In this study, 'Helix Index' is newly defined as the magnitude of chaotic advection. Relationship between Helix Index and Mixing Index is analyzed numerically such as the wide range of Peclet and Reynolds numbers in three dimensional serpentine microchannel when using soluble solutions (water/glycerol). As a result, a simple algebraic equation is derived by this relationship based on a regression analysis. The algebraic equation is found to be able to accurately predict the mixing performance without solving the coupled, complex momentum and mass transfer equations.

• Journal of computational fluids engineering
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• v.8 no.2
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• pp.16-23
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• 2003

A numerical study of the mixing of two fluids(pure water and a solution of glycerol in water) in a microchannel was carried out. By varying the glycerol content of the glycerol/water solution, the variation in mixing behavior with changes in the difference of the properties of the two fluids(e.g., viscosity, density, diffusivity) was investigated. The mixing phenomena were tested for three micromixers: a square mixer, a three-dimensional serpentine mixer, and a staggered herringbone mixer. The governing equations of continuity, momentum and solute mass fraction were solved numerically. To evaluate mixing performance, a criterion index of mixing of mixing uniformity was proposed. In the systems considered, the Reynolds numbers based on averaged properties were 1 and 10. For low Reynolds number (Re = 1), the mixing performance varied inversely with mass fraction of glycerol due to the dominance of molecular diffusion. The mixing performance by diffusion deteriorated due to a significant reduction in the residence time of the fluid inside the mixers.

• Proceedings of the Korean Society of Rheology Conference
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• 2001.06a
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• pp.29-32
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• 2001

• Journal of computational fluids engineering
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• v.11 no.3 s.34
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• pp.37-45
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• 2006

In this study we present the numerical methods that can be used in visualization of the flow and mixing patterns in a cavity driven by a top lid. The basic flow field within the cavity has been obtained by using a simple numerical scheme. The invariant manifold also called unstable manifold was then attained to represent the mixing pattern within the cavity. It was shown that care must be taken in calculating the trajectories of the fluid particles especially near corners of the cavity. The numerical results show excellent agreement with those obtained experimentally by other research group.

• 한국전산유체공학회:학술대회논문집
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• 2006.10a
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• pp.159-162
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• 2006

In the microfluidics devices the most important thing is mixing efficiency of various fluids. In this study a newly designed mixer is proposed to enhance the mixing effect with the purpose to apply it to microchannel mixing in a short future. This design is composed of a channel with cross baffles periodically arranged on the both bottom and top surfaces of the channel. To obtain the flow patterns, the numerical computation was performed by using a commercial code, ANSYS CFX 10.0. To evaluate the mixing performance, we computed Lyapunov exponent and obtained Poincare sections.

• Nuclear Engineering and Technology
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• v.2 no.1
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• pp.19-25
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• 1970

A study was conducted on the coolant mixing between water flowing in two adjacent subchannels. Measurements were made of the quantity of mass transferred between a larger rectangular channel and a smaller triangular channel in a 19-rod fuel bundle under the conditions of single phase flow and air-water two-phase flow. The results of the experiments showed that the low mixing rate appears in single phase flow, and high mixing rate was measured in air-water two-phase flow Mixing rate decreases with the increasing of air void fraction during the air-water flow. It seems that the high mixing rate in the air-water flow was caused due to adequate agitation of the chaotic air void.