• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1016-1020
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• 2003

In this paper, we present a technology of producing anew chaotic micromixer, named Micromixer with Arranged Blocks(MAB), and the experimental result of the mixing performance. Chaotic mixing was successfully achieved by introducing periodic perturbation in the field of the channel flow by means of slanted blocks. The MAB was made by an RP(Rapid Prototyping) technology. We performed flow visualization experiments for the quantification of the mixing performance with the MAB. Lyapunov exponent was measured to be 0.3557 and 0.1305 for the block height 0.8 and 0.2 times the channel width.

• Journal of Power System Engineering
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• v.16 no.4
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• pp.37-43
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• 2012

This paper performed experimental research in order to measure boiling heat transfer coefficient of water in microchannel with hydraulic diameter of $500{\mu}m$. Tests were conducted within the ranges of heat fluxes from 100 to 400 kW/$m^2$, vapor qualities from 0 to 0.2, and mass fluxes of 200, 400, and 600 kg/$m^2s$. From the experimental results, it was found that flow boiling heat transfer coefficient is not dependent on mass flux or vapor quality, but instead on heat flux to a certain degree. The measured data of heat transfer are compared to a few available correlations proposed for mini-channels. Among them, Sun and Mishima's correlation is found to predict the present data well, within the mean absolute error of 17.84%.

• Journal of the Korean Society of Visualization
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• v.8 no.4
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• pp.31-37
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• 2010

In this study, a novel hybrid micro/nano PIV system combining defocusing and TIRFM technique has been developed for the multiscale flow measurement. With the developed system, both far and near field velocity fields have been measured simultaneously in a 2D straight microchannel and the particle trajectories were extracted by the nearest tracking algorithm. The shear rate values taken from experimental results have been estimated by comparing with the analytical solution of 2D Poiseuille flow and it is confirmed that the result shows good agreement with the theoretical value.

• Bulletin of the Korean Chemical Society
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• v.34 no.4
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• pp.1175-1180
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• 2013

A microfabricated electrochemical cell comprising PDMS-based microchannel and in-channel gold microelectrodes was fabricated as a sensitive and a miniature alternative to the conventional electroanalytical systems. A reproducible fabrication procedure enabled patterning of multiple microelectrodes integrated within a PDMS-based fluidic network. The active area of each electrode was $200{\mu}m{\times}200{\mu}m$ with a gap of $200{\mu}m$ between the electrodes which resulted in a higher signal to noise ratio. Also, the PDMS layer served the purpose of shielding the electrical interferences to the measurements. Analytes such as potassium ferrocyanide; amino acid: cysteine and nucleoside: guanosine were characterized using the fabricated cell. The microchip was comparable to bulk electrochemical systems and its applicability was also demonstrated with flow injection based rapid amperometric detection of DNA samples. The device so developed shall find use as a disposable electrochemical cell for rapid and sensitive analysis of electroactive species in various industrial and research applications.

• Journal of computational fluids engineering
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• v.14 no.2
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• pp.46-51
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• 2009

The slip effect from the molecular interaction between fluid particles and solid surface atoms plays a key role in microscale fluid transport and heat transfer since the relative importance of surface forces increases as the size of the system decreases to the microscale. There exist two models to describe the slip effect: the Maxwell slip model in which the slip correction is made on the basis of the degree of shear stress near the wall surface and the Langmuir slip model based on a theory of adsorption of gases on solids. In this study, as the first step towards developing a general purpose numerical code of the compressible Navier-Stokes equations for computational simulations of microscale fluid flow and heat transfer, two slip models are implemented into a finite element numerical code of a simplified equation. In addition, a pressure-driven gas flow in a microchannel is investigated by the numerical code in order to validate numerical results.

• International Journal of Computer Science & Network Security
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• v.22 no.6
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• pp.91-96
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• 2022

The photocatalytic degradation of salicylic acid takes place in several stages involving coupled phenomena, such as the transport of molecules and the chemical reaction. The systems of transport equations and the photocatalytic reaction are numerically solved using COMSOL Mutiphysics (CM) simulation software. CM will make it possible to couple the phenomena of flow, the transport of pollutants (salicylic acid) by convection and diffusion, and the chemical reaction to the catalytic area (bauxite or TiO2 doped by nanoparticles). The simulation of the conversion rate allows to correctly fit the experimental results. The temporal simulation shows that the reaction reaches equilibrium after a transitional stage lasting over one minute. The outcomes of the study highlight the importance of diffusion in the boundary layer and the usefulness of injecting micro-agitation into the microchannel flow. Under such conditions, salicylic acid degrades completely.

• International Journal of Air-Conditioning and Refrigeration
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• v.13 no.1
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• pp.51-60
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• 2005

This paper reviews the studies on the pressure drop and the heat transfer in microchannels. Although a lot of studies about the single-phase flow have been done until now, conflicting results are occasionally reported about flow transition from laminar flow to turbulent flow, friction factor, and Nusselt number. Some studies reported the early flow transition due to relatively greater wall effect like surface roughness, but the other studies showed that the flow transition occurred at the Reynolds number of about 2300 and the early flow transition might be due to less accurate measurement of the channel geometry. Also, there have been arguments whether the conventional relation based upon continuum theory can be applied to the fluid flow and the heat transfer in microchannels without modification or not. The studies about the two-phase flow in microchannels have been mostly about investigating the flow pattern and the pressure drop in rectangular channels using two-component, two-phase flow like air/water mixture. Some studies proposed correlations to predict two-phase flow pressure drop in microchannels. They were mostly based on Lockhart-Martinelli model with modification on C-coefficient, which was dependent on channel geometry, Reynolds number, surface tension, and so on. Others investigated the characteristics of flow boiling heat transfer in microchannels with respect to test parameters such as mass flux, heat flux, system pressure, and so on. The existing studies have not been fully satisfactory in providing consistent results about the pressure drop and the heat transfer in microchannels. Therefore, more in-depth studies should be done for understanding the fundamentals of the transport phenomena in the microchannels and giving the basic guidelines to design the micro devices.

• Advances in aircraft and spacecraft science
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• v.4 no.1
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• pp.21-35
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• 2017

Hydrogen peroxide is being considered as a monopropellant in micropropulsion systems for the next generation of miniaturized satellites ('nanosats') due to its high energy density, modest specific impulse and green characteristics. Efforts at the University of Vermont have focused on the development of a MEMS-based microthruster that uses a novel slug flow monopropellant injection scheme to generate thrust and impulse-bits commensurate with the intended micropropulsion application. The present study is a computational effort to investigate the initial decomposition of the monopropellant as it enters the catalytic chamber, and to compare the impact of the monopropellant injection scheme on decomposition performance. Two-dimensional numerical studies of the monopropellant in microchannel geometries have been developed and used to characterize the performance of the monopropellant before vaporization occurs. The results of these studies show that monopropellant in the lamellar flow regime, which lacks a non-diffusive mixing mechanism, does not decompose at a rate that is suitable for the microthruster dimensions. In contrast, monopropellant in the slug flow regime decomposes 57% faster than lamellar flow for a given length, indicating that the monopropellant injection scheme has potential benefits for the performance of the microthruster.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.6
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• pp.751-757
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• 2011

Subminiature devices such as Lab-on-a-chip and p-TAS(Micro Total Analysis System) have been intensively studied in biotechnology and chemistry, In many cases, a micromixer was widely used to mix different solutions for synthesizing novel materials. However, in microfluidic system, there is generally a laminar flow under very small Reynolds number so it is difficult to mix each solution perfectly. To settle this problem, we propose a new mixing mechanism which generates a horizontal and vertical multi-mixing (HVM) flow for effective mixing within a short mixing section. We evaluated the proposed mechanism using CFD analysis, and the results showed that the HVM mechanism had a relative high-effectiveness comparing to the existing methods.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.581-584
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• 2008

A generation of a particle beam is the key technique in a flow cytometry that measures the fluorescence and light scattering of individual cell and other particulate or molecular analytes in biomedical research. Recent methods performing this function require a laborious and time-consuming assembly. In the present work, we propose a novel device for the generation of an axisymmetrical focusing beam of microparticles (3-D focusing) in a single capillary without sheath flows. This work uses the concept that the particles migrate toward the centerline of the channel when they lag behind the parabolic velocity profile. Particle focusing of spherical particles was successfully made with a beam diameter of about 10 ${\mu}$m. Proposed device provides crucial solutions for simple and innovative 3-D particle focusing method for the applications to the MEMS-based micro-flow cytometry. We believe that this device can be utilized in a wide variety of applications, such as biomedical/ biochemical engineering.