• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.5
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• pp.539-546
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• 2010

In this paper, lattice Boltzmann method(LBM) results for a laminar flow in a microchannel with rough surface are presented. The surface roughness is modeled as an array of rectangular modules placed on the top and bottom surface of a parallel-plate channel. The effects of relative surface roughness, roughness distribution, and roughness size are presented in terms of the Poiseuille number. The roughness distribution characterized by the ratio of the roughness height to the spacing between the modules has a negligible effect on the flow and friction factors. Finally, a significant increase in the Poiseuille number is observed when the surface roughness is considered, and the effects of roughness on the microflow field mainly depend on the surface roughness.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.88.1-88.1
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• 2005

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.45.2-45.2
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• 2005

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.8
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• pp.899-904
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• 2011

This This study aims to verify burr formation and to remove the burrs in micro-channel fabrication using micro-machining tools. The machining processes are combined with micro-milling and magnetic abrasive deburring for AISI316 stainless steel. Depending on the micro-milling conditions that are applied, burrs are formed around the side walls. Magnetic abrasive deburring is used to remove these burrs. AISI316 stainless steel is a nonferrous material and its magnetic flux density, which is an important parameter for efficient magnetic abrasive deburring, is low. To enhance this magnetic flux density, we design and build a magnetic array table. The effect of removing burrs is evaluated via SEM and a surface tester.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.124-129
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• 2000

The flow of liquid and vapor is investigated in trapezoidal grooves. The effect of variable shear stress along the interface of the liquid and vapor is studied for both co-current and counter-current flows. Velocity contours and results fur the friction are obtained for both trapezoidal grooves. An approximate relation that was previously utilized for the friction for the liquid was modified to obtain accurate agreement with the results for trapezoidal grooves.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.1 s.244
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• pp.1-7
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• 2006

The characteristics of micro gaseous flows in microchannels have been analyzed in view of flow resistance using the direct simulation Monte Carlo (DSMC) method which is a molecule-based numerical modeling technique. For this purpose, a DSMC code where the pressure boundary condition was specified at the inlet and outlet, has been developed and the results of simulations showed satisfactory agreements with the analytic solution in the slip flow regime. (0.01 < Kn < 0.1) By varying the height and length of the microchannel, the effect of pressure difference between the inlet and outlet was examined. The present computation indicates that the curvature in pressure distribution along the channel increases due to the effect of compressibility when the pressure difference increases. To obtain the flow resistance regardless of the channel dimensions, a standard curve is devised in the present study by introducing the concept of unit mass flowrate and unit driving pressure force. From this curve, it is shown that in micro flows, a significant deviation from the laminar incompressible flow occurs by reducing the flow resistance.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.179-183
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• 2006

Surface roughness is present in most of the microfluidic devices due to the microfabrication techniques. This paper presents lattice Boltzmann method (LBM) results for laminar flow in a microchannel with surface roughness. The surface roughness is modeled by an array of rectangular modules placed on top and bottom side of a parallel-plate channel. In this study, LBGK D2Q9 code in lattice Boltzmann Method is used to simulate flow field for low Reynolds number in a micro-channel. The effects of relative surface roughness, roughness distribution, roughness size and the results are presented in the form of the product of friction factor and Reynolds number. Finally, a significant increase in Poiseuille number is detected as the surface roughness is considered, while the effect of roughness on the microflow field depends on the surface roughness.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.4
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• pp.587-593
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• 2002

The present research proposes a pressure based approach along with Langmuir slip condition for predicting microscale fluid flows. Using this method, gaseous slip flows in 2 -dimensional microchannels are numerically investigated. Compared to the DSMC simulation, statistical errors could be avoided and computing time is much less than that of the aforementioned molecular approach. Maxwell slip boundary condition is also studied in this research. These two slip conditions give similar results except for the pressure nonlinearity at high Knudsen number regime. However, Langmuir slip condition seems to be more promising because this does not need to calculate the streamwise velocity gradient accurately and to calibrate the empirical accommodation coefficient. The simulation results show that the proposed method using Langmuir slip condition is an effective tool for predicting compressibility and rarefaction in microscale slip flows.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1528-1533
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• 2004

A numerical investigation is made of transient evolutionary prcocess of electroosmotic flow in a two-dimensional microchannel connected to a reservoir. The channel height is very small so that two electric double layers forming on the charged surfaces are overlapped. Transient transports of ions in the electrolyte solution are computed by integrating the Nernst-Planck equation together with the Poisson equation for electric potential. The numerical results illustrate that there are two distinct transient phases. The physical mechanisms and relevant time scales for the transient evolution are described.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.8
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• pp.1097-1104
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• 2003

The current study analyzes Langmuir slip boundary condition theoretically and it is tested in practical numerical analysis for separation-associated flow. Slip phenomenon at the channel wall is properly implemented by various numerical slip boundary conditions including Langmuir slip model. Compressible backward-facing step flow is compared to other analysis results with the purpose of diatomic gas Langmuir slip model validation. The numerical solutions of pressure and velocity distributions where separation occurs are in good agreement with other numerical results. Numerical analysis is conducted for Reynolds number from 10 to 60 for a prediction of separation at T-shaped micro manifold. Reattachment length of flows shows nonlinear distribution at the wall of side branch. The Langmuir slip model predicts fairly the physics in terms of slip effect and separation.