• 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.

• Korea-Australia Rheology Journal
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• v.20 no.3
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• pp.143-152
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• 2008

Simulations of solutions of flexible polymer molecules during flow in simple or complex confined geometries are performed. Concentrations from ultradilute up to near the overlap concentration are considered. As concentration increases, the hydrodynamic migration effects observed in dilute solution unidirectional flows (Couette flow, Poiseuille flow) become less prominent, virtually vanishing as the overlap concentration is approached. In a grooved channel geometry, the groove is almost completely depleted of polymer chains at high Weissenberg number in the dilute limit, but at finite concentration this depletion effect is dramatically reduced. Only upon inclusion of hydrodynamic interactions can these phenomena be properly captured.

• Korea-Australia Rheology Journal
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• v.13 no.1
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• pp.19-27
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• 2001

In this symposium paper, the migration and hydrodynamic diffusion of non-colloidal, spherical particles suspended in polymer solutions are considered under Poiseuille or torsional flows. The migration phenomena in polymer solutions are compared with those in Newtonian fluids and the effect of fluid elasticity is discussed. The experimental results on particle migration in dilute polymer solution reveal that even a slight change in the rheological property of the dispersing medium can induce drastic differences in flow behavior and migration of particles, especially in dilute and semi-concentrated suspensions.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.10
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• pp.1237-1243
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• 2014

The aim of the present paper is to analyze the friction and mass flow in a rough microchannel using Lattice Boltzmann Method (LBM). The LBM is a kinetic method based on the particle distribution function, so it can be fruitfully used to study the flow dependence on Knudsen number including slip velocity, pressure drop in rough microchannel. The surface roughness elements are taken to be considered as a series of circular shaped riblets throughout the channel with relative roughness height up to a maximum 10% of the channel height. The friction coefficients in terms of Poiseuille number (Pn), mass flow rate and the flow behaviors have been discussed in order to study the effect of surface roughness in the slip flow regime at Knudsen number (Kn), ranging from 0.01 to 0.10. It is seen that the friction factor and the flow behaviors in a rough microchannel strongly depend on the rarefaction effect and the relative roughness height. The friction factor in a rough microchannel is higher than that in smooth channel but the mass flow rate is lower than that of smooth channel. Moreover, it is seen that the friction factor increased with relative roughness height but decreased with increasing the Kundsen number (Kn) whereas the mass flow rate is decreased with increasing both of surface roughness height and Knudsen number.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.1
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• pp.49-56
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• 1997

Heat-transfer enhancement is seeked through modifications of fin surface. Real life plate-fin heat exchangers have complex three-dimensional geometries. Fins can have arrays of dimples and are attached to rows of penetrating tubes. To isolate the effect of surface modification, we model the real flow by a two-dimensional channel flow with a dimple on one side. The flow is analysed by solving the incompressible Navier-Stokes equation by a finite volume method on a generalized boundary-fitted coordinate. Results show a trapped vortex inside the dimple for all cases computed. Local maximum of Nusselt number occurs near the downstream end of the dimple, due to such a vortex. Location of the vortex does not change with respect to the wall temperature change, but moved downstream when Reynolds number increases. This, together with the results that in all cases vortex core is somewhat downstream of the dimple center, suggests that the mean flow above continuously feeds the kinetic energy to the recirculating flow. Heat transfer enhancement and pressure losses are studied through analysing the relevant dimensionless parameters like, Nusselt number and friction factor. In all cases computed, dimpled channel flow experiences less pressure loss than two-dimensional Poiseuille flow.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.3
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• pp.84-89
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• 2018

Recently, study on self-healing materials have been performed to increase the life by repairing the damage of structures themselves, which are difficult to repair or require high maintenance costs. A water permeability test has been widely used for the evaluation of self-healing performance. However, in the self-healing performance test method, the initial crack width of the concrete greatly affects on the self-healing performance but it does not have a consistent standard. Therefore, in this study, the correlation between crack and permeability and that between time and permeability were analyzed based on crack width and permeability. In addition, since the initial crack width measured by optical microscope is not reliable, the value is derived from the Poiseuille flow and the tendency of time-permeability and time-crack width are analyzed.

• Journal of computational fluids engineering
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• v.10 no.2
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• pp.30-37
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• 2005

To evaluate LBM we performed the simulation of the unsteady two dimensional flow over a square cylinder in a channel in moderate Reynolds number range, $100\~500$ by using LBM and Fractional-Step method. Frist of all we compared LBM solution of Poiseuille flow applied Farout and periodic boundary conditions with the analytical solution to verify the applicability of the boundary conditions. For LBM simulation the calculation domain was formed by structured 500x100 grids. Prescribed maximum velocity and density inlet and Farout boundary conditions were imposed on the in-out boundaries. Bounceback boundary condition was applied to the channel and the cylinder waifs. The flow patterns and vortex shedding strouhal numbers were compared with previous research results. The flow patterns by LBM were in agreement with the flow pattern by fractional step method. Furthermore the strouhal number computed by LBM simulation result was more accurate than that of fractional step method through the comparison of the previous research results.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.150.1-150.1
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• 2014

Showerhead is used as a main part in the semiconductor equipment. The face plate flatness should remain constant and the cleaning performance must be gained to keep the uniformity level of etching or deposition in chemical vapor deposition process. High operating temperature or long period of thermal loading could lead the showerhead to be deformed thermally. In some case, the thermal deformation appears very sensitive to showerhead performance. This paper describes the methods for robust design using computational fluid dynamics. To reveal the influence of the post distribution on flow pattern in the showerhead cavity, numerical simulation was performed for several post distributions. The flow structure appears similar to an impinging flow near a centered baffle in showerhead cavity. We took the structure as an index to estimate diffusion path. A robust design to reduce the thermal deformation of showerhead can be achieved using post number increase without ill effect on flow. To prevent the showerhead deformation by heat loading, its face plate thickness was determined additionally using numerical simulation. The face plate has thousands of impinging holes. The design key is to keep pressure drop distribution on the showerhead face plate with the holes. This study reads the methodology to apply to a showerhead hole design. A Hagen-Poiseuille equation gives the pressure drop in a fluid flowing through such hole. The assumptions of the equation are the fluid is viscous-incompressible and the flow is laminar fully developed in a through hole. An equation can be expressed with radius R and length L related to the volume flow rate Q from the Hagen-Poiseuille equation, $Q={\pi}R4{\Delta}p/8{\mu}L$, where ${\mu}$ is the viscosity and ${\Delta}p$ is the pressure drop. In present case, each hole has steps at both the inlet and the outlet, and the fluid appears compressible. So we simplify the equation as $Q=C(R,L){\Delta}p$. A series of performance curves for a through hole with geometric parameters were obtained using two-dimensional numerical simulation. We obtained a relation between the hole diameter and hole length from the test cases to determine hole diameter at fixed hole length. A numerical simulation has been performed as a tool for enhancing showerhead robust design from flow structure. Geometric parameters for the design were post distribution and face plate thickness. The reinforced showerhead has been installed and its effective deposition profile is being shown in factory.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2000.11c
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• pp.662-669
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• 2000

Based on the viscous flow characteristics of gas through capillary tube, a simple and low cost system was developed for controlling gas concentration for use in C.A experiments. The gas flow rate through capillary tube had a linear relationship with pressure, $(length)^{-1}$ and $(radius)^4$ of capillary tube, which agreed well with Hagen-Poiseuille's law. The developed system could control the gas concentration in storage chamber within ${\pm}0.3%$ deviation compared to the preset concentration. The required time for producing target gas concentration in storage chamber was exactly predicted by the model used in this study, and it required much longer time than the calculated time which divided the volume of chamber by flow rate. Therefore, for producing target gas concentration as quickly as possible, it needs to supply higher flow rate of gas during the initial stage of experiment when gas concentration in storage chamber has not reached at target value. It appeared that the developed system was very useful for C.A experiments. Because one could decide a desired flow rate by the prediction model, control flow rate freely and easily by changing pressure in the pressure-regulating chamber and the accuracy was high.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.5 s.248
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• pp.438-445
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• 2006

We performed the simulation of the unsteady three dimensional flow over a square cylinder in a wind tunnel in moderate Reynolds number range, $100{\sim}2500$ by using LBM. SGS model was applied for the turbulent flow. Frist of all we compared LBM(Lattice Boltzmann Method) solution of Poiseuille flow applied Farout and bounce back boundary conditions with the analytical and FOAM solutions to verify the applicability of the boundary conditions. For LBM simulation the calculation domain was formed by structured grids and prescribed uniform velocity and density inlet and Farout boundary conditions were imposed on the in-out boundaries. Bounceback and wind tunnel boundary conditions were applied to the cylinder walls and the boundaries of calculation domain respectively. The maximum Strouhal number of the vortex shedding is 0.2025 at Re = 750. and the number maintains the constant value of 0.18 when Re>1000. We also predicted that the critical reynolds number of the turbulent flow is in the range of $250{\sim}500$.