• Journal of the Korean Society of Safety
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• v.28 no.5
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• pp.54-60
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• 2013

In this study, a finite element model based on the SU/PG scheme was developed to solve shallow-water equations and the influences of parameters and internal boundary conditions on depth-averaged flow behavior were investigated. To analyze the effect of roughness coefficient and eddy viscosity on flow characteristics, the developed model was applied to rectangular meandering channel with two bends, and transverse velocities and water depth distributions were examined. As the roughness coefficient adjacent to wall increased, the velocities near the wall decreased, and the reduced velocities were compensated by the expanding mid-channel velocities. In addition, the flow characteristics around a circular cylinder were analyzed by varying the internal boundary conditions as free slip and no slip. The assignment of slip condition changed the velocity distribution on the cylinder surface and reduced the magnitude of the shear stress up to one third.

• The KSFM Journal of Fluid Machinery
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• v.13 no.2
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• pp.5-11
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• 2010

The nanofluidics is characterized by a large surface-to-volume ratio, so that the surface properties strongly affect the flow resistance. We present here the results showing that the effect of wetting properties and the surface roughness may considerably reduce the friction of fluid past the boundaries. For a simple fluid flowing over hydrophilic and hydrophobic surfaces, the influences of surface roughness are investigated by the nonequilibrium molecular dynamics (NEMD) simulations. The fluid slip at near a solid surface highly depends on the wall-fluid interaction. For hydrophobic surfaces, apparent fluid slips are observed on smooth and rough surfaces. The solid wall is modeled as a rough atomic sinusoidal wall. The effects on the boundary condition of the roughness characteristics are given by the period and amplitude of the sinusoidal wall. It was found that the slip velocity for wetting conditions at interface decreases with increasing effects of surface roughness. The results show the surface rougheness and wettability determines the slip or no-slip boundary conditions. The surface roughness geometry shows significant effects on the boundary conditions at the interface.

• Membrane and Water Treatment
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• v.11 no.5
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• pp.353-361
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• 2020

The present study deals with a numerical investigation of heat and mass transfer in a Sweeping Gas Membrane Distillation (SGMD) used for desalination. The governing equations expressing the conservation of mass, momentum, energy and species with coupled boundary conditions were solved numerically. The slip boundary condition applied on the feed saline solution-hydrophobic membrane interface is taken into consideration showing its effects on profiles and process parameters.The numerical model was validated with available experimental data and was found to be in good agreement particularly when the slip condition is considered. The results of the simulations highlighted the effect of slip boundary condition on the velocity and temperature distributions as well as the process effectiveness. They showed in particular that as the slip length increases, the permeate flux of fresh water and process thermal efficiency rise.

• 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.

• Journal of applied mathematics & informatics
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• v.37 no.5_6
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• pp.429-442
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• 2019

This article addresses the influence of partial slip condition in the hydromagnetic flow of Burgers fluid in a rotating frame of reference.The flows are induced by oscillation of a boundary. Two problems for oscillatory flows are considered. Exact solutions to the resulting boundary value problems are constructed. Analysis has been carried out in the presence of magnetic field. Physical interpretation is made through the plots for various embedded parameters.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.3
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• pp.20-26
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• 2008

Nanoimprint lithography(NIL) is becoming next generation lithography of significant interest due to its low cost and a potential patterning resolution of 10nm or less. Success of the NIL relies on the adequate conditions of pressure, temperature and time. To have the adequate conditions for NIL, one has to understand the polymer flowing behavior during the imprinting process. In this paper, an analytical approach of polymer flow in thermal NIL was performed based on the squeeze flow with partial slip boundary conditions. Velocity profiles and pressure distributions of the polymer flow were obtained and imprinting forces and residual thickness were predicted with the consideration of the slip velocity between the polymer and the mold/substrate. The results show that the consideration of the slip is very important for investigating the polymer flow in Thermal NIL.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.163-168
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• 1991

During Compression molding of polymeric composite materials, the flow characteristics should be obtained. Understanding the flow states may be useful for determination of optimum molding conditions, charge pattern etc. So far, for obtaining the flow analysis, no-slip boundary condition was applied on the mold surface. However, The study under consideration of the slip was conducted by Barone and Caulk. They have introduced the nondimensional parameter which is the ratio of viscous to friction resistance and governs the frictional condition. But the method for determining the parameter could not be proposed. In our work, the parameter which explains the interfacial friction is measured under a variety of molding conditions. Two-dimensional rectangular part and circular hollow disk are simulated with the measured parameter using the finite element method. Effects of the parameter on shapes of flow fronts are also presented.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2004.11a
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• pp.221-231
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• 2004

A kinetic theory analysis is made of low-speed gas flows in a microfluidic system consisted of three microchannels in series. The Boitzmann equation simplified by a collision model is solved by means of a finite difference approximation with the discrete ordinate method. For the evaluation of the present method results are compared with those from the DSMC method and an analytical solution of the Navier-Stokes equations with slip boundary conditions. Calculations are made for flows at various Knudsen numbers and pressure ratios across the channel. The results compared well with those from the DSMC method. It is shown that the analytical solution of the Navier-Stokes equations with slip boundary conditions which is suited fur fully developed flows can give relatively good results. In predicting the geometrically complex flows up to a Knudsen number of about 0.06. It is also shown that the present method can be used to analyze extremely low-speed flow fields for which the DSMC method is Impractical.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.178-181
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• 2011

Recently, micro shock tube is being extensively used in various fields of engineering applications. The flow characteristics occurring in the micro shock tube may be significantly different from that of conventional macro shock tube due to very low Reynolds number and Knudsen number effects which are, in general, manifested in such flows of rarefied gas, solid-gas two-phase, etc. In these situations, Navier-Stokes equations cannot properly predict the micro shock tube flow. In the present study, a two-dimensional CFD method has been applied to simulate the micro shock tube, with slip velocity and temperature jump boundary conditions. The effects of wall thermal conditions on the unsteady flow in the micro shock tube were also investigated. The unsteady behaviors of shock wave and contact discontinuity were, in detail, analyzed. The results obtained show much more attenuation of shock wave, compared with macro-shock tubes.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.1
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• pp.1-12
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• 2004