• Title/Summary/Keyword: Slip Boundary Condition

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Numerical Analysis of the Slip Velocity and Temperature-Jump in Microchannel Using Langmuir Slip Boundary Condition (미소채널내의 Langmuir 미끄럼 경계조건을 통한 미끄럼 속도 및 급격한 온도변화에 관한 수치해석)

  • Kim, Sang-Woo;Kim, Hyun-Goo;Lee, Do-Hyung
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.33 no.3
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    • pp.164-169
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    • 2009
  • The slip velocity and the temperature jumps for low-speed flow in microchannels are investigated using Langmuir slip boundary condition. This slip boundary condition is suggested to simulate micro flow. The current study analyzes Langmuir slip boundary condition theoretically and it analyzed numerically micro-Couette flow, micro-Poiseuille flow and grooved microchannel flow. First, to prove validity for Langmuir slip condition, an analytical solution for micro-Couette flow is derived from Navier-Stokes equations with Langmuir slip conditions and is compared with DSMC and an analytical solution with Maxwell slip boundary condition. Second, the numerical analysis is performed for micro-Poiseuille flow and grooved microchannel flow. The slip velocity and temperature distribution are compared with results of DSMC or Maxwell slip condition and those are shown in good agreement.

NUMERICAL STUDY OF WEDGE FLOW IN RAREFIED GAS FLOW REGIME USING A SLIP BOUNDARY CONDITION (희박기체 영역에서 미끄럼 경계조건을 적용한 쐐기 형상 주위의 유동 해석)

  • Choi, Y.J.;Kwon, O.J.
    • Journal of computational fluids engineering
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    • v.19 no.2
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    • pp.40-48
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    • 2014
  • For rarefied gas flow regimes, physical phenomena such as velocity slip and temperature jump occur on the solid body surface. To predict these phenomena accurately, either the Navier-Stokes solver with a slip boundary condition or the direct simulation Monte Carlo method should be used. In the present study, flow simulations of a wedge were conducted in Mach-10 flow of argon gas for several different flow regimes using a two-dimensional Navier-Stokes solver with the Maxwell slip boundary condition. The results of the simulations were compared with those of the direct simulation Monte Carlo method to assess the present method. It was found that the values of the velocity slip and the temperature jump predicted increase as the Knudsen number increases. Also, the results are comparatively reasonable up to the Knudsen number of 0.05.

Predictions of Microscale Separated Flow using Langmuir Slip Boundary Condition (Langmuir 미끄럼 경계조건을 이용한 미소 박리유동의 예측)

  • Lee, Do-Hyung;Meang, Joo-Sung;Choi, Hyung-Il;Na, Wook-Sang
    • 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.

Pressure Correction Method and Slip Boundary Conditions for Microflows (미소유동 해석을 위한 압력수정기법 및 미끄럼 경계조건)

  • Choi, Hyung-Il;Maeng, Joo-Sung;Lee, Do-Hyung
    • Proceedings of the KSME Conference
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    • 2001.06e
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    • pp.430-435
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    • 2001
  • This paper introduces a pressure correction method for microflow computation. Conventional CFD methods with no slip boundary condition fail to predict the rarefaction effect of the wall when simulating gas microflows in the slip-flow regime. Pressure correction method with an appropriate slip boundary condition is an efficient tool in analyzing microscale flows. The present unstructured SIMPLE algorithm adopts both the classical Maxwell boundary condition and Langmuir boundary condition proposed by Myong. The simulation results of microchannel flows show that the proposed method has an effective predictive capability for microscale flows.

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Numerical study of desalination by Sweeping Gas Membrane Distillation

  • Loussif, Nizar;Orfi, Jamel
    • 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.

Sloshing Flow of Highly-Viscous Fluid in a Rectangular Box (사각용기에서 발생하는 고점성 유체의 슬로싱 유동)

  • park, Jun Sang
    • Journal of the Korean Society of Visualization
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    • v.17 no.3
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    • pp.39-45
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    • 2019
  • A study on the sloshing flow of highly-viscous fluid in a rectangular box was made by both of theoretical approach and experimental visualization method. Assuming a smallness of external forcing to oscillate the container, it was investigated a linear sloshing flow of highly-viscous fluid utilizing asymptotic analysis by Taylor-series expansion as a small parameter Re (≪1) in which Re denotes Reynolds number. The theory predict that, during all cycles of sloshing, a linear shape of free surface will prevail in a bulk zone and it has confirmed in experiment. The relevance of perfect slip boundary condition, adopted in theoretical approach, to the bulk zone flow at the container wall was tested in experiment. It is found that quasi-steady coated thin film, which makes a lubricant layer between bulk flow and solid wall, is generated on the wall and the film makes a role to perfect slip boundary condition.

A Study on the Air Foil Journal Bearing Analysis with Perturbed Rarefaction Coefficients

  • Lee, Yong-Bok;Park, Dong-Jin;Kim, Chang-Ho;Jang, Gun-Hee
    • KSTLE International Journal
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    • v.7 no.2
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    • pp.27-34
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    • 2006
  • Knudsen number is the ratio of molecular mean free path versus mm thickness and the criterion to determine the flow form. When its value is lower than 0.01, the flow can be assumed to has no slip boundary condition. And in the case that the value is between 0.01 and 10, then the flow has slip boundary condition at both the adjacent walls. The condition of the air flow between the rotating journal and top foil in the air foil bearing is determined by the rotating speed and load, and the Knudsen number is also varied by those values. Because the molecular mean free path is variable to the pressure and temperature, more exact formulation is necessary to understand and analyze the flow regime. In this study, the analysis considering Knudsen number formulated with those variables (pressure, temperature and mm thickness) was executed. The approximate value was examined using the equation to confirm whether the flow has the slip or no-slip boundary condition. From the analytic investigation, it was decided to range approximately 0.01 to 1.0 and the flow can be supposed to have the slip boundary condition. Under the condition of the slip flow, the static characteristics of the air foil bearing were examined using modified Reynolds equations. The results were compared with those considering no slip condition. It shows that the slip condition makes the flow decelerates and the load carrying capacity decreases compared with no slip condition. And as the bearing number and eccentricity ratio increase, the load carrying capacity also increased at both the cases. From this result, it can be supposed that the bearing torque also increases. In the analysis of the dynamic characteristics, the perturbed Knudsen number was taken into consideration. Because the Knudsen number is expressed as the terms of each variable, the perturbed equation can be simply derived. The results of both cases considering and not considering Knudsen number were compared each other. In the case of the direct terms of the stiffness and damping coefficients, the difference between both cases was little and increased as the bearing number and eccentricity ratio increased. And the cross terms have less or more differences.

A Dynamic Method for Boundary Conditions in Lattice Boltzmann method

  • Suh, Yong-Kweon;Kang, Jin-Fen;Kang, Sang-Mo
    • Proceedings of the KSME Conference
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    • 2007.05b
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    • pp.2797-2802
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    • 2007
  • It has been confirmed that implementation of the no-slip boundary conditions for the lattice-Boltzmann method play an important role in the overall accuracy of the numerical solutions as well as the stability of the solution procedure. We in this paper propose a new algorithm, i.e. the method of the dynamic boundary condition for no-slip boundary condition. The distribution functions on the wall along each of the links across the physical boundary are assumed to be composed of equilibrium and nonequilibrium parts which inherit the idea of Guo's extrapolation method. In the proposed algorithm, we apply a dynamic equation to reflect the computational slip velocity error occurred on the actual wall boundary to the correction; the calculated slip velocity error dynamically corrects the fictitious velocity on the wall nodes which are subsequently employed to the computation of equilibrium distribution functions on the wall nodes. Along with the dynamic selfcorrecting process, the calculation efficiently approaches the steady state. Numerical results show that the dynamic boundary method is featured with high accuracy and simplicity.

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Simulation of Compression Molding Considering Slip at Interface for Polymeric Composite Sheet (섬유강화 고분자 복합판의 압축성형에 있어서 금형-재료계면의 미끄름을 고려한 유동해석)

  • 장수학;김석호;백남주;김이곤
    • 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.

Numerical Analysis of Microchannel Flows Using Langmuir Slip Model (Langmuir 미끄럼 모형을 사용한 미소채널 유동의 수치해석)

  • Maeng, Ju-Seong;Choe, Hyeong-Il;Lee, Dong-Hyeong
    • 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.