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PERIODICAL PRESSURE-DRIVEN FLOWS IN MICROCHANNEL WITH wall slip VELOCITY AND ELECTRO-VISCOUS EFFECTS

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Journal of Hydrodynamics 2010年第6期22卷 829-837页

作者： WANG Lei WU Jian-kang Department of Mechanics Huazhong University of Science and Technology National Laboratory forOptoelectronics Wuhan 430074 China

In a microfluidic system, the flow slip velocity on a solid wall can be the same order of magnitude as the average velocity in the microchannel. The flow-electricity interaction in a complex microfluidic system subjected to a joint action of wall slip and electro-viscosity is an important topic. An analytical solution for the periodical pressure-driven flow in a two-dimensional uniform microchannel, with consideration of wall slip and electro-viscous effect is obtained based on the Poisson-Boltzmann equation for the Electric Double Layer （EDL） and the Navier-Stokes equations for the liquid flow. The analytic solutions agree well with the numerical solutions. The analytical results indicate that the periodical flow velocity and the Flow-Induced Electric Field （FIEF） strongly depend on the frequency Reynolds number （Re = （wh2/v ）, that is a function of the frequency, the channel size and the kinetic viscosity of fluids. For Re 〈 1, the flow velocity and the FIEF behave similarly to those in a steady flow, whereas they decrease rapidly with Re as Re 〉 1. In addition, the electro-viscous effect greatly influences the periodical flow velocity and the FIEF, particularly, when the electrokinetic radius kH is small. Furthermore, the wall slip velocity amplifies the FIEF and enhances the electro-viscous effect on the flow.

关键词： electrokinetic flow frequency Reynolds number wall slip electro-viscous effects Flow-Induced Electric Field (FIEF)

The squeeze flow of a bi-viscosity fluid between two rigid spheres with wall slip

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Particuology 2023年第8期79卷 153-160页

作者： Tianyi Zhou Da Lin Yujia Shen Wei Yang Chunhui Xu Xuedong Chen College of Science China Agricultural UniversityBeijing100083China Chinese Academy of Agricultural Mechanization Sciences Group Co. LtdBeijing100083China

In this paper,the squeeze flow between two rigid spheres with a bi-viscosity fluid is *** on lubrication theory,the squeeze force is calculated by deriving the pressure and velocity *** results of the normal squeeze force are discussed,and fitting functions of the squeeze and correction coefficients are *** squeeze force between the rigid spheres increases linearly or logarithmically with the velocity when most or part of the boundary fluid reaches the yield state,***,the slip correction coefficient decreases with the increase in the *** investigation may contribute to the further study of bi-viscosity fluids between rigid spheres with wall slip.

关键词： Squeeze flow Bi-viscosity fluid Rigid spheres wall slip

Influence of wall slip on the hydrodynamic behavior of a two-dimensional slider bearing

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维普期刊数据库

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Acta Mechanica Sinica 2007年第6期23卷 655-661页

作者： G. J. Ma C. W. Wu P. Zhou State Key Laboratory of Structural Analysis for Industrial Equipment Department of Engineering Mechanics Dalian University of Technology Dalian 116024 China

In the present paper, a multi-linearity method is used to address the nonlinear slip control equation for the hydrodynamic analysis of a two-dimensional （2-D） slip gap flow. Numerical analysis of a finite length slider bearing with wall slip shows that the surface limiting shear stress exerts complicated influences on the hydrodynamic behavior of the gap flow. If the slip occurs at either the stationary surface or the moving surface （especially at the stationary surface）, there is a transition point in the initial limiting shear stress for the proportional coefficient to affect the hydrodynamic load support in two opposite ways： it increases the hydrodynamic load support at higher initial limiting shear stresses, but decreases the hydrodynamic load support at lower initial limiting shear stresses. If the slip occurs at the moving surface only, no fluid pressure is generated in the case of null initial limiting shear stress. If the slip occurs at both the surfaces with the same slip property, the hydrodynamic load support goes off after a critical sliding speed is reached. A small initial limiting shear stress and a small proportionality coefficient always give rise to a low friction drag.

关键词： wall slip Slider beating Multi-linearity method Quadratic programming

Numerical Simulation of Twin-Screw Extrusion with wall slip

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Journal of Beijing Institute of Technology 2004年第1期13卷 85-89页

作者：胡冬冬陈晋南 School of Chemical Engineering and Environment Beijing Institute of Technology Beijing100081 China

wall slip boundary condition is first introduced into twin-screw extrusion with the Navier slip law. Three-dimensional isothermal flow in the twin-screw extruder is simulated by using the finite element package POLYFLOW. Profiles of velocity contours in the screw channel and shear rate distributions in the intermeshing region are presented for different slip coefficients. Curves of axial pressure difference, average shear rate and dispersive mixing index vs. the slip coefficient are plotted and discussed. Comparisons are also made between the wall slip conditions and the non-slip condition. The simulation results indicate that, as the level of wall slip decreases, the axial pressure difference rises, the shear effect is intensified and the axial mixing is also enhanced. All these flow characteristics seem to level off with the increase of the slip coefficient. However, because of the inherent limitation of the Navier slip law, use of an overestimated slip coefficient would predict an over-sticky state between the screw surface and the polymer melt.

关键词： wall slip slip coefficient numerical simulation twin-screw extrusion

wall slip behavior of polymer melts on capillary rheometer

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Wall slip behavior of polymer melts on capillary rheometer

Phase Behaviors in Bi-phase Simulation of Powder Segregation in Metal Injection Molding

The 9th National Conference on Rheology

作者：廖华勇谭中欣邹国享丁永红陶国良 Polymer Materials Key Laboratory of Changzhou City Jiangsu Polytechnic University Guangzhou Institute of Energy Conversion Chinese Academy of Sciences

＜正＞wall slip behavior of three commercial polymer melts polypropylene（iPP）,low-density polyethylene（LDPE）（branched chains）and high-density polyethylene（HDPE）（linear chains）were studied by using a capillary rheometer with twin bores at different *** results show that a sudden first-stick-then-slip transition was observed for HDPE and a first-slip-then-stick transition was observed for LDPE and iPP as the shear rate sweep was done in an increased order,which shows that the chain structure has an obvious effect on the wall slip behavior of *** critical shear stress for the onset of stick-slip transition increases linearly with temperature for HDPE,which accords with the disentanglement mechanism proposed by Brochard and de *** the extrapolation length used to quantify the magnitude of the transition remains about 0.05-0.09 mm for HDPE at 150-230℃.Also the relationship between the critical shear stress for the onset of wall slip and the molecular mass for polymer samples agrees with the disentanglement model of Brochard and de *** onset of slip-stick transition for LDPE and iPP at a critical shear stress may be interpreted as the shear thinning of the polymer chains at high shear rates,preventing further development of wall slip behavior.

关键词： polymer wall slip critical shear stress capillary rheometer temperature dependence

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Journal of Southwest Jiaotong University(English Edition) 2006年第4期14卷 363-371页

作者：柳葆生范小欣成志强 Department of Applied Mechanics and Engineering Southwest Jiaotong University Chengdu 610031 China

Powder segregation induced by mold filling is an important phenomenon that affects the final quality of metal injection molding （MIM）. The prediction of segregation in MIM requires a bi-phase flow model to describe distinctly the flows of metallic powder and polymer binder. Viscous behaviors for the flows of each phase should hence be determined. The coefficient of interaction between the flows of two phases should also be evaluated. However, only viscosity of the mixed feedstock is measurable by capillary tests. wall sticking is supposed in the traditional model for capillary tests, while the wall slip is important to be taken into account in MIM injection. Objective of the present paper is to introduce the slip effect in bi-phase simulation, and search the suitable way to determine the viscous behaviors for each phase with the consideration of wall slip in capillary tests. Analytical and numerical methods were proposed to realize such a specific purpose. The proposed method is based on the mass conservation between the capillary flows in mono-phase model for the mixed feedstock and in bi-phase model for the flows of two phases. Examples of the bi-phase simulation in MIM were realized with the software developed by research team. The results show evident segregation, which is valuable for improving the mould designs.

关键词： Viscous behaviors Bi-phases simulation Powder segregation Metal injection molding wall slip