Three-dimensional viscoelastic simulation of the effect of wall slip on encapsulation in the coextrusion process

2013 ◽  
Vol 33 (7) ◽  
pp. 625-632 ◽  
Author(s):  
Hesheng Liu ◽  
Xiaozhen Deng ◽  
Yibin Huang ◽  
Xingyuan Huang ◽  
Mengshan Li
Keyword(s):  
Flow Rate ◽  
Rectangular Channel ◽  
Three Dimensional ◽  
Wall Slip ◽  
Slip Boundary Condition ◽  
The Finite Element Method ◽  
Slip Coefficient ◽  
Melt Flow Rate ◽  
Slip Boundary ◽  
Interface Profile

Abstract A three-dimensional viscoelastic numerical simulation was developed for a two-layer coextrusion through a rectangular channel by using the finite element method. The Phan-Thien and Tanner model was considered as viscoelastic constitutive equations. The generalized Navier’s law was adopted to found the slip boundary condition. The numerical results of the effects of the wall slip coefficient and the flow rate on the interface profile and the degree of encapsulation were compared with the experimental results of previous researchers. It was found that the interfacial offset and the degree of encapsulation increased with the increase of the wall slip coefficient and the flow rate, and the growing rate was large when the wall slip coefficient was between 106 and 108. We were able to control the interface shape and the degree of encapsulation at the die exit by varying the wall slip coefficient and the magnitude of the melt flow rate.

Numerical Investigation of the Drag and Lift Forces Acting on Impenetrable Rotating Spherical Nano-Particle

2008 ◽  
Author(s):  
M. R. Meigounpoory ◽  
A. Rahi ◽  
A. Mirbozorgi
Keyword(s):  
Lift Coefficient ◽  
Three Dimensional ◽  
Slip Boundary Condition ◽  
Slip Condition ◽  
Nano Particle ◽  
Slip Coefficient ◽  
Slip Boundary ◽  
Lift Forces ◽  
Drag And Lift ◽  
Drag And Lift Coefficient

The drag and lift forces acting on a rotating impenetrable spherical suspended nano-particle in a homogeneous uniform flow are numerically studied by means of a three-dimensional numerical simulation with slip boundary condition. The effects of both the slip coefficient and rotational speed of the nanosphere on the drag and lift forces are investigated for Reynolds numbers in the range of 0.1 < Re < 100. Increase of rotation increases the drag and lift force exerted by flow at the surface of nano-sphere. By increasing slip coefficient the values of drag and lift coefficients decreases. At full slip condition, rotation of the nano-sphere has not significant effects on the drag and lift coefficient values moreover the lift coefficient of flow around the rotating spherical particle will be vanished. Present numerical results at no-slip condition are in good agreements with certain results of flow around of rotating sphere.

Influence of the Key Factors on the Wall Slip Phenomenon in Micro Flow

2012 ◽  
Vol 472-475 ◽  
pp. 2415-2421
Author(s):  
Pei Qian He ◽  
Yan Lou ◽  
Xiao Yu Wu
Keyword(s):  
Shear Stress ◽  
Flow Analysis ◽  
Wall Slip ◽  
Slip Boundary Condition ◽  
Key Factors ◽  
Slip Coefficient ◽  
Slip Boundary ◽  
Navier’S Slip ◽  
Micro Flow ◽  
Slip Phenomenon

Aimed at the wall slip phenomenon of micro flow, the wall slip boundary condition was added to simulate the process of the micro flow by Polyflow based on the traditional flow analysis method. The effect of the wall slip on the micro flow was verified by comparing the pressure difference data obtained from the simulation with the quoted test data. In addition, based on the Generalized Navier’s slip law, the shear stress and slip coefficient were researched by the numerical simulation analyses to find out the influence of the key factors on the phenomenon of wall slip. The results show that the phenomenon of wall slip is an important factor that cannot be ignored in the micro flow. And only under the high shear stress, the wall slip phenomenon will have an obvious influence on the micro flow. Along with the decrease of the slip coefficient, the wall slip phenomenon becomes more apparent and the micro flow tends to be stable.

Numerical Analysis of Rarefaction and Compressibility Effects in Bent Microchannels

2010 ◽  
Author(s):  
O. Rovenskaya ◽  
G. Croce
Keyword(s):  
Gas Flow ◽  
Flow Characteristics ◽  
Wall Slip ◽  
Outer Wall ◽  
Slip Boundary Condition ◽  
Central Line ◽  
Navier Stokes ◽  
Strong Impact ◽  
First Order ◽  
Slip Boundary

Numerical investigation of a gas flow through microchannels with a sharp, 90 degrees bend is carried out using Navier-Stokes (N-S) equations with the classical Maxwell first-order slip boundary condition, including the tangential gradient effect due to the wall curvature, and Smoluchowski first order temperature jump definition. The details of the flow structure near the corner are analyzed, investigating the competing effects of rarefaction and compressibility on the channel performances. The flow characteristics in terms of velocity profiles, slip velocity distribution along inner and outer wall, pressure, average Mach number along central line of the channel have been presented. The results showed that impact of the bend on the channel performances is smaller at high rarefaction levels. The behaviour of pressure and velocity away from the bend is similar to that of a straight microchannel; however, the asymmetry in the flow at the bend, with high velocities and high velocity gradients on its inner side, has a strong impact on wall slip velocities. The presence of a recirculation is detected on both the inner and outer walls of the corner for larger Reynolds. However, rarefaction may delay the onset of recirculation. It is also observed that the mass flux through a bend microchannel can even be slightly larger than that through a straight microchannel of the same length and subjected to the same pressure difference.

STEADY STOKES FLOWS WITH THRESHOLD SLIP BOUNDARY CONDITIONS

2005 ◽  
Vol 15 (08) ◽  
pp. 1141-1168 ◽  
Author(s):  
C. LE ROUX
Keyword(s):  
Stokes Equations ◽  
Stokes Problem ◽  
Nonlinear Function ◽  
Wall Slip ◽  
Slip Boundary Condition ◽  
Dirichlet Condition ◽  
Steady Flows ◽  
Slip Boundary ◽  
Rotationally Symmetric ◽  
Tangential Traction

We prove the existence, uniqueness and continuous dependence on the data of weak solutions to boundary-value problems that model steady flows of incompressible Newtonian fluids with wall slip in bounded domains. The flows satisfy the Stokes equations and a nonlinear slip boundary condition: for slip to occur, the magnitude of the tangential traction must exceed a prescribed threshold, which is independent of the normal stress, and where slip occurs the tangential traction is equal to a prescribed, possibly nonlinear, function of the slip velocity. In addition, a Dirichlet condition is imposed on a component of the boundary if the domain is rotationally symmetric. The method of proof is based on a variational inequality formulation of the problem and fixed point arguments which utilize wellposedness results for the Stokes problem with a slip condition of the "friction type".

Slip over rough and coated surfaces

1994 ◽  
Vol 273 ◽  
pp. 125-139 ◽  
Author(s):  
Michael J. Miksis ◽  
Stephen H. Davis
Keyword(s):  
Slip Boundary Condition ◽  
Slip Condition ◽  
Slip Coefficient ◽  
Outer Flow ◽  
Navier Slip ◽  
Two Fluids ◽  
Slip Boundary ◽  
Lubricating Film ◽  
Effective Slip ◽  
Coated Surfaces

We study the effect of surface roughness and coatings on fluid flow over a solid surface. In the limit of small-amplitude roughness and thin lubricating films we are able to derive asymptotically an effective slip boundary condition to replace the no-slip condition over the surface. When the film is absent, the result is a Navier slip condition in which the slip coefficient equals the average amplitude of the roughness. When a layer of a second fluid covers the surface and acts as a lubricating film, the slip coefficient contains a term which is proportional to the viscosity ratio of the two fluids and which depends on the dynamic interaction between the film and the fluid. Limiting cases are identified in which the film dynamics can be decoupled from the outer flow.

COMPARISON OF GAS SLIP MODELS WITH SOLUTIONS OF LINEARIZED BOLTZMANN EQUATION AND DIRECT SIMULATION OF MONTE CARLO METHOD

2007 ◽  
Vol 18 (02) ◽  
pp. 203-216 ◽  
Author(s):  
G. H. TANG ◽  
Y. L. HE ◽  
W. Q. TAO
Keyword(s):  
Friction Factor ◽  
Flow Rate ◽  
Slip Flow ◽  
Flow Analysis ◽  
Slip Boundary Condition ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Slip Boundary ◽  
Slip Regime ◽  
Linearized Boltzmann Equation

Analytical solutions of the Navier–Stokes equation based on a locally fully-developed flow assumption with various gas slip models are presented and comparisons for velocity profile, flow rate, friction factor, and pressure distribution are performed. The effect of the second-order coefficient in the slip boundary condition becomes significant as the Knudsen number increases. Most slip models are limited to slip regime or marginally transition regime and break down around Kn = 0.1 while Sreekanth's model, followed by Mitsuya's model, gives a good agreement with the linearized Boltzmann solutions from slip regime up to Kn = 2 for flow rate and friction factor predictions. These two models should be of great use for slip flow analysis in micro-electro-mechanical systems (MEMS) and, in particular, in situations where the flow rate and flow resistance are of interest.

Numerical Simulation of Effect of Slip Conditions on PVC Co-Rotating Twin-Screw Extrusion

2011 ◽  
Vol 189-193 ◽  
pp. 1946-1954 ◽  
Author(s):  
Ying Han Cao ◽  
Jin Nan Chen
Keyword(s):  
Flow Rate ◽  
Volumetric Flow Rate ◽  
Wall Slip ◽  
Slip Condition ◽  
Twin Screw Extruder ◽  
Slip Coefficient ◽  
Twin Screw Extrusion ◽  
Screw Extruder ◽  
Slip Conditions ◽  
Twin Screw

The effect of wall conditions on the co-rotating parallel twin-screw extrusion of rigid polyvinyl chloride (RPVC) is studied. The relationship between the shear stress at the screw wall and the slip velocity of the flowing melt obeys Navier’s linear law. At zero pressure difference between the entrance and exit of the melting section of twin-screw extruder, the volumetric flow rate and 3D isothermal flow fields of RPVC are calculated under different wall slip conditions in the metering section of the twin-screw extruder by using the evolution technique in POLYFLOW. The results show that when the slip coefficient is smaller than 104Pa*s/m , the volumetric flow rate of the melt is constant, corresponding to the full slip condition. When the slip coefficient is larger than 104Pa*s/m , with the slip coefficient decreasing, the volumetric flow rate and viscosity increase, but the gradients of velocity, pressure, and shear rate decrease. The residual stress of the product is thus reduced. Therefore, increasing wall slip is good for the stability of polymer extrusion and the product quality. The dispersive and the distributive mixing of the twin-screw extruder under full slip and no slip conditions are also studied. Results show that the mixing performance under no-slip condition is better than under full-slip condition, but slip at the wall is good for the extrusion of heat-sensitive materials.

WEAK SOLUTIONS TO EQUATIONS OF STEADY COMPRESSIBLE HEAT CONDUCTING FLUIDS

2010 ◽  
Vol 20 (05) ◽  
pp. 785-813 ◽  
Author(s):  
PIOTR B. MUCHA ◽  
MILAN POKORNÝ
Keyword(s):  
Boundary Condition ◽  
Three Dimensional ◽  
Large Data ◽  
Slip Boundary Condition ◽  
Regularity Of Solutions ◽  
Energy Estimates ◽  
Navier Stokes ◽  
Heat Conducting ◽  
Existence Of A Solution ◽  
Slip Boundary

We consider the steady compressible Navier–Stokes–Fourier system in a bounded three-dimensional domain. We prove the existence of a solution for arbitrarily large data under the assumption that the pressure p(ϱ, θ) ~ ϱθ + ϱγ for [Formula: see text] assuming either the slip or no-slip boundary condition for the velocity and the Newton boundary condition for the temperature. The regularity of solutions is determined by the basic energy estimates, constructed for the system.

Three-dimensional viscoelastic numerical analysis of the effects of gas flow on L-profiled polymers in gas-assisted coextrusion

2018 ◽  
Vol 38 (5) ◽  
pp. 503-512 ◽  
Author(s):  
Xiaozhen Deng ◽  
Hesheng Liu
Keyword(s):  
Layer Thickness ◽  
Flow Rate ◽  
Gas Flow ◽  
Three Dimensional ◽  
Gas Pressure ◽  
Melt Flow ◽  
Flow Zone ◽  
Melt Flow Rate ◽  
Gas Layer ◽  
The Relationship

AbstractIn this study, polymer gas-assisted coextrusion experiments were performed. The influence of a traditional coextrusion flow zone on the gas groove and the relationship between the gas pressure and the melt flow rate were studied. To determine the effects of the gas flow on gas-assisted coextrusion, a three-dimensional simulation was developed in which the gas layer was considered as an independent flow zone. The influence of the gas pressure, gas layer thickness and melt flow rate on the melts’ profile and the deflection deformation degree (DDD) was studied, and the relationship between the gas pressure, gas layer thickness and melt flow rate was obtained. The numerical results indicated that a traditional coextrusion flow zone in front of a gas-assisted coextrusion flow zone could allow products to avoid a gas groove. The quality of the products could be improved by decreasing the gas pressure and gas layer thickness or increasing the melt flow rate. Additionally, the minimum gas pressure decreased as the gas layer thickness increased and increased as the melt flow rate increased. The numerical results were in good agreement with the experimental results, despite a slight quantitative error. Therefore, reasonably controlling the gas flow condition is key in practical applications of gas-assisted coextrusion, and the effects of the gas layer should be considered in gas-assisted coextrusion simulations.

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