Wall slip and absence of interfacial flow instabilities in capillary flow of various polymer melts

1998 ◽  
Vol 42 (1) ◽  
pp. 63-80 ◽  
Author(s):  
Xiaoping Yang ◽  
Hatsuo Ishida ◽  
Shi-Qing Wang
Keyword(s):  
Polymer Melts ◽  
Capillary Flow ◽  
Wall Slip ◽  
Flow Instabilities ◽  
Interfacial Flow

Extrusion of Polymer Melts and Melt Flow Instabilities. I. Experimental Study of Capillary Flow and Extrudate Distortion

1969 ◽  
Vol 42 (3) ◽  
pp. 675-681 ◽  
Author(s):  
Gene A. Bialas ◽  
James L. White
Keyword(s):  
Experimental Data ◽  
Polymer Melts ◽  
Capillary Flow ◽  
Flow Instability ◽  
Research Effort ◽  
Flow Instabilities ◽  
Melt Flow ◽  
Considerable Research ◽  
Extrudate Distortion ◽  
First Descriptions

Abstract The extrusion of molten plastics, elastomers and fibers represent an important industrial operation. The rate of extrusion of melts through dies is limited by the onset of a flow instability. This phenomenon consists of a change in flow from uniform to irregular that results in the production of rough and distorted extradates drastically different from the smooth cylinders obtained at lower rates. Extrusion melt flow instability is observed in the entire spectrum of polymer melts ranging from silicone gums through nylon and polyolefin plastics to raw elastomers. Since the first descriptions of this phenomena in the 1940's considerable research effort has been expended in this area with limited agreement. It is the purpose of part I to: (1) present new experimental data on capillary flow of polymer melts and extrudate distortion, and (2) to review critically the literature on extrudate distortion.

Experimental Study of Rheological Characteristics of Polymer Melts in the Micro-Die

2012 ◽  
Vol 550-553 ◽  
pp. 716-723
Author(s):  
Tofek Abddiem ◽  
Da Ming Wu ◽  
Jian Zhuang ◽  
Li Jun Hou ◽  
Ying Liu ◽  
...  
Keyword(s):  
Experimental Study ◽  
Shear Rate ◽  
Polymer Melts ◽  
Capillary Flow ◽  
Slip Rate ◽  
Polymer Melt ◽  
Wall Slip ◽  
Rheological Characteristics ◽  
Capillary Rheometer ◽  
Measured Viscosity

Compared with in the conventional scales, the rheological properties of polymer melts have changed in the micro-scales. Based on the principle of capillary flow and modified with the method of Bagley or zero die micro-die, the rheological characteristics of polypropylene (PP) were investigated using the HAAKE capillary rheometer under the micro-die and conventional die. The results show that: the viscosity of polymer melt modified with the method of bagley or zero die micro-die in the different L/D ratio of micro-die is the same and the shear viscosity of PP decreases with the increase of shear rate; Compared with the viscosity in the conventional scales, the measured viscosity of PP in the micro-scales was reduced by 46% in 0.25mm diameter die, 44% in the 0.20mm diameter die and 88% in the 0.15mm diameter die at the same shear rate; a layer of fixed polymer melt was found in the inwall of the micro-die through the calculation of wall slip rate.

A Numerical Approach for the Evaluation of a Capillary Viscometer Experiment

2018 ◽  
Author(s):  
Felix Fischer ◽  
Julian Bartz ◽  
Katharina Schmitz ◽  
Ludwig Brouwer ◽  
Hubert Schwarze
Keyword(s):  
Pressure Difference ◽  
Cfd Simulation ◽  
Polymer Melts ◽  
Capillary Flow ◽  
Input Parameter ◽  
Numerical Approach ◽  
Capillary Viscometer ◽  
Inlet Section ◽  
Arbitrary Geometries ◽  
Poiseuille Equation

The dynamic viscosity of a fluid is an important input parameter for the investigation of elastohydrodynamic contacts within tribological simulation tools. In this paper, a capillary viscometer is used to analyse the viscosity of a calibration fluid for diesel injection pumps. Capillary viscometers are often used for the determination of viscosities that show a significant dependence on shear rate, pressure and temperature such as polymer melts or blood. Therefore most of the research on corrections of measured viscosities have been made using polymer melts. A new method is presented to shorten the effort in evaluating the capillary experiment. The viscosity itself can be calculated from experimental data. Essential parameters are the radius of the capillary, its length, the capillary flow and the pressure difference over the capillary. These quantities are used in the Hagen-Poiseuille equation to calculate the viscosity, assuming laminar and monodirectional flow. According to said equation, the viscosity depends on the geometry and the pressure gradient. A typical capillary viscometer contains three main flow irregularities. First the contraction of the flow at the capillary inlet, second the expansion of the flow at the capillary outlet and third the inlet section length of the flow after which the velocity profile is fully developed. These flow phenomena cause pressure losses, which have to be taken into account, as well as the altered length of the laminar flow in the capillary. Furthermore, the temperature difference over the capillary also affects the outlet flow. Therefore, in this paper, a newly developed method is proposed, which shortens the effort in pressure and length correction. The method is valid for viscometers, which provide a single phase flow of the sampling fluid. Furthermore, the proposed correction is suited for arbitrary geometries. A numerical approach is chosen for the analysis of the experiment. In order to facilitate the experimental procedure of a capillary viscometer, a special algorithm was developed. The numerical approach uses a static CFD simulation, which is recursively passed through. If a termination condition, regarding the pressure difference between two cycles, is fulfilled, the real viscosity can be calculated in the usual way from the Hagen-Poiseuille equation. A special advantage of the proposed experimental evaluation is the general applicability for arbitrary geometries. In this paper, the procedure is validated with a well-known reference fluid and compared to data, which was gathered from a quartz viscometer experiment with the same fluid. Therefore, experiments are conducted with the capillary viscometer and compared at various pressure and temperature levels.

Stochastic chain simulation of wall slip in entangled polymer melts

2007 ◽  
Vol 51 (3) ◽  
pp. 451-464 ◽  
Author(s):  
Fang Xu ◽  
Morton M. Denn ◽  
Jay D. Schieber
Keyword(s):  
Polymer Melts ◽  
Wall Slip ◽  
Entangled Polymer ◽  
Entangled Polymer Melts

Pressure dependent wall slip of wood flour filled polymer melts

2017 ◽  
Vol 247 ◽  
pp. 178-187 ◽  
Author(s):  
Valentina Mazzanti ◽  
Francesco Mollica
Keyword(s):  
Polymer Melts ◽  
Wood Flour ◽  
Wall Slip ◽  
Filled Polymer

Capillary Flow of Yield-Stress Fluids in Microchannels

2006 ◽  
Author(s):  
V. Bertola
Keyword(s):  
Yield Stress ◽  
Flow Regime ◽  
Capillary Flow ◽  
Capillary Tube ◽  
Plug Flow ◽  
Wall Slip ◽  
Critical Distance ◽  
Tube Diameter ◽  
Force Balance ◽  
Theoretical Argument

The wicking of a model yield-stress fluid (hair-gel solution in water) in a capillary tube is studied experimentally. By changing the hair-gel concentration in the solution, the yield stress varied from 5 to 20 Pa. A simple force balance between capillary and viscous forces suggests that the fluid should stop flowing as soon as the wall shear stress reaches the yield value, at a critical distance from the inlet which is independent of the tube diameter. However, this theoretical argument is not confirmed by experiments, which show that the fluid moves well beyond the critical distance determined theoretically, and that there is a well-defined effect of the tube diameter. It is proposed that such behavior may be determined by wall slip, which causes the flow to switch from the Poiseuille flow regime to the plug flow regime.

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