Studies on Wall-Slip in Entangled Polymeric Liquids

Abstract In this work, it is attempted to theoretically understand the phenomenon of wall slip through empirical and molecular models. Initially, we use the framework a transient network theory. We show that the severe disentanglement in the interfacial region can give rise to non-monotonic flow curve locally in that region. Further, we generalize this model into a unified slip model, which predicts wall slip by either disentanglement or by debonding mechanism, depending upon the adhesive energy of the wall-polymer pair. The model predictions of the critical wall shear stress are in good agreement with experiments for various adhesive energies of the wall-polymer pair. The model predicts that the temperature dependence of the critical wall shear stress for debonding is different than that of disentanglement mechanism under certain experimental conditions. To validate the predictions of unified model, we measure the critical stress for sudden slip due to debonding for various temperatures using cone and plate viscometer with fluoroelastomer-coated cone. The temperature dependence of the critical stress for instability (slip) on a coated cone is found out to be inversely dependent on temperature, which expected for the case of debonding. In the final part of this thesis, we develop a parameter-free tube model for predicting the stick-slip phenomenon. The model, which is based on the contour variable model [Mead et al., 1998, Macromolecules, 31, 7895], considers the dynamics of the tethered chains, which are grafted on a high-energy wall and which are entangled with the bulk chains flowing past them. We show that the restricted relaxation modes of the tethered molecule give rise to discontinuous slip instability. More specifically, the slow relaxation of the tethered chain due to the restricted convective constraint release is unable to randomize its flow-induced orientation above a critical shear rate or stress. This decreases the resistance to flow for the bulk chains, which suddenly slip past the oriented tethered chains.

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WALL SLIP EFFECTS MEASURING THE RHEOLOGICAL BEHAVIOR OF ELECTRORHEOLOGICAL (ER) SUSPENSIONS

International Journal of Modern Physics B ◽

10.1142/s0217979211102150 ◽

2012 ◽

Vol 26 (01) ◽

pp. 1250006 ◽

Cited By ~ 3

Author(s):

STEFFEN SCHNEIDER

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Flow Behavior ◽

Wall Slip ◽

Hydraulic Test ◽

Slip Effects ◽

Measured Flow ◽

Wall Shear ◽

Er Fluids ◽

Electrorheological Suspensions

In this work, a new method to determine the wall shear stress was developed step by step. To determine the wall shear stress, methods of the suspension rheology are being used for the first time to characterize ER fluids. This work focuses on investigations of the flow behavior of electrorheological suspensions in flow channels with different geometries at different electrical field strengths. Careful interpretation of the results with respect to different gap geometries has shown that the measured flow curves should undergo a combination of corrections. As a result it can be shown that wall slip effects can be measured under application like conditions on a hydraulic test bench.

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In an attempt to generalize wall slip in fluid flows using a series expansion of the wall shear stress: Case of non-Newtonian [Phan–Thien–Tanner fluid]

European Journal of Mechanics - B/Fluids ◽

10.1016/j.euromechflu.2015.02.007 ◽

2015 ◽

Vol 52 ◽

pp. 109-119 ◽

Cited By ~ 4

Author(s):

Martin Ndi Azese

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Series Expansion ◽

Fluid Flows ◽

Wall Slip ◽

Wall Shear

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Evaluation of Slip Effects in the Capillary Flow of Foams

Applied Rheology ◽

10.1515/arh-2009-0001 ◽

1999 ◽

Vol 9 (1) ◽

pp. 10-16 ◽

Cited By ~ 3

Author(s):

Karim Bekkour

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Slip Velocity ◽

Capillary Flow ◽

Strong Dependence ◽

Sodium Dodecyl ◽

Wall Slip ◽

Reynolds Analogy ◽

Slip Effects ◽

Wall Shear

Abstract Foams have been prepared from water added with a surfactant (Sodium-Dodecyl-Sulfate, SDS) and a polymer (Poly-Ethylene-Oxide, PEO) at different concentrations. This work was devoted to a study of the flow properties of the foams. The pressure drops were measured during flow in capillary tubes (2.5, 3.5 and 4 mm) in laminar regime. It was found a strong dependence of the flow curves on capillary diameter showing that pronounced wall slip effects exist. Two known approaches were applied to quantify the slip velocity: (a) the Mooney method, in which the key assumption is that the slip velocity depends only on the wall shear stress, was not applicable and (b) the Oldroyd-Jastrzebski method, in which the assumption is that the slip velocity depends not only on the wall shear stress but also on the flow geometry, yielded satisfactory results. The determination of the pressure drop coefficient showed that the Metzner and Reed correlation, i.e., the Reynolds analogy based on the generalised Reynolds number, could be applied if the data are corrected for slip effects.

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Numerical Analysis of Wall Slip Effects on Flow of Newtonian and Non-Newtonian Fluids in Macro and Micro Contraction Channels

Journal of Fluids Engineering ◽

10.1115/1.2375127 ◽

2006 ◽

Vol 129 (1) ◽

pp. 23-30 ◽

Cited By ~ 15

Author(s):

Alfeus Sunarso ◽

Takehiro Yamamoto ◽

Noriyasu Mori

Keyword(s):

Shear Stress ◽

Shear Rate ◽

Wall Shear Stress ◽

Newtonian Fluid ◽

Stress Function ◽

Slip Velocity ◽

Wall Slip ◽

Average Shear ◽

Wall Shear ◽

Shear Stress Function

We performed numerical simulation to investigate the effects of wall slip on flow behaviors of Newtonian and non-Newtonian fluids in macro and micro contraction channels. The results show that the wall slip introduces different vortex growth for the flow in micro channel as compared to that in macro channel, which are qualitatively in agreement with experimental results. The effects of slip on bulk flow behaviors depend on rheological property of the fluid. For Newtonian fluid, the wall slip always reduces the vortex length, while for non-Newtonian fluid, the strength of the slip determines whether the vortex length is reduced or increased. Analyses on the velocity and stress fields confirm the channel size dependent phenomena, such as the reduction of wall shear stress with the decrease in channel size. With the increase in average shear rate, the Newtonian fluid shows the reduction of wall shear stress that increases in the same trend with slip velocity-wall shear stress function, while for non-Newtonian fluid, the effect of the slip is suppressed by shear thinning effect and, therefore, the reduction of wall shear stress is less sensitive to the change in average shear rate and slip velocity-wall shear stress function.

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Determination of Viscosity and Wall Slip Behavior of a Polymer-Gel Used for Leakage Control From Couette Viscometry Data

Journal of Energy Resources Technology ◽

10.1115/1.4038384 ◽

2017 ◽

Vol 140 (3) ◽

Author(s):

Gui Wang ◽

Hui Du ◽

Boyun Guo

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Wall Slip ◽

Rheological Parameters ◽

Viscosity Data ◽

Polymer Content ◽

Polymer Gel ◽

Annular Gap ◽

Leakage Control ◽

Wall Shear

Polymer-gel, as a rheological complex fluid, is vulnerable to slip at solid walls. If wall slip occurs, the accuracy of viscosity measurements that are based on the no-slip boundary condition assumption is affected. This paper presents a general numerical procedure based on Tikhonov regularization for correcting Couette viscometry data in the presence of wall slip. This procedure needs only two-measurement viscosity data from two different annular gap sizes. Using the presented procedure, we determined the viscosity and wall slip behavior of a special polymer-gel used for leakage control. The results show that, the polymer-gel ZND-2 does not always exhibit significant wall slip, until the polymer content reaches a critical level of 0.3–0.5% by mass. An empirical correlation was proposed in power law form to describe the relationship between wall slip velocity and wall shear stress. It indicates that there is a minimum wall shear stress that needs to be overcome for a given polymer-gel sample manifesting wall slip phenomenon. The critical minimum wall shear stress and the gel structure strength increase drastically when the polymer content increases beyond a certain value, which is 1.0% by mass for ZND-2. When wall slip occurs, the difference is remarkable between the slip-corrected and apparent rheological parameters for different annular gap sizes. The slip-corrected rheological properties indicate that the polymer-gel ZND-2 used for leakage control behaves as a yield plastic fluid and has good shear thinning capability.

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