Formation of Boundary Layer in the Flow of Shear-Dependent-Viscosity Fluids Between Parallel Plates

2017 ◽  
Author(s):  
Nariman Ashrafi ◽  
Ali Sadeghi ◽  
Mehdi Shafahi
Keyword(s):  
Boundary Layer ◽  
Flow Behavior ◽  
Vertical Wall ◽  
Shear Thickening ◽  
Finite Volume Scheme ◽  
Parallel Plates ◽  
Flow Behavior Index ◽  
Shear Dependent Viscosity ◽  
Shear Thickening Fluids ◽  
Dependent Viscosity

Formation of the boundary layer in the laminar flow of Herschel–Bulkley fluid between parallel plates is taken into consideration. In particular, the study is focused on the flow of the shear thinning and shear thickening fluids past a partial vertical wall in between the plates. Upon numerically solving the continuity and momentum equations the flow is analyzed throughout the domain using a finite volume scheme. The shear stress at the wall together with velocity distribution are evaluated and compared with experimental results for several values of Herschel-Bulkley coefficients for fluidity and flow behavior index.

Herschel-Bulkley Fluid Flow Characteristics in a Duct With an Obstacle

2018 ◽  
Author(s):  
Nariman Ashrafi ◽  
Ali Sadeghi ◽  
Armin Chegini ◽  
Mehdi Shafahi
Keyword(s):  
Flow Behavior ◽  
Vertical Wall ◽  
Flow Characteristics ◽  
Shear Thickening ◽  
Finite Volume Scheme ◽  
Flow Behavior Index ◽  
Shear Thickening Fluids ◽  
Flow Domain ◽  
Fluid Flow Characteristics ◽  
Flow Variables

This study is focused on the flow of the shear thinning and shear thickening fluids of Herschel-Bulkley type past a partial vertical wall in between the plates. Upon numerically solving the continuity and momentum equations the flow is analyzed throughout the domain using a finite volume scheme. The shear stress at the wall together with velocity distribution are evaluated and compared to experimental results for several values of Herschel-Bulkley coefficients for fluidity and flow behavior index. Dynamic viscosity and other flow variables are calculated throughout the flow domain.

Stability of Shear-Thickening Liquids Between Rotating Cylinders

2010 ◽  
Author(s):  
Nariman Ashrafi ◽  
Habib Karimi Haghighi
Keyword(s):  
Couette Flow ◽  
Dynamical Behavior ◽  
Shear Thickening ◽  
Shear Thinning ◽  
Taylor Vortex ◽  
Shear Dependent Viscosity ◽  
Shear Thinning Fluids ◽  
Shear Thickening Fluids ◽  
The Stability ◽  
Dependent Viscosity

The effects of nonlinearities on the stability are explored for shear thickening fluids in the narrow-gap limit of the Taylor-Couette flow. It is assumed that shear-thickening fluids behave exactly as opposite of shear thinning ones. A dynamical system is obtained from the conservation of mass and momentum equations which include nonlinear terms in velocity components due to the shear-dependent viscosity. It is found that the critical Taylor number, corresponding to the loss of stability of Couette flow becomes higher as the shear-thickening effects increases. Similar to the shear thinning case, the Taylor vortex structure emerges in the shear thickening flow, however they quickly disappear thus bringing the flow back to the purely azimuthal flow. Naturally, one expects shear thickening fluids to result in inverse dynamical behavior of shear thinning fluids. This study proves that this is not the case for every point on the bifurcation diagram.

Shear-Thickening Flow Between Coaxial Cylinders

2011 ◽  
Author(s):  
Nariman Ashrafi ◽  
Habib Karimi Haghighi
Keyword(s):  
Couette Flow ◽  
Dynamical Behavior ◽  
Shear Thickening ◽  
Shear Thinning ◽  
Taylor Vortex ◽  
Shear Dependent Viscosity ◽  
Shear Thinning Fluids ◽  
Shear Thickening Fluids ◽  
The Stability ◽  
Dependent Viscosity

The effects of nonlinearities on the stability are explored for shear thickening fluids in the narrow-gap limit of the Taylor-Couette flow. A dynamical system is obtained from the conservation of mass and momentum equations which include nonlinear terms in velocity components due to the shear-dependent viscosity. It is found that the critical Taylor number, corresponding to the loss of stability of Couette flow becomes higher as the shear-thickening effects increases. Similar to the shear thinning case, the Taylor vortex structure emerges in the shear thickening flow; however they quickly disappear thus bringing the flow back to the purely azimuthal flow. Naturally, one expects shear thickening fluids to result in inverse dynamical behavior of shear thinning fluids. This study proves that this is not the case for every point on the bifurcation diagram.

First instability of the flow of shear-thinning and shear-thickening fluids past a circular cylinder

2012 ◽  
Vol 701 ◽  
pp. 201-227 ◽  
Author(s):  
Iman Lashgari ◽  
Jan O. Pralits ◽  
Flavio Giannetti ◽  
Luca Brandt
Keyword(s):  
Circular Cylinder ◽  
Shear Thickening ◽  
Shear Thinning ◽  
Base Flow ◽  
Rheological Parameters ◽  
Recirculation Bubble ◽  
The Core ◽  
Shear Dependent Viscosity ◽  
Shear Thickening Fluids ◽  
Dependent Viscosity

AbstractThe first bifurcation and the instability mechanisms of shear-thinning and shear-thickening fluids flowing past a circular cylinder are studied using linear theory and numerical simulations. Structural sensitivity analysis based on the idea of a ‘wavemaker’ is performed to identify the core of the instability. The shear-dependent viscosity is modelled by the Carreau model where the rheological parameters, i.e. the power-index and the material time constant, are chosen in the range $0. 4\leq n\leq 1. 75$ and $0. 1\leq \lambda \leq 100$. We show how shear-thinning/shear-thickening effects destabilize/stabilize the flow dramatically when scaling the problem with the reference zero-shear-rate viscosity. These variations are explained by modifications of the steady base flow due to the shear-dependent viscosity; the instability mechanisms are only slightly changed. The characteristics of the base flow, drag coefficient and size of recirculation bubble are presented to assess shear-thinning effects. We demonstrate that at critical conditions the local Reynolds number in the core of the instability is around 50 as for Newtonian fluids. The perturbation kinetic energy budget is also considered to examine the physical mechanism of the instability.

Thermal Analysis of Power-Law Fluid Flow in a Circular Microchannel

2016 ◽  
Vol 139 (3) ◽  
Author(s):  
Amir-Hossein Sarabandi ◽  
Ali Jabari Moghadam
Keyword(s):  
Entropy Generation ◽  
Flow Behavior ◽  
Shear Thickening ◽  
Entropy Generation Rate ◽  
Fluid Temperature ◽  
Brinkman Number ◽  
Flow Behavior Index ◽  
Shear Thinning Fluids ◽  
Shear Thickening Fluids ◽  
Behavior Index

The steady-state fully developed laminar flow of non-Newtonian power-law fluids is analytically studied in a circular microchannel under an imposed uniform and constant wall heat flux. Increasing the flow behavior index results in broadening the dimensionless temperature distribution, i.e., in enlarging the wall and bulk fluid temperature difference. Similar behavior may also be observed when heating or cooling flux is reduced. For any particular value of the flow behavior index, a critical Brinkman number exists in which the bulk mean fluid temperature equals the wall temperature; in this special case of surface cooling, the Nusselt number tends to infinity. Dilatants (shear-thickening fluids) demonstrate more tangible reactions than pseudoplastics (shear-thinning fluids) to changes in the Brinkman number. Entropy generation increases with the flow behavior index as well as the Brinkman number. For shear-thickening fluids, the entropy generation rate from heat transfer is more than the entropy generation rate from fluid friction, while an opposite trend is observed for shear-thinning fluids.

Rheological effects on the levelling dynamics of thin fluid films

2015 ◽  
Vol 25 (8) ◽  
pp. 1850-1867 ◽  
Author(s):  
Gulraiz Ahmed ◽  
Mathieu Sellier ◽  
Yeaw Chu Lee ◽  
Mark Jermy ◽  
Michael Taylor
Keyword(s):  
Flow Behavior ◽  
Shear Thickening ◽  
Shear Thinning ◽  
Lubrication Approximation ◽  
Fluid Films ◽  
Flow Behavior Index ◽  
Shear Thickening Fluid ◽  
Content Type ◽  
Shear Thinning Fluid ◽  
Behavior Index

Purpose – The purpose of this paper is to investigate numerically the effect of rheology on the leveling of thin fluid films on horizontal solid substrates. Design/methodology/approach – A mathematical model based on the lubrication approximation which defines non-Newtonian rheology using a Power-law model is presented. The rheology is described by two parameters: the consistency factor and the flow behavior index. The resulting highly non-linear coupled set of equations is discretized using Finite-Difference and the resulting algebraic system is solved via an efficient Multigrid algorithm. Findings – Importantly, the non-dimensionalization process leads to a pair of Partial Differential Equations which depends on one parameter only, the flow behavior index. The authors show that the consistency factor only affects the time scale of the leveling process, hence stretching or contracting the time line. Results for the leveling of sinusoidal perturbations of the fluid film highlights important differences between the leveling of shear-thinning and shear-thickening fluids. In a normalized time frame, the onset of leveling occurs earlier for the shear-thinning fluid than for the shear-thickening one. However, the dimensionless leveling rate is higher for the shear-thickening fluid than the shear-thinning one. This results in a “threshold thickness” which delimits two regimes: the shear-thinning fluid levels to a thickness above this threshold faster than the shear-thickening fluid but the opposite is true for a film thickness below this threshold. An important aspect of this study is the verification of the numerical implementation using the Method of Manufactured Solutions (MMS), a first in the context of thin film studies. The paper also highlights differences between the leveling of two-dimensional and three-dimensional thickness perturbations. Originality/value – The study of the leveling of disturbances at the free surface of a liquid film using a Power-law rheological model does not appear to have been covered in the literature. Also, the paper uses the MMS to test the validity of the implementation. This appears to be the first time it has been used in the context of the lubrication approximation. Finally, unlike most prior studies, the work does away with the planar assumption.

Some Aspects of the Relationship between Molecular Structure and Flow Behavior of Polymer Melts

1969 ◽  
Vol 42 (3) ◽  
pp. 823-834 ◽  
Author(s):  
L. L. Blyler
Keyword(s):  
Molecular Structure ◽  
Activation Energy ◽  
Molecular Weight ◽  
Molecular Mechanisms ◽  
Flow Behavior ◽  
Average Molecular Weight ◽  
Melt Fracture ◽  
Flow Activation Energy ◽  
Shear Dependent Viscosity ◽  
Dependent Viscosity

Abstract The shear dependent viscosity and related properties of a number of ethylene polymers of differing molecular structure have been characterized using a capillary extrusion rheometer. The structural aspects of interest were average molecular weight, branching, and the presence of strong intermolecular secondary forces. It was found that average molecular weight influences the degree of shear dependence of the viscosity, branching affects both flow activation energy and the nature of the observed “melt fracture” phenomenon, and intermolecular hydrogen bonding enhances viscosity and activation energy and leads to increased shear dependence of flow behavior. The results are interpreted in terms of specific molecular mechanisms.

scholarly journals Influence of Chemically Reacting Ferromagnetic Carreau Nanofluid over a Stretched Sheet with Magnetic Dipole and Viscous Dissipation

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
R. M. Akram Muntazir ◽  
M. Mushtaq ◽  
S. Shahzadi ◽  
K. Jabeen
Keyword(s):  
Boundary Layer ◽  
Magnetic Dipole ◽  
Shear Thickening ◽  
Shear Thinning ◽  
Nusselt Numbers ◽  
Similarity Transformations ◽  
Highly Nonlinear ◽  
Shear Thickening Fluids ◽  
Carreau Nanofluid ◽  
Chemically Reacting

Due to potential implications, boundary layer analysis of chemically reacting Carreau nanofluid has been carried out to examine flow properties of ferromagnetic fluid over a stretched sheet in the presence of magnetic dipole, for shear thinning and shear thickening fluids. Furthermore, the transportation of heat under thermal radiation, heat generation, the Brownian, and thermophoresis aspects has been evaluated. The dimensionless form of highly nonlinear coupled partial differential equations is obtained using suitable similarity transformations and then solved numerically by well-known bvp 4 c technique via MATLAB based on the shooting method. The outcomes of physical quantities are presented through graphs and numerical benchmarks. Moreover, outcomes for skin fraction, Sherwood and Nusselt numbers for velocity, concentration, and temperature are also estimated in this study. The present study reveals that the concentration and thermal boundary layer thicknesses were higher for shear thinning n < 1 fluid when compared with shear thickening n > 1 fluids, but reverse effects are to be observed for momentum boundary layer thickness.

Spread of a non-Newtonian liquid jet over a horizontal plate

2008 ◽  
Vol 613 ◽  
pp. 411-443 ◽  
Author(s):  
JIANGANG ZHAO ◽  
ROGER E. KHAYAT
Keyword(s):  
Boundary Layer ◽  
Power Law ◽  
Hydraulic Jump ◽  
Shear Thickening ◽  
Flow Region ◽  
Shear Thinning ◽  
Similarity Solutions ◽  
Viscous Boundary Layer ◽  
Power Law Fluids ◽  
Shear Thickening Fluids

The flow of an impinging non-Newtonian jet onto a solid flat plate is examined theoretically in this study. Similarity solutions are sought for both shear-thinning and shear-thickening fluids of the power-law type. The jet is assumed to spread out in a thin layer bounded by a hydraulic jump. In addition to the stagnation-flow region, the flow domain is divided into three main regions: a developing boundary layer, fully viscous boundary layer and hydraulic jump. The anomalous behaviour of power-law fluids at small shear rate is remedied by seeking a two-layer solution in each domain. Such anomalies include the singularity of viscosity for shear-thinning fluids, and the vanishing of viscosity as well the overshoot in velocity for shear-thickening fluids. Although the rate of shear-thinning appears to affect significantly the film profile and velocity, only the overall viscosity influences the position of the hydraulic jump.

Effects of Greek Pomegranate Extracts in the Antioxidant Properties and Storage Stability of Kefir

2019 ◽  
Vol 15 (4) ◽  
pp. 437-441 ◽  
Author(s):  
Vasiliki Lagouri ◽  
Georgia Dimitreli ◽  
Aikatarini Kouvatsi
Keyword(s):  
Antioxidant Activity ◽  
Dairy Products ◽  
Storage Time ◽  
Storage Stability ◽  
Flow Behavior ◽  
Antioxidant Properties ◽  
Flow Behavior Index ◽  
Ph Values ◽  
Dpph Activity ◽  
Behavior Index

Background: Oxidation reactions are known to shorten the shelf life and cause damage to foods rich in fat, such as dairy products. One way to limit oxidation and increase the shelf life of fermented dairy products is to use natural antioxidants. The aim of this study was to examine the effect of adding pomegranate extracts in the antioxidant properties, rheological characteristics and the storage stability of the fermented product of kefir. Methods: The Pomegranate Juice (PGJ) and Peel Extracts (PGPE) (5%, 10% w/v) were added to kefir and the antioxidant properties were evaluated by using the methods of radical scavenging activity (DPPH) and Ferric Reducing Antioxidant Power Activity (FRAP). Spectrophotometric and instrumental methods were used to determine the Total Phenols (TPs), pH values, viscosity and flow behavioral index values of enriched with pomegranate kefir samples. The same properties were tested when kefir samples stored at 4°C for 7, 14, 21 and 28 days. Results: The addition of PGJ and PGPE results in an increase in the antioxidant activity (DPPH, FRAP) and total phenol content (TPs) of kefir samples. Increasing the concentration of the added PGJ and PGPE, results in an increase in the TP content and the DPPH activity of kefir. As far as the storage time is concerned, the results showed an increase in the amount of TP at 7th day and a reduction in the DPPH activity in the 14th day of storage. In contrary to the DPPH method, the increase in storage time has resulted in a reduction in antioxidant activity by the FRAP method. The addition of PGJ and PGPE in kefir results in a decrease in pH values while the pH of kefir samples increased during storage at 4°C for 28 days. The addition of PGJ and PGPE to kefir samples results to a decrease in viscosity and an increase in the flow behavior index. Increasing storage time results in increased flow behavior index of kefir samples. Conclusion: The addition of PGJ and PGPE increased the antioxidant activity and total phenols of the kefir product and preserved its properties during the total storage time of 28 days at 4°C.

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