scholarly journals Absolute Rheological Measurements of Model Suspensions: Influence and Correction of Wall Slip Prevention Measures

Materials ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 467
Author(s):  
Sebastian Pawelczyk ◽  
Marieluise Kniepkamp ◽  
Steffen Jesinghausen ◽  
Hans-Joachim Schmid
Keyword(s):  
Wall Slip ◽  
Shear Thinning ◽  
Newtonian Fluids ◽  
Measuring System ◽  
Correction Function ◽  
Prevention Measures ◽  
Measuring Systems ◽  
Shear Thinning Fluids ◽  
Gap Height ◽  
Real Fluids

Since suspensions (e.g., in food, cement, or cosmetics industries) tend to show wall slip, the application of structured measuring surfaces in rheometers is widespread. Usually, for parallel-plate geometries, the tip-to-tip distance is used for calculation of absolute rheological values, which implies that there is no flow behind this distance. However, several studies show that this is not true. Therefore, the measuring gap needs to be corrected by adding the effective gap extension δ to the prescribed gap height H in order to obtain absolute rheological properties. In this paper, we determine the effective gap extension δ for different structures and fluids (Newtonian, shear thinning, and model suspensions that can be adjusted to the behavior of real fluids) and compare the corrected values to reference data. We observe that for Newtonian fluids a gap- and material-independent correction function can be derived for every measuring system, which is also applicable to suspensions, but not to shear thinning fluids. Since this relation appears to be mainly dependent on the characteristics of flow behaviour, we show that the calibration of structured measuring systems is possible with Newtonian fluids and then can be transferred to suspensions up to a certain particle content.

Capillary imbibition of non-Newtonian fluids in a microfluidic channel: analysis and experiments

2020 ◽  
Vol 476 (2242) ◽  
pp. 20200496
Author(s):  
Srinivas R. Gorthi ◽  
Sanjaya Kumar Meher ◽  
Gautam Biswas ◽  
Pranab Kumar Mondal
Keyword(s):  
Early Stage ◽  
Microfluidic Channel ◽  
Shear Thinning ◽  
Newtonian Fluids ◽  
Experimental Results ◽  
Scaling Analysis ◽  
Theoretical Understanding ◽  
Link Type ◽  
Shear Thinning Fluids ◽  
Capillary Dynamics

We have presented an experimental analysis on the investigations of capillary filling dynamics of inelastic non-Newtonian fluids in the regime of surface tension dominated flows. We use the Ostwald–de Waele power-law model to describe the rheology of the non-Newtonian fluids. Our analysis primarily focuses on the experimental observations and revisits the theoretical understanding of the capillary dynamics from the perspective of filling kinematics at the interfacial scale. Notably, theoretical predictions of the filling length into the capillary largely endorse our experimental results. We study the effects of the shear-thinning nature of the fluid on the underlying filling phenomenon in the capillary-driven regime through a quantitative analysis. We further show that the dynamics of contact line motion in this regime plays an essential role in advancing the fluid front in the capillary. Our experimental results on the filling in a horizontal capillary re-establish the applicability of the Washburn analysis in predicting the filling characteristics of non-Newtonian fluids in a vertical capillary during early stage of filling (Digilov 2008 Langmuir 24 , 13 663–13 667 ( doi:10.1021/la801807j )). Finally, through a scaling analysis, we suggest that the late stage of filling by the shear-thinning fluids closely follows the variation x ~ t . Such a regime can be called the modified Washburn regime (Washburn 1921 Phys. Rev. 17 , 273–283 ( doi:10.1103/PhysRev.17.273 )).

scholarly journals Linear stability of Taylor–Couette flow of shear-thinning fluids: modal and non-modal approaches

2015 ◽  
Vol 776 ◽  
pp. 354-389 ◽  
Author(s):  
Y. Agbessi ◽  
B. Alibenyahia ◽  
C. Nouar ◽  
C. Lemaitre ◽  
L. Choplin
Keyword(s):  
Couette Flow ◽  
Power Law ◽  
Reynolds Numbers ◽  
Shear Thinning ◽  
Base Flow ◽  
Newtonian Fluids ◽  
Transient Growth ◽  
Time Behaviour ◽  
Optimal Perturbation ◽  
Shear Thinning Fluids

In this paper, the response of circular Couette flow of shear-thinning fluids between two infinitely long coaxial cylinders to weak disturbances is addressed. It is highlighted by transient growth analysis. Both power-law and Carreau models are used to describe the rheological behaviour of the fluid. The first part of the paper deals with the asymptotic long-time behaviour of three-dimensional infinitesimal perturbations. Using the normal-mode approach, an eigenvalue problem is derived and solved by means of the spectral collocation method. An extensive description and the classification of eigenspectra are presented. The influence of shear-thinning effects on the critical Reynolds numbers as well as on the critical azimuthal and axial wavenumbers is analysed. It is shown that with a reference viscosity defined with the characteristic scales $\hat{{\it\mu}}_{ref}=\hat{K}(\hat{R}_{1}\hat{{\it\Omega}}_{1}/\hat{d})^{(n-1)}$ for a power-law fluid and $\hat{{\it\mu}}_{ref}=\hat{{\it\mu}}_{0}$ for a Carreau fluid, the shear-thinning character is destabilizing for counter-rotating cylinders. Moreover, the axial wavenumber increases with $\mathit{Re}_{2}$ and with shear-thinning effects. The second part investigates the short-time behaviour of the disturbance using the non-modal approach. For the same inner and outer Reynolds numbers, the amplification of the kinetic energy perturbation becomes much more important with increasing shear-thinning effects. Two different mechanisms are used to explain the transient growth, depending on whether or not there is a stratification of the angular momentum. On the Rayleigh line and for Newtonian fluids, the optimal perturbation is in the form of azimuthal streaks, which transform into Taylor vortices through the anti-lift-up mechanism. In the other cases, the optimal perturbation is initially oriented against the base flow, then it tilts to align with the base flow at optimal time. The scaling laws for the optimal energy amplification proposed in the literature for Newtonian fluids are extended to shear-thinning fluids.

scholarly journals Concentric cylinder viscometer flows of Herschel-Bulkley fluids

2019 ◽  
Vol 29 (1) ◽  
pp. 173-181 ◽  
Author(s):  
Hans Joakim Skadsem ◽  
Arild Saasen
Keyword(s):  
Shear Rate ◽  
Yield Stress ◽  
Couette Flow ◽  
Newtonian Fluid ◽  
Shear Thinning ◽  
Newtonian Fluids ◽  
Drilling Fluids ◽  
Concentric Cylinder ◽  
Shear Thinning Fluids ◽  
Cylinder Viscometer

Abstract Drilling fluids and well cements are example non-Newtonian fluids that are used for geothermal and petroleum well construction. Measurement of the non-Newtonian fluid viscosities are normally performed using a concentric cylinder Couette geometry, where one of the cylinders rotates at a controlled speed or under a controlled torque. In this paper we address Couette flow of yield stress shear thinning fluids in concentric cylinder geometries.We focus on typical oilfield viscometers and discuss effects of yield stress and shear thinning on fluid yielding at low viscometer rotational speeds and errors caused by the Newtonian shear rate assumption. We relate these errors to possible implications for typical wellbore flows.

Collision Dynamics and Internal Mixing of Equal-Size Droplets of Non-Newtonian Liquids

2016 ◽  
Author(s):  
Peng Zhang
Keyword(s):  
Newtonian Fluid ◽  
Shear Thinning ◽  
Internal Motion ◽  
Newtonian Fluids ◽  
Rocket Engines ◽  
Phase Reaction ◽  
Shear Thinning Fluids ◽  
Internal Mixing ◽  
Highly Nonlinear ◽  
The Impact

The efficient internal mixing of colliding non-Newtonian droplets upon coalescence is critical to various technological processes, specifically involving the initiation of the liquid-phase reaction of gelled hypergolic propellants, which are promising fuels for next-generation rocket engines. However, most previous studies on droplet collision used Newtonian fluids, and the non-Newtonian fluids that can be highly nonlinear and even trend reversing are much less understood to date. Motzigemba et al. [1] experimentally found that the deformation of colliding droplets of shear-thinning fluids is substantially larger than that of the Newtonian fluid. In a previous work [2], we numerically studied the initially stationary equal-sized droplet coalescence between a Newtonian and non-Newtonian droplet. Because of the reduced local viscosity and thereby smaller viscous dissipation for shear-thinning fluids, the flow in the non-Newtonian droplet is faster than that in the Newtonian droplet, resulting in unsymmetrical, albeit small, mixing induced by the shear-thinning effect. The above findings are encouraging since the droplet internal motion is driven solely by the surface tension of the initially stationary droplets regardless of the impact inertia. However, as the published references of Newtonian fluid characteristics, internal mixing of non-Newtonian fluid definitely can be substantially augmented because of the correspondingly substantial internal motion generated through the impact inertia. Thus, in terms of the equal-sized head-on colliding droplets, efficient mixing must require breaking the collision symmetry by varying the impact inertia and the rheological properties as well.

scholarly journals The cost of swimming in generalized Newtonian fluids: experiments with C. elegans

2016 ◽  
Vol 800 ◽  
pp. 753-765 ◽  
Author(s):  
D. A. Gagnon ◽  
P. E. Arratia
Keyword(s):  
Shear Viscosity ◽  
Model Organism ◽  
Shear Thinning ◽  
Newtonian Fluids ◽  
Mechanical Power ◽  
Zero Shear Viscosity ◽  
Generalized Newtonian Fluids ◽  
Shear Thinning Fluids ◽  
The Cost ◽  
Shear Thinning Fluid

Numerous natural processes are contingent on microorganisms’ ability to swim through fluids with non-Newtonian rheology. Here, we use the model organism Caenorhabditis elegans and tracking methods to experimentally investigate the dynamics of undulatory swimming in shear-thinning fluids. Theory and simulation have proposed that the cost of swimming, or mechanical power, should be lower in a shear-thinning fluid compared to a Newtonian fluid of the same zero-shear viscosity. We aim to provide an experimental investigation into the cost of swimming in a shear-thinning fluid from (i) an estimate of the mechanical power of the swimmer and (ii) the viscous dissipation rate of the flow field, which should yield equivalent results for a self-propelled low Reynolds number swimmer. We find the cost of swimming in shear-thinning fluids is less than or equal to the cost of swimming in Newtonian fluids of the same zero-shear viscosity; furthermore, the cost of swimming in shear-thinning fluids scales with a fluid’s effective viscosity and can be predicted using fluid rheology and simple swimming kinematics. Our results agree reasonably well with previous theoretical predictions and provide a framework for understanding the cost of swimming in generalized Newtonian fluids.

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