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.

Simulation and Analysis of Fluid Dynamic Behaviour of Foods during Filling Processes

2007 ◽  
Vol 2 (3) ◽  
Author(s):  
Eleonora Bottani ◽  
Roberto Rizzo ◽  
Giuseppe Vignali
Keyword(s):  
Dynamic Behaviour ◽  
Fluid Dynamic ◽  
Shear Thinning ◽  
High Viscosity ◽  
Inlet Section ◽  
Shear Thinning Fluids ◽  
Filling System ◽  
Time Required ◽  
Shear Thinning Fluid ◽  
Steady State Predictions

This research presents a model describing the behaviour of a non-Newtonian shear-thinning fluid during aseptic filling processes, in order to determine the influence of the behaviour of fluids on the performance of filling valves in aseptic beverage plants, mainly in terms of the time required to perform the filling process. The ultimate aim of the study is to explore the possibility of improving the accuracy of industrial filling processes, so as to be able to utilise them with high viscosity fluids.The numerical model, exploiting the Finite Elements Method (FEM), was designed using the commercial software Comsol Multiphysics, and validated by comparing the steady state predictions with outcomes of filling experiments performed in industrial laboratories. Hence, subsequent numerical simulations were performed to investigate the transition from laminar to turbulent flow for shear-thinning fluids under different pressure conditions, in 3D time-dependent configurations. Results of the simulations, performed on a low fat yoghurt, show that laminar flow subsists within the whole filling system when the Metzner-Reed Reynolds number at the inlet section of the valve is lower than approx 444.

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 Rheology by Design: A Regulatory Tutorial for Analytical Method Validation

Pharmaceutics ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 820 ◽  
Author(s):  
Ana Simões ◽  
Margarida Miranda ◽  
Catarina Cardoso ◽  
Francisco Veiga ◽  
Carla Vitorino
Keyword(s):  
Yield Point ◽  
Shear Viscosity ◽  
Loss Modulus ◽  
Shear Thinning ◽  
Critical Parameters ◽  
Relative Area ◽  
Zero Shear Viscosity ◽  
Analytical Method Validation ◽  
Lower Shear ◽  
The Impact

The increasing demand for product and process understanding as an active pursuit in the quality guideline Q8 and, more recently, on the draft guideline on quality and equivalence of topical products, has unveiled the tremendous potential of rheology methods as a tool for microstructure characterization of topical semisolid dosage forms. Accordingly, procedure standardization is a dire need. This work aimed at developing and validating a methodology tutorial for rheology analysis. A 1% hydrocortisone cream was used as model cream formulation. Through a risk assessment analysis, the impact of selected critical method variables (geometry, temperature and application mode) was estimated in a broad range of rheological critical analytical attributes—zero-shear viscosity, upper-shear thinning viscosity, lower-shear thinning viscosity, infinite-shear viscosity, rotational yield point, thixotropic relative area, linear viscoelastic region, oscillatory yield point, storage modulus, loss modulus, and loss tangent. The proposed validation of the approach included the rheometer qualification, followed by the validation of numerous operational critical parameters regarding a rheology profile acquisition. The thixotropic relative area, oscillatory yield point, flow point and viscosity related endpoints proved to be highly sensitive and discriminatory parameters. This rationale provided a standard framework for the development of a reliable and robust rheology profile acquisition.

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.

scholarly journals Secondary instabilities in Taylor–Couette flow of shear-thinning fluids

2021 ◽  
Vol 933 ◽  
Author(s):  
S. Topayev ◽  
C. Nouar ◽  
J. Dusek
Keyword(s):  
Numerical Simulations ◽  
Couette Flow ◽  
Vortex Flow ◽  
Shear Thinning ◽  
Taylor Vortex ◽  
Shear Thinning Fluids ◽  
Taylor Vortex Flow ◽  
Viscous Shear ◽  
Taylor Couette ◽  
Shear Thinning Fluid

The stability of the Taylor vortex flow in Newtonian and shear-thinning fluids is investigated in the case of a wide gap Taylor–Couette system. The considered radius ratio is $\eta = R_1/R_2=0.4$ . The aspect ratio (length over the gap width) of experimental configuration is 32. Flow visualization and measurements of two-dimensional flow fields with particle image velocimetry are performed in a glycerol aqueous solution (Newtonian fluid) and in xanthan gum aqueous solutions (shear-thinning fluids). The experiments are accompanied by axisymmetric numerical simulations of Taylor–Couette flow in the same gap of a Newtonian and a purely viscous shear-thinning fluid described by the Carreau model. The experimentally observed critical Reynolds and wavenumbers at the onset of Taylor vortices are in very good agreement with that obtained from a linear theory assuming a purely viscous shear-thinning fluid and infinitely long cylinders. They are not affected by the viscoelasticity of the used fluids. For the Newtonian fluid, the Taylor vortex flow (TVF) regime is found to bifurcate into a wavy vortex flow with a high frequency and low amplitude of axial oscillations of the vortices at ${Re} = 5.28 \, {Re}_c$ . At ${Re} = 6.9 \, {Re}_c$ , the frequency of oscillations decreases and the amplitude increases abruptly. For the shear-thinning fluids the secondary instability conserves axisymmetry. The latter is characterized by an instability of the array of vortices leading to a continuous sequence of creation and merging of vortex pairs. Axisymmetric numerical simulations reproduce qualitatively very well the experimentally observed flow behaviour.

scholarly journals Modeling the motion of a Taylor bubble in a microchannel through a shear-thinning fluid

2021 ◽  
Vol 312 ◽  
pp. 05006
Author(s):  
Andrea Aquino ◽  
Davide Picchi ◽  
Pietro Poesio
Keyword(s):  
Shear Thinning ◽  
Current Theory ◽  
Continuous Phase ◽  
Bubble Velocity ◽  
Recent Theory ◽  
Taylor Bubble ◽  
Lubrication Film ◽  
Shear Thinning Fluids ◽  
Validity Range ◽  
Shear Thinning Fluid

Applications of multiphase flows in microchannels as chemical and biological reactors and cooling systems for microelectronic devices typically present liquid slugs alternated with bubbles of elongated shape, the Taylor bubbles. These occupy almost entirely the cross-section of the channel and present a hemispherical front and a liquid layer, the lubrication film, which separates the gas from the tube wall. The Taylor bubble perturbs the surrounding fluids activating many transport mechanisms in the proximity of the gas-liquid interface; therefore, the bubble motion significantly influences the heat and mass transfer rates. Although many works deeply investigate the bubble hydrodynamics in Newtonian fluids, the knowledge about the relation between bubble hydrodynamics and rheological properties is insufficient, and studies where the continuous phase exhibits a shear-thinning behavior are missing. Our numerical analysis tries to fill this gap by investigating the motion of a Taylor bubble in a non-Newtonian shear-thinning fluid, modeled by the Carreau viscosity model. First, we validate the results against the Newtonian case and a recent theory for shear-thinning fluids (Picchi et al., Journal of Fluid Mechanics, 2021, 918). Then, we investigate the bubble hydrodynamics far from the validity range of the current models. Finally, we study the scaling of the bubble velocity and lubrication film thickness, extending the current theory to shear-thinning fluids.

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