Shear-thinning Fluids Research Articles

Low-cost rolling ball viscometer for the evaluation of Newtonian and shear-thinning fluids

Abstract This article describes the design and testing of a low-cost automatic rolling-ball viscometer. The device has been manufactured from three-dimensional printed parts and conventional and affordable mechanical and electronic components. It is controlled by an Arduino MEGA with a custom code that includes manual and automatic measuring modes. Both the type of viscometer and the models used are, in principle, valid for Newtonian and power-law fluids. However, measurement and calculation procedures have been developed that also makes it possible to determine the viscosity of Herschel–Bulkley fluids that might exhibit a yield stress behaviour within the range studied. By these procedures, viscosity values have been obtained for model fluids – Newtonian, power-law, and Herschel–Bulkley fluids – and compared to those obtained with a commercial rotational rheometer. The proposed setup and measuring method have thus proven to provide very reasonably accurate viscosity values for a low-cost device.

Weak solutions for steady, fully inhomogeneous generalized Navier-Stokes equations

We consider the question of existence of weak solutions for the fully inhomogeneous, stationary generalized Navier–Stokes equations for homogeneous, shear-thinning fluids. For a shear rate exponent p∈(2dd+1,2), previous results require either smallness of the norm or vanishing of the normal component of the boundary data. In this work, combining previous methods, we propose a new, more general smallness condition.

Steady motions of single spherical microswimmers in non-Newtonian fluids

In biological systems, microswimmers often propel themselves through complex media. However, many aspects of swimming mechanisms in non-Newtonian fluids remain unclear. This study considers the propulsion of two types of single spherical microswimmers (squirmers) in shear-thickening and shear-thinning fluids. The slip-driven squirmer propels faster/slower in shear-thickening/thinning fluids than in Newtonian fluids [C. Datt et al., J. Fluid Mech. 784, R1 (2015)]. In contrast, we discovered that a traction-driven squirmer exhibits the opposite trend, moving slower/faster in shear-thickening/thinning fluids than in Newtonian fluids. In addition, we have shown theoretically that Purcell's scallop theorem does not hold in non-Newtonian fluids when a squirmer with reciprocal surface motions is used. The present findings open up possibilities for the design of new types of microswimmers that can achieve translational motion from a single reciprocal motion in non-Newtonian fluids. Furthermore, we demonstrated that traction-driven squirmers swim faster and more efficiently in shear-thinning fluids than in Newtonian fluids. These findings highlight how the non-Newtonian rheology enhances both swimming speed and efficiency, suggesting further potential for optimizing locomotion performance otherwise impossible in Newtonian fluids.

Effect of shear-thinning rheology on the dynamics and pressure distribution of a single rigid ellipsoidal particle in viscous fluid flow

This paper evaluates the behavior of a single rigid ellipsoidal particle suspended in homogeneous viscous flow with a power-law generalized Newtonian fluid rheology using a custom-built finite element analysis (FEA) simulation. The combined effects of the shear-thinning fluid rheology, the particle aspect ratio, the initial particle orientation, and the shear-extensional rate factor in various homogeneous flow regimes on the particles dynamics and surface pressure evolution are investigated. The shear-thinning fluid behavior was found to modify the particle's trajectory and alter the particle's kinematic response. Moreover, the pressure distribution over the particle's surface is significantly reduced by the shear-thinning fluid rheology. The FEA model is validated by comparing results of the Newtonian case with results obtained from the well-known Jeffery's analytical model. Furthermore, Jeffery's model is extended to define the particle's trajectory in a special class of homogeneous Newtonian flows with combined extension and shear rate components typically found in axisymmetric nozzle flow contractions. The findings provide an improved understanding of key transport phenomenon related to physical processes involving fluid–structure interaction such as that which occurs within the flow field developed during material extrusion–deposition additive manufacturing of fiber-reinforced polymeric composites. These results provide insight into important microstructural formations within the print beads.

Boundary layer flow and heat-mass transfer of shear-thinning nanofluid past a thin needle: electroperiodic magnetic field and thermo-diffusion effects

Heat and mass transfer in a boundary layer flow (BLF) of shear-thinning nanofluid (NF) around a thin needle has various practical applications including industrial processes, like medical devices, complicated cooling systems, high-efficiency thermal control in microelectronic devices, and chemical reactors designs. With a focus on its practical applications, this work investigates the heat and mass transfer effectiveness in a BLF of shear-thinning fluid containing alumina-copper nanoparticles around a thin needle subject to electroperiodic magnetic field in a nonlinear radiative environment. A comparative analysis is done for heat-mass transfer performance of alumina-copper-water-tangent hyperbolic fluid and water-tangent hyperbolic in order to optimize thermal and mass transmission efficiency by highlighting the importance of latent heat, nanomaterial load and thermo-diffusion processes. This work is novel because such comparative investigation on heat-mass transfer for alumina-copper-water-tangent hyperbolic fluid and water-tangent hyperbolic is not taken yet. The governing model for a BLF around a thin needle are solved using Runge Kutta fourth order (RK-4) method. The findings shows that the action of electroperiodic magnetic field greatly improves mass transfer and heat transfer performance. Latent heat effect and needle thickness enlargement improve the rate of heat-mass. Elevating the Weissenberg number modifies the flow dynamics. Adding more alumina-copper nanoparticles to the mixture increases its thermal conductivity and as a result increases the heat transfer rate. The Dufour number had a positive effect on temperature distribution. The activation energy, and Soret numbers all worked together to significantly alter the concentration profile. The mixture () show better heat-mass transfer efficiency as compared to () fluid.

Analysis of the shear thickening behavior of a fumed silica suspension using QL-LAOS approach

The feasibility of applying quasi-linear large amplitude oscillatory shear (QL-LAOS) approach to a shear thickening (ST) fumed silica suspension was tested. While the characteristic time has been used as the parameter for the original QL-LAOS analysis of shear thinning fluids, we obtained that a description based upon increasing stiffness is more appropriate for ST fumed silica suspensions. Very low (≤1.5) third to first harmonics ratio were obtained indicating the need of alternative criteria to identify QL-LAOS behavior in ST suspensions. Consequently, a method based upon the best fit of an ellipse to the experimental Lissajous-Bowditch curves was proposed. Compliances were obtained from areas of viscous and elastic fitted ellipses. The dependence of the material functions obtained by using a Jeffrey´s mechanical viscoelastic framework with angular frequency supports the idea of ST microstructure evolves by increasing with shear the number of small hydroclusters.

Stress boundary layers for the Phan-Thien–Tanner fluid at the static contact line in extrudate swell

The method of matched asymptotic expansions is used to examine the behaviour of the Phan-Thien–Tanner (PTT) fluid in the neighbourhood of the contact line singularity in extrudate swell. The solution structure for this shear-thinning viscoelastic fluid model has solvent stresses that dominate the polymer stresses, but requires stress boundary layers to fully resolve the solution at the die wall and free surface. The sizes and mechanism of the boundary layers at the two surfaces are different. We derive and present a similarity solution for the boundary layer at the die wall and an exact solution for the boundary layer at the free surface. An expression for the local behaviour of the free surface is also derived. The results for the boundary layers completes the preliminary asymptotic results for the PTT model presented in previous work.

Maximizing Blue Energy via Densely Grafted Soft Layers in Nanopores.

We investigate energy generation from salinity gradients inside a nanopore that is connected to reservoirs at both ends. We consider that the inner wall surfaces are grafted with a densely grafted polyelectrolyte layer (PEL). We developed the PEL grafting density-dependent correlation of dielectric permittivity, molecular diffusivity, and dynamic viscosity in this endeavor. Using these correlations, we employ the finite element framework to solve the equations describing the ionic and fluidic transport. We use a partially hydrolyzed polyacrylamide polymer solution, which exhibits a shear-thinning fluid, in combination with the KCl electrolyte for energy-harvesting analysis. To describe the shear-rate-dependent apparent viscosity of non-Newtonian liquid, we have employed the Carreau model. For a window of right-side reservoir concentration, we investigate the effects of ion-partitioning in conjugation with the change in PEL grafting density on the ionic field, ionic selectivity, pore current, osmotic power, energy conversion efficiency, and flow field. The findings of this endeavor demonstrate how the ion-partitioning effect lowers the screening effect and raises the electrical double layer (EDL) potential by reducing the counterions in PEL. We show that the unique distribution of the ionic field leads to a higher prediction of generated osmotic power and power density due to the ion-parting effect. Additionally, we establish that the augmentation in PEL space charge density leads to improvement in average flow velocity, osmotic power, and consequently energy conversion efficiency. We establish that the generated osmotic power density and the energy conversion efficiency become very high at the higher grafting density. In summary, inferences of this analysis are deemed pertinent in designing the nanoscale device intended for high and efficient osmotic energy generation.

Influence of Ultrasound on the Rheological Properties, Color, Carotenoid Content, and Other Physical Characteristics of Carrot Puree

This study aimed to investigate the effect of ultrasonic frequencies (21 and 35 kHz) on the physical properties of carrot puree at different concentrations (9, 12, and 21 °Brix). The viscosity, total soluble content, density, color, and β-carotene content were tested. It was found that the viscosity of the puree, determined with respect to shear rate, concentration, and the use of ultrasonic treatment, indicates that the purees should be defined as shear thinning fluids. Moreover, a decrease in activation energy was observed with the increase in extract and ultrasonic treatment, which may cause changes in the rate of reactions occurring in the tested material. A significant effect of this may be the observed change in the color of the puree after ultrasonic treatment; the increase in frequency from 21 to 35 kHz caused an increase in redness and yellowness and a decrease in lightness, independently of concentration. The most significant color difference was noted in the puree with a 21 °Brix concentration, where a ΔE value of 21 was recorded. In contrast, the ΔE values for the other purees post-treatment remained below 5. The content of carotenoids did not change after sonication, independently of the concentration of carrot puree.

Flagellum Pumping Efficiency in Shear-Thinning Viscoelastic Fluids.

Microorganism motility often takes place within complex, viscoelastic fluid environments, e.g., sperm in cervicovaginal mucus and bacteria in biofilms. In such complex fluids, strains and stresses generated by the microorganism are stored and relax across a spectrum of length and time scales and the complex fluid can be driven out of its linear response regime. Phenomena not possible in viscous media thereby arise from feedback between the swimmer and the complex fluid, making swimming efficiency co-dependent on the propulsion mechanism and fluid properties. Here we parameterize a flagellar motor and filament properties together with elastic relaxation and nonlinear shear-thinning properties of the fluid in a computational immersed boundary model. We then explore swimming efficiency, defined as a particular flow rate divided by the torque required to spin the motor, over this parameter space. Our findings indicate that motor efficiency (measured by the volumetric flow rate) can be boosted or degraded by relatively moderate or strong shear-thinning of the viscoelastic environment.

Optimizing the low-temperature performance of high-wax-content crude oil with emulsion-based wax inhibitors: Mechanisms and efficacy.

Wax deposition in constant-temperature transportation of waxy oil with high pour points poses a significant challenge for the oil industry. The demand for efficient methods to solve wax deposition has gained attention. To elucidate the impact of emulsion-based wax inhibitors on the performance of crude oils with varying wax content at low temperatures, experiments, rheological analyses, and microscopic analyses were conducted to study their pour point regulation, low-temperature flow improvement, wax prevention effectiveness, and wax crystallization behavior. The results indicate that emulsion-based wax inhibitors significantly reduce the pour point of crude oil, especially for high-wax-content oil, while for low-wax-content oil, the pour point only decreased by 3°C. By penetrating and dispersing wax crystals, the inhibitor reduced the viscosity of crude oil at low temperatures, enhancing its flowability. At 28°C, crude oil transitioned from a shear-thinning non-Newtonian fluid to a Newtonian fluid at wax inhibitor dosages of 500-750ppm. At 1000ppm, the wax prevention rate for high-wax-content oil reached 87.5%, but the effect plateaued beyond this concentration. Additionally, the wax prevention and removal mechanism of the emulsion-based wax inhibitors is discussed. This study confirms that emulsion-based wax inhibitors significantly enhance the low-temperature processability of crude oil, offering a viable strategy for the conveyance and refinement in cold climates.

Heat Transfer and Entropy Generation in Vibrational Flow: Newtonian vs. Inelastic Non-Newtonian Fluid

A computational method is employed to solve heat transfer and entropy generation within a circular pipe. The thermal boundary condition assumes a constant wall temperature, while viscosity is taken to be dependent on temperature. A power-law type shear-thinning fluid is utilized in the analysis, with sinusoidal vibration applied horizontally perpendicular to the flow direction. Temperature distributions across the pipe are illustrated. Additionally, the entropy generation rate over the entire fluid volume under vibration was examined, comparing the results between steady flow and vibrational flow for both types of fluids. It was found that radial mixing is more pronounced in non-Newtonian fluids as vibration increases the strain rate, which is higher for low Reynolds numbers. The research provides a quantitative analysis of heat transfer and entropy generation for both Newtonian and shear-thinning fluids at different Reynolds numbers. It was observed that the effectiveness of superimposed vibrational flow is limited, especially for low Reynolds numbers and flow behavior index characteristic of shear-thinning fluids.

Effects of Viscosity and Shear-thinning Characteristics of a Liquid Jet in Air Crossflow

In the present study, we performed numerical simulations of a single liquid jet with varying viscosities and non-Newtonian characteristics in uniform gas crossflows at different velocities, to investigate the effects of liquid properties on jet deformation and breakup behavior. By utilizing air as the gas and examining both Newtonian fluids with different viscosities and a shear-thinning fluid as the liquid, we aimed to uncover the intricate dynamics governing liquid jet deformation and breakup under crossflow conditions. At lower air velocities, the liquid jet bent and elongated without undergoing breakup, regardless of the viscosity and shear-thinning characteristics. Notably, in the case of the shear-thinning fluid, the effect of the viscosity was more pronounced in the outer regions of the liquid jet than at its center. In contrast, at higher air velocities, viscosity and shear-thinning characteristics significantly affected jet breakup; the high-viscosity Newtonian liquid jet resisted breakup, while the low-viscosity jet broke up into threads, with a decrease in apparent viscosity leading to increased penetration height.This study introduces a novel method for quantifying the energy transfer from gas to liquid jet, using pressure differences between a deformable liquid jet and an equivalent rigid cylinder as a reference. This approach allows for the separation of bending and breakup energy components, offering new quantitative insights into the forces driving jet deformation and breakup. These insights advance the current understanding of fluid-structure interactions in crossflow conditions.

Spreading of graphene oxide suspensions droplets on smooth surfaces

Understanding and predicting the spreading of droplets on solid surfaces is crucial in many applications such as printed electronics and spray coating where the fluid is a suspension and in general non-Newtonian. However, many models that predict the maximum spreading diameter usually only apply to Newtonian fluids. Here, we study experimentally and theoretically the maximum spreading diameter of graphene oxide suspension droplets impacting on a smooth surface for a wide range of concentrations and impact velocities (5≤We≤700, 30≤Re≤2000). As the particle concentration increases the rheological behavior changes from a viscous fluid to a shear-thinning yield stress fluid and the maximum spreading diameter decreases. The rheology for all concentrations is well described by a Herschel–Bulkley model that allows us to determine the characteristic viscosity and corresponding Reynolds number Re during spreading. Analogous to Newtonian fluids, the spreading ratio follows the Re1/5 scaling in the viscous spreading regime. Furthermore, we use this characteristic viscosity to develop an energy balance model that takes into account the viscous dissipation and change in surface energies to find the maximum spread diameter for a given impact velocity. The model contains one non-dimensional parameter α that encodes both the dynamic contact angle during spreading and the droplet shape at maximum spread. Our model is in good agreement with our data at all concentrations and agrees well with literature data on Newtonian fluids. Furthermore, the model gives the correct limits in the viscous and capillary regime and can be solved analytically for Newtonian fluids.

Comprehensive investigation of gas hold-up in a double coaxial mixer with shear-thinning fluids exhibiting yield stress: Experimental, numerical, and artificial neural network approaches

This study addresses the challenge of uneven gas dispersion in yield-stress, non-Newtonian fluids, commonly encountered in industries such as biopharmaceuticals, cosmetics, and food processing. While previous research demonstrated the advantages of dual coaxial mixers for pseudoplastic fluids, limited attention has been given to aerating yield-pseudoplastic fluids with higher aspect ratios. This study bridges that gap by investigating both local and global gas hold-up under various conditions, utilizing electrical resistance tomography and computational fluid dynamics. Key findings showed that increasing the anchor speed from stationary to 30 rpm significantly enhanced aeration efficiency (gas hold-up per specific power consumption), with improvements of 78 % in UP-CO mode and 25 % in UP-COUNTER mode at Nc = 350 rpm and Qg = 20 L/min. These results underscore enhanced gas dispersion under specific operating conditions, driving overall process intensification. To ensure accurate prediction of gas hold-up, both dimensional and dimensionless empirical correlations, along with an artificial neural networks (ANNs) model, were developed. The ANNs model exhibited superior accuracy, achieving R² values of 0.99 for both rotation modes, outperforming empirical models, which achieved R² values of 0.90 and 0.89 for UP-CO and UP-COUNTER modes, respectively.

Flow enhancement produced by a pulsatile flow of shear-thinning fluids in circular and concentric annular tubes

Although the analysis of the flow enhancement of non-Newtonian fluids produced by pulsatile flows through tubes is common in the literature, the case of Carreau fluid has not been analyzed, which is the aim of this work. This study determines the flow enhancement caused by the pulsatile fluid flow through (a) a circular tube and (b) a concentric annular tube. We show that the flow rate enhancement of the shear-thinning fluid is controlled by the Carreau number Cu, the Womersley number Wo, the fluid power-law index n, the ratio between the outer and inner radii κ, a parameter β that represents the ratio between the infinite and zero-shear viscosities, and the amplitude of the oscillatory signal ɛ. In both cases (a) and (b), a numerical solution of the start-up of the hydrodynamic is evaluated. With the aid of the velocity solution, the volumetric flow rate is determined under periodic conditions after the initial transient has vanished. Then, the fractional increase in the mean flow rate I due to the pulsatile pressure gradient is calculated. Furthermore, an asymptotic solution for small, intermediate, and very large values of the Carreau number is performed to provide physical insight into flow enhancement.

Mixing of inelastic non-Newtonian fluids with inlet swirl

In the present work, the tangential (swirl) velocity component is superimposed at the intake of a narrow fluidic cylindrical pipe to achieve the desired mixing of inelastic non-Newtonian fluids/solutes at the outlet. We discuss an analytical method for obtaining the swirl velocity profile, considering the nonlinear viscous effects for both shear-thinning and shear-thickening fluids, represented by the power-law model. We numerically solve the species transport equation, coupled with the analytically derived swirl velocity, using our in-house developed code for the concentration distribution in the flow field. The results show that the inlet swirl and an increase in the shear-thinning fluid property improve advection-dominated mixing. Additionally, higher Reynolds numbers significantly enhance advection's dominance, as more rotation leads to the generation of vortices, resulting in an engulfment flow (chaotic convection) based mixing. We demonstrate that considering the increase in the shear-thinning fluid property with swirl intake reduces the amount of mixing time required in the convective regime.

Biopharmaceutical modulatory effects of newly engineered bile acid-Tyloxapol nanogels for attenuation of cytotoxicity in auditory cells

This study presents novel thermoresponsive nanogels composed of chenodeoxycholic acid and Tyloxapol for potential inner ear drug delivery. The nanogels exhibit non-Newtonian, shear-thinning fluid behaviour and rapid gelation at body temperature. Biocompatibility studies were conducted on auditory and macrophage cell lines. Nanogels had a minimal impact on cellular viability, glycolysis, and mitochondrial respiration of auditory cells after 24 h of exposure. However, mitochondrial function analysis in macrophages revealed a significant decrease in oxidative phosphorylation and coupling efficiency after nanogel exposure, accompanied by increased proton leakage. Despite these metabolic disruptions, glycolysis remained unaffected. The Poloxamer matrix appears to be responsible for these effects, independent of the presence of bile acids or Tyloxapol. This study highlights the potential of bile acid-enriched nanogels in drug delivery, particularly their biocompatibility and injectability while acknowledging challenges related to mitochondrial dysfunction in immune cells. These findings suggest that thermoresponsive bile acid and Tyloxapol nanogels have the potential to be safe and effective drug delivery vehicles for inner ear applications.

Multiphase Viscoelastic Non‐Newtonian Fluid Simulation

AbstractWe propose an SPH‐based method for simulating viscoelastic non‐Newtonian fluids within a multiphase framework. For this, we use mixture models to handle component transport and conformation tensor methods to handle the fluid's viscoelastic stresses. In addition, we consider a bonding effects network to handle the impact of microscopic chemical bonds on phase transport. Our method supports the simulation of both steady‐state viscoelastic fluids and discontinuous shear behavior. Compared to previous work on single‐phase viscous non‐Newtonian fluids, our method can capture more complex behavior, including material mixing processes that generate non‐Newtonian fluids. We adopt a uniform set of variables to describe shear thinning, shear thickening, and ordinary Newtonian fluids while automatically calculating local rheology in inhomogeneous solutions. In addition, our method can simulate large viscosity ranges under explicit integration schemes, which typically requires implicit viscosity solvers under earlier single‐phase frameworks.

Study on the motion characteristics of Janus based on the squirmer model in the flow

The motion characteristics of Janus in the flow are studied numerically using the lattice Boltzmann method based on the squirmer model. The effects of velocity ratio J on the right and left hemisphere surface of Janus, particle Reynolds number Rep, flow Reynolds number Rec, initial orientation angle φ0 on Janus trajectory, and lateral equilibrium position yeq/H are analyzed. The results showed that, for the motion of Janus in stationary power-law fluids in a channel, Janus moves randomly in a small space in shear-thickening fluids when Rep is low and exhibits three motion modes at Rep = 5. The larger the J value, the easier it is for Janus to reach yeq/H. The higher the Rep, the closer the yeq/H is to the lower wall. In shear-thinning fluids, the motion of Janus exhibits significant randomness at Rep = 0.5 and 1, reaches the same yeq/H at Rep = 2 and 3, and tends toward yeq/H near the centerline and along the upper wall, respectively, at Rep = 4 and 5. For the motion of Janus particles in a channel flow of power-law fluids, in shear-thinning fluids, no matter what value J is, Janus reaches yeq/H on the centerline. The lower the Rep, the closer the yeq/H is to the wall. Two particles move toward yeq/H when Rep ≥ 1. The higher the Rep, the closer the yeq/H is to the centerline. The two particles will exhibit the upstream mode at Rep = 2. Two particles eventually reach yeq/H at different Rec. When φ0 > 0°, the two particles first eventually tend toward yeq/H = 0.2 and 0.8. When the value of φ0 is negative, the larger the absolute value of φ0 and higher the Rep, the more likely particles are to exhibit upstream mode.