Shear-thinning Liquids Research Articles

Entropy generation in Casson nanofluid flow over a lubricated wall in the presence of induced magnetic field and activation energy

ABSTRACT The research on entropy generation in a mechanical system is quite imperative owing to its immense applications in the production of advanced cooling devices and medical appliances. The basic need on this research is how to optimize the irreversibilities within the systems and channelize that energy towards the benefit. This study elucidates the entropy generation analysis of a Casson nanofluid near a stagnation point over a lubricated vertical wall. A thin film of shear-thinning liquid with power law index of 0.5 is employed on the wall to ensure the lubrication. The effect of induced magnetic field and the chemical reaction stimulated by the activation energy is also incorporated within the flow. The non-linear PDEs of the substantive problem along with the compatible interfacial and boundary conditions are reverted into ODEs with the aid of suitable similarity transformation, and then cracked numerically using the sixth-order Runge Kutta method assisted with Nachtsheim–Swigert shooting practice. One of the significant findings reveals that the fluid friction irreversibilities in the entropy generation are diminished with the magnetic parameter and the Casson parameter, whereas the thermal irreversibility predominates over the total entropy generation for the escalating values of the activation energy parameter.

Flow Properties o f Tannery Waste Liquor

Objective: A water treatment facility is to be erected nearby the industrial tanning complex, recently established East of Cairo, Egypt. This paper represents a contribution to studying the flow characteristics of the produced tannery waste effluents. A dried sample of tannery waste was chemically analyzed by X-ray fluorescence and its particle size distribution was determined. Next, rheological measurements were carried out on the waste slurry produced at temperatures ranging from 10°C to 40°C and three different solid concentrations, by weight: 20%, 25%, and 30%. The results showed that all waste suspensions under all conditions of solid content and temperature behaved as shear-thinning liquids. Flow indices of all suspensions generally tended to increase with temperature and solid concentration. Activation energies for viscosity were correlated to an increase in solid concentration and showed a decreasing pattern. All samples exhibited a thixotropic character that decreased with increased temperature and dilution of the suspension. The maximum pressure drops per unit length of a pipeline used to transport the waste suspension to the treatment unit was evaluated and found to increase with solid concentration and decrease with increasing temperature. Keywords: Rheology, Tannery waste slurry, Solid content, Temperature

Flow transitions and effective properties in multiphase Taylor–Couette flow

The properties of multiphase flows are challenging to measure, and yet effective properties are fundamental to modelling and predicting flow behaviour. The current study is motivated by rheometric measurements of a gas-fluidized bed using a coaxial rheometer in which the fluidization rate and the rotational speed can be varied independently. The measured torque displays a range of rheological states: quasistatic, dense granular flow behaviour at low fluidization rates and low-to-moderate shear rates; turbulent toroidal-vortex flow at high shear rates and moderate-to-high fluidization rates; and viscous-like behaviour with rate-dependent torque at high shear rates and low fluidization or at low shear rates and high fluidization. To understand the solid-like to fluid-like transitions, additional experiments were performed in the same rheometer using single-phase liquid and liquid–solid suspensions. The fluidized bed experiments are modelled as a Bingham plastic for low fluidization rates, and as a shear-thinning Carreau liquid at high fluidization rates. The suspensions are modelled using the Krieger–Dougherty effective viscosity. The results demonstrate that, by using the effective properties, the inverse Bingham number marks the transition from solid-like to viscous-flow behaviour; a modified gap Reynolds number based on the thickness of the shear layer specifies the transition from solid-like to turbulent vortical flow; and a gap Reynolds number distinguishes viscous behaviour from turbulent vortical flow. The results further demonstrate that these different multiphase flows undergo analogous flow transitions at similar Bingham or Reynolds numbers and the corresponding dimensionless torques show comparable scaling in response to annular shear.

Fluconazole Microemulsions: Preparation, Statistical Optimization by Two-Level Factorial Design, and Physicochemical Evaluation

Background:: Candida albicans is the yeast that causes the fungal infection known as candidiasis. One of the standard methods for treating candida is the application of fluconazole. The low solubility of fluconazole in aqueous media is a big problem in the use of this agent. Novel drug delivery systems, such as microemulsions, could be applied to solve this problem. The main aim of this study was to perform statistical optimization of the formulation and physicochemical characterization of fluconazole microemulsion. Methods:: Optimization of the microemulsion formulation was done by using experimental design software, and then fluconazole was loaded onto the best formulation at a concentration of 1 % w/w. The physiochemistry of the microemulsion formulation was assessed by pH measurement, rheology measurement, simultaneous thermal analysis, and Scanning Electron Microscopy (SEM). Results:: The two-level fractional factorial design application demonstrated the optimum formulation to consist of surfactant, co-surfactant, oil content, and water, comprising 58%, 27%, 10%, and 5% of the formulation, respectively. Desirable thermal mass was observed up to 150°C. The formulation was a non-Newtonian shear-thinning liquid in terms of viscosity, with a reported pH between 6.5-7. Conclusion:: Considerably stable, high-quality microemulsion formulations containing fluconazole are presented, which are applicable for antifungal skin candidiasis treatment in clinical trials.

Dip coating of shear-thinning particulate suspensions.

Dip coating a planar substrate with a suspension of particles in a shear-thinning liquid will entrain particles in the liquid film, facilitating filtration and sorting of particles. Experiments were performed for both monodisperse and bidisperse particle suspensions of shear-thinning Xanthan Gum solutions. Particle entrainment occurs when the coating thickness at the stagnation point of the thin film flow is larger than the particle diameter. A model is developed to predict the entrainment criteria using lubrication theory applied to an Ostwald power-law fluid which yields a modified Landau-Levich-Derjaguin (LLD) law governing the coating film thickness that depends upon a properly defined capillary number Ca. The critical withdrawal velocity for particle entrainment depends upon the particle size and fluid rheology through a relationship between Ca and the bond number Bo, which agrees well with our model predictions and prior experimental results of A. Sauret et al. Phys. Rev. Fluids, 2019, 4, 054303 for the limiting case of Newtonian suspensions. Single particle entrainment and particle clustering is observed for monodisperse suspensions, which depends on Ca and the particle volume fraction ϕ. In bidisperse suspensions, particle sorting can occur whereby only the smaller particles are entrained in the film over an active filtration range of Ca and Bo, which also agrees well with our model predictions.

Analysis of natural planar jump in power-law liquids—A generalized “shallow flow” approach

The study presents a generalized “shallow flow” analysis of natural planar hydraulic jump in power-law liquids. It is based on self-similar velocity profile defined as function of flow behavior index, n, and shows significant improvement over the previous analysis which assumed a quadratic velocity profile and failed for n < 0.5. Thus, the study enables a deeper understanding of the influence of n for shear thinning vis-a-vis shear thickening liquids and emphasizes that the power-law description is adequate for highly shear thinning liquids if the flow parameters are valid over the range of interest.

Analysis of particle size distribution and electro-kinetics of submicron particles in shear-thinning liquids

Analysis of particle size distribution and electro-kinetics of submicron particles in shear-thinning liquids

Rheological behaviour of Carreau liquid past a wedge surface with binary chemical reaction

The time-dependent stream of rheological Carreau nanoliquid carrying microbes through a rotating lodge through porous media in addition to irregular heat source or sink characteristics is the subject of this article. Due to the fact that the Carreau liquid can reveal the rheology of liquids with short-chain suspended particles, liquid crystals, surfactants, and human and animal blood, it is helpful to depict a range of physical problems. The influence of infinite shear rate thickness is combined to provide the mathematical formulation. Both the static and moving physical features are covered in great depth. Prior to using the finite element technique to solve revised equations numerically, pertinent similarity transformations are used to get equations in their dimensionless form. According to the findings of our study, the temperature and the thickness of the thermal boundary layer that corresponds to that temperature both improves the function that the thermal radiation factor plays in shear thickening and thinning liquids. Additionally, a moving wedge has a greater velocity than a static wedge. The thermophoresis factor's rising function is the concentration field. Furthermore, by increasing the Piclet number's magnitudes, the profile of microbes is diminished.

Flow of shear-thinning liquids in channels with superhydrophobic surfaces

Flow of shear-thinning liquids in channels with superhydrophobic surfaces

A novel correlation of bubble aspect ratio through analysis of gas/shear-thinning liquid two-phase flow in a bubble column

Gas/shear-thinning liquid two-phase flow is often involved in the petroleum, chemical, and food industries, with the bubble shape playing a vital role in the theoretical analysis and numerical simulation of the flow. This study investigates the bubble shape variation in a shear-thinning liquid (carboxymethyl cellulose sodium solution) under the bubble swarm condition using high-speed imaging and a bubble recognition algorithm. The results show that trailing bubbles accelerate as they rise along the flow path of leading bubbles. During acceleration, the bubbles are subjected to lateral forces that cause them to deform from an oblate spheroid to a prolate spheroid. The effect of the shear-thinning property is enhanced owing to the increased superficial gas velocity and solution concentration, leading to an increase in the number of prolate spherical bubbles. Considering the significant difference in energy transfer in the flow fields around oblate and prolate particles, new aspect ratio correlations were developed for the two shapes based on the correlations of Re·Eo derived from the Newtonian fluid case. Compared to the previous correlation developed by assuming that the two shapes have the same aspect ratio, the proposed method significantly improves the prediction accuracy of the bubble aspect ratio for a shear-thinning fluid case.

Dynamics of a Rising Taylor Drop in a Stagnant Shear-Thinning Liquid

Dynamics of a Rising Taylor Drop in a Stagnant Shear-Thinning Liquid

Numerical study of an individual bubble rise in a shear-thinning viscoelastic liquid based on a combination of the Carreau and FENE-CR models

The rise behavior of a single bubble in shear-thinning viscoelastic liquids was investigated using a volume of fluid method based on a combination of the Carreau and FENE-CR models. The effects of Weissenberg number (Wi), polymer stretching parameter (L), Eötvös number (Eo) and rheological index (n) on bubble shape and typical characteristics of flow fields were investigated in detail. The results show that bubble tail becomes pointed under the influence of elastic stress, and the bubble becomes longer along the longitudinal direction with a decrease in Wi. When the magnitude of n is relatively large, the bubble appears as an ellipsoidal shape with a cusp; however, when the magnitude of n is relatively small, bubble shape is closer to a disc, and the tip of bubble tail disappears. Wi affects the magnitude of elastic tensile stress, and affects the action rang of the large tensile stress. With an increase in Wi, the action rang of elastic tensile stress develops from both sides of the bubble towards regions below bubble tail. The appearance of negative wake is not directly related to bubble shape, but to the relaxation of elastic stres.

Bioconvective Carreau nanofluid flow with magnetic dipole, viscous, and ohmic dissipation effects subject to Arrhenius activation energy

This article mainly involves a novel study of electric as well as magnetic field effects in the presence of magnetic dipole on Carreau nanofluid flow filled by gyrotactic microorganisms over a stretched sheet under the influences of nonlinear thermal radiation, activation energy, chemical reaction, viscous and ohmic dissipation. Bioconvection becomes an important area of research when magneto nanoparticles (ferrofluid) suspended with motile microorganisms, as collectively they have wide range of applications. The suspension of nanoparticles in microorganisms are found beneficial in nanofluid stability. A class of appropriate similarity functions is utilized to convert steady nonlinear PDEs into a set of ODEs and then computed numerically by applying two distinct techniques bvp4c in MATLAB and Maple ′ dsolve ′ command. For limited cases, we have also compared our outcomes with already published work and found in good agreement. The impact of various controlling parameters active in the velocity, temperature, concentration, and density profiles are observed and presented extensively. Additionally, for engineering aspects, the numerical computations as well as graphical presentations for surface drag force, Nusselt/Sherwood numbers(the wall heat and mass fluxes) and density of motile organisms are also performed for both types of fluids (i.e., n = 0.5 and n = 1.5). All the four profiles, i.e., density of motile microorganisms ( Ψ ( η ) ) concentration ( ϕ ( η ) ), thermal ( θ ( η ) ), and velocity ( f ′ ( η ) ) vary for shear thinning and thickening cases. The concentration profile decelerates for rising Chemical reaction rate and fitted rate constant but rises by increasing the activation energy. Outcomes of Skin friction coefficient and heat transfer rate are higher for shear thickening liquid as compared with shear thinning liquid.

Natural convective non-Newtonian nanofluid flow in a wavy-shaped enclosure with a heated elliptic obstacle

A numerical investigation has been carried out in a wavy-shaped enclosure with an elliptical inner cylinder to find out the effect of an inclined magnetic field and a non-Newtonian nanofluid on fluid flow and heat transfer. Here, the dynamic viscosity and thermal conductivity of the nanofluid are also taken into account. These properties change with the temperature and nanoparticle volume fraction. The vertical walls of the enclosure are modeled through complex wavy geometries and are kept at a constant cold temperature. The inner elliptical cylinder is deemed to be heated and the horizontal walls are considered adiabatic. Temperature difference between the wavy walls and the hot cylinder leads to natural convective circulation flow inside the enclosure. The dimensionless set of the governing equations and associated boundary conditions are numerically simulated using the COMSOL Multiphysics software, which is based on finite element methods. Numerical analysis has been scrutinized for varying Rayleigh number (Ra), Hartmann number (Ha), magnetic field inclination angle (γ), rotation angle of the inner cylinder (ω), power-law index (n), and nanoparticle volume fraction (ϕ). The findings demonstrate that the solid volumetric concentration of nanoparticles diminishes the fluid movement at greater values of φ. The heat transfer rate decreases for larger nanoparticle volume fractions. The flow strength increases with an increasing Rayleigh number resulting in a best possible heat transfer. A higher Hartmann number diminishes the fluid flow but converse behavior is exhibited for magnetic field inclination angle (γ). The average Nusselt number (Nuavg) values are maximum for γ = 90°. The power-law index plays a significant role on the heat transfer rate, and results show that the shear-thinning liquid augments the average Nusselt number.

Bead-on-fibre morphology in shear-thinning flow

Thin-film flow down a fibre exhibits rich dynamics and is relevant to applications such as desalination, fibre coating and fog harvesting. These flows are subject to instabilities that result in dynamic bead-on-fibre patterns. We perform an experimental study of shear-thinning flow down fibres using 20 different xanthan gum solutions as our working liquid. The bead-on-fibre morphology can be oriented either symmetrically or asymmetrically on the fibre, and this depends upon the surface tension, fibre diameter and liquid rheology, as defined by the Ostwald power-law index. For highly shear-thinning liquids, it is possible for the pattern to be complex and exhibit simultaneously both asymmetric large beads and symmetric small beads in the isolated and convective flow regimes. We quantify the transition between flow regimes and bead dynamics for the asymmetric morphology, and compare with Newtonian flow, as it depends upon the experimental parameters. Finally, the dimensionless bead frequency is shown to scale with the Bond number for all of our experimental data (symmetric and asymmetric).

Development of a generalized Richards equation for predicting spontaneous imbibition of highly shear-thinning liquids in gas recovery applications

A new generalized Richards equation (GRE) valid for highly shear-thinning liquids obeying the power-law model is developed using the concept of the effective viscosity. The mathematical model developed this way is validated against experimental data reported recently for one-dimensional spontaneous imbibition of two pusher liquids by a tight sandstone. The GRE model was then used for evaluating the applicability of shear-thinning liquids for enhanced gas recovery. For a homogenous tight sandstone, it is shown that shear-thinning can dramatically shorten the time needed for the gas recovery to reach equilibrium. Based on the obtained numerical results, the mass of the gas recovered using spontaneous imbibition is increased if use is made of highly shear-thinning liquids. At prolonged times, however, it is predicted that gas recovery might slightly drop below its Newtonian counterpart even for highly shear-thinning fluids. The effect was attributed to the fact that, in spontaneous imbibition, the viscosity of power-law fluids increases with time and can eventually become larger than its Newtonian counterpart. For a two-layered non-homogeneous system, numerical results suggest that depending on the microstructure of the two layers, the liquid mass uptake can be smaller than that of the homogenous case. It is predicted that if the liquid is sufficiently shear-thinning, gas recovery can reach levels much above the homogeneous case.

Influence of variable thermal conductivity and diffusion coefficients in the flow of Jeffrey fluid past a lubricated surface with homogeneous-heterogeneous reactions: A finite-difference approximations

The key function of lubricants is to reduce the friction, wear, and heat between the parts that are in contact with each other. The main applications of the lubricants are to control temperature, and reduction in wear and corrosion of the machinery. Keeping in mind the importance of lubrication and its applications in varied machines. The goal of this research is to inspect the heat transmission impact in the magnetohydrodynamic flow of Jeffrey liquid near a stagnation point through a lubricated surface. Lubrication is accomplished by a shear-thinning liquid. The velocity, continuity, and shear stress, amalgamated with power-law fluids, are used to develop interfacial conditions. The exclusivity of the anticipated model is the inclusion of variable thermal conductivity and diffusion coefficients in the existence of homogeneous-heterogeneous reactions. Using the Keller–Box finite-difference approximation approach, the numerical results are accomplished. The outcomes are portrayed and tabulated in the form of diagrams and tables, respectively. It is witnessed that a greater magnetic field affects the fluid flow velocity and the drag force coefficient. Moreover, it is also inferred that the heat transfer rate dwindled for the greater thermal conductivity parameter. Authentication of the presented model is also part of this investigation.

Bi-stability Bifurcation in Convection Double Diffusion Through a Shallow Horizontal Layer Saturated with a Complex Fluid

The onset of non-linear convection in a porous layer saturated by a shear-thinning liquid is studied. The Carreau-Yasuda model is utilized for modeling the behavior of the working medium. Constant fluxes of heat and mass are defined on the horizontal surfaces of the cavity, while the vertical sides are assumed adiabatic. The parallel flow approximation and the finite difference approach are used to conduct the investigation analytically and numerically, respectively. The linear stability inspection of the convective and diffusive circumstances is carried out by taking into account an infinitesimal perturbation. The theory of linear stability is employed to determine the critical Rayleigh number for the motion from the rest state, Hopf bifurcation, and the transition from the stationary to oscillatory convection. Overall, the Carreau-Yasuda rheological parameters have a significant impact on the thresholds of convection. The most interesting findings of this study is highlighting the existence of a bi-stability phenomenon, i.e., the existence of two steady-state solutions, which was not observed before in non-Newtonian fluids convection.

Tribology and rheology of water-in-water emulsions stabilized by whey protein microgels

This study aimed to investigate the microstructural, tribological and rheological properties of water-in-water (W/W) emulsion droplets with or without stabilization by proteinaceous microgel particles. The W/W emulsions were prepared from mixtures of gelatinized corn starch (GS) and κ -carrageenan ( κ C) in the two-phase regime and when particle-stabilized whey protein microgel particles (WPM) were used. The W/W emulsions were shear thinning liquids. The viscosity values of the emulsions were higher than the corresponding weight average values, calculated on individual samples irrespective of shear rates. Tribological results revealed that the frictional properties of W/W emulsions formed from 1.0 wt% GS + 0.1 w% κ C were dominated by the κ C properties alone in the mixed and hydrodynamic regimes, even though the starch played an essential role in decreasing friction coefficient ( μ ) in the boundary regime. Unlike the corresponding solutions of GS and κ C, W/W emulsions containing higher concentrations of the biopolymers (3.0 wt% starch + 0.3 wt% κ C) decreased μ in the mixed and boundary regimes, probably due to water droplets becoming entrained and forming a hydration film in the contact region. In the case of W/W emulsions containing WPM, confocal and cryo-scanning electron microscopy confirmed the presence of WPM at the interface and hence a Pickering-like stabilization. The WPM-stabilized W/W emulsions showed higher apparent viscosity (than those without WPM) and lower μ in the boundary and mixed regimes. Stabilization of W/W emulsions via microgel particles therefore seems to be a useful tool to improve the lubrication performance of such systems. • Water-in-water (W/W) emulsion was designed using starch (GS) and κ -carrageenan ( κ C). • Whey protein microgel (WPM) was used to stabilize W/W emulsion droplets. • WPM at the W–W interface was observed using microscopy across length scales. • The viscosity of W/W droplets was enhanced in presence of WPM. • WPM improved lubricity of W/W droplets in the boundary and mixed regimes.

Numerical Study of the Coalescence and Mixing of Drops of Different Polymeric Materials.

In this study, we employ direct numerical simulation (DNS) to investigate the solutal hydrodynamics dictating the three-dimensional coalescence of microscopic, identical-sized sessile drops of different but miscible shear-thinning polymeric liquids (namely, PVAc or polyvinyl acetate and PMMA or polymethylmethacrylate), with the drops being in partially wetted configuration. Despite the ubiquitousness of the interaction of different dissimilar droplets in a variety of engineering problems ranging from additive manufacturing to understanding the behavior of photonic crystals, coalescence of drops composed of different polymeric and non-Newtonian materials has not been significantly explored. Interaction of such dissimilar droplets often involves simultaneous drop spreading, coalescence, and mixing. The mixing dynamics of the dissimilar drops are governed by interphase diffusion, the residual kinetic energy of the drops stemming from the fact that coalescence starts before the spreading of the drops have been completed, and the solutal Marangoni convection. We provide the three-dimensional velocity fields and velocity vectors inside the completely miscible, dissimilar coalescing droplets. Our simulations explicate the relative influence of these different effects in determining the flow field at different locations and at different time instances and the consequent mixing behavior inside the interacting drops. We also show the non-monotonic (in terms of the direction of migration) propagation of the mixing front of the miscible coalescing drops over time. We also establish that the overall mixing (on either side of the mixing front) speeds up as the Marangoni effects dictate the mixing. We anticipate that our study will provide an important foundation for studying miscible multi-material liquid systems, which will be crucial for applications such as inkjet or aerosol jet printing, lab-on-a-chip, polymer processing, etc.