Shear Thinning Effect Research Articles

Preparation and control mechanism of nano-phase change emulsion with high thermal conductivity and low supercooling for thermal energy storage

In order to investigate the control mechanism of composite phase change materials (PCM), a series of composite nano-phase change emulsion (NPCE) were prepared in this paper with high thermal conductivity, high heat storage and low supercooling using hexadecane, octadecane, hexadecanol, octadecanol and various metal nano-particles. Through the control mechanism, it is expected to adjust the phase transition range of NPCE to a desirable range. The NPCEs were characterized by particle size analyser, cryogenic transmission electron microscope (Cryo TEM), differential scanning calorimeter (DSC), thermal conductivity meter and rheometer. The results showed that the NPCEs was successfully prepared with uniform dispersion, great stability, low viscosity and narrow particle size distribution. DSC results showed that the latent heat of NPCE with 20 wt. % hexadecane was 55.86 kJ/kg. The supercooling degree of prepared NPCEs using 1.25 wt. % of hybrid nucleating agents was reduced by 81%. Metal oxides effectively improved the thermal conductivity of NPCEs. The thermal conductivity of the NPCEs with 1wt. % nano Al2O3 was 0.70 W/(m ⋅ K), which was increased by 21%. The viscosity of the NPCEs increased with the increase of metal oxide concentrations and decreased with the increase of temperature. Importantly the NPCEs presented a shear thinning effect and can be considered as Newtonian fluid after shear rate of 2 s−1, which had great potential in the thermal energy storage system.

Influence of lactose on the rheological properties of reconstituted casein micelles concentrates

Despite increasing demand for lactose-reduced and lactose-free dairy products, little is known about the influence of lactose on the flow behaviour of casein micelles. Therefore, we investigated the rheological influence of lactose on reconstituted casein micelles over a wide concentration range of casein and lactose (wCasein = 2.9–13.4%, w/w; wLactose = 0–15%, w/w). Analysis of the relative viscosity curves with the Ostwald-de Waele model shows that the flow consistency index and the flow behaviour index as well as thixotropic effects depend on the lactose-casein mass ratio. In the range of small ratios, the relative viscosity hardly changes with increasing lactose, while at a mass ratio close to 1, the shear thinning effect changes strongly leading to maximum values of flow consistency and flow behaviour index n. With excess lactose, the shear thinning effect decreases again, which we explain with a decreasing voluminosity of the casein micelles.

Analytical study of isothermal blade coating process using Rabinowitsch fluid model

Blade coating process is widely applied in the industry for its practical applications in photographic films, paint industries, and magnetic storage devices. Also for manufacturing newspaper, metal coating, electronic circuit boards, and textile fibers. The blade coating process passes a fluid into the gap between the moving substrate and blade. This study uses the Rabinowitsch model which represents the Newtonian, shear thickening, and shear thinning effects by changing a non-linear parameter. Lubrication theory is used to simplify the dimensionless governing expressions. Then perturbation technique is used up to second order to solve the resultant system and validated by the numerical shooting technique. The graphs and tables present how the non-linear parameter affects the dimensionless velocity, pressure profile, coating thickness, and blade load. The non-linear model parameter proves to be the controlling parameter for the coating thickness, blade load, and pressure distribution, helping in determining the coating efficiency and improving the substrate life. This paper provides the theoretical framework for engineers to be applied in many industrial applications. In future, further validation of results can be done through experiments.

Numerical analysis of thermophoresis of charged colloidal particles in non-Newtonian concentrated electrolyte solutions.

Thermophoresis of colloidal particles in aqueous media is more frequently applied in biomedical analysis with processed fluids as biofluids. In this work, a numerical analysis of the thermophoresis of charged colloidal particles in non-Newtonian concentrated electrolyte solutions is presented. In a particle-fixed reference frame, the flow field of non-Newtonian fluids has been governed by the Cauchy momentum equation and the continuity equation, with the dynamic viscosity following the power-law fluid model. The numerical simulations reveal that the shear-thinning effect of pseudoplastic fluids is advantageous to the thermophoresis, and the shear-thickening effect of dilatant fluids slows down the thermophoresis. Both the shear-thinning and shear-thickening effects of non-Newtonian fluids on a thermodiffusion coefficient are pronounced for the case when the thickness of electric double layer (EDL) surrounding a particle is moderate or thin. Finally, the reciprocal of the dynamic velocity at the particle surface is calculated to approximately estimate the thermophoretic behavior of a charged particle with moderate or thin EDL thickness.

An Experimental Investigation on the Thermo-Rheological Behaviors of Lactic Acid-Based Natural Deep Eutectic Solvents.

The rheological studies of Lactic Acid (LA)-based Natural Deep Eutectic Solvents (NADES) are provided in the present investigation. Those mechanisms were also studied in which three distinct Hydrogen Bond Acceptors (HBAs) of Choline Chloride (ChCl), Betaine (Be), and β-Alanine (β-Al), after being added to a specific Hydrogen Bond Donor (HBD) at a predefined mole-to-mole ratio of 1:1, affected the rheological properties of the prepared NADES. The alterations in the rheology-related characteristics in association with the mechanical and physical properties indicate the tolerance of the material under various operational conditions in the field and show their potential utilization as environmentally suitable and feasible solvents for industrial applications. In the present research, the viscoelastic properties of the three samples of NADES were assessed along with their shear flow properties. The backward and forward temperature change in the Apparent Viscosity (AV) pattern related to the NADES system was described by a rheogram. Furthermore, the density was determined and compared with the AV while considering the temperature-related factor. On a further note, the viscoelastic characteristics were utilized in describing and investigating the network disturbance on the level of the microstructure of NADES upon frequency sweep. A series of experiments were carried out using Thermogravimetry Analysis (TGA) to investigate the thermo-physical properties to optimize them. The rheological properties of shear flow measurements were analyzed using the Bingham model that is best suited for the AV developed with the shear rate with the dynamic yield stress of three systems. The Bingham model was used to determine the lowest stress necessary to disturb the network structure and commence the flow of LA-based NADES. Overall, the viscoelastic behavior of the LA-based NADES revealed the dissimilarity between their strength and viscosity. In addition, shear flow investigations demonstrated that LA-based NADES systems exhibit non-Newtonian properties and substantial shear-thinning effects equivalent to those of alternative IL sorbents. Assessing the rheological properties of LA-based NADES is crucial for a better understanding the key challenges associated with high viscosity. Defining the transport yield stress requirements for NADES systems under different conditions benefits their future development and potentially opens the door to more challenging applications.

Printing and electromagnetic characteristics of 3D printing frequency selective surface using graphene

• Graphene modifies silver ink from shear thinning effect to fluid model behavior. • Cross model ink presents better printing precision than Carreau-Yasuda ink. • High static viscosity contributes to high printing precision in direct ink writing. • Connected graphene sheets contribute to highly electromagnetic performance matching. The study of Frequency Selective Surface (FSS) by Direct ink writing (DIW) has attracted much attention due to the convenience and effectiveness of 3D printing technology. However, the limited printing precision of DIW has heavily restricted its applications as the electromagnetic performance is highly sensitive to it, especially the precision at the microscale. Herein, the ultra-high printing precision of FSS was achieved through DIW by the uniformly dispersed graphene sheets to deeply modify the rheological behavior and the steric hindrance effect. Thus, the highly precision of the printed filament width as thin as 67 μm with a space of only 42 μm were achieved, which is difficult for conventional DIW, and no structural distortion is found after 3D printing, no matter it was 2D printed on a flat surface or the sharply skewed hook face, or even 3D printed to architectural structures. According to the highly improved precision, the electromagnetic performance matching between the designed model and the printed physical FSS device was perfectly achieved, reducing the center frequency error less than 0.3 GHz, and the transmission coefficient error less than 0.046. Our work promises an effective and easy preparation of high-quality FSS from the aid of graphene.

Theoretical study of transport of MHD peristaltic flow of fluid under the impact of viscous dissipation

ABSTRACT This article studies irreversibility analysis in the peristaltic transport of a non-Newtonian fluid. Jeffrey fluid is treated as the blood transport through a flexible artery/vessel. A peristaltic wave travels on the porous opposite wall of the inclined channel under the magnetic environment. Heating effects cause the shear thinning in the viscosity of the base liquid, transferring tiny particles. The efficiency of peristalsis is improved by reducing the irreversibility factor by means of entropy generation. The perturbation technique is applied to understand the nonlinear flow dynamics of heat and mass transfer with Jeffrey fluid with the help of convective boundary conditions. Comparative analysis is carried out with the available literature for the limiting case and found to have complete coherence. A detailed parametric study is carried out to comprehend the contribution of significant parameters which reveals that magnetic fields and slippery walls induce a resistive force on the nanoflow. The motion of the base liquid expedites subject to variation in Darcy number and shear-thinning effects. The energy is contributed to the nanofluid system in response to the Brinkman number. More, the number density of nanospecies reduces in the region of higher concentration subject to the Soret number and Schmidt number, respectively.

Mechanical, thermal, rheological assessment of polyamide-6 reinforced composites by addition of lamellar zirconium phosphate

The improvement of properties has been pursued through the addition of an immense variety of fillers in polymers. In this work we studied the effect of lamellar zirconium phosphate (ZrP) on the physico-mechanical properties of polyamide-6 (PA-6). The ZrP was synthesized and incorporated into PA-6 matrix at 1, 2 and 3 wt.%. Structural, thermal, relaxometric, tensile, melt flow and rheologic characteristics were assessed. Thermogravimetry indicated a low influence of the filler on thermal stability. The deconvolution of the melting peaks indicated transformation of the PA-6 α to γ phase and increase in crystallinity degree. Sample with 1 wt.% of ZrP showed an additional peak at higher relaxation time indicating restriction of polymer molecular mobility. By infrared, amine and carbonyl indices evaluation suggested ZrP interfered on the PA-6 hydrogen bonds. The elastic modulus increased slightly for all composition. Melt flow rate decreased with the amount of ZrP. The composite with 1 wt.% of ZrP exhibited the highest storage modulus and shear thinning effect noticed in the complex viscosity.

Shear thinning effect on liquid foam distribution in heterogeneously constricted in vitro airway models

Treating diseased lung regions using inhalation therapy is often limited due to airway constrictions and obstructions that significantly reduce aerosol deposition efficiency. Intratracheal administration of liquid foams is a potential strategy to improve pulmonary drug delivery to these affected airway regions. Here, we use effective viscosity measurements and in vitro small-airway models to examine how shear thinning effects in the foam can be leveraged to achieve a more uniform distribution within heterogeneously constricted or partially obstructed airways. We find that a foamed solution based on the formulation of Tacholiquin® exhibited a 5.75-fold decrease in effective viscosity across a shear rate range spanning 970 to 14′500 s−1. As a result, the foam volume penetrating through the constricted airway models was up to 154% higher compared with air, depending on the cross-sectional area of the constrictions. This proof-of-concept study represents a first step towards understanding the transport mechanics of liquid foams towards future pulmonary delivery applications.

Ag metal interconnect wires formed by pseudoplastic nanoparticles fluid imprinting lithography with microwave assistant sintering

Nanoimprint technology has the advantages of low cost, high precision, high fidelity and high yield. The metal nanoparticle fluid is non-Newtonian fluid, which is used as the imprint transfer medium to realize high fidelity of pattern because of its shear thinning effect. In order to functionalize the metal nanoparticles microstructure, the subsequent sintering step is required to form a metal interconnect wire. Metal interconnect wire with fewer grain boundaries and fewer holes have excellent mechanical and electronic properties. In this paper, the pseudoplastic metal nanoparticle fluid was formed by Ag nanoparticle and precursor solution, and then the thermal diffusion process was completed by microwave sintering after interconnects were embossed. The influence of microwave and thermal atmosphere on the microstructure and performance of Ag Interconnect wires was analyzed and discussed, and the Ag Interconnect wires performance was determined under the influence of time and temperature parameters. In our experiments, the interconnects after microwave sintering can achieve 39% of the conductivity of bulk silver. The microwave sintering module might be integrated as the heat treatment module of the metal micro/nano pattern directly imprint lithography.

Droplet deformation and breakup in shear-thinning viscoelastic fluid under simple shear flow

A three-dimensional lattice Boltzmann method, which couples the color-gradient model for two-phase fluid dynamics with a lattice diffusion-advection scheme for the elastic stress tensor, is developed to study the deformation and breakup of a Newtonian droplet in the Giesekus fluid matrix under simple shear flow. This method is first validated by the simulation of the single-phase Giesekus fluid in a steady shear flow and the droplet deformation in two different viscoelastic fluid systems. It is then used to investigate the effect of Deborah number De, mobility parameter α, and solvent viscosity ratio β on steady-state droplet deformation. We find for 0.025<α<0.5 that as De increases, the steady-state droplet deformation decreases until eventually approaching the one in the pure Newtonian case with the viscosity ratio of 1/β, which is attributed to the strong shear-thinning effect at high De. While for lower α, the droplet deformation exhibits a complex nonmonotonic variation with De. Under constant De, the droplet deformation decreases monotonically with α but increases with β. Force analysis shows that De modifies the droplet deformation by altering the normal viscous and elastic stresses at both poles and equators of the droplet, while α mainly alters the normal stresses at the poles. Finally, we explore the roles of De and α on the critical capillary number Cacr of the droplet breakup. By establishing both Ca–De and Ca–α phase diagrams, we find that the critical capillary number increases with De or α except that a plateau critical capillary number is observed in Ca–De phase diagram.

Numerical investigation of shear-thinning and viscoelastic binary droplet collision

In this work we present a 2D numerical study of the binary collision of viscoelastic drops under surface tension effects. The governing equations for incompressible fluids with free surface are completed with constitutive equations that represent three models for non-Newtonian fluids. We analyze a viscous shear-thinning Carreau–Yasuda (CY) equation and the viscoelastic constitutive models of Oldroyd-B and Phan–Thien–Tanner (PTT). From a computational point of view, the 2D free surface dynamic is handled using the Front-Tracking representation with marker particles, combined with the Marker-And-Cell (MAC) method. In order to discretize the equations, we employ a finite differences scheme. We provide maps of outcomes associated with the categories of Bouncing , Coalescence , and Separation as functions of the dimensionless numbers that govern the problem. In addition to the traditional space defined by the Weber and the impact factor, associated with the collision angle, commonly adopted in Newtonian studies, we explore the power-law index of the CY model, the Weissenberg number in the viscoelastic models, and the extensibility parameter in the PTT model. The transient interface dynamics of the problem is illustrated in a variety of cases. For non-bouncing scenarios, the results show that surface tension and elasticity act to maintain the integrity of the merged drop and avoid Separation . On the other hand, shear-thinning effects induce the Separation outcome. Hence, in the PTT model there are opposite trends associated with elasticity and shear-thinning, what can lead to non-monotonic responses. • Numerical simulations of binary droplets undergoing off-center collisions. • Viscoelastic effects on different post-impact outcomes. • Maps of outcomes associated with the categories of Bouncing, Coalescence , and Separation .

Surfactant effects on microfluidic extensional flow of water and polymer solutions

Surfactants are often added to particle suspensions in the flow of Newtonian or non-Newtonian fluids for the purpose of reducing particle-particle aggregation and particle-wall adhesion. However, the impact on the flow behavior of such surfactant additions is often overlooked. We experimentally investigate the effect of the addition of a frequently used neutral surfactant, Tween 20, at the concentration pertaining to microfluidic applications on the entry flow of water and three common polymer solutions through a planar cavity microchannel. We find that the addition of Tween 20 has no significant influence on the shear viscosity or extensional flow of Newtonian water and Boger polyethylene oxide solution. However, such a surfactant addition reduces both the shear viscosity and shear-thinning behavior of xanthan gum and polyacrylamide solutions that each exhibit a strong shear-thinning effect. It also stabilizes the cavity flow and delays the onset of flow instability in both cases. The findings of this work can directly benefit microfluidic applications of particle and cell manipulation in Newtonian and non-Newtonian fluids.

Melt Conveying in Single-Screw Extruders: Modeling and Simulation.

Numerous analyses have modeled the flow of polymer melts in the melt-conveying zones of single-screw extruders. While initial studies mainly provided exact analytical results for combined drag and pressure flows of Newtonian fluids, more recently developed, numerical methods seek to deepen the understanding of more realistic flow situations that include shear-thinning and non-isothermal effects. With the advent of more powerful computers, considerable progress has been made in the modeling and simulation of polymer melt flows in single-screw extruders. This work reviews the historical developments from a methodological point of view, including (1) exact analytical, (2) numerical, and (3) approximate methods. Special attention is paid to the mathematical models used in each case, including both governing flow equations and boundary conditions. In addition, the literature on leakage flow and curved-channel systems is revisited.

Comparison of the Effect of Hydrostatic and Dynamic High Pressure Processing on the Enzymatic Activity and Physicochemical Quality Attributes of 'Ataulfo' Mango Nectar.

The effects of hydrostatic (HHP) and dynamic (HPH) high-pressure treatments on the activity of pectin methylesterase (PME) and polyphenol oxidase (PPO) as well as the physicochemical quality attributes of ‘Ataulfo’ mango nectar were assessed. HHP reduced PME relative activity by 28% at 100 MPa for 5 min but increased PPO activity almost five-fold. Contrarily, HPH did not affect PME activity, but PPO was effectively reduced to 10% of residual activity at 300 MPa and at three passes. Color parameters (CIEL*a*b*), °hue, and chroma were differently affected by each type of high-pressure processing technology. The viscosity and fluid behavior were not affected by HHP, however, HPH changed the apparent viscosity at low dynamic pressure levels (100 MPa with one and three passes). The viscosity decreased at high shear rates in nectar samples, showing a shear-thinning effect. The results highlight how different effects can be achieved with each high-pressure technology; thus, selecting the most appropriate system for processing and preserving liquid foods like fruit beverages is recommended.

On the polydisperse particle migration and formation of chains in a square channel flow of non-Newtonian fluids

The migration of polydisperse particles and the formation of self-organized particle chains in a square channel flow of non-Newtonian fluids is studied. The effects of rheological behaviour of the fluid, solution concentration and flow rate are explored experimentally. The direct forcing/fictitious domain method is adopted to qualitatively verify the experiments and further analyse the mechanisms of particle migration and particle chain self-organization. The results show that only particles in viscoelastic fluids with negligible shear-thinning effect will remain at the channel centreline as the flow rate increases. The monodisperse particles reach the same velocity when migrating to the equilibrium position. However, in polydisperse suspensions, the smaller the particle diameter, the greater the velocity when the particle migrates to the equilibrium position. In a viscoelastic fluid, the polydisperse particles are more likely to self-organize into long particle chains along the channel centreline than the monodisperse particles, where the large and small particles are at the front and end of the chain. The dimensionless alignment factor (Af) is adopted to quantify the formation of particle chains, which is the largest in viscoelastic fluids and rapidly increases before decreasing to a stable value as the flow rate increases. For larger particle diameter ratios and stronger shear-thinning effect, the long particle chain self-organization is less obvious. The self-organizing particle chains at the channel centreline are strongly influenced by the fluid elastic properties and weakly by the inertial effect; however, the shear-thinning effect disperses the particles and prevents the formation of long straight particle chains.

Development and decay of vortex flows in viscoelastic fluids between concentric cylinders

We study the development and decay of vortex in viscoelastic fluids between coaxial cylinders by means of experiments with solutions of polyacrylamide and glycerin and numerical simulations. The transient process is triggered when the inner cylinder is either abruptly started or stopped while the outer is kept fixed. The azimuthal velocity, obtained by means of digital particle velocimetry, exhibits oscillations before reaching the stationary state. The development of the vortex is characterized by means of the overshoot, i.e. the difference between the maximum and the stationary velocity. Analogously, in the decay of the vortex, the azimuthal velocity changes its direction and the relevant parameter is the undershoot defined as the maximum reversed transient velocity. To get a deeper insight into this phenomenon, the experimental results are supplemented with numerical simulations of rheological models as the Oldroyd-B and White–Metzer. The results obtained with the first model reveal the dependence of the overshoot and undershoot with the elasticity number of the fluid. Using the White–Metzer model we explain the increase of the overshoot produced by the reduction of the solvent viscosity in terms of the shear-thinning effects.

Reduced and increased flow resistance in shear-dominated flows of Oldroyd-B fluids

We present a comprehensive analytical and numerical study of shear-dominated flows of Oldroyd-B fluids. Starting from transient ideal Couette flow, we show that less work is required to increase the shear rate than to decrease it. Generalizing this observation to non-homogeneous steady flows, we show that reduced flow resistance is present around streamlines with increasing shear rate and increased flow resistance is present around streamlines with decreasing shear rate. We demonstrate this effect in smoothly converging or diverging Couette and Poiseuille flows. Finally, we show that the reduced flow resistance observed in the flow past a cylinder in a straight channel is caused by the contraction-expansion-like flow that takes place at the sides of the cylinder. Our findings are validated by a wide parametric analysis regarding the geometrical characteristics of the flow domains and the material parameters of the Oldroyd-B model. • Shear-thinning and shear-thickening effects can be predicted by the Oldroyd-B model. • Reduced flow resistance is present along streamlines with increasing shear rate. • Increased flow resistance is present along streamlines with decreasing shear rate. • The variations in pressure drop and drag force in viscoelastic flows are explained.

Frequency-dependent complex viscosity obtained for a liquid two-dimensional dusty plasma experiment.

Strongly coupled plasmas in a liquid phase can be characterized by a complex viscosity η(ω), which is a function of frequency. Data from a single experiment with dusty plasma were analyzed to compare η(ω) obtained by two fundamentally distinct methods. In a nonequilibrium method, a pair of counterpropagating laser beams, separated by a gap, applied a sinusoidal shear to a two-dimensional liquid, and η(ω) was determined using the constitutive relation. In an equilibrium method, there was no externally applied shear, so η(ω) could be calculated with a generalized Green-Kubo relation. The results for these two methods are compared for the real and imaginary parts of η(ω). For both parts, it is confirmed that the two methods yield results that agree qualitatively in their trends with frequency, with the real part diminishing with ω and the imaginary part increasing with ω, as expected for viscoelastic liquids. Quantitatively, the values of η(ω) obtained by the two methods differ slightly. For the experiment that we analyze, values for the real and imaginary parts of η(ω) are substantially greater than those reported in an earlier experiment, which we attribute to shear thinning effects in the earlier experiment. The experiment we analyze was designed to minimize shear thinning, unlike the earlier experiment.

An analytical theory for the forced convection condensation of shear-thinning fluids onto isothermal horizontal surfaces

We present an analytical theory for laminar forced convection condensation of saturated vapor on horizontal surfaces. The condensation produces shear-thinning film moving downstream due to the viscous-drag occurring at the vapor-liquid interface. The mathematical model is built based on a few input parameters, viz. power-law index (n), nondimensional film-thickness (ηδ,l), Prandtl number (Pr), and inertia number (Mc). A set of output parameters is used to analyze the distinct characteristics of the fluid-flow and condensation, viz. the condensate’s nondimensional mass flow rate (m^), Nusselt number, specific enthalpy ratio (Rh), thermal retention coefficient (Θ), and nondimensional wall-shear stress (τ^w). We have identified the subtlety of shear-thinning film flow when liquid’s thermophysical properties vary according to the changes in wall-shear and the interfacial drag. Contextually, we illustrate that a rise in shear-thinning effect (obtained by decreasing n), keeping Mc and ηδ,l fixed, results in a decrease of m^, Rh, τ^w, and (1/Θ). We have demonstrated that for a fixed Rh, a shear-thinning film, compared to the Newtonian film, would exhibit a greater ηδ,l but a smaller interfacial velocity (fi′). Furthermore, a greater film thickness is required for low Pr liquids to attain the same degree of subcooling compared to high Pr liquids. We perform systematic investigation over a wide range of ηδ,l. We observe that for small ηδ,l values, the vapor boundary-layer moving onto the liquid-film exhibits similar flow-features as found in the well-known Blasius boundary-layer. Conversely, at large ηδ,l, the present solution would remarkably differ from the Blasius solution. Finally, we establish an approximate theory for small ηδ,l motivated by the linearity in the cross-stream variations of velocity and temperature within the thin-film. This approximate theory gives rise to analytical correlations for Rh, Θ, τ^w, and m^, which would be useful for engineers.