Time-dependent Viscosity Research Articles

Transportation of modified nanofluid flow with time dependent viscosity over a Riga plate: Exponentially stretching

In this analysis, the modified nanofluid flow at a nonlinear stretching Riga plate is considered. The impacts of variable viscosity are considered. The modified nanofluid is the extended version of the hybrid nanofluid. This is the mixture of three nanoparticle and base fluid. The heat transfer rate depends on the thermal conductivity because heat transfer rate and thermal conductivity directly proportion which provided in the literature. The developed model solved through numerical technique. The basic achievement of this analysis is to explore about the heat transfer improvement that gains higher as compared to Hybrid nanofluid and nanofluid, (see Fig. 1). Heat transfer properties and modified nanofluid show exciting behavior which deserve further study on the modified nanofluid. The ϕ3 disperse the energy in the shape of heat than the mixture of more nanoparticles may more exert energy in the form of heat.

Control of viscous fingering through variable injection rates and time-dependent viscosity fluids: Beyond the linear regime.

During the past few years, researchers have been proposing time-dependent injection strategies for stabilizing or manipulating the development of viscous fingering instabilities in radial Hele-Shaw cells. Most of these studies investigate the displacement of Newtonian fluids and are entirely based on linear stability analyses. In this work, linear stability theory and variational calculus are used to determine closed-form expressions for the proper time-dependent injection rates Q(t) required to either minimize the interface disturbances or to control the number of emerging fingers. However, this is done by considering that the displacing fluid is non-Newtonian and has a time-varying viscosity. Moreover, a perturbative third-order mode-coupling approach is employed to examine the validity and effectiveness of the controlling protocols dictated by these Q(t) beyond the linear regime and at the onset of nonlinearities.

An integral equation method for the simulation of doubly-periodic suspensions of rigid bodies in a shearing viscous flow

With rheology applications in mind, we present a fast solver for the time-dependent effective viscosity of an infinite lattice containing one or more neutrally buoyant smooth rigid particles per unit cell, in a two-dimensional Stokes fluid with given shear rate. At each time, the mobility problem is reformulated as a 2nd-kind boundary integral equation, then discretized to spectral accuracy by the Nyström method and solved iteratively, giving typically 10 digits of accuracy. Its solution controls the evolution of particle locations and angles in a first-order system of ordinary differential equations. The formulation is placed on a rigorous footing by defining a generalized periodic Green's function for the skew lattice. Numerically, the periodized integral operator is split into a near image sum—applied in linear time via the fast multipole method—plus a correction field solved cheaply via proxy Stokeslets. We use barycentric quadratures to evaluate particle interactions and velocity fields accurately, even at distances much closer than the node spacing. Using first-order time-stepping we simulate, for example, 25 ellipses per unit cell to 3-digit accuracy on a desktop in 1 hour per shear time. Our examples show equilibration at long times, force chains, and two types of blow-ups (jamming) whose power laws match lubrication theory asymptotics.

Effects of Exponential Variable Viscosity on Heat Transfer Flow of MHD Fractional Maxwell Fluid

This research article presents the unsteady natural convection of Maxwell viscoelastic fluid based on boundary layer heat transfer. The stretching sheet on lower wall of fluid with exponential time dependent viscosity is implemented. The fractional derivative based governing equations of Maxwell fluid model are derived. These governing equations are used to derive nonlinear coupled partial differential equations (PDEs) which involves space and time derivatives in convection terms. By employing the Finite Difference Method with L1-algorithm, to solve system of nonlinear coupled PDEs and presented via graphically. The effects of fractional and physical parameters on velocity, temperature and particular fractional parameters effect on average skin friction coefficient $$\bar{Cf}$$ and average Nusselt number $$\bar{Nu}$$ are discussed in details. For instance, the thickness of velocity boundary layer increases in response to increase in fractional parameter $$\alpha $$ , whereas heat conduction reduces in response to increase in fractional parameter $$\gamma $$ .

A novel study on time-dependent viscosity model of magneto-hybrid nanofluid flow over a permeable cone: applications in material engineering

The dominating features of hybrid nanofluid such as high heat transfer rates, excellent electrical and thermal conductivity, and low cost, have been successfully attracted the attention of global researchers. In light of these amazing features, the current mathematical research explores the effects of variable viscosity on radiative magneto-hybrid nanofluid (Cu–Fe $$_{3}$$ O $$_{4}$$ /water) flow over a vertical cone inside porous medium. In addition, variable heat flux relation with boundary layer flow in the presence of heat generation/absorption is scrutinized. The Crank–Nicolson scheme together with Thomas algorithm is implemented to obtain the numerical solutions of constructed mathematical model with the aid of MATLAB software. The impact of various controlling parameters on virtual flow properties, temperature and velocity is scrutinized, and the obtained outcomes are exhibited graphically. The physically important quantities such as heat transfer coefficient and wall shear stress are evaluated versus governing constraints, and the results are summarized in the tables and illustrated graphically as well. The results unveil that the thermal performance of the system increases in the presence of nanoparticles, magnetic field and thermal radiation. Moreover, velocity of the fluid increases due to high permeability effects. The results of this work may have useful applications in materials science and engineering.

Dynamic characteristics of modified bitumen systems

Thiokol-modified bitumens are investigated. Based on the measurements of time-dependent viscosity parameters (melting point, penetration, and spin-spin relaxation time T2 ), it is established that at a content of thiokol more than 25%, formation of a continuous phase is possible, which shows up as a sudden change in the bitumen properties and is associated with the phase inversion. The method of bitumen modification suggested can be recommended for obtaining roofing materials.

Riemann Problem for a $2 \times 2$ Hyperbolic System with Linear Damping

In this paper, we study the Riemann problem for a $2 \times 2$ nonstrictly hyperbolic system with linear damping. We introduce the special time-dependent viscosity to obtain approximate solutions. Therefore, we solve the Riemann problem (1.1)–(1.2) by limiting viscosity approach.

Numerical simulation of dynamic water grouting using quick-setting slurry in rock fracture: the Sequential Diffusion and Solidification (SDS) method

Abstract The two-liquid mixing grouting method of quick-setting slurry and its time-dependent viscosity characteristics lead to an uneven distribution of viscosity in the slurry diffusion zone. At present, there still lacks reasonable and effective slurry-water interaction analysis method to reveal the diffusion behavior of quick-setting slurry in dynamic water. Therefore, a Sequential Diffusion and Solidification (SDS) method was proposed in this study, taking the spatial-temporal evolution of slurry viscosity into account. In addition, the validity and necessity of the SDS method were verified. The maximum error between the calculation result and the test result was less than 15%. Based on the SDS method, the slurry diffusion process under different flow velocities was analyzed and the effects of flow velocities on the changes of the grouting pressure, the counter-flow diffusion distance, and the down-flow diffusion behavior were explored. The applicability and the feasibility of studying the slurry diffusion mechanism in a wide fracture on an engineering scale were determined. This further confirmed the adequacy and the power of the numerical approach. Therefore, the SDS method could be used to simulate the dynamic water grouting. The SDS method could also provide an improved method for the simulation of permeation grouting and compaction grouting.

Rheological measurement of the nonlinear viscoelasticity of the ABS polymer and numerical simulation of thermoforming process

The thickness distribution of thermoformed products is greatly affected by the viscoelastic behavior of the extruded polymer sheet. In this work, linear and nonlinear rheological experiments are carried out to characterize the viscoelastic properties of acrylonitrile-butadiene-styrene sheets under thermoforming conditions including a wide range of temperatures, strains, and strain rates. First, aspects of linear viscoelasticity such as the storage modulus and loss modulus are measured by small-amplitude oscillatory shear experiments. The discrete relaxation spectra and the Williams-Landel-Ferry parameters are obtained from the constructed linear master curves. Then, nonlinear time-dependent extensional viscosity is measured by uniaxial extensional experiments. The parameters of the damping function are evaluated using an optimization method. In addition, the effect of the orientation of the polymer is analyzed. The uniaxial extensional stress and viscosity in the extruder direction demonstrate higher resistance against tearing and extreme thickness reduction during processing. Finally, the linear and nonlinear input parameters for the numerical simulation are prepared. Numerical simulations are performed using the Wagner model with the obtained nonlinear viscoelasticity. The thickness distribution in thermoformed ABS sheets, obtained numerically, shows good agreement with the experimentally obtained values.

A Pictorial View of Viscosity in Ionic Liquids and the Link to Nanostructural Heterogeneity.

Prototypical ionic liquids (ILs) are characterized by three structural motifs associated with (1) vicinal interactions, (2) the formation of positive-negative charge-alternating chains or networks, and (3) the alternation of these networks with apolar domains. In recent articles, we highlighted that the friction and mobility in these systems are nowhere close to being spatially homogeneous. This results in what one could call mechanical heterogeneity, where charge networks are intrinsically stiff and charge-depleted regions are softer, flexible, and mobile. This Letter attempts to provide a clear and visual connection between friction-associated with the dynamics of the structural motifs (in particular, the charge network)-and recent theoretical work by Yamaguchi linking the time-dependent viscosity of ILs to the decay of the charge alternation peak in the dynamic structure function. We propose that charge blurring associated with the loss of memory of where positive and negative charges are within networks is the key mechanism associated with viscosity in ILs. An IL will have low viscosity if a characteristic charge-blurring decorrelation time is low. With this in mind, engineering new low-viscosity ILs is reduced to understanding how to minimize this quantity.

A new nonlinear viscoelastic model and mathematical solution of solids for improving prediction accuracy

We developed an innovative material nonlinear viscoelastic model with physical mechanism and mathematical solution to improve existing ones. The relaxation modulus transits from the glassy stage to the rubbery stage through a time-dependent viscosity in a continuous spectrum considering the nonlinear strain hardening. Experimental results of differential solid materials including asphalt concrete, agarose gel, vaginal tissue, polymer, agar, bone, spider silk, and hydrogel demonstrate that the developed model is superior to generalized Maxwell model or Prony series for more accurate prediction outside of the range for data fitting while using much less model parameters. Numerical simulation results indicate that the new model has improved accuracy. It is stable numerically, and does not reduce computation speed. Therefore, the model may be used to simulate a broad range of viscoelastic solids for predicting experimental data and responses with improved accuracy.

Illuminating subduction zone rheological properties in the wake of a giant earthquake.

Deformation associated with plate convergence at subduction zones is accommodated by a complex system involving fault slip and viscoelastic flow. These processes have proven difficult to disentangle. The 2010 M w 8.8 Maule earthquake occurred close to the Chilean coast within a dense network of continuously recording Global Positioning System stations, which provide a comprehensive history of surface strain. We use these data to assemble a detailed picture of a structurally controlled megathrust fault frictional patchwork and the three-dimensional rheological and time-dependent viscosity structure of the lower crust and upper mantle, all of which control the relative importance of afterslip and viscoelastic relaxation during postseismic deformation. These results enhance our understanding of subduction dynamics including the interplay of localized and distributed deformation during the subduction zone earthquake cycle.

Up-down asymmetric exact solutions to the Navier-Stokes equations

Exact up-down asymmetric solutions to the Navier-Stokes equations for a viscous and incompressible fluid with time-dependent viscosity ν(t) are derived. Transformations of the exact solutions are defined that produce an infinite sequence of new solutions from each known one. The solutions are presented in terms of elementary functions and have no singularities. Three infinite-dimensional families of new exact axisymmetric unsteady solutions to the viscous magnetohydrodynamics equations are derived. Dynamics of vortex rings and vortex blobs is studied for some exact up-down asymmetric incompressible viscous fluid flows and viscous plasma flows.

Study of Melt Spinning Processing Conditions for a Polyacrylonitrile Copolymer with a Water/Ethanol Mixture as a Plasticizer

Abstract This paper is concerned with the feasibility of melt spinning of polyacrylonitrile (PAN) copolymer (acrylonitrile/methylacrylate 95.6/4.4 mol% ratio) plasticized with water-ethanol (EtOH) mixtures. The melting point and rheological and stability behaviors of PAN/water/ethanol mixture are reported. The objective is to determine whether this mixture is appropriate for allowing the PAN to be melt spun. The melting point results from differential scanning calorimetry show the Tm of PAN/water/ethanol (70/15/15 wt%) mixture can be reduced to 150 °C from 300 °C. The time-dependent viscosity results showed that this mixture can be processed at 170 °C for more than 100 min without degradation. The steady-shear viscosity results indicated the shear-thinning behavior is observed for this mixture at a temperature ranging from 170 °C to 190 °C. These rheological data are also highly similar to the reference condition and other potential conditions reported in our previous paper, which indicates PAN/water/ethanol (70/15/15 wt%) at 170 °C is a potential condition for PAN melt spinning. The scanning electron microscopy diagrams show the copolymer strand melt extruded from PAN/water (70/30 wt%) mixture contains many more voids and bubbles than the PAN/water/ethanol (70/15/15 wt%) system. In conclusion, PAN/water/ethanol (70/15/15 wt%) at 170 °C is the most benign set condition (i. e. the composition and temperature) for carrying out the PAN melt spinning process.

Characterizing Time-Dependent Stability and Viscosity of Acid–Crude Emulsions for Matrix-Acidizing Applications

The process of matrix acidizing, while aiming at enhancing near-wellbore flow conditions, can result in damaging effects when acid–oil emulsions form. Understanding the behavior of these emulsions, especially when it comes to its stability and viscosity, is an essential step in the design of acid jobs that can lead to successful well productivity enhancement. In this study, we investigate the time-dependent nature of these emulsions using bottle tests and coreflooding experiments. The results of the work provide new insights into the formation of in situ emulsion. This has direct impact on the design of acid jobs in well stimulation treatments.

Influence of the nanoparticles and uniform magnetic field on the slip blood flows in arterial vessels

The present study investigates the combined influence of the nanoparticles and uniform magnetic field applied on the slip blood flow. Blood conveyed through the hollow arterial tube is described as a third-grade non-Newtonian fluid with time dependent viscosity and formulated by the second-order nonlinear ordinary differential equations. Therefore, the regular perturbation method as an approximate analytical method can be applied providing a solution to the coupled system of equations. The results obtained from the solution are used to show the effect of parameters including the magnetic parameter, the viscous dissipation and the pressure gradient on the slip blood flow. Analytical results reveal augmentation of the pressure gradient and the magnetic parameter decrease the velocity value whilst the viscous dissipation augmentation increases the temperature. Also, the comparison between the analytical results with the results obtained from numerical solution shows the good agreement.

W1FINITE ELEMENT ANALYSIS OF PIPES CONVEYING FLUID MOUNTED ON VISCOELASTIC FOUNDATIONS

AbstractIn this study, the stability of a simply supported pipeline conveying fluid with different velocities and resting on viscoelastic foundation is investigated by using finite element analysis, and the critical fluid velocity with different parameters such as stiffness and viscous coefficients of foundation are obtained. This structural system could be found in pipes conveying petrol, water, and sewage. The foundation is simulated using the modified Winkler's model to introduce the effect of time dependent viscosity term. Some known results are confirmed and some new ones obtained. Two components of foundation, stiffness and viscosity, seemed to act on the critical flow velocity of the pipe in contrary trend. Where, increasing the foundation stiffness tended to increase the critical flow velocity in the pipe. While, increasing foundation viscosity attempted to decrease it. At some ranges of pipe length, the foundation viscosity effect seems to be more extreme. Increasing the fluid velocity leads to monotonic reduction in the system damping ratio. Two parameters, pipe length and fluid density which relate to the natural frequency of pipeline conveying fluid are studied in detail and the results indicate that the effect of Coriolis force on natural frequency is become more effective by increasing pipe length and fluid density besides increasing fluid flow velocity.

Study on Time-dependent Viscosity of Slurry and Its Diffusion Model

Floor water disasters have occurred frequently, which can be treated by grouting and reinforcement of floor. The purpose of this paper is to study on time-dependent viscosity of slurry and its diffusion model for guiding grouting and reinforcement engineering by observing of the change of slurry viscosity with time in laboratory. The result showed that the slurry viscosity had an exponential trend with time. A slurry diffusion model based on the time-dependent viscosity of slurry is derived, according to the diffusion model of grouting in horizontal single fracture under hydrostatic condition. These results will provide theoretical basis for grouting process adjustment and regional grouting transformation.

Rheology and sheet extrusion of Novatein thermoplastic protein/polybutylene adipate‐co‐terephthalate blends

ABSTRACTNovatein is a thermoplastic polymer made from blood meal proteins, but it has rheological properties very different from commodity thermoplastics. Capillary rheometry revealed an apparent time dependent shear viscosity for Novatein, evident from a decreasing pressure drop over time, measured at constant shear rate. However, blending with polybutylene adipate‐co‐terephthalate (PBAT) reduced the time dependence for uncompatibilized blends and virtually eliminated time dependence for compatibilized blends containing 30 wt % PBAT. Novatein's extensional viscosity is three orders of magnitude more than its shear viscosity and explained the difficulty in sheet extrusion. In contrast, 30% compatibilized blends had an extensional viscosity similar to neat PBAT and was also the only blend that could be successfully sheet extruded. Although uncompatibilized blends at the same or lower PBAT content also had a lower extensional viscosity, they could not be sheet extruded and the difference was the 30% compatibilized blends had a fine PBAT phase structure (co‐continuous in this case), which was sufficiently adhered to the Novatein phase. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47977.

Numerical investigation on a grouting mechanism with slurry-rock coupling and shear displacement in a single rough fracture

A slurry diffusion model of a single random-roughness fissure is established to consider the slurry and geological fracture coupling based on the Navier-Stokes equation. The slurry flow characteristics and coupling response in a rough fracture are investigated. The influencing mechanism of roughness on the slurry flow was revealed. The calculation model of effective aperture is determined in a rough fracture. The shear displacement effects on the slurry flow are studied. The results show that this slurry diffusion model can more accurately reflect the grouting. A rougher fracture has a great effect on the flow because of the larger low-speed domains. The pressure gradient and maximum diffusion velocity increase parabolically with changes in the relative roughness. The conventional flat-panel model can cause an increasing deviation rate for determination of grouting parameters. The coupling degree distribution is temporal with spatial variations, and increases with the time-dependent viscosity, roughness (decreasing effective aperture), and a shortening path. The viscosity is the key controlling factor in grouting pressure. The roughness response after shear displacement is more significant, further revealing that on-site grout splitting often occurs at the narrow undulating tip with high viscosity and shear on a rough flow surface. The rough fracture model considering fluid-solid coupling is more consistent with the grouting phenomenon in engineering. And the roughness and shear are the key geological factors of grout splitting.