Shear Thinning Effect Research Articles

Graetz problem for the Rabinowitsch fluid model: A comparative analysis for circular tube and flat channel

The current set of themes related to the analysis of heat transfer by convection and heat transfer in a tube or channel is commonly referred to as the Graetz problem, which is to investigate the evolution of the temperature profile for a fluid flow in hydrodynamic developed laminar flow. The current research, in this regard, reports the Graetz problem for the constant wall(s) temperature case using the Rabinowitsch fluid model. The associated energy equation is solved via a classical separation of variable approach. The special case of the Rabinowitsch fluid model is also highlighted. The resultant boundary value problem is addressed computationally using the Matlab bvp4c function and the Runge–Kutta method. The real and positive eigenvalues along with the numerical solutions are obtained for the calculation of the temperature field. This study also explains that the Rabinowitsch model has both shear-thinning and shear-thickening effects. The impact of model parameters on mean temperature and Nusselt numbers are thoroughly examined with various graphs.

Numerical simulation of in-depth profile control for dispersed particle gel in heterogeneous reservoirs

Introduction: As a new agent of enhancing oil recovery, the dispersed particle gel (DPG) has been gradually used for in-depth profile control in mature oilfields. Many researchers investigated the preparation, profile control mechanism and application of DPG based on a series of laboratory experiments. However, few numerical studies have been carried out on profile control mechanism of DPG.Methods: This paper proposes a novel mathematical model to proceed numerical simulation of profile control for DPG, considering DPG particles adsorption and weak shear thinning effects. The numerical codes are verified by the UTCHEM simulator.Results and discussion: The effects of the DPG viscosity, the DPG concentration, the water saturation of high permeable regions and the permeability ratio between high and low permeable regions on decreasing the water-cut of producing well are studied. Simultaneously, this paper also investigates the influence of different mobility ratios between high and low permeable regions on water shutoff of DPG. The numerical simulation results show that the effects of DPG profile control become better as the DPG solution viscosity, the suspension concentration and the permeability ratio increase. But the increased water saturation of high permeable regions is not helpful to improve oil recovery. Water plugging effect of DPG becomes worse with increasing mobility ratio between different regions. According to comparison results between DPG profile control and polymer flooding, it is found that DPG profile control is more suitable for heterogeneous reservoirs. These findings are of benefit to guide the efficient field application of DPG profile control in heterogeneous reservoirs.

An experimental study of the merging flow of polymer solutions in a T-shaped microchannel.

The merging flow through a T-junction is relevant to sample mixing and particle manipulation in microfluidic devices. It has been extensively studied for Newtonian fluids, particularly in the high inertial regime where flow bifurcation takes place for enhanced mixing. However, the effects of fluid rheological properties on the merging flow have remained largely unexplored. We investigate here the flow of five types of polymer solutions along with water in a planar T-shaped microchannel over a wide range of flow rates for a systematic understanding of the effects of fluid shear thinning and elasticity. It is found that the merging flow near the stagnation point of the T-junction can either be vortex dominated or have unsteady streamlines, depending on the strength of elasticity and shear thinning present in the fluid. Moreover, the shear thinning effect is found to induce a symmetric unsteady flow in comparison to the asymmetric unsteady flow in the viscoelastic fluids, the latter of which exhibits greater interfacial fluctuations.

Characteristic analysis of magnetorheological fluid porous fabric composite with a novel constitute model

As a novel material, magnetorheological fluid porous fabric composite (MRF-PF) has not been further analyzed and modeled. In this paper, mechanical properties of MRF-PF are analyzed quantitatively and qualitatively with a novel constitute model. Considering the wall slip, viscoelasticity and internal porous network of MRF-PF, a constitute model of MRF-PF is derived firstly which can describe the performance precisely. According to experimental results, mechanical properties of MRF-PF are different from conventional MRF. Shear stress τ decreases first, then increases slowly at off-state. Under low magnetic field, shear stress τ presents the opposite variation. It increases at first, and then decreases rapidly. With the further increase of magnetic field, Shear stress τ increases dramatically at high shear rate. This effect is determined by the internal porous network and absorption degree of MRF-PF. A possible flow mechanism of MRF-PF has been proposed. Comparing with different types of MRF-PFs, pre-immersed MRF-PF without relative rotation has a better performance. The maximum shear stress can reach as high as 62.35 kPa with an increase of 22.37% under the magnetic field of 0.7 T. The corresponding dynamic yield stress τ y increases to 55.18 kPa with an increase of 26.6%. What is more, internal porous network can support the particle chains to reinforce the shear-resistance property. The shear thinning effect of MRF-PF can be improved significantly. However, MR effect of MRF-PF decreases largely. These attractive mechanical properties make MRF-PF a potential choice for critical engineering applications.

Shear viscosity in two-dimensional dipole systems.

The results of modeling shear flows in classical two-dimensional (2D) dipole systems are presented. We used the method of nonequilibrium molecular dynamics to calculate the viscosity at various shear rates. The coefficients of shear viscosity are given in the limit of low shear rates for various regimes of interparticle correlation from a weakly correlated gaseous state to a strongly nonideal liquid state near the crystallization point. The calculations were carried out for bare (unscreened) dipole systems, as well as for dipole systems in a polarizable medium that provide screening of the dipole-dipole interaction. The effect of shear thinning in 2D dipole systems is reported for low values of the coupling parameter. In addition, it is shown that dipole systems can become both less and more viscous due to the presence of a screening medium, depending on the degree of interparticle correlation. The optimal simulation parameters are discussed within the framework of the method of nonequilibrium molecular dynamics for determining the shear viscosity of two-dimensional dipole systems. Moreover, we present a simple fitting curve which provides a universal scaling law for both bare dipole-dipole interaction and screened dipole-dipole interaction.

Experimental observation of a confined bubble moving in shear-thinning fluids

The motion of a long gas bubble in a confined capillary tube is ubiquitous in a wide range of engineering and biological applications. While the understanding of the deposited thin viscous film near the tube wall in Newtonian fluids is well developed, the deposition dynamics in commonly encountered non-Newtonian fluids remains much less studied. Here, we investigate the dynamics of a confined bubble moving in shear-thinning fluids with systematic experiments, varying the zero-shear-rate capillary number $Ca_0$ in the range of $O(10^{-3}\unicode{x2013}10^2)$ considering the zero-shear-rate viscosity. The thickness of the deposited liquid film, the bubble speed and the bubble front/rear menisci are measured, which are further rationalized with the recent theoretical studies based on appropriate rheological models. Compared with Newtonian fluids, the film thickness decreases for both the carboxymethyl cellulose and Carbopol solutions when the shear-thinning effect dominates. We show that the film thickness follows the scaling law from Aussillous & Quéré (Phys. Fluids, vol. 12, no. 10, 2000, pp. 2367–2371) with an effective capillary number $Ca_e$ , considering the characteristic shear rate in the film as proposed by Picchi et al. (J. Fluid Mech., vol. 918, no. A7, 2021, pp. 1–30). $Ca_e$ is calculated by the Carreau number and the power-law index from the Carreau–Yasuda rheological model. The shear-thinning effect also influences the bubble speed and delays the transition to the parabolic region in the bubble front and rear menisci. In particular, a high degree of undulations on the bubble surface results in an intricate rear viscosity distribution for the rear meniscus and the deviation between the experiments and theory may require a further investigation to resolve the axial velocity field. Our study may advance the fundamental understandings and engineering guidelines for coating processes involving thin-film flows and non-Newtonian fluids.

Quasi-steady imbibition of physiological liquids in paper-based microfluidic kits: Effect of shear-thinning

In the present work, spontaneous imbibition of shear-dependent fluids is numerically investigated in a two-layered, rectangular/fan-shaped, paper-based diagnostic kit using the modified Richards equation. It is shown that the average velocity at the test line of the kit is strongly influenced by the absorbent pad's microstructure with its contact angle playing a predominant role. Assuming that the test fluid is shear-thinning, a generalized version of the Richards equation, valid for power-law fluids, was used to investigate the effect of shear-thinning on the quasi-steady regime. The shear-thinning behavior of the test fluid is predicted to shorten the duration of the constant-velocity regime on the nitrocellulose membrane used as the test cell. By manipulating the contact angle and/or choosing appropriate microstructure for the absorbent pad, it is still possible to establish a constant velocity regime at the test line for nearly five minutes even for such fluids. A comparison between our numerical results and published numerical results obtained using simplistic theories has revealed the key role played by the transition, partially saturated zone near the advancing front during the liquid imbibition. The general conclusion is that use should preferably be made of robust models such as Richards equation for the design of lateral-flow, paper-based assays.

Motion of a Taylor bubble in a realistic shear-thinning fluid

<h2>Abstract</h2> This talk will focus on the motion of a gaseous Taylor bubble in a capillary tube. Although the dynamics of a bubble in a Newtonian liquid has been the subject of several studies since the seminal works Taylor and Bretherton, the case where the fluid exhibits a shear-thinning behaviour is much less understood. To fill this gap, we derive a lubrication model in the film region to identify the scaling laws for the bubble speed and the film thickness as a function of the Ellis number and the degree of shear-thinning. Our model identifies a universal scaling law for the effective viscosity that accounts for the interplay of the zero-shear-rate and shear-thinning effects. After discussing the features of the front and rear menisci, we present an analysis of the recirculation vortexes ahead of the bubble. In the final part of the talk, we show the results of recent numerical simulations that validate the proposed theory and suggest a strategy to account for the effect of finite capillary numbers on the scaling law for the film thickness in the case of shear-thinning fluids.

A study of misaligned compliant journal bearings lubricated by non-Newtonian fluid considering surface roughness

To study the static behavior of misaligned journal bearings under heavy loads using a non-Newtonian lubricant (pseudoplastic fluid, the flow behavior obeys a power-law relationship). And the generalized average Reynolds equation for rough journal bearing under pseudoplastic lubricant flow is derived. The establishment method of the model equation adopts the average flow method of Patir and Cheng. The numerical solution of bearing performance parameters applies the finite difference method and the successive over-relaxation method. And surface roughness can partially offset the effects of liner elastic deformation and lubricant shear thinning. The generalized average Reynolds equation derived in this paper is not only used in the research of hydrodynamic lubrication but also can be used in the research of mixed lubrication.

Characterization of magnetorheological fluids based on capillary magneto-rheometer

Magnetorheological fluids (MRFs) are a class of smart magnetic controlled materials whose rheological properties can be controlled by a magnetic field. These materials have advantages of short response time, high dynamic range and low energy consumption. Due to their excellent properties, MRFs have a widely application potential in the field of impact mitigation. As the shear rate dependent viscosity of MRFs is astonishing for the shear thinning effect, thus it is crucial to study the rheological properties cross a wide range of shear rates for guiding the design and application of MRFs based adaptive impact absorbers. Commercial rotational rheometers are usually used to test the rheological properties of MRFs, but their range of measuring shear rates are limited. Commercial capillary rheometers are designed to measure the rheological behavior over a wide range of shear rates, but they’re usually lack of ability to measure with magnetic field. In order to study the rheological properties of MRFs under higher shear rate and applied magnetic field, a lab-made speed-controlled capillary magneto-rheometer is developed in the presnt work; The expressions for equivalent shear rate and apparent viscosity of MRFs under the dimensional constraint of the set-up are derived. In addition, the theoretical expression of shear rate of MRFs is modified by Rabinowitsch correction. Then, the rheological properties of three particle volume fractions (10%, 15%, and 20%)of MRFs with different magnetic field strengths (6 mT, 13 mT, 20 mT, and 25 mT)are tested and analyzed, and the rheological characteristic curves of MRFs with shear rate range of 101s−1–105s−1 are obtained with the normalized characterization using Mason number. According to the experimental results, the MRFs show an obvious shear thinning phenomenon as shear rate increases, and in the Mason number based normalized characterization, the curves of different particle volume fractions are collapse to a master curve.

Novel and Facile Synthesis of Biodegradable Plastic Films from Cornmeal by Using the Microwave Polymerization Technique

Millions of tons of plastic are produced annually, but a major portion of plastic waste remains unrecycled. The uncycled plastic ultimately becomes a major source of solid trash and releases a variety of chemicals into our environment which can adversely affect the human health and marine life. In this study, a novel approach has been opted to synthesize a biodegradable plastic by using the microwave polymerization technique. In this novel approach, raw material (cornmeal), plasticizer (glycerin), and additive (vinegar) have been combined together to fabricate biodegradable plastic films from the microwave polymerization method. A number of rheological properties such as shear stress (Pa), shear rate (1/s), strain, and viscosity (Pa.s) of newly synthesized plastic were studied. These properties confirmed the presence of a shear thinning effect in the biodegradable plastic films on the basis of flow behavior of cornmeal. In order to check the water uptake ability and biodegradability of the cornmeal-based plastic films, water uptake and biodegradation tests were carried out. The fabricated films were neat, thin, and chewable and demonstrate promising characteristics. Therefore, these synthesized films can potentially become a suitable candidate in the packaging industry.

Scrutinization of coating thickness of Sutterby fluid during isothermal blade coating using lubrication theory: the case of plane coater and exponential coater

In the literature, there is a gap regarding the analysis of coating thickness of Sutterby fluid during isothermal blade coating using lubrication theory, focusing on the case of plane coater and exponential coater. During the blade coating processes, this report presents the outcome of a study on an isothermal and incompressible flow of a Sutterby fluid. Both the planar and exponential coaters were considered in the analysis. Lubrication theory was used to simplify the non-dimensional governing equations, which were then solved using the numerical shooting approach and perturbation technique for small values of the fluid parameter. Furthermore, the perturbation results are compared to the numerical results and are in good agreement. As the fluid parameter increases, the shear-thinning effect is noted, leading to an increased velocity profile and coating thickness while reducing blade load. Sutterby fluid parameter develops to be the controlling parameter for Pressure profile and blade load compared to the Newtonian case, which leads to an effective coating process and improves the substrate life.

A modified viscosity approach for shear thinning lubricants

Lubrication is essential to minimize wear and friction between contacting surfaces in relative motion. Oil based lubricants are often enhanced via polymer additives to minimize self-degradation due to the shear thinning effect. Therefore, an accurate estimate of the load carrying capacity of the thin lubricating film requires careful modeling of shear thinning. Available models such as the generalized Reynolds equation (GR) and the approximate shear distribution have drawbacks such as large computational time and poor accuracy, respectively. In this work, we present a new approach, i.e., the modified viscosity (MV) model, based on calculating the strain rate only in one point along the vertical direction. We investigate, for both MV and GR, the load, the maximum pressure, and the computational time for (i) sliding (non-cavitating) contacts, (ii) cavitating, and (iii) squeezing contacts. We observe that the computational time is reduced (i) considerably for non-cavitating sliding and rolling contacts and (ii) by several orders of magnitudes for cavitating and squeezing contacts. Furthermore, the accuracy of MV is comparable with the GR model within an appreciable range of bearing numbers. Finally, for each type of boundary motion, we have determined the optimal vertical location to calculate the shear strain rate for MV; while this optimal value is close to half the height of the contact for sliding configurations, for rolling dominated and squeezing contacts it is around one quarter (or three quarter) of their height. We finally provide an analysis to a priori estimate the optimal location of the strain rate.

Physicochemical characterisation of graphene-ammonium lactate ionic liquid nanofluid

A new series of nanofluids based on graphene dispersed in 2-hydroxyethylammonium lactate (ML) ionic liquid was developed. Concentrations of 0.1, 0.5 and 1 wt% of graphene were studied and these dispersions were stable after 2 months. Raman spectra showed a strong interaction between ML and graphene. The effect of the concentration of graphene and temperature on the viscoelastic behaviour and conductivity of the nanofluids was studied. An unexpected decrease in the viscosity was found with a low concentration of graphene due to the suppression of hydrogen bonding of the ionic liquid. Shear thinning effects appeared with higher concentrations of graphene and Ostwald and Herschel-Bulkley equations were used to describe the steady-state viscosity results. Creep-recovery tests were also performed, and the data were fitted to a complex Burgers model for the nanofluid with 1 wt% of graphene, with a 47 % of elastic response. The complexity of the model was related to the presence of different molecular arrangements in the nanofluid. An enhancement of the conductivity was observed with increasing values of the graphene concentration. The effect of temperature on viscosity and electrical conductivity was successfully modelled by using both Vogel-Fulcher-Tammann and Power Law equations. Electrochemical characterisation at room temperature was also carried out, finding an irreversible oxidation at 1 V only for the highest concentration (1 wt%). The concentration of percolation was estimated in the range of 0.5 to 1 wt% of graphene.

Walnut Oil Oleogels as Milk Fat Replacing System for Commercially Available Chocolate Butter.

A breakfast spread named chocolate butter exists on the market. For economic and technological reasons, cream in the original recipe is replaced with vegetable oils such as palm oil or by partially hydrogenated sunflower oil. The study aims to reformulate chocolate flavor butter, using cold pressed walnut oil (WO) oleogels (OGs) structured with 10% waxes and monoglyceride (MG), as a milk fat replacing system. The rheological, textural and microscopic characteristics of the oleogels and the spreads were compared. Oil binding capacity (OBC) and colorimetry were also assessed. Fourier transform infrared studies were used to monitor the composition of the samples. Oleogels and oleogel based chocolate butter behaved like strong gels (G’ > G”). The use of candelilla wax (CW) led to the formation of a much firmer spread (S-CW), with a hardness of 3521 g and G’LVR of 139,920 Pa, while the monoglyceride-based spread (S-MG) registered a hardness of 1136 g and G’LVR 89,952 Pa. In the spreadability test, S-CW registered a hardness of 3376 g and hardness work of 113 mJ, comparable to the commercially available chocolate butter. The formulated spreads exhibited shear thinning effects, and increased viscosity with decreasing temperature. A large round peak at 3340 cm−1 was present in the spectra of the candelilla wax-based oleogel (OG-CW) and the reference spreads due to hydrogen bonding, but was absent in S-CW or S-MG. The FTIR spectra of the alternative spreads exhibited the same peaks as the WO and the oleogels, but with differences in the intensities. S-CW exhibited a dense crystal network, with spherulitic crystals of 0.66–1.73 µm, which were statistically similar to those of the reference made from cream (S-cream). S-MG exhibited the lowest stability upon centrifugation, with an OBC of 99.76%. Overall, both oleogel-based chocolate spreads can mimic the properties of the commercially existing chocolate butter references.

Design and Optimization of the Surface Texture at the Hydrostatic Bearing and the Spindle for High Precision Machining

Hydrostatic bearing spindles are widely applied in high precision grinding and turning machines due to their good dynamic stability and rotational accuracy. However, under the condition of high-speed rotations, the heat generated by the friction of the oil film will cause the shear thinning effect. It not only reduces the rotation accuracy of the spindle but also reduces the service life of the spindle. The surface texture structure and configuration between the planes play the role of homogenizing oil film temperature and preventing the bearing surface wear caused by excessive concentration of temperature, which can change the relative motion from the inside of the oil film and thus improve the performance of the hydrostatic spindle more effectively. In this paper, the influence of the surface texture shape and height on the thrust bearing performance of the hydrostatic spindle is systematically investigated by comparative analysis. The CFD simulations are developed to analyze the computational results based on the theory of viscosity-temperature characteristics. The results show that when the height of the surface structure is 1 ~ 2 times the oil film thickness, the spindle bearing performance is the best. The average temperature in the bearing region is the lowest and the accuracy of the simulations was verified by experimental results.

Numerical approach for enhanced oil recovery with polymer flooding using CMG-STARS program

The polymer recovery efficiency of cationic polyacrylamide (PAM) has been evaluated for use as polymer flooding in the Basra oil reservoir Initially, rheological, physical and petro physical were studied. Additionally, the polymer flooding core flooding experiment has been tested to see how well PAM solutions can be recovered. The comparative study between experimental and numerical study for PAM solution has been accomplished in terms of rheological properties , relative permeability curve and oil production. The results showed that PAM solution exhibit shear thinning effect which can efficiently improve the macroscopic sweep efficiency as well as microscopic displacement efficiency, and viscosity increase with high concentration. The overall recovery efficiency of 94.61 % from sandstone was determined for 2500ppm PAM flooding. By contrast, brine water flooding was found to be 47.76%, showing that it was less effective than PAM solution. Cost analysis is another factor that affects a project's success. To support the experimental results, a simulation by the Computer Modelling Group (CMG) study has also been conducted.

Magnetic nanodrug delivery in non-Newtonian blood flows

With the goal of determining strategies to maximise drug delivery to a specific site in the body, we developed a mathematical model for the transport of drug nanocarriers (nanoparticles) in the bloodstream under the influence of an external magnetic field. Under the assumption of long (compared to the radius) blood vessels the Navier-Stokes equations are reduced, to a simpler model consistently with lubrication theory. Under these assumptions, analytical results are compared for Newtonian, power-law, Carreau and Ellis fluids, and these clearly demonstrate the importance of shear thinning effects when modelling blood flow. Incorporating nanoparticles and a magnetic field to the model we develop a numerical scheme and study the particle motion for different field strengths. We demonstrate the importance of the non-Newtonian behaviour: for the flow regimes investigated in this work, consistent with those in blood micro vessels, we find that the field strength needed to absorb a certain amount of particles in a non-Newtonian fluid has to be larger than the one needed in a Newtonian fluid. Specifically, for one case examined, a two times larger magnetic force had to be applied in the Ellis fluid than in the Newtonian fluid for the same number of particles to be absorbed through the vessel wall. Consequently, models based on a Newtonian fluid can drastically overestimate the effect of a magnetic field. Finally, we evaluate the particle concentration at the vessel wall and compute the evolution of the particle flux through the wall for different permeability values, as that is important when assessing the efficacy of drug delivery applications. The insights from our work bring us a step closer to successfully transferring magnetic nanoparticle drug delivery to the clinic.

Numerical simulation of the coalescence-induced polymeric droplet jumping on superhydrophobic surfaces

Self-propelled jumping of two polymeric droplets on superhydrophobic surfaces is investigated by three-dimensional direct numerical simulations. Two identical droplets of a viscoelastic fluid slide, meet and coalesce on a surface with contact angle 180 degrees. The droplets are modelled by the Giesekus constitutive equation, introducing both viscoelasticity and a shear-thinning effects. The Cahn-Hilliard Phase-Field method is used to capture the droplet interface. The simulations capture the spontaneous coalescence and jumping of the droplets. The effect of elasticity and shear-thinning on the coalescence and jumping is investigated at capillary-inertial and viscous regimes. The results reveal that the elasticity of the droplet changes the known capillary-inertial velocity scaling of the Newtonian drops at large Ohnesorge numbers; the resulting viscoelastic droplet jumps from the surface at larger Ohnesorge numbers than a Newtonian drop, when elasticity gives rise to visible shape oscillations of the merged droplet. The numerical results show that polymer chains are stretched during the coalescence and prior to the departure of two drops, and the resulting elastic stresses at the interface induce the jumping of the liquid out of the surface. This study shows that viscoelasticity, typical of many biological and industrial applications, affects the droplet behaviour on superhydrophobic and self-cleaning surfaces.

Effect of shear-thinning of non-Newtonian fluid on the crossover from capillary fingering to viscous fingering in porous media

In this study, we constructed the pore network model for simulation of non-Newtonian two-phase flow. The pore network is initially saturated with the Ellis non-Newtonian fluid and water is then injected with various capillary numbers to simulate water flooding. We observed that there is also a crossover from the capillary fingering to the viscous fingering. In the crossover, the invading fluid tends to fill large-radius pipes, forming a small number of flow paths and low invading fluid saturation. The results show that the stronger the shear-thinning of the Ellis fluid, the easier it is for the injected fluid to invade the smaller-radius pipe, thereby suppressing viscous fingering and increasing the displacement efficiency, resulting in a smaller crossover zone. The findings of this study can help for a better understanding of the complex fluid-fluid displacement patterns in porous media for improving geological CO2 sequestration and enhanced oil recovery.