Shear Thinning Behavior Of Fluid Research Articles

Highly stable GO/formamide based GOLLCs for free standing film fabrication and their photodegradation applications against organic dyes

In this context, formamide is explored as an efficient solvent for the dispersion of GO sheets and preparation of graphene oxide lyotropic liquid crystals (GOLLCs). Polarizing optical microscopy (POM) studies confirm that GO/formamide dispersion shows smectic phase at lower concentration (< 2 mg/mL) and nematic phase up to 300 mg/mL. GOLLCs are found stable for up to 24 months. Probably it is the first report on the formation of GOLLCs in formamide and their long-term stability up to 24 months. GOLLCs are studied for steady and dynamic rheological behavior at room temperature. All the GOLLCs exhibit shear-thinning fluid behavior under the shear rate 1–100 s−1. Dynamic rheology reveals that GOLLCs follow solid viscoelastic behavior till 20 mg/mL concentration and then depict long range viscoelastic behavior at higher concentrations. Complex moduli behavior of GOLLCs has been studied to predict their elasticity. The scaling analysis of tunable viscoelastic GOLLCs is computed from Er=Ax−xc4.43. The free-standing film is prepared via thermal treatment method from 2 mg/mL GOLLCs and studied for structural and photocatalytic degradation behavior. rGO film shows 99.18% and 97.87% degradation efficiency for malachite green and methyl orange organic dyes respectively under UV light and is found stable up to 3 cycles.

Electroosmotic transport and current rectification of viscoelastic electrolyte in a conical pore nanomembrane

Nanomembranes have received a wide range of applications in water treatment, gas separation, molecular and supramolecular separations. Nanopores offer the separation of the components even at nano- or picomolar concentrations. In addition, DNA translocation, DNA sequencing of nucleotides, single molecular analyses for biomedical nanoscopic devices are perhaps the unique feature of nanomembranes that convectional membranes may not achieve. Despite such an overwhelming application, the theoretical understanding of electroosmotic transport in nanopores is still in infancy and it is limited to simple Newtonian-like fluids. This work has numerically investigated the ionic current rectification (ICR) in a conical nanopore filled with viscoelastic electrolyte. ICR quantifies the unequal upstream and downstream ionic flow rates during the forward and reverse potential bias. This is similar to a semiconductor transistor’s current potential (I−V) response. The ICR exhibits several potential applications in the design of biosensors for the measurement and analysis of biofluids such as blood, lymph, and plasma, micro-scale pumping devices, ion-selective membranes, etc. The electroosmotic flow (EOF) in the conical nanopore of Carreau fluid is investigated by solving a set of Poisson, Nernst–Planck, and momentum equations to account for the electric potential, transport of ionic species, and velocity field. The behaviors of ICR in Carreau fluid are examined by varying the shear-thinning index (0.6≤n≤1), Debye length (1≤κRt≤50), Deborah number (1≤De≤100), and applied electric potential (−50≤V≤50). The electroosmotic flow is observed to be significantly stronger in shear-thinning fluids. All else being equal, the volumetric flow rate increases several folds in shear-thinning fluids. Shear-thinning fluid behavior enhances the magnitude of the current in the conical nanopore.

Analyzing flow behavior of shear-thinning fluids in a planar abrupt contraction/expansion microfluidic geometry

Due to its vast range of industrial applications, viscoelastic entry flow behavior and stability in abrupt contraction/expansion geometries have been a subject of interest for quite some time. However, due to the strong dependence of flow instabilities and vortex formation near the constriction entrance in non-Newtonian fluids on the geometry and the fluid rheology, generalizations can not easily be made. In the present study, we examine and compare the flow behavior of several shear-thinning fluids in a new planar contraction/expansion geometry that is symmetric in the flow direction and about the midplane of the depth but asymmetric with respect to the ``contraction'' direction.

The integrated MHD thermal performance with slip conditions on metachronal propulsion: the engineering material for biomedical applications

PurposeParticular attention is given to the viscous damping force parameter, stiffness parameter, rigidity parameter, and Brinkman number and plotted their graph for thermal distribution, momentum profile and concentration profile.Design/methodology/approachIn the field of engineering, biologically inspired propulsion systems are getting the utmost importance. Keeping in view their developmental progress, the present study was made. The theoretical analysis explores the effect of heat and mass transfer on non-Newtonian Sisko fluid with slip effects and transverse magnetic field in symmetric compliant channel. Using low Reynolds number, so that the authors neglect inertial forces and for keeping the pressure constant during the flow, channel height is used largely as compared to the ratio of wavelength. The governing equations of fluid flow problem are solved using the perturbation analysis.FindingsResults are considered for thickening, thinning and viscous nature of fluid models. It is found that the velocity distribution profile is boosted for increasing values of the Sisko fluid parameter and porous effect, while thermal profile is reducing for Brinkman number (viscous dissipation effects) for all cases. Moreover, shear-thicken and shear-thinning behavior of non-Newtonian Sisko fluid is also explained through the graphs.Originality/valueHear-thicken and shear-thinning behavior of non-Newtonian Sisko fluid is also explained through the graphs.

Computational Modeling of Hybrid Sisko Nanofluid Flow over a Porous Radially Heated Shrinking/Stretching Disc

The present study reveals the behavior of shear-thickening and shear-thinning fluids in magnetohydrodynamic flow comprising the significant impact of a hybrid nanofluid over a porous radially shrinking/stretching disc. The features of physical properties of water-based Ag/TiO2 hybrid nanofluid are examined. The leading flow problem is formulated initially in the requisite form of PDEs (partial differential equations) and then altered into a system of dimensionless ODEs (ordinary differential equations) by employing suitable variables. The renovated dimensionless ODEs are numerically resolved using the package of boundary value problem of fourth-order (bvp4c) available in the MATLAB software. The non-uniqueness of the results for the various pertaining parameters is discussed. There is a significant enhancement in the rate of heat transfer, approximately 13.2%, when the impact of suction governs about 10% in the boundary layer. Therefore, the heat transport rate and the thermal conductivity are greater for the new type of hybrid nanofluid compared with ordinary fluid. The bifurcation of the solutions takes place in the problem only for the shrinking case. Moreover, the sketches show that the nanoparticle volume fractions and the magnetic field delay the separation of the boundarylayer.

CFD simulation and statistical experimental design analysis of core annular flow in T-junction and Y-junction for oil-water system

One of the big challenges in transporting heavy oils through the pipelines is the high pressure drop due to the effect of viscosity and shear-thinning fluid behaviour of oil. Core annular technique has been applied in industry for transporting heavy oil via pipelines to considerably reduce pressure drop. Several studies have been conducted related to oil-water core annular flow (CAF) within pipelines. However, limited works are found in cases of CAF in widely used T and Y-shaped junction pipes which have important roles for dividing or combining the flow. In this study, a computational fluid dynamic (CFD) approach was applied to simulate the high viscous oil-water CAF through T and Y-shaped junction pipe configurations. The 2k factorial statistical experimental design was applied to investigate the effect of pipe diameter and junction angle on the flow performance through T and Y-shaped junction pipes. Eight cases were run with different junction pipe configuration combinations. By applying the factorial designs method, all possible combinations of factors were able to be investigated with lowest numbers of simulation run. The selected response variables of the flow system were the average values of oil hold up and pressure gradient as well as the standard deviation of pressure from inlet to outlets of pipes. It was observed that the stability of CAF was not achieved at the downstream region. The flow transformed into stratified and slug flow. The most attractive design was measured by the small average of pressure gradient and standard deviation of pressure but with a high value of oil holdup. The T-shaped pipe with smaller inlet diameter combined with larger outlet diameter showed the most considerable effect for a better flow performance.

Effects of shear-thinning rheology on near-wall turbulent structures

Turbulent channel flow simulation of a shear-thinning fluid is considered – see Arosemena et al. (J. Fluid Mech., vol. 908, 2021, p. A43) – and compared with a Newtonian base case to reveal the effects of the shear-dependent rheology on the near-wall structures. Analyses of different flow statistics revealed that, for the shear-thinning fluid case, the streamwise vortices appear to grow in size, depart from the wall and present a lessening in their intensity. Information regarding variations in the quasi-longitudinal vortices is also obtained from three-dimensional structures identified through a normalized $Q$-criterion. With shear-thinning rheology, it is shown that the structures are comprised of wall-attached and -detached families which are taller than for a Newtonian fluid. Also, for a given height, the structures appear to be longer, with approximately the same width and overall larger volume for the shear-thinning fluid case; albeit their fractal dimension remains the same when compared to the Newtonian base case. Moreover, it is observed that the number density of vortical structures decreases with shear-thinning fluid behaviour. These observations, in conjunction with the known changes to the longitudinal velocity structures which appear to be less streaky, more spanwise separated and thickened with shear-thinning rheology, strongly suggest that the near-wall self-sustaining process has been disrupted. As we move slightly away from the wall and with shear-thinning behaviour, the local increase in viscosity seems to lead to less energetic vortices whereas the streaks are provided with an additional source of energy due to fluctuations in viscosity.

Low-pressure injection molding of magnesium aluminate nanoparticles: Rheological behavior and flexural properties of sintered component

This research aims to investigate the density and flexural strength of nanostructured spinel parts fabricated using the low-pressure injection molding (LPIM) method. For this purpose, firstly, the effect of the amount of binder was tested on the rheology behavior of the feedstocks containing spinel nanopowder for producing ceramic parts using the LPIM method. The rheometric analysis indicated that the feedstocks containing 80 wt% powder and 20 wt% binders showed shear-thinning fluid behavior and were chosen as the optimal low-viscosity feedstocks for the LPIM process. After binder removal from LPIMed part, secondly, the effect of sintering temperature was examined on the relative density and flexural strength of the spinel parts. The results indicated that by increasing sintering temperature from 1550 °C to 1700 °C, the size of pores was reduced and grain size was increased from 2 μm to 6 μm. Furthermore, the flexural strength of the parts sintered at 1700 °C was 10 MPa greater than that of the sample sintered at 1650 °C.

Complex interplay of power-law rheology and non-Oberbeck-Boussinesq effects on natural convection heat transfer in a confined domain

As the first endeavor, the classical differentially heated square cavity problem is revisited to study the non-Oberbeck-Boussinesq (NOB) effects on laminar natural convection heat transfer to non-Newtonian power-law fluids. The augmentation and diminution in both momentum and heat transfer characteristics due to the interplay of power-law rheology and NOB effects are investigated numerically using a finite-volume based open-source solver OpenFOAM®. Moreover, significant non-intuitive changes in thermal and flow fields, due to the temperature-dependent fluid properties, are studied for practical temperature difference ranges. In the present study, both shear-thinning and shear-thickening power-law fluids are taken into account. The NOB results are compared with the corresponding Oberbeck-Boussinesq (OB) results to ascertain qualitative and quantitative inevitable changes in the intricate phenomena. The accelerating NOB effect on heat transfer trend augmented due to shear-thinning fluid behavior, whereas it diminished by the shear-thickening fluids, with reference to a Newtonian case. In particular, for the range of power-law index and temperature difference considered in this study, the average Nusselt number enhances in excess of 40% due to the consequent NOB effects at the extreme case. Results without ascertaining NOB effects would be quite misleading and thus, it should not be neglected in practical scenarios and for their implications. The primary objective of this work is to investigate the natural convection in a square cavity accounting the NOB effects and ascertain the regimes of validity of the Boussinesq approximation. This work finds application in thermal processing of polymeric melts and solutions in several process industries.

Experimental evaluation of surge/swab pressure in varying annular eccentricities using non-Newtonian fluid under Couette-Poiseuille flow for drilling applications

Global energy demand is rapidly increasing at a rate of 8% between 2004 and 2019, and conventional energy sources are unable to meet this requirement. Therefore, the oil and gas energy industry is working continuously to produce unconventional energy sources such as deepwater oil and gas reservoirs, gas hydrates, and geothermal energy using drilling operations. In the drilled borehole, the stability and integrity issues are encountered that are related to pressure differential generated by the Couette-Poiseuille (CP) fluid flow phenomenon occurred during pipe tripping operation. There is a lack of experimental data to comprehend the impact of CP flow on pressure differential using non-Newtonian fluid in concentric and eccentric annuli, especially in petroleum exploration. Hence, an experimental investigation is performed to replicate the tripping operations during oil and gas well drilling. The investigation provides an extensive understanding of the physical and mechanical characteristics of non-Newtonian fluids under CP flow at varying inner pipe tripping speeds (0.030481–0.21336 m/s), rheological properties, and geometrical dimensions. The results indicate that surge/swab pressure gradient tends to decrease with increasing eccentricity (ε) and increase with increasing diameter ratio (δ) and pipe tripping speed (Vp). Furthermore, the pressure differential rate is considerably high at low tripping speed but reduces at high pipe tripping speed due to the shear-thinning behavior of YPL fluid. The study also reveals that gel strength increases the surge/swab pressure gradient by approximately 18%. A multi-variable correlation is developed to predict surge/swab pressure gradient, exhibiting an excellent agreement with experimental data and existing theoretical models.

Conditional and unconditional second-order structure functions in bubbly channel flows of power-law fluids

The influence of non-Newtonian fluid behavior and the Eötvös number on conditional and unconditional second-order structure functions of bubbly channel flows has been investigated by conducting a series of direct numerical simulations at a friction Reynolds number of 127.3. Two Eötvös numbers have been considered (Eo = 0.3125 and Eo = 3.75) together with three different power-law indexes representing shear-thinning (n = 0.7), Newtonian (n = 1.0), and shear-thickening (n = 1.3) fluid behavior. The scaling of the second-order structure functions (SFs) can be translated into an inertial range scaling of the turbulent kinetic energy spectrum. However, because of the discontinuous character of the fluid properties in bubbly flows, SFs are more easily accessible than turbulence spectra, which are based on Fourier transform. It has been found that the different parameters (i.e., Eo, n) have an influence on the energy content as well as the peak location of the compensated second-order SFs (i.e., the dimensions of the large scales). However, after appropriate scaling, the curves nearly collapse. To confirm and further explain the above findings, directional length scales have been evaluated and discussed in detail. Finally, the anisotropy of the Reynolds stress tensor and dissipation tensor has been analyzed in terms of the Lumley triangle, showing that bubbly channel flows are less isotropic than their single-phase counterpart, although they are more homogeneous in the channel center. While the dissipation tensor is slightly more isotropic than the Reynolds stress tensor in the bulk region of the channel flow, overall, a very similar behavior is observed.

Turbulent channel flow of generalized Newtonian fluids at a low Reynolds number

Abstract

Effects of ultrasound modification at different frequency modes on physicochemical, structural, functional, and biological properties of citrus pectin

Ultrasonic irradiation for modified pectin preparation has become a research hotspot, but the influence of ultrasonic frequency is rarely studied. Therefore, in this study, mono frequency (MFU) and simultaneous dual frequency (SDFU) ultrasounds were used to modify citrus pectin (CP), and the effects of different ultrasonic frequency modes on the physicochemical, structural, functional, and biological properties of CP were comparatively investigated. The results showed that ultrasonic irradiation at 40 kHz in the MFU mode led to a larger increment in the galacturonic acid content of CP, but greater reductions in its intrinsic viscosity, molecular weight, and degree of methoxylation than in the SDFU modes. Ultrasonic frequency had no significant influence on the main CP chain, but rather on its neutral sugar side chains. The scanning electron microscopy (SEM) results suggested that CP treated by ultrasound at 40 kHz in the MFU mode exhibited fewer aggregates or looser networks than other ultrasonic treatments. Compared with the original CP, ultrasound treatment at different frequency modes effectively enhanced the thermal stability of CP, but remarkably lowered its shear thinning fluid behavior and liquid-like property. Moreover, among ultrasonically treated CPs, the CP obtained through ultrasound at 40 kHz in MFU mode exhibited the best antioxidant activity and bile acid-binding capacity in vitro.

Enhancement lubricity properties of water-based mud with nanoparticles

Currently, a great number of drilling fluids with different additives are used all over the world. Such additives are applied to control the properties of the drilling mud. The main purpose for controlling is to achieve more effective and safe drilling process. This research work aims to develop Water-Based Mud (WBM) with a Coefficient of Friction (CoF) as low as Oil-Based Mud (OBM) and better rheological properties. As it is known, produced CoF by WBM is higher than OBM, which means high friction between wellbore or casing and drill string. It was the reason for studying the effect of nanosilica on drilling fluid properties such as lubricity, rheological parameters and filtrate loss volume of drilling mud. The procedures were carried out following API RP 13B and API 13I standards. Five concentrations of nanosilica were selected to be tested. According to the results obtained, it was defined that adding nanosilica into the mud decreases CoF of basic WBM by 26 % and justifies nanosilica as a good lubricating agent for drilling fluid. The decreasing trend in coefficient of friction and plastic viscosity for nanosilica was obtained until the concentration of 0.1 %. This reduction is due to the shear thinning or pseudoplastic fluid behavior. After 0.1 %, an increase at PV value trend indicates that it does not follow shear thinning behavior and after reaching a certain amount of dissolved solids in the mud, it acts like normal drilling fluid. The yield point of the mud containing nanoparticles was higher than the basic one. Moreover, a growth in the concentration leads to an increase in yield point value. The improvement of this fluid system cleaning capacity via hydraulics modification and wellhole stability by filter cake endurance increase by adding nanosilica is shown as well. The average well construction data of “Neft Dashlary” field was used for the simulation studies conducted for the investigation of hydraulics parameters of reviewed fluids for all series of experiments. The test results were accepted reliable in case of at least 3 times repeatability.

Thermal mixing performances of shear-thinning non-Newtonian fluids inside Two-Layer Crossing Channels Micromixer using entropy generation method: Comparative study

In this work, a numerical comparative study is carried out to investigate a laminar steady flow behavior of shear-thinning non-Newtonian fluids in three chaotic geometries: Two-Layer Crossing Channel Micromixer, C-shaped channel and serpentine channel. The process is validated for non-Newtonian flow in a complex geometry which heated by a constant flux. Secondary flow structures are formed in the chosen geometries enhance significantly the fluid dynamic performances. To characterize this performance Poincaré map method is presented for different geometries with various cases of fluid power-law index. Thermal mixing behavior with two different inlet temperatures of shear-thinning fluids in the considered geometries is performed. For various cases of fluid power-law indexes, the TLCCM displayed thermal mixing degree enhancement of 42–84% relative to the thermal mixing degree in both C-shaped and serpentine channels. The second law of thermodynamics is controlled in terms of entropy generation due to the thermal and hydrodynamic process, as a function of low rates of generalized Reynolds number and power-law index, under the effects chaotic advection. Thereby, the TLCCM configuration exhibited very important enhancement of mixing degree than that obtained in other considered geometries, with minimization of friction and thermal irreversibilities.

Effect of Horizontal Spacing on Natural Convection to Power-Law Fluids from Two Horizontally Aligned Cylinders

This paper expounds the effect of horizontal spacing between two horizontally aligned circular cylinders on laminar natural convection to non-Newtonian power-law fluids. Numerical computations have been carried out for the following range of conditions: Grashof number (10 to 105), Prandtl number (0.71 to 100), horizontal spacing (0 to 20 times the cylinder diameter), and power-law index (0.4 to 1.6). The flow, pressure, and thermal fields are pictorially visualized in terms of streamlines, pressure contours, and temperature contours, respectively. The average Nusselt number shows a positive reliance on both Grashof and Prandtl numbers, whereas an adverse dependence is observed on power-law index. Irrespective of all other parameters, shear-thinning fluid behavior is seen to promote the convection, whereas shear-thickening behavior impedes it with reference to the Newtonian fluid. With decrease in the horizontal spacing, the average Nusselt number increases and attains a maximum value corresponding to the optimal spacing, however, it diminishes greatly with further reduction in spacing. Furthermore, the average Nusselt number is in excess of 21-89% at the optimal spacing compared to no-spacing. Finally, this paper is concluded with producing a new correlation for the average Nusselt number.

Natural Convection in Power-Law Fluids from a Pair of Two Attached Horizontal Cylinders

Laminar natural convection in unconfined power-law fluids from two attached horizontal cylinders has been investigated numerically to elucidate the non-Newtonian behavior of the fluid over a wide range of pertinent parameters: Grashof number (10 to 105), Prandtl number (0.71 to 100), and power-law index (0.2 to1.8). The heat transfer characteristics are elucidated in terms of isotherms, local Nusselt number distributions, and average Nusselt number values, whereas the flow characteristics are interpreted in terms of streamlines, local distribution of the pressure drag, and skin friction drag coefficients along with the total drag coefficient values. Under identical conditions, the average Nusselt number shows a positive dependence on both Grashof and Prandtl number, whereas it shows an adverse dependence on power-law index. Overall, shear-thickening fluid behavior impedes the convection heat transfer, whereas shear-thinning fluid behavior promotes it with reference to the Newtonian fluids. The heat transfer from an individual cylinder in attached condition has been degraded compared to the case of a single horizontal cylinder. Furthermore, the heat transfer rate of the top cylinder is reduced by 29%–41% relative to that of the bottom cylinder due to preheating of the thermal plume.

Thermal Mixing of Impinging Laminar Streams of Shear-Thinning Fluids

Thermal mixing behavior of shear-thinning fluids with the specified heat flux boundary condition at mixing zone walls is studied numerically to investigate the effect of Reynolds number (10 to 50), power-law index (0.6161 to 1), Nusselt number (104 to 106) for external air flows and dimensionless ambient temperature (−2.7 to 1.3). The temperature is a passive tracer that quantifies the degree of mixing in this study. Detailed kinematics shows the formation of recirculation zones at the mixing channel walls. Length required to achieve the well mixed condition (i.e., a flat temperature profile across the channel height) is shorter at low Reynolds number, convective heat transfer coefficient and ambient temperature, and high power-law index values. In the impingement zone, a faster reduction in mixing index has been observed with respect to mixing length at high power-law index and low Reynolds numbers, while Nusselt number and ambient temperature exert only a weak influence. Under appropriate conditions, significant energy exchange between the system and surroundings can occur and has been analyzed in detail in this work. This work finds its applications in the improved mixing as practiced in the processing and production of food-stuffs, fine chemicals, personal care products, etc.

Controlling the elongational flow behavior of complex shear-thinning fluids without affecting shear viscosity

Complex flow fields including high elongational deformation occur in numerous industrial processes such as spraying, coating, fiber spinning, and screen or inkjet printing. Fully exploiting the potential of these technologies suffers from a lack of knowledge regarding how elongational flow properties of the processed fluids affect the results of these operations. Here, we present two strategies that allow for varying the elongational flow behavior independent of shear rheology. First, two acrylic thickener solutions that differ with respect to the fraction of hydrophobic co-monomers and hence with respect to their degree of inter- and intramolecular hydrophobic association were mixed to vary the elongational relaxation time, as determined using capillary breakup elongational rheometry (CaBER), by almost two orders of magnitude without affecting shear viscosity of these solutions in a wide, processing-relevant shear rate range. Second, a substantial increase in the elongational flow resistance was achieved by adding a small amount of plate-like particles without affecting the shear viscosity of these thickener solutions. A fourfold increase of the elongational relaxation time was observed upon the addition of 3.5 vol.% of glass flakes to such a highly shear-thinning system. A similar effect was also observed for an industrial waterborne automotive basecoat due to added aluminum flakes. This work may be useful for product development since the control of extensional viscosity can improve technological applications, and the introduced model systems may therefore be used for systematic, goal-oriented investigations of the relevance of elongational flow properties in the technological processes mentioned above.

Effects of Ionic Strength on Lateral Particle Migration in Shear-Thinning Xanthan Gum Solutions.

Viscoelastic fluids, including particulate systems, are found in various biological and industrial systems including blood flow, food, cosmetics, and electronic materials. Particles suspended in viscoelastic fluids such as polymer solutions migrate laterally, forming spatially segregated streams in pressure-driven flow. Viscoelastic particle migration was recently applied to microfluidic technologies including particle counting and sorting and the micromechanical measurement of living cells. Understanding the effects on equilibrium particle positions of rheological properties of suspending viscoelastic fluid is essential for designing microfluidic applications. It has been considered that the shear-thinning behavior of viscoelastic fluid is a critical factor in determining the equilibrium particle positions. This work presents the lateral particle migration in two different xanthan gum-based viscoelastic fluids with similar shear-thinning viscosities and the linear viscoelastic properties. The flexibility and contour length of the xanthan gum molecules were tuned by varying the ionic strength of the solvent. Particles suspended in flexible and short xanthan gum solution, dissolved at high ionic strength, migrated toward the corners in a square channel, whereas particles in the rigid and long xanthan gum solutions in deionized water migrated toward the centerline. This work suggests that the structural properties of polymer molecules play significant roles in determining the equilibrium positions in shear-thinning fluids, despite similar bulk rheological properties. The current results are expected to be used in a wide range of applications such as cell counting and sorting.