Shear-thinning Flow Research Articles

Rheological Behavior of the Composites of Carboxymethylcellulose-Zinc Oxide/Starch

The rheological behavior of the carboxymethylcellulose (CMC) / starch blends with and without zinc oxide (ZnO) have been investigated by controlled shear rate testing ramps. All blends showed high shear thinning flow behavior, (n=0,10 - 0,32) without ZnO and (n=0,10-0,29) with ZnO. The consistency index (K) and apparent viscosity (ηa,100 ) decreased with increasing amount of starch and with the addition of 1% wt ZnO. The results also showed that occurs an inversion in the elastic and viscous modulii behavior between 25 and 700C, obeying the Arrhenius equation. The study of activation energy showed that ZnO acts in the CMC phase, increase of viscosity of mixtures. The creep and recovery test indicated a decrease in the viscosity zero shear rate, indicating an increase of viscous character. The phase angle results also confirm an increase of viscosity with addition of ZnO.

Rheological Properties and Ignition and Combustion Characteristics of Biochar–Algae–Water Slurry Fuels

This study examined the rheological properties, ignition, and combustion characteristics of biochar–algae–water (BAW) slurry fuels. A pine sawdust biochar with a median particle size (D50) of approximately 12 μm and algae Chlorella vulgaris in dry powder form with D50 of approximately 19 μm were used. The BAW slurries with a constant solid loading of 40 wt % and algae/biochar ratio varying from 0 to 0.2 by weight were prepared. The apparent viscosity was measured using a Haake VT550 cone-and-plate viscometer. The stability of the slurries was characterized using a “drop rod” method. Ignition and combustion characteristics of the slurries were studied using a suspended single-droplet technique. A single droplet of a slurry fuel with a diameter ranging from 0.5 mm to 1.5 mm was suspended on a silicon carbide fibre and burned in air at 1023 K in an electrically heated tube furnace. The ignition and combustion processes of the droplet were recorded using a CCD camera at 200 fps. The ignition delay time, burnout time, and burning rate were determined. The BAW slurries showed shear-thinning flow behavior. The slurries had higher viscosity and greater stability at higher algae proportion in the solid. The ignition and combustion process of BAW slurries followed the sequence of water evaporation, devolatilization, ignition, and combustion of the solid residue. The combustion of the residual solid was diffusion controlled under the experimental conditions and the burning rates of the BAW slurry droplets ranged from 0.15 to 0.25 mm2 s−1.

Heat transfer enhancement in suddenly expanding annular shear-thinning flows

Heat transfer enhancement in suddenly expanding annular pipe flows of Newtonian and shear-thinning non-Newtonian fluids is studied within the steady laminar flow regime. Conservation of mass, momentum, and energy equations, along with the power-law constitutive model are numerically solved. The impact of inflow inertia, annular-diameter-ratio, k, power-law index, n, and Prandtl numbers, is reported over the following range of parameters: Re = {50, 100, 150}, k = {0, 0.5, 0.7}; n = {1, 0.8, 0.6}; and Pr = {1, 10, 100}. Heat transfer enhancement downstream of the expansion plane, i.e., Nusselt numbers greater than the downstream fully developed value, Nu/Nufd > 1, is only observed for Pr = 10 and 100. In general, higher Prandtl numbers, power-law index values, and annular-diameter-ratios, result in more significant heat transfer enhancement downstream of the expansion plane. Heat transfer augmentation, for Pr = 10 and 100, increases with the annular-diameter-ratio. For a given annular-diameter-ratio and Reynolds numbers, increasing the Prandtl number from Pr = 10 to Pr = 100, always results in higher peak Nu values, Numax, for both Newtonian and shear-thinning flows. All Numax values are located downstream of the flow reattachment point, in the case of suddenly expanding round pipe flows, i.e., κ = 0. However, for suddenly expanding annular pipe flows, i.e., κ = 0.5 and 0.7, Numax values appear upstream the flow reattachment point. For Pr = 10 and 100, shear-thinning flows display two local peak Nu/Nufd values, in comparison with one peak value in the case of Newtonian flows. The highest heat transfer enhancement, Numax/Nufd ≈ 5, is observed at κ = 0.7, n = 0.6, and Pr = 100.

Rheological flow models of banana peel pectin jellies as affected by sugar concentration

ABSTRACTIn the present study, peel pectin jellies (PPJ) were isolated from banana peel Musa acuminata Colla (AAA, cv ‘Berangan’) varieties using water bath extraction; five jellies were produced, namely, PPJ_68%, PPJ_70%, PPJ_71%, PPJ_72%, and PPJ_76%. The effect of sugar content on the rheology of the PPJ and commercial fruit jelly was conducted at 25°C within 0.05–100 s−1 shear rate. Flow behaviour was evaluated on the test dispersions while frequency sweeps (Ea) to obtain the viscoelastic (G’ and G”) were performed on the jellies. PPJ dispersion showed shear thinning flow behaviour, a good fit to the Casson model. Sugar concentration does not affect Casson parameters (Kc, Koc, ɳca, and σoc). Frequency sweep decreased as viscosity increased which revealed high dependence for both G’ and G”. Tan δ for PPJ was more than unity which showed that jelly has less elastic properties. PPJ with the lowest sugar concentration, PPJ_68%, conducted at a high shear rate showed it was compatible with validation of the Cox–Merz rule.

Effect of shear thinning on superhydrophobic slip: Perturbative corrections to the effective slip length

We find expressions for the change in hydrodynamic slip length when a weakly shear-thinning fluid flows longitudinally, or transversely, over a periodic array of flat, unidirectional no-shear slots from a modified reciprocal theorem of Stokes flow and exact solutions for a Newtonian fluid.

Impact of mechanochemical treatment of organophilic Indian bentonites: implications for their rheology

To study and determine the dependency of rheological properties and flow behaviour of organobentonites on mechanochemical modification viz. grinding and preparation temperature of organobentonite, stearyldimethylbenzylammonium-bentonites (SDMBA-bentonites) were prepared by interacting stearyldimethylbenzylammonium chloride with Indian bentonite at different reaction temperature of 40, 60, 80, 90 and 100 °C and the products were ground and passed through sieve (micronization) of 100 mesh BSS (< 150 µm) and also the product obtained at 40 °C was further processed for micronization using 150 (< 105 µm), 240 (< 63 µm) and 350 (< 45 µm) mesh BSS sieves. As there was increase in the micronization and the reaction temperature, the bulk density and particle size decreased with simultaneous increase in the surface area of SDMBA-bentonites. The enhancement of the viscosity, rheological parameters and gel index of the toluene dispersions of these SDMBA-bentonites was also observed. The decrease in particle size and bulk density with simultaneous increase in specific surface area and swelling in nitrobenzene SDMBA-bentonites leads to the formation of larger hydrogen bond network to generate improved rheological properties by increased magnitude of chemical interaction between SDMBA cations and toluene. The rheological behaviour study revealed that all the toluene–SDMBA-bentonite dispersions exhibit the shear-thinning flow behaviour and the micronization and reaction temperature influence the degree of shear-thinning, stability of the gel structures and yield stress of the dispersions. The incorporation of a mixture of 5 vol% of H2O in methanol as polar activator studied in the range of 33–100 wt% of SDMBA-bentonite reinforced the rheological properties, viscosity and gel volume, degree of shear-thinning, stability of the gel structures and yield stress of the toluene–SDMBA-bentonite dispersions. The SDMBA-bentonites with polar activator having concentration of 65 wt% exhibited the optimum rheological reinforcement. The rheological properties were found to be more enhanced by the ultrasonication relative to conventional stirring/shearing. Power law and Casson equations have been used to describe the rheological properties of the toluene–SDMBA-bentonite dispersions.

Rheological characterization of the exopolysaccharide Paenan in surfactant systems

Rheology-controlling agents are of importance for numerous products in a variety of industries. Replacement of synthetic chemicals with natural additives is desired in light of current environmental awareness and limited fossil resources. This study investigates the rheological features of Paenan, an exopolysaccharide produced by Paenibacillus polymyxa. Paenan exhibits highly shear-thinning flow behavior at concentrations ≥0.1% in 0.5% NaCl. Because of its pronounced intermolecular network, it forms stable, weak gels, thereby delivering elasticity as well as thixotropy. Application-relevant flow behavior is obtained with 60–65% less polymer as compared to the benchmark commercial products Xanthan and Gellan. In mixtures with surfactants (sodium lauryl ether sulfate, cetrimonium chloride, cocamidopropyl betaine, or lauryl glucoside), Paenan displays outstanding compatibility with every class of surfactant, making it superior to the partially incompatible Xanthan and Gellan. The weak-gel character of Paenan/surfactant systems is retained with three out of four surfactants, rendering Paenan highly interesting for various applications.

Dynamical feature of particle dunes in Newtonian and shear-thinning flows: Relevance to hole-cleaning in pipe and annulus

Cuttings transport under laminar and turbulent liquid flow in horizontal and deviated pipes were investigated. Several experiments were conducted both for single-phase liquid flow and liquid-particle flow in order to study the impact of rotation of a drill string, as well as fluid rheology and particle size on dynamic feature of particle dunes. Long time series of pressure gradients and flow patterns of the liquid-particle flow were obtained for off-line analysis. Fast Fourier Transform (FFT) was the methodology used to study the time series of pressure gradient signals. The time series were recorded as long continuous experimental sequences, while the flow conditions were changed in time stamped steps. The off-line analysis could then be carried out on each sequence which was easily extracted from the original based on the time intervals. The analysis indicated an existence of dominant frequencies corresponding to liquid and particle dynamics, and to the rotational speed of the drill string. It was found that the distribution and width of the frequency spectrum can be used as an indicator of the particle concentration at given flow conditions. Particle size has a large impact on the frequency spectrum, mostly when the drill string is rotating. The results of this study could help in real time prediction of downhole conditions in petroleum geology, exploration, and drilling operations.

Rheological characterisation of biologically treated and non-treated putrescible food waste

Food waste is gaining increasing attention worldwide due to growing concerns over its environmental and economic costs. Understanding the rheological behaviour of food waste is critical for effective processing so rheological measurements were carried out for different food waste compositions at 25, 35 and 45 °C. Food waste samples of various origins (carbohydrates, vegetables & fruits, and meat), anaerobically digested and diluted samples were used in this study. The results showed that food waste exhibits shear-thinning flow behaviour and viscosity of food waste is a function of temperature and composition. The composition of food waste affected the flow properties. Viscosity decreased at a given temperature as the proportion of carbohydrate increased. This may be due to the high water content of vegetable & fruits as the total solids fraction is likely to be a key controlling factor of the rheology. The Herschel–Bulkley model was used successfully to model food waste flow behaviour. Also, a higher strain was needed to break down the structure of the food waste as digestion time increased.

Pectin from Husk Tomato (Physalis ixocarpa Brot.): Rheological behavior at different extraction conditions

A rheological study was carried out to evaluate formulations of test dispersions and gels of high methoxyl pectins (HTHMP) obtained at different conditions from husk tomato waste (Physalis ixocarpa Brot.). The effect of extraction agent (hydrochloric acid or citric acid), blanching time (10 or 15min) and extraction time (15, 20 or 25min) on the rheology of the tested samples was evaluated. Flow behavior and activation energy were evaluated on the test dispersions, while (Ea) frequency sweeps, temperature sweep, creep-recovery test and penetration test were performed on the gels. HTHMP dispersions showed shear thinning flow behavior, while showing a good fit to Cross model. Extraction agent, blanching time and extraction time did not have effect on Cross parameters (ηz, η∞, C, and m). Ea decreased as blanching time and extraction time increased. Frequency sweeps revealed high dependence on frequency for both G’ and G”, while temperature sweeps (25- 95°C) showed thermostable husk tomato pectin gels. Hydrocloric acid (HCl) extracted pectin gels showed stronger structure than citric acid (CA) gels.

Influence of water deficit on the main polysaccharides and the rheological properties of Aloe vera (Aloe barbadensis Miller) mucilage

The aim of this study was to evaluate the effect of water deficit on the composition of the main polysaccharides and rheological behaviour from Aloe vera (Aloe barbadensis Miller) mucilage. In particular, plants with 0 (D0), 40 (D40) and 60% (D60) water deficits were used. Water-soluble polysaccharides were isolated and subjected to carbohydrate and glycosidic linkage analysis. The steady-shear and linear oscillatory flows were studied, not only in fresh but also in reconstituted mucilages. Acemannan and pectic substances were the predominant polysaccharides in the Aloe vera mucilage, being the bioactive polymer acemannan the most affected by water deficit. Thus, increasing the water deficit by up to 60% promoted a mannose decrease of 41%, although a significant increase in its average molecular weight, from 54 to 98kDa, was detected. Interestingly, acemannan did not undergo deacetylation as a consequence of the water deficits applied. All Aloe vera mucilages, either fresh or reconstituted, exhibited a shear-thinning flow behaviour (n <1). However, water deficit affected the mechanical properties, changes being more noticeable in the reconstituted mucilages. Thus, the viscosity (η1) of reconstituted mucilages increased, from 0.12 to 0.28 Pa·s, as water deficit increased, whereas their flow index (n) decreased from 0.57 to 0.47. Further, D40 and D60 reconstituted mucilages exhibited an Ea of 17.4 and 17.6kJ/mol, respectively, whilst, for D0, Ea was 16.7kJ/mol. Interestingly, only the D40 reconstituted mucilage showed a crossover point at 7.39rad/s between viscous and elastic modulus. The understanding of the influence of water deficit on the main physico-chemical characteristics of Aloe vera polysaccharides and, in turn, of its effect on the rheology of the mucilages could be a useful tool for the design, development and control of biologically active ingredients based on the Aloe vera plant.

The pharmaceutical applications of a biopolymer isolated from Trigonella foenum-graecum seeds: Focus on the freeze-dried matrix forming capacity

The aim of the present study was to evaluate the funtion of fenugreek seed mucilage (FSM) as potential matrix forming agent for orodispersible pharmaceutical lyophilisates. The FSM was isolated and characterized. FSM colloidal dispersions were prepared and the rheological evaluation was performed. Oral lyophilisates (OLs) with different FSM concentrations, containing meloxicam as model drug were prepared by freeze drying method. The OLs were characterized and compared to gelatin containing tablets, prepared under the same conditions.The FSM dispersions revealed shear thinning flow type. Based on colloidal dispersions' rheological properties, five FSM concentrations were taken forward to the lyophilization step. Completely dry and elegant tablets were obtained. Texture analysis indicated highly porous structures, confirmed by SEM analysis, which explain the fast disintegration properties. All the prepared tablets disintegrated in less than 47 s. The disintegration process was prolonged by the increase in FSM content, due to the high viscosity the polymer creates in aqueous media. FSM tablets presented longer disintegration times, as compared to gelatin tablets, but also higher crushing strength. Considering the fast disintegration and the high crushing strength, FSM is a good candidate as matrix forming agent for fast disintegrating dosage forms or other freeze-dried preparations.

Graphene Oxide: An All-in-One Processing Additive for 3D Printing.

Many 3D printing technologies are based on the development of inks and pastes to build objects through droplet or filament deposition (the latter also known as continuous extrusion, robocasting, or direct ink writing). Controlling and tuning rheological behavior is key for successful manufacturing using these techniques. Different formulations have been proposed, but the search continues for approaches that are clean, flexible, robust and that can be adapted to a wide range of materials. Here, we show how graphene oxide (GO) enables the formulation of water-based pastes to print a wide variety of materials (polymers, ceramics, and steel) using robocasting. This work combines flow and oscillatory rheology to provide further insights into the rheological behavior of suspensions combining GO with other materials. Graphene oxide can be used to manipulate the viscoelastic response, enabling the formulation of pastes with excellent printing behavior that combine shear thinning flow and a fast recovery of their elastic properties. These inks do not contain other additives, only GO and the material of interest. As a proof of concept, we demonstrate the 3D printing of additive-free graphene oxide structures as well as polymers, ceramics, and steel. Due to its amphiphilic nature and 2D structure, graphene oxide plays multiple roles, behaving as a dispersant, viscosifier, and binder. It stabilizes suspensions of different powders, modifies the flow and viscoelasticity of materials with different chemistries, particle sizes and shapes, and binds the particles together, providing green strength for manual handling. This approach enables printing complex 3D ceramic structures using robocasting with similar properties to alternative formulations, thus demonstrating the potential of using 2D colloids in materials manufacturing.

Influence of sage seed gum on some physicochemical and rheological properties of wheat starch

The effect of sage seed gum at different concentrations (0, 0.1, 0.25, and 0.5% w/w) on swelling power, solubility index, paste clarity, and steady shear flow behavior of wheat starch dispersion (2%, w/w) was evaluated. Sage seed gum addition enhanced the swelling power at all temperatures chosen (50–90°C). It also increased leakage of starch polymers at temperatures &lt;80°C. In contrast, this addition decreased the activation energy needed for swelling (up to 34.17%) and solubilization (up to 30.85%). The paste clarity of wheat starch significantly decreased in the presence of SSG (p &lt; 0.05). The apparent viscosity increased with the increasing SSG concentration and all the samples exhibited shear thinning flow behavior. Among the rheological model used, Sisko's model fitted well to the experimental data (R2 = 0.988–0.999, RMSE = 0.001–0.0018). Accordingly, addition of sage seed gum up to 0.5% resulted in an approximately twofold increase in η∞, 251‐fold in ks, but a 19% decrease in ns values of wheat starch dispersion. The concentration dependence of the apparent viscosity at a shear rate range of 10–100 s−1 was also analyzed using well‐defined models.

Stability of the shear-thinning boundary-layer flow over a flat inclined plate

In this study, we consider the boundary-layer flow of an inelastic non-Newtonian fluid over an inclined flat plate. Using two popular generalized Newtonian models, we determine base flow profiles and associated linear stability results for a range shear-thinning fluids. In addition to neutral stability curves, we also present results concerning the linear growth of the Tollmien–Schlichting waves as they propagate downstream. Furthermore, to gain an insight into the underlying physical mechanisms affecting the destabilization of the disturbances, an integral energy equation is derived and energy calculations are presented. Results from all three analyses suggest that the effect of shear-thinning will act to stabilize the boundary-layer flow. Consequently, it can be argued that the addition of shear-thinning agents could act as a passive control mechanism for flows of this nature.

Effects of Pore and Grain Size on Water and Polymer Flooding in Micromodels

We have conducted a comprehensive series of experiments to evaluate the effects of pore size distribution of porous media on the dynamics of shear-thinning fluid flow and oil displacement efficiency. To do so, we have conducted microfluidic experiments, using micromodels fabricated from X-ray computed tomography images of sand-packs with varying grain sizes to create a realistic pore network. Three micromodels with well-defined particle size distribution were fabricated and used in our experiments. The use of micromodels to assess the effectiveness of polymer flooding is often superior to methods such as core flooding because of the detailed pore-scale information obtained during the experiments. The micromodels were initially saturated by oil, and the displacing fluids were prepared as aqueous solutions with dissolved xanthan gum. The dynamics and patterns of the interface displacement as well as the size distribution of the trapped oil ganglia were visualized using an optical microscope. The main findin...

A model for non-Newtonian flow in porous media at different flow regimes

Polymeric liquids are of great practical importance for porous media flow as they can be used to improve the sweep of water in the reservoir and therefore improve the recovery of oil. Due to the non-Newtonian behavior of these liquids, they are extremely challenging to model. In this paper, we present a model that is capable of describing the most commonly observed flow regimes in porous media: (i) Newtonian, (ii) Shear thinning, (iii) Shear thickening, and (iv) Mechanical degradation. The novel feature of our model is that the time constants for the shear thinning and shear thickening behavior are related to variations in reservoir properties and conditions, thus making it possible to translate lab results to larger scale without introducing new fitting parameters. Furthermore, we present a way to estimate polymer mechanical degradation in porous media. In our model, the polymer degradation rate is linked to the effective pore radius (using a Kozeny-Carman type equation), shear stress, and polymer molecular weight, M w . The degradation results in a lower M w , while the polymer volumetric concentration is unaffected. The model is applied to a series of laboratory core flood experiments conducted with partially hydrolyzed polyacrylamide, HPAM, of different initial M w ranging from 5 to 20 MDa in seawater, and core permeability varied from 137 to 2019 mD. The flow rate is varied approximately three orders of magnitude and covers the shear thinning, shear thickening, and degradation flow regimes. We show that our model is able to reproduce experimental rate-dependent flow resistance, as well as viscosity of effluent samples. An important aspect supporting the use of the model as a predictive tool is that all the simulations with a given brine have made use of a single set of input parameters to describe the observed shear thickening and degradation behavior. Simulation of a second experimental series using low salinity brine required a separate set of input parameters for the shear thickening and shear degradation. The onset of shear thickening was not affected while shear thickening was reduced and degradation appeared to be slower.

An experimental study of the rheological properties and stability characteristics of biochar–algae–water slurry fuels

ABSTRACTAn innovative technology to integrate the utilization of biochar and algae in the form of slurry fuel for power generation was conceptualized. This study aimed to understand the rheological properties and stability characteristics of biochar–algae–water (BAW) slurry fuels. The BAW slurries were prepared by mixing pine sawdust biochar and Chlorella vulgaris in different proportions first and then dispersing the mixtures in deionized water. The BAW slurries showed shear-thinning flow behavior, which became more apparent as the algae proportion in the solid increased. The slurries displayed better stability at higher algae proportion due to increased water uptake capacity and enhanced flocculation.

Laminar convective heat transfer of shear-thinning liquids in rectangular channels with longitudinal vortex generators

Heat and fluid flow in a rectangular channel heat sink equipped with longitudinal vortex generators have been numerically investigated in the range of Reynolds numbers between 25 and 200. Aqueous solutions of carboxymethyl cellulose (CMC) with different concentrations (200–2000ppm), which are shear-thinning non-Newtonian liquids, have been utilised as working fluid. Three-dimensional simulations have been performed on a plain channel and a channel with five pairs of vortex generators. The channels have a hydraulic diameter of 8mm and are heated by constant wall temperature. The vortex generators have been mounted at different angles of attack and locations inside the channel. The shear-thinning liquid flow in rectangular channels with longitudinal vortex generators are described and the mechanisms of heat transfer enhancement are discussed. The results demonstrate a heat transfer enhancement of 39–188% using CMC aqueous solutions in rectangular channels with LVGs with respect to a Newtonian liquid flow (i.e. water). Additionally, it is shown that equipping rectangular channels with LVGs results in an enhancement of 24–135% in heat transfer performance vis-à-vis plain channel. However, this heat transfer enhancement is associated with larger pressure losses. For the range of parameters studied in this paper, increasing the CMC concentration, the angle of attack of vortex generators and their lateral distances leads to an increase in heat transfer performance. Additionally, heat transfer performance of rectangular channels with longitudinal vortex generators enhances with increasing the Reynolds number in the laminar flow regime.

Rheology, microstructural characterization and physical stability of W/α-PINENE/W emulsions formulated with copolymers

In this work the microstructure and the physical stability of emulsions containing α-pinene and gellan gum were studied as a function of Atlas™ G-5000/Atlox™ 4912 copolymer mass ratio, R, used as emulsifier. In order to reach this objective, electrolytic conductivity measurements, laser diffraction, confocal laser scanning microscopy (CLSM) and rheology were used. Electrolytic conductivity tests along with CLSM supported the formation of W/α-pinene/W multiple emulsions in all systems containing the most hydrophilic copolymer. Parameter R did not significantly influence either the mean diameters or the span when both copolymers were used. However the lack of Atlas G-5000, not only did it provoke an important increase of mean diameter of droplets, but it also caused the formation of a simple O/W emulsion instead of a multiple emulsion. All emulsions showed shear thinning flow behaviour. The mechanical spectra of multiple emulsions with R≥2 were similar to each other and independent of aging time. A reduction of R led to a decrease in G′ and G″ values and aging time yielded increasing G′ values probably due to the occurrence of incipient creaming. Conversely, the emulsion without Atlas™ G-5000 showed a drop of viscoelastic moduli with aging time due to a coalescence process. These multiple emulsions may find applications in agrochemistry since some active ingredients may be encapsulated in the inner phase, enabling the delivery of hazardous ingredients in a safer way, along with the use of α-pinene which is an easily biodegradable green solvent.