non-Newtonian Rheological Behavior Research Articles

Non-Newtonian Viscosity Modeling of Crude Oils—Comparison Among Models

The presence of precipitated wax or even just low temperatures may induce non-Newtonian rheological behavior in crude oils. Such behavior can be found at operating conditions, for instance, in reservoirs at deep-water conditions. Therefore, reliable rheological models for crude oils applicable over the wide range of conditions the fluid may encounter are essential for a large number of oil technology applications. Such models must also be composition dependent, as many applications require predicting the rheological behavior of the fluid under strong compositional changes, e.g., recovery applications such as vapor extraction (VAPEX) processes or blending of fluids for improved rheological characteristics for piping, among many other applications. In this study, a comparative analysis between some published models applicable to the description of the non-Newtonian behavior of crude oils is carried out. Emphasis is placed on the stability of the model predictions within the wide range of conditions that may be encountered.

Rheological properties of biopolymers drilling fluids

Drilling muds are complex fluids, generally used to clean the well, maintain hole integrity, transport the rock cuttings, lubricate the drill bit and control formation pressures. Two basic types of drilling fluids are used, water based muds (WBM) and oil based muds (OBM). OBM are very effective but polluting, and environmental regulations continue to restrict the use of oil based muds in many areas of the world. In order to reduce the mud toxicity, we developed water based mud systems using two biopolymers, which are xanthan gum and scleroglucan, generally proposed for high permeability reservoirs or for complex geometries such as horizontal wells. In this study, we evaluated the rheological behaviour of different samples and we determined the effect of components such as clay, calcium carbonate and potassium chloride. This formulations exhibit non-Newtonian rheological behaviour which can be described well by the tree parameter in Herschel–Bulkley rheological model.

Microrheology of a Swollen Lyotropic Lamellar Phase

Dynamics of nano-sized colloidal particles in a swollen lyotropic lamellar phase of a nonionic surfactant has been studied by three methods of microrheology. By electrophoretic microrheology (EPM), we find two relaxation processes respectively relating to the fluctuation of membranes and topological defects in lamellar structure. By direct tracking of particles under a microscope and manipulating them with an optical tweezers, we obtained detailed information on diffusion of a particle at low frequencies. We observed the jump-trap motion of a particle and the non-Newtonian rheological behavior at low frequencies.

Influence of polyethylene oxide on absorption of carbon dioxide into aqueous N-methyldiethanolamine solution

Carbon dioxide was absorbed into aqueous polyethylene oxide (PEO) solution containing N-methyldiethanolamine (MDEA) in a flat-stirred vessel to investigate the effect of non-Newtonian rheological behavior of PEO on the chemical absorption rate of CO2, where the reaction between CO2 and MDEA was assumed to be a first-order reaction with respect to the concentration of CO2 and MDEA, respectively. A unified correlation equation containing the Deborah number, which reflects the viscoelastic properties of a non-Newtonian liquid, was used to obtain the volumetric liquid-side mass transfer coefficient of carbon dioxide in aqueous PEO solution. The elastic properties of PEO accelerated the absorption rate of CO2 compared with that of a Newtonian liquid based on the same values of viscosity.

Optimal determination of rheological parameters for Herschel–Bulkley drilling fluids and impact on pressure drop, velocity profiles and penetration rates during drilling

Drilling fluids containing bentonite and bentonite–lignite as additives exhibit non-Newtonian rheological behavior which can be described well by the three parameter Herschel–Bulkley rheological model. It is shown that determination of these parameters using standard techniques can sometimes provide non-optimal and even unrealistic solutions which could be detrimental to the estimation of hydraulic parameters during drilling. An optimal procedure is proposed whereby the best value of the yield stress is estimated using the Golden Section search methodology while the fluid consistency and fluid behavior indices are determined with linear regression on the transformed rheometric data. The technique yields in many cases results which are as accurate as these obtained by non-linear regression but also gives positive yield stress in cases where numerical schemes give negative yield stress values. It is shown that the impact of the values of the model parameters can be significant for pressure drop estimation but less significant for velocity profile estimation for flow of these fluids in drill pipes and concentric annuli. It is demonstrated that very small differences among the values of the model parameters determined by different techniques can lead to substantial differences in most operational hydraulic parameters in oil-well drilling, particularly pressure drop and apparent viscosity of the fluid at the drilling bit affecting penetration rates, signifying thus the importance of making the best simulation of the rheological behavior of drilling fluids.

Identification of rheological parameters describing the physico-chemical properties of anaerobic sulphidogenic sludge suspensions

This work determined rheological parameters able to describe the rheological properties of the flocculant sludge presents in sulphidogenic anaerobic bioreactors, i.e. a MBR (membrane bioreactor) and a CSTR (continuous stirred tank reactor). Both sludges displayed a non-Newtonian rheological behaviour with shear thinning properties, slightly thixotropic for a TSS content ranging from 0 to 23 g l −1. Both sulphidogenic sludges displayed pseudoplastic properties. To predict the rheological properties of other sludges, three rheological models (Casson, Bingham and Herschel–Buckley) were selected and fitted to the experimental rheological data obtained. The mathematic equations of these three models give seven rheological parameters. To select relevant rheological parameters, exponential and second-order polynomial equations were tested to evaluate the relationship between the rheological parameters and the sludge TSS content. These two last variables were statistically fitted with a second-order polynomial correlation, which allows to select rheological parameters able to describe the evolution of the sludges in both bioreactors. The Bingham model applied on the pseudo-Newtonian area of a rheogram gives the more suitable rheological parameters to describe the evolution of the rheological properties of anaerobic sulphidogenic flocculant sludge. The selected rheological parameters of the sulphidogenic sludges are affected by the bioreactor type and its operation time. This is likely linked to changes in microbial consortia involving a change in biomass morphology and a decrease in floc strength.

Hydrodynamics and mass transfer coefficient in three-phase air-lift reactors containing activated sludge

This study was to investigate the impacts of operating conditions and liquid properties on the hydrodynamics and volumetric mass transfer coefficient in activated sludge air-lift reactors. Experiments were conducted in internal and external air-lift reactors. The activated sludge liquid displayed a non-Newtonian rheological behavior. With an increase in the superficial gas velocity, the liquid circulation velocity, gas holdup and mass transfer coefficient increased, and the gas residence time decreased. The liquid circulation velocity, gas holdup and the mass transfer coefficient decreased as the sludge loading increased. The flow regime in the activated sludge air-lift reactors had significant effect on the liquid circulation velocity and the gas holdup, but appeared to have little impact on the mass transfer coefficient. The experimental results in this study were best described by the empirical models, in which the reactor geometry, superficial gas velocity and/or power consumption unit, and solid and fluid properties were employed.

Effect of inoculum and sludge concentration on viscosity evolution of anaerobic granular sludges

The rheological behaviour of granular sludges (diameter 20-315 microm) originating from different anaerobic reactors was carried out using rotation tests. The sieved granular sludges suspensions display a non-Newtonian rheological behaviour and the limit viscosity was therefore used as a rheological parameter. The values obtained, which depend on the shear rate used, were strongly influenced by the total suspended solids (TSS) content of granular sludge and an exponential relation was found between the TSS and the rheological parameter limit viscosity. The increase of viscosity as a function of TSS content of the granular sludge as well as the increase of granule size underlines the importance of the interaction between granules in the evolution of this rheological parameter. Significant differences in granular sludge limit viscosity were found for granular sludge of different origins. All measurements performed with 10 g.l(-1) TSS granular sludge indicate the ability of the chosen rheological parameter to describe different granular sludge quality.

Hydrodynamics and mass transfer coefficient in activated sludge aerated stirred column reactor: experimental analysis and modeling

The aerated stirred reactor (ASR) has been widely used in biochemical and wastewater treatment processes. The information describing how the activated sludge properties and operation conditions affect the hydrodynamics and mass transfer coefficient is missing in the literature. The aim of this study was to investigate the influence of flow regime, superficial gas velocity (U(G)), power consumption unit (P/V(L)), sludge loading, and apparent viscosity (mu(ap)) of activated sludge fluid on the mixing time (t(m)), gas hold-up (epsilon), and volumetric mass transfer coefficient (k(L)a) in an activated sludge aerated stirred column reactor (ASCR). The activated sludge fluid performed a non-Newtonian rheological behavior. The sludge loading significantly affected the fluid hydrodynamics and mass transfer. With an increase in the U(G) and P/V(L), the epsilon and k(L)a increased, and the t(m), decreased. The epsilon, k(L)a, and t(m), were influenced dramatically as the flow regime changed from homogeneous to heterogeneous patterns. The proposed mathematical models predicted the experimental results well under experimental conditions, indicating that the U(G), P/V(L), and mu(ap) had significant impact on the t(m), epsilon, and k(L)a. These models were able to give the t(m), epsilon, and k(L)a values with an error around +/-8%, and always less than +/-10%.

CFD simulations and experimental validation of homogenisation curves and mixing time in stirred Newtonian and pseudoplastic liquids

The aim of this work is to identify a proper Computational Fluid Dynamics (CFD) simulation strategy for the calculation of mixing time in stirred tanks for fluids characterised by either Newtonian or non-Newtonian rheological behaviour. Two different baffled tanks are considered, both stirred with multiple down-pumping 45 ∘ pitched blade turbines (PBT): a small one for extensive, preliminary simulations conducted with water and aimed at determining a generic procedure suitable with low-viscosity, Newtonian liquids; and a bigger one for testing the results with moderately viscous liquids and non-Newtonian fluids. The influence on the predicted mixing time of the tracer injection position, turbulence modelling and numerical parameters is investigated. The results of the simulations are compared with original experimental data and good agreement is obtained in all cases, once the proper mathematical models, solution procedure and relevant parameters are established.

Mass transfer of carbon dioxide in aqueous polyacrylamide solution with methyldiethanolamine

Carbon dioxide was absorbed into aqueous polyacrylamide (PAA) solution containing methyl-diethanolamine (MDEA) in a flat-stirred vessel to investigate the effect of non-Newtonian rheological behavior of PAA on the rate of chemical absorption of CO2, where the reaction between CO2 and MDEA was assumed to be a first-order reaction with respect to the molar concentration of CO2 and MDEA, respectively. The liquid-side mass transfer coefficient (kL), which was obtained from the dimensionless empirical equation containing the viscoelasticity properties of a non-Newtonian liquid, was used to estimate the enhancement factor due to chemical reaction. PAA with elastic property of non-Newtonian liquid made the rate of chemical absorption of CO2 accelerate compared with a Newtonian liquid

Properties of epoxy nanocomposites filled with carbon nanomaterials

Abstract Rheological, mechanical, electrical, and thermal properties of epoxy nanocomposites containing carbon nanomaterials (CNMs) were investigated with different loading. Two kinds of CNMs - multiwalled carbon nanotubes (MWNTs) and carbon blacks (CBs) - were selected to examine the effect of their geometrical structure on various properties. Under sonication, MWNTs and CBs (0.5, 1.0, and 1.5 wt.-%) were mixed with the epoxy resin by using a solvent. Dispersion of the CNMs in the epoxy nanocomposites was characterized by means of transmission electron microscopy and field emission scanning electron microscopy. Carbon nanotubes (CNTs)/epoxy composites show significant differences from the CBs/ epoxy composites due to their high aspect ratio. It was found that the CNTs/epoxy composites exhibit non-Newtonian rheological behaviour, while the CBs/epoxy composites with the same weight content show Newtonian behaviour. The CNTs/ epoxy composites have better mechanical and thermal properties than the CBs/ epoxy composites. In the CNTs nanocomposites, the percolation threshold of electrical conductivity is found to be less than 0.5 wt.-%, which is too low to be obtained by using other carbon materials such as carbon fibre in polymer composites. Effects of CNM content on the various properties were also examined. As loading of the CNMs increased, improved results were obtained.

Modeling the Flow in the Metering Zone of Single Screw Extruders Using a Helical Geometry Model

Abstract This research work is devoted to the development of a finite element model for the simulation of the flow of polymer melts through the metering zone of single screw extruders. The sets of the governing equations (flow and energy) were solved using the continuous penalty scheme and a streamline upwinding Petrov-Galerkin method, respectively. The non-Newtonian rheological behavior of the fluid was also taken into account by the use of the power-law model. The novelty of this work is the application of this model on the flow of a polypropylene melt through the helical geometry of a single screw extruder. To validate this model, the results of the computer simulations were compared with experimentally measured mass flow rate and also results from a previous model, which was based on the simulation of the flow in a flat flow domain. Comparisons showed that not only there are very good agreements between the model predictions and actual data but also inclusion of the curvature of the screw flights has an important influence on the accuracy of the results.

Lecithin-based oil-in-water microemulsions for parenteral use: Pseudoternary phase diagrams, characterization and toxicity studies

Pseudoternary phase diagrams have been constructed to evaluate the phase behavior of systems containing water/lecithin/polysorbate 80/isopropyl myristate at different polysorbate 80:lecithin weight ratios (K(m)). Oil-in-water microemulsion regions were accurately determined and the influence of the K(m) on the area of existence of such disperse systems was also examined. Viscosity studies as well as particle size analysis by dynamic light scattering were carried out on oil-water microemulsions, and the influence of the oil phase content, the total amount of surfactants and K(m) on the rheological behavior, viscosity, and droplet size of such disperse systems was evaluated. All systems studied showed a water-rich isotrope region (oil-in-water microemulsion area), that was seen to be highly dependent upon the surfactant/cosurfactant weight ratio. Most of the microemulsions analyzed showed a non-Newtonian rheological behavior and both, droplet size, and viscosity of the disperse systems, were found to be much more influenced by the total content of oil phase and surfactants present in the microemulsion than by the K(m). The selected system underwent both stability and in vivo acute toxicity studies, and seemed to be highly stable, even at extreme conditions, and very low toxic according to the results obtained.

Comportamento de propriedades físicas, químicas e reológicas do suco de acerola armazenado a baixa temperatura

Estudou-se o comportamento físico, químico e reológico do suco de cinco genótipos de acerola (CL2, CL5, CL11, R1 e R2) depois de lavadas, as frutas (2 kg) foram esmagadas em um processador manual. Do extrato obtido, em peneira de 1,6 mm, para separar o suco dos resíduos e sementes, foi acondicionado 20 mL de suco de cada amostra em tubos plásticos com dimensões 5 x 3 cm, que foram armazenados em freezer a uma temperatura de -10 °C, durante 10 meses. As leituras de sólidos solúveis totais foram refratométricas, o pH foi aferido através de um potenciômetro, o teor de vitamina C pela técnica da redução do iodo e a viscosidade aparente com viscosímetro de cilindros concêntricos. As determinações foram realizadas inicialmente (mês 0) e bimestralmente (2°, 4°, 6°, 8° e 10° mês). Os parâmetros de viscosidade e vitamina C foram os que mais variaram. O genótipo CL-2 se destacou no teor de sólidos solúveis totais e os R1 e R2 em teores de vitamina C. Os sucos analisados mostraram comportamento reológico não-newtoniano e pseudoplástico.

Investigation of the Contamination of Fractured Formations by Non-Newtonian Oil Pollutants

In many practical applications, non-aqueous phase liquid (NAPL) pollutants exhibiting a clearly non-Newtonian rheological behavior (e.g. crude oil, suspensions of engine oils, asphalt, creosote, etc.) may migrate through fractured formations and contaminate aquifers. The present work is the first step toward the development of non-Darcian models concerning the non-linear NAPL flow in single fractures, and determination of the coupled effects of non-Newtonian NAPL rheology and flow rate on the transient immiscible displacement of an aqueous phase by a NAPL. Initially, a protocol is developed for the preparation and rheological characterization of synthetic non-Newtonian NAPLs, which are based on waxy oils. Then, an artificial transparent glass-etched single fracture of controlled morphology is fabricated and used for the measurement of the non-linear pressure gradient—superficial velocity relationship for the flow of NAPL of varying rheology. Pore network simulations and effective medium approximation (EMA) are used for the interpretation of the experimental results and derivation of an analytic non-Darcian one-phase flow model. Visualization experiments of the immiscible displacement of an aqueous phase by Newtonian and non-Newtonian NAPLs are performed on the artificial fracture under controlled values of the viscosity ratio and capillary number (ratio of viscous to capillary forces). Comparative study of the Newtonian and non-Newtonian NAPL flow patterns allows us to evaluate the interactive effects of NAPL rheology, flow rates and fracture morphology on the spatial and temporal distribution of such liquid pollutants within single fractures.

Structural and rheological properties of microheterogeneous systems ‘solid hydrocarbons–liquid hydrocarbons’

Due to the aggregation of paraffin crystallites, the paraffin-containing disperse system in a nonpolar dispersion medium exhibits non-Newtonian and thixotropic rheological behavior. Experimental flow curves for the highly paraffinaceous crude oil as well as the model systems ‘paraffin–vaseline oil’ were described by the Casson equation. The Casson model was used to connect rheological coefficients and colloidal characteristics of the dispersion. For this purpose, the evaluation of the radius of the primary particle was made, based on the Casson model and those concerned with the interactions between the paraffin particles in nonpolar medium.

Rheological testing of p-tert-butylphenol epoxy–acrylic resin in the presence of reactive diluents

The rheological testing of synthesized para-tert-butylphenol epoxy–acrylic resin in the presence of reactive diluents based on epoxy–acrylic compounds of phenol, para-tert-butylphenol and para-nonylphenol was carried out with a “Rheotest 2” type viscometer. The synthesized resin, the tested reactive diluents, as well as the mixtures based on the resin and the reactive diluents, show non-Newtonian rheological behaviour of the pseudoplastic type. This behaviour can be explained by taking into consideration the possible interactions among the chains of the phenolic reactive diluents, and with the chain of the resin. These interactions can also be due to –OH phenolic groups. As a result, a false increase is registered in the molecular weight of the systems studied.

Finite element analysis of thermoplastic melts flow through the metering and die regions of single screw extruders

This research work is devoted to the development of a mathematical model for the simulation of the flow of polymer melts through the metering and die regions of single screw extruders. The sets of the governing equations (flow and energy) are solved using the finite element method. The power-law model is used to describe the non-Newtonian rheological behavior of the fluid. The standard Galerkin technique is used in conjunction with the continuous penalty scheme to solve the flow equations. Due to the low thermal diffusivity of the polymer melts, a streamline upwinding Petrov-Galerkin method is used to obtain convergent and stable results for the energy equation. This method is based on the extension of a previously developed scheme. The overall solution strategy is based on the Picard iterative scheme. Simulation results are obtained for the flow of a polypropylene melt through the metering and die zones of a laboratory scale extruder. To validate the proposed model, the results of the computer simulations are compared with experimentally measured mass flow rate and pressure profile. These comparisons show that there is very good agreement between the model predictions and actual data.

Rheology of bubble-bearing magmas

The physical effects of air or argon bubbles on the rheology of a calcium aluminosilicate melt have been measured at temperatures ranging from 830° to 960°C, at 1 bar pressure. The melt composition is SiO 2:64, Al 2O 3:23, and CaO:13 (wt%), while bubble volume fractions are: 0, 0.06, 0.13, 0.32, 0.41 and 0.47. Measured Newtonian viscosities range from 10 10 to 10 14 dPa s. Melts with bubble fractions of 0.06 and 0.13 show with increasing temperature ( T) an increasing relative viscosity for T < 850°C. However at T > 850°C, for all bubble fractions the viscosity decreases markedly with temperature. The observed maximum decrease of the relative viscosity is 75% for a bubble fraction of 0.47 at 907°C. At all bubble fractions the viscosity is independent of the applied stress, which ranged from 11 to 677 bars. No clear indications were observed of non-Newtonian rheological behavior. Under our experimental conditions the relative viscosity of the two phase liquid depends primarily on the bubble fraction. Physical and volcanological implications of these measurements are discussed.