Showing papers on "Apparent viscosity published in 1985"

Mechanisms of foam flow in porous media: apparent viscosity in smooth capillaries

Abstract: The apparent viscosity of foam flowing through smooth capillaries was measured experimentally and a mathematical model was developed. Foam texture (a measure of bubble volume) is a key parameter in determining the following properties of foam flowing through a capillary: whether the foam exists as bulk foam or as a chain of bubbles where each pair of bubbles is separated by an individual lamella, the number of lamellae per unit length of the capillary, and the radius of curvature of the gas-liquid interface. The apparent viscosity is the sum of three contributions: that from slugs of liquid between bubbles, the resistance to deformation of the interface of a bubble passing through a capillary, and the surface tension gradient that results when surface active material is swept from the front of a bubble and accumulates at the back of it. The sensitivity of both measured and calculated apparent viscosity is presented as a function of bubble size, capillary radius, ratio of bubble radius to capillary radius, velocity, quality, and surface tension gradient.

Thixotropic behaviour of concentrated bauxite residue suspensions

Abstract: An experimental study on the time-dependent rheology of highly concentrated and flocculated suspensions of bauxite residue (red mud) is presented. Both the thixotropic breakdown with shear and recovery at rest have been quantitatively examined using a vane-shear instrument and a capillary rheometer. It is demonstrated that both the yield stress and the apparent viscosity of the material can be drastically reduced, by orders of magnitude, by shear-induced agitation with a simple anchor impeller. The rate of thixotropic decay is a function of solids concentration, agitation time and speed. With prolonged agitation, the flow properties are brought to an equilibrium level characterized by a finite yield stress and a shear rate-dependent (shear-thinning) viscosity. In the absence of shear, the yield stress gradually increases with time but at a rate considerably slower than the rate of decay in the shear field. Even after an extended rest period of several months, only a fraction of the initial yield stress can be regained. The observed behaviour has been interpreted in terms of a time-dependent but non-reversible transformation of a network structure of flocculated particles initially developed in the red mud. Using a structural kinetic approach, models have been developed for correlating the experimental kinetic data. The paper concludes with a discussion on the practical consequences of the work.

Method for fracturing subterranean formations

Abstract: The present invention provides a method of forming an easily pumpable gelled fluid which is capable of yielding an apparent viscosity of in excess of about 100 centipoise at a shear rate of 40 sec-1 for in excess of about six hours at a temperature in excess of 250° F. An initial gel is formed by adding a selected basic aluminum compound and a phosphoric acid ester to a hydrocarbon liquid. This mixture is aged to form the initial gel and an additional quantity of a basic aluminum compound then is admixed with the initial gel. The crosslinked gel then is introduced into a subterranean formation at a rate and pressure sufficient to fracture the formation.

High‐Shear Viscometry with a Rotational Parallel‐Disk Device

Abstract: A novel technique for measuring viscosity at high shear rates is described. The technique is an extension of a well‐established method, parallel‐disk viscometry, which has been limited traditionally to low shear rates ( 50,000 s−1) to be attained without disrupting the torsional flow field, and thus controlled measurements of viscosity could be made at those shear rates. The presence of flow disturbances such as shear heating, surface fracture, and radial migration, common impediments in high‐shear measurements, can be readily detected with a thixotropic loop program, and the effect of such disturbances can be separated from the actual rheological response of the fluid. Data are presented on some well‐defined fluids, both Newtonian and shear‐thinning, and the limitations of this technique are discussed.

Viscosity of light and heavy water and their mixtures

Abstract: The paper presents measurements of the viscosity of light and heavy water and their mixtures at temperatures between 25°C and 220°C and at pressures from the saturation pressure up to 30 MPa. A comparison with the international formulations for the viscosity of fluid H2O and D2O adopted by the International Association for the Properties of Steam reveals some systematic differences from the previously accepted values for the viscosity of liquid D2O. A unified representative equation is proposed which yields the viscosity of mixtures of liquid H2O and D2O at all concentrations, at temperatures from the freezing point up to 350°C, and at pressures up to approximately 100 MPa.

Rheological Characterization of Grain Legume Pastes and Effect of Hydration Time and Water Level on Apparent Viscosity

Abstract: An extrusion capillary viscometer was employed to obtain shear stress-shear rate data of two types of cowpea pastes, traditional and experimental. The power law model was found to describe adequately flow behavior of the pastes with consistency coefficients of 77.45 and 59.02, and flow behavior indices of 0.456 and 0.458 for experimental and traditional pastes, respectively. Effect of hydration time (0 - 180 min) and water level (54 - 62%) on the apparent viscosity of experimental paste was determined by extrusion capillary and Brookfield viscometers with correlation coefficient of 0.953. Water level had a significantly greater effect than hydration time on apparent viscosity of cowpea paste.

Rheological properties of poly(dimethylsiloxane) filled with fumed silica: I. Hysteresis behaviour

Abstract: The apparent viscosity and primary normal stress difference were measured for dispersions of fumed silica in poly(dimethylsiloxane). Dispersions with less than 4.75% by weight of filler exhibit hysteresis in both the viscosity and normal stress, when the shear rate was increased and then decreased in discrete steps. The shape of the hysteresis loops were sensitive to the details of the deformation history. By using the appropriate deformation history, the material properties determined during the increasing shear rate part of the hysteresis experiment compare favourably with the steady-state rheological properties. The rheological properties of the dispersion were quite sensitive to the age of the fluid with no hysteresis behaviou exhibited by dispersions less than three days old. For dispersions with at least 4.75% by weight of fumed silica, neither the apparent viscosity nor the primary normal stress coefficient exhibited significant hysteresis behaviour. The relationship between the observed rheological behaviour and the dispersion's microstructure is discussed.

On the penetration of a hot diapir through a strongly temperature-dependent viscosity medium

Abstract: The ascent of a hot spherical body through a fluid with a strongly temperature-dependent viscosity has been studied using an axisymmetric finite element method. Numerical solutions range over Peclet numbers of 0.1 - 1000 from constant viscosity up to viscosity variations of 100,000. Both rigid and stress-free boundary conditions were applied at the surface of the sphere. The dependence of drag on viscosity variation was shown to have no dependence on the stress boundary condition except for a Stokes flow scaling factor. A Nusselt number parameterization based on the stress-free constant viscosity functional dependence on the Peclet number scaled by a parameter depending on the viscosity structure fits both stress-free and rigid boundary condition data above viscosity variations of 100. The temperature scale height was determined as a function of sphere radius. For the simple physical model studied in this paper pre-heating is required to reduce the ambient viscosity of the country rock to less than 10 to the 22nd sq cm/s in order for a 10 km diapir to penetrate a distance of several radii.

Rheological behaviour and microstructure of stir-casting zinc-aluminium alloys

Abstract: The influence of processing variables on the rheological and microstructural behaviour of stir-cast (rheocast) ZA-27 alloy (Zn-27 wt % Al-2wt % Cu) has been investigated experimentally. A concentric cylinder viscometer with shear rate range up to 650 sec−1 was used to measure the apparent viscosity of the slurries. During continuous cooling and at high shear rates (300–640 sec−1), non-dendritical materials obey the power-law fluid model, i.e.\(\eta _{\text{a}} = k\dot \gamma ^n \) where ηa is the apparent viscosity and\(\dot \gamma \) the shear rate. At lower shear rates (125 sec−1), the slurries display dendritical-liquid mixture with viscosity up to 50 poises. Microstructural studies of continuously cooled materials reveal a clear tendency of primary particles to cluster. This phenomenon could be explained by the reduction of the amount of entrapped liquid in the particles.

Couette Viscometer Data Reduction for Materials with a Yield Stress

Abstract: Prior studies have shown that the local power law approximation [I. M. Krieger, Trans. Soc. Rheol., 12, 5 (1968)] for calculation of the shear rate in a Couette viscometer provides accurate results for non‐Newtonian fluids which do not exhibit a yield stress, but is less accurate for those that do. An evaluation of this approximation is presented here for the Bingham and Casson plastic (yield) materials in dimensionless form. The magnitude of the error in shear rate, and the conditions under which the maximum error occurs, are shown to depend upon the gap width and location of the yield point as well as the rheological model. The error for a Casson fluid is less than half that for the Bingham material. Furthermore, the maximum error in the apparent viscosity function occurs under different conditions of gap width and yield point, and is considerably less than the error in shear rate for both materials.

Effect of successive contractions and expansions on the apparent viscosity of dilute polymer solutions

Abstract: In this paper, we examine the flow of dilute polymer solutions through a succession of contraction-expansion. A strong increase of the apparent viscosity, i.e., a thickening behavior is observed beyond a critical flow rate. The influence of geometrical parameters (number of contraction-expansion, length-to-radius ratio of the constricted sections) and physico-chemical parameters (visocsity and salinity of the solvent, nature of the polymer), on the onset and the magnitude of this thickening behavior has been displayed. The results are interpreted in terms of an increase of the elongational viscosity of the solution, associated with a stretching of the deformable macromolecules.

Rheological properties of rice flour slurries and pastes.

Abstract: Apparent viscosity of rice (high amylose var. (i) Taichung Native 1 and low amylose var. (ii) Changlei) pastes and slurries was measured with a coaxial cylinder viscometer. The cooked pastes (cooked at 95 degree C for 2 min and measured at 27 degree C) of both the rice var. showed thixotropic loops in plots of viscosity vs. shear rate. Viscosities of both the pastes increased with concn. but the curve was steeper with (i) than with (ii). Viscosity was always higher at 27 degree C than at 60 degree C. In another set of experiments viscosities of the slurries of 8 quality types of rice (ranging from Type 1 which cooks hard and flaky and Type VIII which cooks very soft and sticky) were tested after cooking at 95 degree C for 2 min. It was found that at 10 and 12% (dry basis) concn. of the paste, apparent viscosity decreased continuously from Type I to Type VIII. At 3% concn. apparent viscosity decreased from Type VIII to Type I rice. But between 5 and 8% paste concn. the viscosities were close together. With uncooked slurry, the viscosity was tested at 20, 25 and 30% concn. (dry basis) as the readings were low and unreliable at lower concn. The results indicated that the apparent viscosity was highest for Type VIII and lowest for Type I rice in that order. Uncooked slurries of rice flour dispersed in 2% carboxymethyl cellulose at 10-15% concn. behaved similarly to cooked rice paste of 3% concn.

Adsorption-entanglement layers in flowing high-molecular weight polymer solutions

Abstract: This four-part series is concerned with thick multimolecular layers, termed “adsorption-entanglement layers”, which according to our observations develop during flow of high molecular weight polymer solutions along the solid surfaces defining the flow channels It is concerned with the formation and nature of these layers and with the effect they have on fluid transport in general and viscosity measurements in particular In the present first part the existence of such layers is established through a flow visualization method and the layer formation diagnosed in situ is correlated with macroscopic flow effects Two flow geometries are used, Couette and channel flow In the Couette flow, where the shear rate is kept constant, the adsorption-entanglement layers first form, then thicken and eventually partially break off until a steady layer thickness is reached These effects are reflected by a concommitant increase and subsequent decrease and final levelling off of the apparent viscosity as a function of shearing time, there being a near quantitative correlation between the measured changes in apparent viscosity and layer thickness In channel flow, where it is the pressure head which is kept constant, the formation and thickening of layers leads to a decrease in flow rate with flow time, amongst others giving the impression of shear thickening It is demonstrated that owing to the fact that adsorption entanglement layers alter the geometry of the flow channel the time dependence of flow effects, per se need not indicate shear thickening (or thinning), in fact that there is any departure from Newtonian flow behaviour The above is of obvious consequence for the rheological interpretation of flow behaviour of solutions of very high molecular weight polymers

Apparatus and method for viscosity measurements for newtonian and non-newtonian fluids

Abstract: The present invention relates to an apparatus and method for determining the viscosity of Newtonian and non-Newtonian fluids More particularly, the present invention relates to an apparatus and method for determining the viscosity of a fluid by measuring the time of fall of a needle through a predetermined distance of the fluid held in a container The method further provides exact equations according to a modified power law model and Ellis model for the calculation of viscosity, shear stress and shear rate

Foam enhancement of controlled pulse fracturing

Abstract: The effectiveness of controlled pulse fracturing treatment ("CPF") is enhanced by creating a foam when energy is released from the pulse device. Foam created by a foaming agent in the wellbore fluid increases said fluid's apparent viscosity and controls fluid loss. The increased viscosity causes additional fracture propagation. Upon commencement of production of hydrocarbonaceous fluids, fines and debris resultant from CPF are transported from the fractures which cleans up the well.

Rheological properties of certain processed rice products.

Abstract: The effects of processing conditions on the rheological properties of products prepared from parboiled rice, i.e. expanded and flaked rice, were investigated. Diagrams show the effects of slurry concn., shear rate and shear stress on apparent viscosity of the rice products. The products displayed properties resembling those of pre-gelatinized starch. Cold slurries of the heat-moisture processed rice products showed time-dependent thinning, and can be visualized as thixotropic systems. The cold-swelling properties of these products indicate potential use of their flour as substitute for pre-gelatinized starch.

Sonically produced heat in a fluid with bulk viscosity and shear viscosity.

Abstract: In a viscous fluid, sound produces heat in a spatial pattern which, in general, depends on the relative magnitudes of the shear viscosity coefficient η and the bulk viscosity coefficient B’. It is well known that when the particle velocity components ui relative to Cartesian coordinates xi are given for an arbitrary sound field, or any field of flow, the volume rate of heat production qv can be determined from a dissipation function in the form B’T1+ηT2. Here, T1 and T2 are quadratic functions involving derivatives of the type ∂ui/∂xj. In this paper, examples are discussed for continuous monofrequency sound fields, including crossed plane waves, as well as focused and unfocused fields. In these examples, spatial distributions of the time‐averaged quantity 〈qv〉 for media in which the loss mechanism is primarily bulk viscosity are compared to those for media in which shear viscosity dominates.

Viscosity Profiles of Printing Thickeners at High Shear Rates and Their Use in Predicting Paste Flow in Screen Printing

Abstract: Apparent viscosities of various natural and synthetic printing thickeners were measured at shear rates from 0.05 to 7000 s-1. Log viscosity-log shear rate plots (viscosity profiles) were curves, not straight lines as generally believed. Nonlinear regression equations were computed and required significant second or third order terms or both to fit the data. The slopes and shapes (or curvature) of the profiles were distinctly different for synthetic copolymers, for nonionic cellulose or starch ethers, and for anionic polysaccharides (either carboxylmethyl cellulose or sodium alginate). The interaction efforts on both apparent viscosity and slope of viscosity profiles of such variables as pH, temperature, concentration of thickener and added electrolyte, thickener composition, and molecular weight were estimated by analysis of variance.The appearance of prints made with different thickeners was compared visually, photometrically, and microscopically. Prints with optimum sharpness of mark, levelness, and pen...

Adiabatic shearing of an incompressible fluid with temperature-dependent viscosity under periodic or steady-boundary conditions

Abstract: We consider adiabatic shearing flows of Newtonian fluids with temperature-dependent viscosity under periodic boundary conditions for velocity and stress. We show that the flows exist and are well behaved for all time, provided the rate of change of viscosity with temperature and the initial temperature satisfy appropriate bounds. We compare the results with the case of shearing under steady boundary conditions.

Use of low M.S. hydroxyethyl cellulose for fluid loss control in oil well applications

Abstract: Improved drilling operations for recovery of gas and/or oil from a porous subterranean formation are achieved using a drilling fluid, circulated in a well penetrating the subterranean formation, which minimizes loss of said drilling fluid into the surrounding porous formation. The improvement comprises employing a drilling fluid comprising water and an effective amount of hydroxyethyl cellulose having a molar substitution value of from about 1.1 to about 1.6, and an apparent viscosity in water of at least about 15 cps.

An Experimental Study of the Viscosity of Polymer Melts at High Shear Rate

Abstract: Effects of shear heating on the measurement of polymer melt viscosity was studied for AS and ABS copolymers where A, S, and B stand for acrylonitrile, styrene, and butadiene, respectively. Melt viscosity under the high shear rate γ in a range from 102 to 105 s−1 was observed by two slit dies of different thicknesses and connected to the head of the injection molding machine. Agreement between the data for the dies became poor with increasing shear rate and the discrepancy could not be neglected at shear rates higher than 103 s−1. The discrepancy was assumed to be caused by shear heating and an attempt was made to correct the viscosity curve by taking this effect into account. By introducing an Arrhenius type relation for the temperature dependence of viscosity, fairly good agreement was obtained for measurement of viscosity with different dies. A single curve of the shear stress τw as a function of γ was obtained.

Viscometric Properties of Waxy Rice Starches

Abstract: Viscometric properties of japonica(Olchal) and japonicaindica(Hankang and Suwon 317) waxy rice starches were investigated. Light transmittance of starch suspension increased from and remained constant after . Swelling power was in the order of Hankang, Suwon 317 and Olchal. Amylograph data revealed that Hankang had the highest viscosity at all reference points. The apparent viscosity of 5% starch suspension indicated that the jindica starches were completely gelatinized after 30 min cooking at whereas japonica starch at . The apparent viscosity of gelatinized starch at (15 psig) was higher compared to that of gelatinized one at . Hankang was the most susceptable to alkali gelatinization followed by Suwon 317 and Olchal.

Agitation, mixing and mass transfer in simulated high viscosity fermentation broths

Abstract: Gas-liquid mass transfer, agitator power consumption, rheology, gas-liquid mixing and gas hold-up have been studied in an agitated, sparged vessel of diameter, T = 0.3 m, with a liquid capacity of 0.02 m\(^3\), unaerated liquid height = 0.3 m. The solutions of sodium carboxymethylcellulose used exhibit moderate viscoelasticity and shear thinning behaviour, obeying the power law over the range of shear rates studied. The gas-liquid mass transfer was studied using a steady state technique. This involves monitoring the gas and liquid phase oxygen concentrations when a microorganism (yeast) is cultured in the solutions of interest. Agitator power consumption was measured using strain gauges mounted on the impeller shaft. Various agitator geometries were used. These were: Rushton turbines ( D = T/3 and D = T/2 ), used singly and in pairs; Intermig impellers ( D = 0.58T ), used as a pair; and a 45° pitched blade turbine ( D = T/2 ), used in combination with a Rushton turbine. Gas hold-up and gas-liquid flow patterns were visually observed. In addition, the state of the culture variables, (oxygen uptake rate and carbon dioxide production rate), were used to provide a respiratory quotient, the value of which can be linked to the degree of gas-liquid mixing in the vessel. Measurement of point values of the liquid phase oxygen concentration is also used to indicate the degree of liquid mixing attained. The volumetric mass transfer coefficient, k\(_L\)a, was found to be dependent on the conditions in which the yeast was cultivated, as well as being a function of time. These variations were associated with variations in solution composition seen over the course of each experiment. Steps were taken to ensure that further k\(_L\)a values were measured under identical conditions of the culture variables, in order to determine the effect on k\(_L\)a of varying viscosity, agitator speed and type and air flow rate. Increasing solution viscosity results in poorer gas-liquid mixing and a reduction in k\(_L\)a, as has been found by earlier workers. Thus high agitator speeds and power inputs are required to maintain adequate mass transfer rates. In the more viscous solutions used, large diameter dual impeller systems were required, to mix the gas and liquid phases. Of these a pair of Rushton turbines ( D = T/2 ) gave the highest k\(_L\)a values at a given power input. In these solutions the dependence of k\(_L\)a on the gassing rate, which is seen in intermediate and low viscosity solutions, virtually disappears, with k\(_L\)a highly dependent on the power input and the apparent viscosity. At intermediate viscosities a smaller pair of Rushton turbines showed the most efficient mass transfer characteristics, here k\(_L\)a is dependent on the power input and the gassing rate, but independent of viscosity. This is linked to the flow regime force in the vessel, which at intermediate viscosities lies in the transition region between the laminar and turbulent flow regimes. Variations in gas hold-up, rising then falling with increasing impeller speed, were linked to variations in the gassed power number, falling then rising with increasing impeller speed. These effects are considered to be due to variations in the size of the gas filled cavities behind the impeller blades.