Showing papers on "Rheometer published in 1973"

Deformation and burst of a liquid droplet freely suspended in a linear shear field

Abstract: A theoretical method is presented for predicting the deformation and the conditions for breakup of a liquid droplet freely suspended in a general linear shear field. This is achieved by expanding the solution to the creeping-flow equations in powers of the deformation parameter epsilon and using linear stability theory to determine the onset of bursting. When compared with numerical solutions and with the available experimental data, the theoretical results are generally found to be of acceptable accuracy although, in some cases, the agreement is only qualitative.

Non-parallel flow corrections for the stability of shear flows

Abstract: The proper corrections for non-parallel flow to the eigenvalues for small disturbances on a nearly parallel shear flow have been determined through a perturbation about the parallel flow solutions. The resulting shifts in the neutral stability curves have been calculated for the Blasius boundary layer, for the two-dimensional jet, and for the two-dimensional flat-plate wake.

Comparison of network theory predictions with stress/time data in shear and elongation for a low-density polyethylene melt

Abstract: Experimental data are presented which show the variation with time of the shear stress and primary normal stress difference during shear flow with a stepfunction shear rate; the material (“Melt I” at 150 °C) is a low-density polyethylene melt for which stress-growth and elastic recovery data in elongational flow experiments have been previously reported. A method of comparing the data with the predictions of the rubberlike-liquid constitutive equations is given, based on the use of a specially-chosen rate-of-strain invariantIIV, defined in [4.1]. From this comparison, it is shown that the disagreement between theory and experiment is about the same for shear flow and for elongational flow, and that the extent of disagreement does not exceed 10% for short-duration flows such thatIIVt ⩽ 3.

Rheological Properties of Dispersions of Spherical Particles in Polymer Solutions

Abstract: The steady flow and dynamic viscoelastic properties of disperse systems consisting of polystyrene copolymer particles of different sizes in polystyrene solutions were measured by means of rotating cylinder type rheometers over wide ranges of temperature, rate of shear, and frequency. The yield values, evaluated by use of the modified Casson equation for disperse systems, were found to be independent of temperature. Time‐temperature superposition was applied to the flow curves and the frequency dependence curves of the dynamic properties, giving identical shift factors which obeyed the WLF type equation and were almost independent of the size and content of the particles. The yield value increased with increasing particle content and polymer concentration in the disperse medium. The smaller the particle size, the larger the yield value. The frequency dependence curves of the storage shear modulus G′ and the loss modulus G″ showed second plateaus lower than the rubbery plateau at lower frequencies. The correlation between the yield value and the complex shear stress is discussed.

A rheometer for oscillatory studies of nonlinear fluids

Abstract: This paper describes the coupling of a minicomputer with two rotational rheometers. In the first instance, the computer acquires output data from aWeissenberg Rheogoniometer in oscillatory shear, andFourier-analyzes stress and strain signals. The second instance utilizes a rotational rheometer specifically designed to be controlled by the computer, employing a servo-driven torque motor. The computer-rheometer system is used to analyze steady-state non-Newtonian viscosity and linear viscoelasticity, as well as non-linear dynamic behavior.

A concentric-cylinder rheometer for polymer melts

Abstract: If one wishes to measure the viscosity of a polymer melt at high shear rates there are substantial fluid dynamical and heat transfer difficulties. Cone-plate instruments are limited because of secondary flows and because the fluid tends to leave the gap. In capillary-flow instruments, there are substantial radial temperature gradients and the possibility of flow irregularities.

A shear plate for use in oscillatory flow

Abstract: In this paper a flexurally supported shear plate is described. It was designed for use under oscillatory flow where the periods of motion range from 0.5 to 15 seconds. The range of possible shear measurements is ± 100 N/m2 with sensitivities as low as 0.015 N/m2. Special emphasis is placed on the calculation of corrections for secondary forces which may contribute a large proportion of the recorded apparent shear. Comparison of the corrected shear with laminar theory gives very good agreement. An example is given to illustrate the results obtained using this shear plate in an oscillating water tunnel for laminar and turbulent flow over both smooth and rough beds.

A comparison of measurements of the viscoelastic properties of polymer melts by means of the Han slit/capillary rheometer and the Weissenberg rheogoniometer

Abstract: Measurements were taken of the viscoelastic properties of six polymer melts by mean of the Weissenberg rheogoniometer and the Han slit/capillary rheometer. Polymers in vestigated were three high-density polyethylenes of different polydispersity, a low-density polyethylene, a polypropylene, and a polystyrene. The range of shear rates tested was from about 5.0 × 10−3 to 10 sec−1 with the Weissenberg rheogoniometer, from about 10 to 102 sec−1 with the slit rheometer, and from about 102 and 103 with the capillary rheometer: the temperature of measurement was 200°C. The three different apparatuses give consistent results over almost six decades of shear rates, yielding satisfactory correlations of shear viscosity to shear rate and of normal stress difference to shear rate.

Structure of thixotropic suspensions in shear flow: I. Mechanical properties

Abstract: A theory of the opacity of bentonite‐water suspensions as a function of the shear rate is given. The experimental opacity behavior confirms previous theoretical predictions of the aggregate size distribution. The extinction coefficient of bentonite was determined at two wavelengths.

A simple device allowing blood viscometry at low rates of shear with the Wells-Brookfield-viscometer.

Abstract: A viscometer chamber (combination of cone plate and Couette-type) adaptable to the standard Wells-Brookfield-Microviscometer is described. The instrument allows measurements at shear rates between 0.23 and 160 sec−1; it incorporates a guard ring against surface artefacts. Measurements with normal human blood, standardized for hematocrit value, give excellent agreement with data obtained previously on the GDM-viscometers.

Velocity Lag, Axial Thrust, and Edge Effects in The Eccentric Disc Rheometer

Abstract: Velocity lag between the two discs in the eccentric disc rheometer is determined analytically for a Newtonian fluid, the second order fluid, and for general simple fluids when the offset and slip are small It is established that the normal thrust between the discs does not measure the second normal stress difference Experimental measurements of the velocity lag are in good agreement with the analytical expressions which are developed The influence of the velocity lag on the forces exerted on the free disc is predicted Experimental results with two different edge geometries indicate the strong influence of edge effects on the forces exerted on the free disc The correct relationship between the fluid viscosity and the measured forces, therefore, may require detailed analysis of the flow situation in the edge region or careful experimental extrapolation procedures

Transient shear flow of fluids with deformable microstructure

Abstract: The case of fluids which experience small microstructure deformations from an initially spherical shape is examined. Solutions are presented for transient shear flows.

A modified air turbine viscometer.

Abstract: A cone and plate air turbine viscometer is described which is suitable for the rheological testing of biological materials. The instrument produces a minimum shear stress of about 0.027 N m-2.

Rotating cylinder viscometers.

Abstract: Publisher Summary The floating rotor viscometer has found widespread use for studying the viscosity of deoxyribonucleic acid (DNA) solutions under conditions of low shear and for examining different types of non-Newtonian behavior, such as the increase or decrease in viscosity with change in shearing force or time of shear. In the past few years, this viscometer has also been used to study the shear-dependent viscosity of certain protein solutions. The viscosity of a solution, measured in poises, is simply the ratio of the shear stress exerted on the solution, in dynes/cm 2 , divided by the shear rate, in sec –1 . Rotating cylinder viscometers can either fix the shear stress and measure the shear rate or fix the shear rate and measure the shear stress. The latter type includes viscometers where either the inner or the outer cylinder is rotated, and the stress on the opposing cylinder is measured directly. These viscometers are usually complicated in construction and are designed for specific applications. Some incorporate a guard ring for circumventing the problem of surface films when working with protein-containing solutions. Others measure the rheological properties of blood by providing special geometries so that normal stresses and time-dependent phenomena can be investigated.

Polymers as Structured Continua: Superposed Oscillatory Shear Flows

Abstract: A microstructure model of polymer rheology is applied to study the behavior of the dynamic viscosities under superposed in‐line and transverse oscillations. A general solution valid to first order in oscillatory shear rate is obtained, and the limiting cases of small and large values of the frequency of oscillation are examined. The results for these limiting cases are found to be in agreement with results based on the incompressible BKZ and simple fluid models. A solution valid to third order in oscillatory shear rate is obtained, and for this case the shear stress response is found to contain harmonics of the driving frequency.

Nearly viscometric flows in the new rheometers

Abstract: The linear time-dependent behaviour of elasticoviscous liquids may be determined by conventional rheometers, or by any one of a number of new rheometers which have recently appeared in which the test fluid is contained between two surfaces which rotate with the same angular velocity about axes which are not coincident. (The Orthogonal, Balance and Eccentric-Cylinder rheometers are perhaps the most well known examples of such instruments at the present time.) In this communication, we consider the more general situation in the new rheometers in which the angular velocities of the two surfaces are different.

Rheological Properties of Disperse Systems of Spherical Particles in Polystyrene Solution at Long Time Scales

Abstract: The dynamic and steady flow properties of disperse systems of styrene–divinylbenzene copolymer particles in a polystyrene solution have been measured over wide ranges of frequency, shear rate, and strain amplitude by means of a cone‐and‐plate type rheometer. The main results may be summarized as follows. 1) These systems show Newtonian behavior at extremely low rates of shear, that is, the apparent viscosity is approximately constant. This fact indicates that the systems have no yield stress, although they appear to show one if only the behavior at high shear rates is considered. 2) They show linear viscoelastic behavior at strain amplitudes less than 0.5%, but striking nonlinearities at larger strains. However, at very long time‐scales, these systems are linearly viscoelastic and independent of the strain amplitude. 3) The nonlinear viscoelastic functions G1′ and G1″ decrease with increasing strain amplitude, but they are almost independent of strain for strains larger than 50%, over the entire frequency...

Laminar Radial Flow between Parallel Stationary Disks-Cross Viscosity Effect

Abstract: The laminar radial flow between the parallel stationary disks is one of the basic flows used to evaluate the viscous behaviour of the fluid, and its application to the viscometer or the rheometer is worth noting.Here, using the Reiner-Rivlin model, how a non-Newtonian fluid behaves in the abovementioned flow was studied analytically. And, on the basis of the results of the numerical calculation, the cross viscosity effect to the pressure-and the stress-distributions on the disk was discussed. And the present solution was compared with those of the author's approximate analysis as well as the Schwarz-Bruce's analysis in the radial flow between the parallel stationary disks.It was found possible to obtain the exact solution of the flow field by the series expansion method. And, the solution in this paper was effective in the region of RE-1 and/or RC-1 and agreed with the Schwarz-Bruce's solution in this range. Furthermore the agreement with the present analysis confirmed the usefulness of the approximate analytical method for the power law fluid.

Some suggestions for new rheometer designs: III. Anomalous results for highly viscous fluids

Abstract: In this paper, certain anomalous effects are investigated which appear when results recorded on the eccentric-cylinder and displaced-hemisphere rheometers are compared (cf parts I and II) with results obtained from oscillatory tests on a Weissenberg rheogoniometer. These irregularities are prominent in highly viscous, nearly Newtonian, and elastico-viscous liquids, and it will be shown how they occur in direct contrast to results taken for more mobile systems. Interpretation of experimental results for highly viscous fluids from the rheometers suggests that the fluids are less viscous and more elastic than would be indicated by the rheogoniometer results. For a given material these irregular effects increase with rotational speed, while for a constant rotational speed, they increase for increasingly viscous fluids. The zero-shear viscosity in the case of the elastico-viscous systems does not appear to be a significant factor; it is rather the dynamic viscosity appropriate to the operating frequency which determines the extent of the irregular effects. Various possible causes of the anomalous effects are systematically eliminated, and it is ultimately concluded that they are due to `cavitation' effects in the new rheometers.

Dynamic deformation of a stationary rubber flow

Abstract: The effect of dynamic deformation on the stationary flow of a rubber composition has been experimentally investigated for comparable values of the stationary and dynamic strain rates. The dependence of the effective viscosity on the stationary shear rate is not equivalent to its dependence on the periodic shear rate amplitude. An expression is given for calculating the effective viscosity in the case of combined stationary and dynamic shear deformation. The effectiveness of the dynamic deformation, estimated in terms of the effective viscosity, depends on whether it is superimposed on the stationary flow at constant stationary shear rate or at constant stress. It is proposed to estimate the effectiveness of dynamic deformation of a stationary non-Newtonian flow in terms of the change in the power of the stationary forces. When the effective viscosity is reduced by dynamic deformation of the stationary flow, the power of the stationary forces increases at constant shear stress and falls at constant stationary shear rate.