摘要:

A six‐bladed vane was used to measure the gel strength and dynamic yield strength of a thixotropic cement slurry of a type used in oil well cementing. It was established that when the combined parameters of rotation speed, measuring system stiffness, and gel strength give a time to maximum torque of less than 100 milliseconds, sophisticated data recording systems are necessary. It is shown that gel strength is only marginally affected by nominal vane rotation speed between 0.06 and 6 rpm whereas dynamic yield strength is sensitive to rotation rate in this speed range.

ISSN:0148-6055    

DOI:10.1122/1.550043

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

摘要:

Empirical and theoretical relationships are developed to describe the viscosity/concentration behavior of Newtonian and non‐Newtonian emulsions having dispersed‐phase concentrations less than 74% by volume. The developed equations are valid for both oil in water and water in oil types of emulsions. Emulsions exhibiting electroviscous effect (increase in viscosity due to presence of electric charge on the surface of droplets) could also be described adequately by these equations. The proposed equations have the ability to predict the emulsion viscosity as a function of dispersed‐phase concentration and shear rate if the flow curve (shear stress versus shear rate plot) is known experimentally at a single value of the dispersed‐phase concentration.

ISSN:0148-6055    

DOI:10.1122/1.550044

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

摘要:

The performance of integral constitutive equations in the numerical modeling of two simple viscoelastic flows is examined. These flows include one‐dimensional, steady Poiseuille flow, and one‐dimensional, nonhomogeneous, extensional sink flow. The integral constitutive relations examined include the upper‐convected Maxwell, the Wagner, the Doi‐Edwards, and the Curtiss‐Bird models. The numerical solutions, produced via a Galerkin finite‐element procedure and Newton iteration, are compared with analytic solutions for the same flows. It is shown that unrealistic predictions by the constitutive equations, shown by the analytic solution (e.g., nonmonotonic shear or normal stress) result in divergence of the Newton iteration.

ISSN:0148-6055    

DOI:10.1122/1.550045

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

摘要:

We have measured the shear and complex viscosities of a thermotropic liquid crystalline copolymer ofp‐hydroxybenzoic acid and 2,6‐hydroxynaphthoic acid as a function of capillary diameter and parallel‐plate gap spacing. In constrast to a study by Wissbrun, Kiss, and Cogswell, who reported that the viscosity increases significantly at small gaps, we find no dependence on the capillary diameter and a smalldecreasein complex viscosity with parallel‐plate spacing. In an appendix we address an experimental artifact that can lead to an apparent decrease of the viscosity with gap spacing even for flexible polymers.

ISSN:0148-6055    

DOI:10.1122/1.550007

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

摘要:

The microstructural relaxation equation for a symmetric, traceless, second‐order tensor is analyzed near equilibrium from a point of view that includes many proposed models for liquid crystals, liquid crystal polymers, and fiber suspensions. The steady states of the equation near a uniaxial equilibrium are determined for the fluid in slow, steady, affine flows. Formulae are given for locating the limiting (at zero flow) steady states and determining their linearized stability from a reduced set of constitutive parameters. The various possibilities are graphed so that the dynamical behavior of the relaxation equation in this context may be easily seen.

ISSN:0148-6055    

DOI:10.1122/1.550046

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

摘要:

Finite element calculations, theoretical predictions, and experimental observations are combined to analyze wall and end effects for a wide range of ball sizes in falling ball rheometry. We find that reflection solutions, finite element calculations, and experimental data are indistinguishable for small balls approaching the cylinder bottom. For larger falling balls, finite element modeling predicts a significant increase in drag in comparison with the reflection solution. Our experimental measurements are in very good agreement with the predictions of the finite element calculations and confirm the relative drag increase. For balls falling off the centerline of the cylinder, analytical solutions are restricted to the limiting cases of very small balls and large balls only slightly smaller than the containing cylinder. In this report, intermediate ball sizes are studied with three‐dimensional finite element codes. The finite element predictions for the intermediate ball sizes are qualitatively similar to the results of reflection solutions for very small balls, with the minimum drag found when the center of the falling ball is located approximately 40% of a cylinder radius off the centerline. This qualitative similarity suggests anad hocmodification of the centerline wall correction. This modified expression is shown to predict to within 1% the terminal velocity during eccentric settling of balls of intermediate sizes.

ISSN:0148-6055    

DOI:10.1122/1.550008

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

摘要:

This work investigates the two‐ and three‐dimensional description of fiber orientation in homogeneous flow fields. Motion of the fibers is described using the Dinh‐Armstrong model which was developed for semiconcentrated fiber suspensions. The calculation of rheological properties for fiber suspensions requires the determination of fourth‐order moments of orientation distribution function which is defined as the fourth‐order orientation tensor. Solution of the distribution function is obtained in terms of the velocity gradients and transient calculations are presented for simple shear, planar elongational, and uniaxial extensional flows. Second‐ and fourth‐order tensors are calculated by using the distribution function and the components of the second‐order tensor are utilized to define an orientation ellipsoid for the graphical representation of the orientation state. The fourth‐order tensor is approximated from second‐order tensors through quadratic and hybrid closure equations, and compared with the exact results. Despite the qualitative agreement between the exact and approximated results, considerable quantitative discrepancy is observed which may result in inaccurate prediction of suspension behavior.

ISSN:0148-6055    

DOI:10.1122/1.550047

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

摘要:

Williams and Watts have shown that a fractional exponential form for the decay function is able to describe dielectric relaxation in polymeric systems. The possible use of the fractional exponential form for the relaxation modulus in rheology is discussed. The elongational stress growth function and the complex viscosity function are simulated via the defect‐diffusion model.

ISSN:0148-6055    

DOI:10.1122/1.550048

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

摘要:

With falling ball rheometry, we have measured the apparent relative viscosity of suspensions of large, neutrally buoyant, rigid rods in a viscous Newtonian fluid, while approximately maintaining the rods in a randomly oriented configuration. A new technique for measuring the time of flight of a ball between two positions is used. This computerized technique, based upon an eddy current detector, enables us to determine the position of a metallic (nonmagnetic) ball falling through an opaque suspension, with high accuracy (less than 1.5% error). The rods for the suspensions had a nominal aspect ratio of 10 and experiments were carried out at a single volume fraction, 0.05. Two populations of rods were used to having nominal diameters of 1.5875 mm and 3.175 mm. To within the errors of these experiments, suspensions from both populations had the same relative viscosity, with the overall average being 1.457. This viscosity was significantly different from that of a similar suspension (volume fraction=0.05) of rods of nominal aspect ratio 20 and it agreed well with theoretical results for the viscosity of a dilute suspension of randomly oriented rods.

ISSN:0148-6055    

DOI:10.1122/1.550054

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.550070

出版商:The Society of Rheology    

年代:1989

数据来源: AIP