摘要:

Large amplitude oscillatory shear experiments were carried out on a polyurethane melt using a sliding plate rheometer incorporating a shear stress transducer. Three types of nonlinear behavior are described: periodic, quasi‐periodic, and chaotic, and common methods for characterizing these types of behavior are given. Spectral analysis is shown as the best way to distinguish between each type of behavior. Attractor reconstruction from chaos theory is introduced as a way to understand the dynamics of a system from only one dependent variable. At a low strain amplitude and frequency the behavior of the polyurethane melt is periodic but at higher amplitudes the response becomes quasi‐periodic.

ISSN:0148-6055    

DOI:10.1122/1.550309

出版商:The Society of Rheology    

年代:1992

数据来源: AIP

摘要:

The flow properties of emulsions of oil in non‐Newtonian polymeric media were studied using a coaxial cylinder viscometer. The emulsions were prepared using a petroleum oil and aqueous solutions of poly(ethylene oxide) resins. Three different molecular weight poly(ethylene oxide) resins were studied. The effects of polymer concentration and oil concentration on the viscous properties of emulsions were determined. The polymer solutions and their emulsions followed the well‐known Ellis model. The relative viscosities for polymer‐thickened emulsions were found to be significantly lower than the corresponding values for emulsions without polymer. These findings are explained in terms of an increase in the viscosity ratio ηc/ηd(where ηcis the viscosity of the polymer‐thickened continuous medium and ηdis the viscosity of the dispersed oil). An increase in this ratio enhances the internal circulation effect which leads to a decrease in the relative viscosity. A new equation is proposed which describes the relative viscosity versus dispersed‐phase concentration data for polymer‐thickened emulsions rather well. The equation takes into account the internal circulation effect in emulsions and it reduces to the classical Taylor equation in the limit of dilute concentration.

ISSN:0148-6055    

DOI:10.1122/1.550310

出版商:The Society of Rheology    

年代:1992

数据来源: AIP

摘要:

Equilibrium‐averaged hydrodynamic interaction is included in the dilute solution Manke–Williams model for stress jumps at the inception of shear and elongational flows due to internal viscosity (IV), which was developed previously for free‐draining chains. As in the free‐draining case, rigorous expressions are used for the IV forces in a multibead chain, and closed form solutions are obtained that show viscosity jumps to be directly dependent on the IV coefficient, but independent of deformation rate. Overall, hydrodynamic interaction is found to enhance the magnitude of stress jumps relative to the free‐draining case.

ISSN:0148-6055    

DOI:10.1122/1.550368

出版商:The Society of Rheology    

年代:1992

数据来源: AIP

摘要:

A concise review of the literature and new experimental results are given concerning the effects of particle shape, density, size, and surface charge on the rheology of concentrated noncolloidal suspensions. While the literature review covered both Newtonian and non‐Newtonian liquid media, the experimentation was focused on Newtonian liquid media and shear rates ranging from 1 to 2000 s−1. Rheological similarities regarding these effects exist between the concentrated suspensions in Newtonian liquid media with viscosities as low as 3 cP and those in polymeric media with viscosities as high as 5×104P. The measured relative viscosity of a nonaggregated Newtonian suspension as a function of particle volume fraction was found to agree well with the predictions of both the Krieger–Dougherty and the Maron–Pierce–Kitano equations. Also, the sole parameter of the former equation, maximum packing fraction, was found to be in much better agreement with that determined from sedimentation than that of the latter equation. In addition, we found that the relative viscosity of a pseudoplastic noncolloidal suspension correlates well with the particle Peclet number for both spherical and irregularly shaped particles even though Brownian motion is negligible. Specifically, since particle diffusional relaxation time increases with particle radius cubed, larger particles in an aggregated system diffuse to a lesser extent than smaller particles within the same time scale of shear, and less energy is dissipated as a result. Particle density, up to 2.5 g/cc, was found to have no effect on the relative viscosity.

ISSN:0148-6055    

DOI:10.1122/1.550260

出版商:The Society of Rheology    

年代:1992

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.550261

出版商:The Society of Rheology    

年代:1992

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.550262

出版商:The Society of Rheology    

年代:1992

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.550263

出版商:The Society of Rheology    

年代:1992

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.550264

出版商:The Society of Rheology    

年代:1992

数据来源: AIP

摘要:

Mixed stress‐velocity‐pressure finite element techniques are frequently used to solve differential viscoelastic flow problems of the Maxwell (Oldroyd‐B) type. In the present paper, simplified models are introduced to analyze the stability and the accuracy of a class of methods used to solve differential viscoelastic problems. In particular, a one‐dimensional equation is presented which exhibits most of the difficulties of the coupled Maxwell flow problem but requires only a fraction of the CPU time. The performance of some formulations (EEME, EVSS, 4×4, 4×4 SU, 4×4 SUPG, MIX1, ... ) are analyzed on the basis of this equation. New numerical techniques which enhance both the stability and the accuracy of those mixed formulations are also presented. Those techniques are based on a combination of two streamline integration techniques, in such a way as to maintain the elliptic character to the coupled system.  

ISSN:0148-6055    

DOI:10.1122/1.550265

出版商:The Society of Rheology    

年代:1992

数据来源: AIP

摘要:

A higher order Galerkin finite element scheme for simulation of two‐dimensional viscoelastic fluid flows has been developed. The numerical scheme used in this study gives rise to a stable discretization of the continuum problem as well as providing an exponential convergence rate toward the exact solution. Hence, with this method, spurious oscillatory modes are effectively eliminated by increasing the order of the interpolant within each subdomain. In our calculations, an upper limit for the Weissenberg number due to numerical instability was not encountered. However, the memory requirements of the discretization grow quadratically with the polynomial order. Consequently, the maximum attainableWeis determined by the availability of computational resources. The algorithm was tested for flow of upper convected Maxwell and Oldroyd‐B fluids in the undulating tube problem and it was subsequently applied to viscoelastic flow past square cylindrical arrangements. The results obtained show no increase in the flow resistance with increasing elasticity. These findings are in contrast to the experimental data reported in the literature. However, recent experimental investigations have indicated that this dramatic increase in flow resistance is due to a purely elastic instability. Hence, numerical simulation based on two‐dimensional steady flow of viscoelastic fluids cannot be expected to capture this phenomenon.

ISSN:0148-6055    

DOI:10.1122/1.550370

出版商:The Society of Rheology    

年代:1992

数据来源: AIP