摘要:

A “modified cone and plate” is presented as an alternative geometry for the measurement of material functions in a rotational rheometer. It gives a significant improvement in the quality of the signal for the normal force and makes it possible to reach higher shear rates prior to the point at which the sample fails. A theoretical and experimental study of this new geometry which can be used for normal force and torque measurements has been developed to obtain the first normal stress coefficient and viscosity information.

ISSN:0148-6055    

DOI:10.1122/1.549877

出版商:The Society of Rheology    

年代:1986

数据来源: AIP

摘要:

A general‐purpose finite element program has been used to simulate the flow of two immiscible viscous fluids extruded concentrically from a capillary and from an annular die. The interface and free surfaces are found iteratively by taking into consideration that these surfaces are streamlines. The pressure discontinuities across the interface have been simulated numerically by double nodes to ensure continuity of the stresses and the velocities. A range of viscosity ratios is studied for several cases of inner/outer diameter ratios of the fluids. Extrudate swell calculations show that for inelastic Newtonian fluids, shrinkage occurs when the less viscous layer encapsulates the more viscous, which is also the preferential configuration in coextrusion from long dies. Swelling occurs when the more viscous fluid wets the capillary wall. These results are in general agreement with Tanner's inelastic theory of extrudate swell. In flow from annular dies, bending of the extrudate stream occurs toward the more viscous component due to the viscosity mismatch. The present results reveal some important trends that can be expected in actual coextrusion operations, depending upon viscosity and feed ratios.

ISSN:0148-6055    

DOI:10.1122/1.549878

出版商:The Society of Rheology    

年代:1986

数据来源: AIP

摘要:

The fully‐established friction factors of non‐Newtonian fluids in laminar and turbulent flow through a square duct were experimentally determined. The laminar friction factors of both purely viscous and viscoelastic fluids show good agreement with the well‐known laminar correlation for circular pipe flow,16/Re*,whereRe*is the Reynolds number proposed by Kozicki etal. for non‐Newtonian fluids in non‐circular duct flow. The established friction factors of purely viscous fluids in turbulent flow through rectangular channels agree well with the Dodge and Metzner equation for power law fluids in circular pipe flow if their generalized Reynolds number,Re′,is replaced byRe*.In the case of viscoelastic aqueous polymer solutions, it was found that the experimental asymptotic friction factors for fully established turbulent flow through a square duct are much higher than the corresponding circular tube results when compared at a fixed value of the Kozicki Reynolds number,Re*.In contrast, the turbulent rectangular duct asymptotic friction factor results for the viscoelastic fluid are in good agreement with the circular tube results when compared at a constant Reynolds number based on the apparent viscosity at the wall.

ISSN:0148-6055    

DOI:10.1122/1.549904

出版商:The Society of Rheology    

年代:1986

数据来源: AIP

摘要:

A new method for facilitating the transport of very viscous materials through lubrication of the inside wall of pipes was studied in model inclined plane and pipe geometries using 26 and 38% tomato paste as examples of very viscous suspensions and carboxymethyl cellulose dispersions as model lubricants. It was shown that a high apparent yield stress was necessary and that 17 to 53‐fold increases in flow rates in pipe flow at pressure drops ∼10.0 psi were obtained. Experimental flow times using an inclined plane and flow rates in pipe flow geometries were predicted in a mathematical analysis. An impact loading squeezing flow analysis was used in the case of inclined plane experiments; plug flow of tomato paste surrounded by a thin film of lubricant was assumed in the case of pipe flow. For inclined plane experiments the correlation coefficient was 0.98 and for pipe flow the correlation coefficient was 0.88 signifying reasonably good agreement between predictions of models and the results obtained from the experiments.

ISSN:0148-6055    

DOI:10.1122/1.549879

出版商:The Society of Rheology    

年代:1986

数据来源: AIP

摘要:

In this article, we consider the uniaxial and planar elongational flows of a dilute suspension of identical rigid spheroids. We show that the associated diffusion equation has closed‐form solutions for these two flows. The elongational viscosities are calculated for three cases of interest: when the spheroid is very slender, when it is nearly spherical, and when it is disklike.

ISSN:0148-6055    

DOI:10.1122/1.549880

出版商:The Society of Rheology    

年代:1986

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549905

出版商:The Society of Rheology    

年代:1986

数据来源: AIP

摘要:

Efforts to relate thermodynamic equilibrium and nonequilibrium phenomena have a long‐standing history. Examples of the latter include transport processes and relaxations to a new equilibrium state in response to an imposed perturbation. From the point of view of theory, the ultimate goal is a nonequilibrium statistical mechanics with a proper equilibrium limit. Attempts in this direction date back to van der Waals' times. For low molecular weight fluids, some success has been achieved by correlating semiempirically equation‐of‐state properties and viscosity. The starting point for our considerations is an equilibrium theory. Its central feature is an excess free volume function with known temperature and pressure dependence, which serves as a measure of disorder in a lattice model. This function moreover serves as a connecting link to the glass, generated from the melt by a specified formation history. Two aspects are under consideration. One is the initial response of the system to an imposed perturbation before time phenomena become observable. The second is the relaxation of thermodynamic and other properties. This may be viewed from a correlative point of view. That is, the measurement of one set allows the prediction of the other, time‐dependent set. Here the free volume function can be shown to provide the basis for the correlation. The other point of view involves kinetic theory, which treats volume relaxation as a gradual collapse of free volume. The results obtained in this context, and those following from probe studies in aging glasses by electron spin resonance, indicate the significance of our free volume function as a measure of molecular mobility in condensed systems.

ISSN:0148-6055    

DOI:10.1122/1.549910

出版商:The Society of Rheology    

年代:1986

数据来源: AIP

摘要:

A time evolution equation that implies on the one hand the Simha‐Somcynsky equilibrium theory of polymeric fluids and on the other hand a rheological equation of state describing viscoelastic behavior is called a nonequilibrium extension of the Simha‐Somcynsky theory. A framework allowing a systematic search for such extensions is introduced and illustrated in this paper.

ISSN:0148-6055    

DOI:10.1122/1.549866

出版商:The Society of Rheology    

年代:1986

数据来源: AIP

摘要:

New equations of state have been derived from our multiple hole energy model that describe the pressure‐volume‐temperature (PVT) behavior of amorphous polymers in both the equilibrium liquid and nonequilibrium glassy states. Good agreement between the theoretical and experimental results is achieved over a broad range of temperatures and pressures with asingleset of molecular parameters. Significantly, all molecular parameters are independent of temperature and pressure and can be determined separately. This approach differs from the basic concept of the existing free volume model in that the temperature dependence of the equilibrium free volume is nonlinear in the glassy state and the structural changes belowTgare described by a non‐Markovian process in which the redistribution of holes is constrained by the multiple levels of hole energies.

ISSN:0148-6055    

DOI:10.1122/1.549867

出版商:The Society of Rheology    

年代:1986

数据来源: AIP

摘要:

Since equations of state relate only pressure, volume, and temperature, they exclude stress fields other than pure hydrostatic pressure/tension. As such—they are not of themselves useful in describing the general stress‐deformation‐temperature response. Constitutive equations are required. The latter are, in turn, subsets of still more general expressions, the free energy functions. Rheological constitutive equations incorporate time, but introduce the need to carefully distinguish the independent variable as the stress or the deformation. Moreover, for glassy solids they must incorporate at least two distinct, yet interacting, memory functions, while providing for the physical aging process. The paper comments on thermodynamics and free energy functions and on some conceptual difficulties, including the definition of reference states for strain, especially volumetric strain. For glasses, the volumetric reference state is a particular problem because the unloaded state is metastable, and physical aging can occur. Hence, equation‐of‐state information in the otherwise undeformed state can provide a starting point for the development of constitutive equations. The underlying free energy function might be derived via statistical mechanics or taken from continuum mechanics. The Simha‐Somcynsky equation of state, based on statistical mechanics, is used to discussV‐Teffects explicitly. A possible means of modifying the underlying cell model is indicated, showing how the model can in principle be modified to produce a constitutive equation. Continuum mechanics approaches are then discussed. Examples are given of developments based on linear viscoelasticity theory, but directly incorporating stress‐induced volume changes (Knauss‐Emri and Shay‐Caruthers), and on large‐strain elastic theory (Peng‐Landel). Problems with all approaches to trying to describe glassy response are pointed out, especially in that they attack different facets of the overall problem.

ISSN:0148-6055    

DOI:10.1122/1.549906

出版商:The Society of Rheology    

年代:1986

数据来源: AIP