Effect of ultrasonic vibrations on the flow of a viscoelastic liquid

The rheological characteristics of a viscoelastic liquid flow, on which finite-amplitude ultrasonic shear vibrations have been superimposed, are investigated. It is shown that at periodic deformation amplitudes of 5 µ or more there is a thixotropic reduction of the viscosity and elasticity of the system owing to the destruction of certain types of structural bonds. The experimental apparatus is described.Moscow Institute of Chemical Machine Building. Translated from Mekhanika Polimerov, No. 6, pp. 1097–1099, November–December, 1971.     

Influence of an electric field on the rheological behavior of a dilute suspension of dipolar dumbbells in a viscoelastic oldroyd liquid

Conclusions 1. Rheological equations of state of a dilute suspension of dipolar dumbbels in a viscoelastic Oldroyd liquid have been obtained for a stationary orientation of suspended particles in steady flows and electric fields.2. Study of the rheological properties of such a medium in simple shear flow in the presence of an electric field, the intensity vector of which lies in the shear plane and is perpendicular to the velocity vector, has shown that the medium examined conducts itself as a viscoelastic liquid. This is the result of both the viscoelastic properties of the dispersion medium and the orientation of the suspended particles under the action of frictional forces and the electric field. The effective viscosity of the suspension and difference in normal stresses resulting from the presence of the suspended particles are greater if one does not take the elastic properties of the dispersion medium into account.T. G. Shevchenko Kiev State University. Translated from Mekhanika Polimerov, No. 3, pp. 519–524, May–June, 1978.     

Multicritical phenomena in flow of viscoelastic liquids. 3. Liquid-crystalline polymers. The Akay-Leslie anisotropic liquid. Viscometric functions

The advances in determination of the rheological material functions of liquid-crystalline polymers (LCP) in a wide range of concentrations or temperatures are briefly examined. Special attention is focused on a discussion of the concentration region of the existence of liquid-crystalline order and textures initiated by shear flow. The phenomenological rheological equation for an anisotropic liquid proposed by Akay and Leslie (A-L model) was selected for describing the flow resistance of LCP, and the problem of simple shear flow of a liquid was solved. It was shown that the A-L model can describe all of the basic characteristics of the viscometric functions of LCP, including the phenomenon of negative values of the first normal stress difference for some range of concentrations and shear rates. The available data on the initial viscosity of lyotropic LCP were classified based on the types of cohesion (dimensionality) of the system, characterized by the exponent of the concentration dependence of the viscosity. It was found that each type of cohesion has its own kind of viscometric functions and that the A-L rheological model can reflect their basic characteristics. It was shown that by varying the initial ordering parameter of the A-L model, linear (or almost linear) functions N₁(q) and ₁₂(q) can be described in the region of low shear rates. It was hypothesized that region 1 of the flow curve (Onogi and Asada) inevitably exists in the continuous liquid crystalline phase, which could be outside of the region of measurements accessible to rheometry.See [23] for Communication 2.Institute of Polymer Mechanics. Riga. LV-1047 Latvia. Translated from Mekhanika Kompozitnykh Materialov. No. 6. pp. 821–839. November–December, 1997.     

Rheological Properties of Nanosized AlN Powder Suspensions for Advanced Ceramics

The rheological properties (flow curves and viscoelastic behavior) of injection molding suspensions of a plasma-processed AlN nanosized powder (nanopowder) in paraffin are investigated over a broad range of shear rates (0.07–1350 s^–1). Two viscosity plateaux are observed on the flow curves and two values of the yield stress are obtained. The lower value of the strain amplitude (0.66%), exceeding the linearity limit of periodic shear, is restricted by the rheometer resolution. The ultrasound treatment and shear deformation of suspensions affect the structure of particle packing, which is responsible for the dependence of their rheological properties on the prehistory of mechanical actions.     

Method of determining the volume and shear characteristics of elastico-viscous hereditary media from uniaxial-tension (compression) experiments

A method is proposed for determining the elastic constants — instantaneous modulus of elasticity, Poisson's ratio, shear modulus, bulk modulus, and the shear and volume influence functions — the shear creep kernel, the shear creep rate kernel, and the corresponding relaxation kernels from the data of creep or relaxation tests.Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 754–758, July–August, 1969.     

Viscosity,rubber elasticity,and viscoelasticity of concentrated polymer solutions

The results of a comparative investigation of the effect of the nature of the polymer and the solvent on the viscosity, rubber elasticity, and viscoelasticity of concentrated polymer solutions in the region of linear mechanical behavior are presented. It is established that in the case of nonpolar polymers the solvent affects only the free volume of the solution, whereas for polar polymers it also affects the entanglement network. This leads to the equality of the viscosities of solutions of nonpolar polymers in different solvents when compared in corresponding states (relative to the glass transition temperature) and to the dependence of the shear modulus of solutions of polar polymers on the nature of the solvent and temperature. It is shown that there is a universal relaxation spectrum in the flow zone for solutions of different polydisperse polymers after normalization with the shear modulus and the natural relaxation time determined as the ratio of the viscosity to the shear modulus.A. M. Gor'kii Ural State University, Sverdlovsk, A. V. Topchiev Institute of Petrochemical Synthesis, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 729–736, July–August, 1973.     

Multicritical phenomena in flow of viscoelastic liquids. 2. Zaremba-Fromm-De Witt liquid model generalized to the relaxation time spectrum

The effect of the relaxation time spectrum on the critical, i.e., limiting, conditions of stable shear flow of viscoelastic liquids at small Reynolds numbers was investigated. The approach developed in [1] was generalized to the Zimm, Rouse, Spriggs, and Ferry-Landel-Williams (FLW) viscoelastic relaxation time spectra. The FLW spectrum depicts the plateau of the viscoelasticity of high-molecular-weight polymer melts. The problem of the frequency dependence of the components of the complex shear modulus at different steady-state flow rates for the case of periodic shear directed both parallel to steady-state flow and orthogonal to it was solved for all of the listed models. The results of the experiment on superposition of periodic shear on the steady-state flow of a moderately concentrated solution of polyisobutylene were compared with the results of calculating the effect of steady-state flow on the frequency viscoelastic functions for liquids whose viscoelasticity is approximated by a Spriggs relaxation time spectrum. The calculation showed that in flow of liquids approximated by Rouse, Zimm, or Spriggs spectra, only parallel and orthogonal elastic losses of stability occur and dissipative loss of stability does not. Three types of instability (two elastic — parallel and orthogonal - and one dissipative — parallel) predict the prospects for use of the FLW spectrum. For this model, like the models using the Rouse and Zimm spectra, the shear rate at which instability is generated, especially dissipative instability, is a function of the number of relaxation times considered in the calculation. It was found that the predicted generation of dissipative instability begins for shear rates qD^* greater than the critical rates of generation of elastic parallel qE^* and elastic orthogonal qE^* instabilities, in contrast to the ZFD model which predicts that qE^*<qD^*<qE^*. The critical shear rates are correlated with the appearance of supermolecular viscoelastic structures caused by shear flow, called elastic-dissipative by analogy with dissipative structures.For communication 1 see [1].Institute of Polymer Mechanics, Latvian Academy of Sciences, Riga, LV-1006, Latvia. Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 119–135, January–February, 1997.     

Variant of the variable-modulus theory of elasticity

A variant of the variable-modulus theory — a generalization of the ideas of the classical theory of elasticity in which the observed difference in the moduli of elasticity in uniaxial tension and compression and homogeneous shear is taken into account — is considered. Quasilinear expressions are proposed for the stresses in terms of the strains and the strains in terms of the stresses.Tula Polytechnic Institute. Translated from Mekhanika Polimerov, Vol. 5, No. 2, pp. 363–365, March–April, 1969.     

Effect of steady-state flow of a polyisobutylene solution on its dynamic characteristics measured in the direction of flow

The effect of steady-state flow on the linear dynamic characteristics of a 10% solution of polyisobutylene in cetane, measured in the direction of flow, is investigated. The material characteristics in steady-state flow quantitatively describe the dynamic viscosity and elasticity at deformation frequencies small as compared with the steady-state shear rate.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 913–919, September–October, 1970.     

Fluid polymeric systems and their fillings. 2. Polymers characterized by their molecular mass distribution

Conclusions Much progress has been made in recent years toward understanding the mechanism of anomalous viscosity, elasticity, and the regularities of flow of melts, solutions, and filled systems as well as the mechanisms of periodic shear of finite amplitude. Nonlinear phenomenological models of viscoelastic fluids have been developed. The review does not include the group of problems related to combinations of stationary flow and linear periodic deformations, and combinations of linear periodic deformations with nonlinear ones. Nor have we discussed the development of methods for predicting the effects of extrudate swelling, manifestation of viscoelasticity in systems filled with short fibers, and nonisothermal flow conditions. The review does not contain new data obtained by using laser anemometry and double light refraction. The nature of the resistance in a capillary in the range of nonsteady flow has not been discussed either. The progress in these subjects is dealt with in this journal, "Mekhanika Polimerov." Insufficient attention has been paid to the rheology of viscoelastic biological fluids (blood, synovial fluids, etc.) and their substitutes, to the hydrodynamics of these liquids, and to the problem of pulsed flow. Little work has been done on the rheology of mixtures of melts of different polymers. It is also necessary to investigate the deformation of solutions and melts under superhigh velocities and under high pressures as well as the effect of constant and varying magnetic and electromagnetic fields on the mechanical flow characteristics of polymeric fluids.The second part of a paper by G. V. Vinogradov and L. A. Faitel'son (see [1]), submitted to the Third All-Union Conference on Polymer Mechanics, Riga, 1976.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 1, pp. 113–124, January–February, 1978.     

Thermal instability of a horizontal layer of viscoelastic liquid

The convective instability of a horizontal layer of viscoelastic liquid during heating from below has been examined. Critical values of the Rayleigh numbers for two forms of limiting conditions have been determined.S. M. Kirov Kazansk Chemicotechnological Institute. Translated from Mekhanika Polimerov, No. 2, pp. 331–335, March–April, 1976.     

Hybrid Simulation of Space Plasmas: Models with Massless Fluid Representation of Electrons. IV. Kelvin–Helmholtz Instability

This is a survey of the literature on hybrid simulation of the Kelvin–Helmholtz instability. We start with a brief review of the theory: the simplest model of the instability—a transition layer in the form of a tangential discontinuity; compressibility of the medium; finite size of the velocity shear region; pressure anisotropy. We then describe the electromagnetic hybrid model (ions as particles and electrons as a massless fluid) and the main numerical schemes. We review the studies on two-dimensional and three-dimensional hybrid simulation of the process of particle mixing across the magnetopause shear layer driven by the onset of a Kelvin–Helmholtz instability. The article concludes with a survey of literature on hybrid simulation of the Kelvin–Helmholtz instability in finite-size objects: jets moving across the magnetic field in the middle of the field reversal layer; interaction between a magnetized plasma flow and a cylindrical plasma source with zero own magnetic field.     

On the theory of non-Newtonian polymer flow

The Eyring-Frenkel theory of viscosity of low-molecular liquids has been extended to solutions of high-molecular compounds. It is shown that there are flow units of different sizes in the system, their mean size being proportional to the molecular weight of the polymer. An expression is obtained for the non-Newtonian viscosity of polymer solutions. In the limiting case of high shear rates the viscosity of the solution coincides with that of the solvent. At low shear rates Flory's empirical relation for the viscosity of polymer solutions is theoretically obtained.Mekhanika Polimerov, Vol. 2, No. 5, pp. 779–784, 1966     

Rheology and molecular structure of polyethylene melts 1. Melt identification from mechanical properties

It is proposed to use periodic deformation for the identification of the molecular structure of polyethylenes. By comparing the dependence of the complex and apparent viscosities on frequency and shear rate, respectively, it is shown that these functions are not equivalent for low-density polyethylene melts. The need for a numerical characteristic of the rheological functions, which should be related to the numerical characteristics of the molecular structure of the polymer, is established. The possibilities of using generalized relations for investigating the molecular structure are discussed. It is shown that the dynamic viscosity of polyethylene melts, described by a three-parameter equation, quite accurately reflects the viscoelastic properties of polyethylene melts and makes it possible, with the aid of the calculated function of the relaxation spectrum, to construct a frequency dependence of the modulus corresponding to the experimental data. Three numbers characterizing the viscoelasticity of polyethylene, which must be related with three molecular characteristics, are established.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 523–532, May–June, 1975.     

Thermal-fluctuation model of a thixotropic rubbery liquid

The isothermal deformation of a viscoelastic liquid, whose structural elements are simulated by the Maxwell elements of the relaxation spectrum, is considered. It is assumed that in the presence of temperature fluctuations the elements of the spectrum can be destroyed and restored. A comparison is made with experiment. A procedure for calculating the relaxation spectrum from the results of shear and normal stress measurements in the steady-state shear flow regime is proposed.Presented at the Symposium on Polymer Rheology, Institute of Petrochemical Synthesis, Academy of Sciences of the USSR, Moscow, May, 1970.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 2, pp. 307–317, March–April, 1971.     

Theory of flow of concentrated polymer solutions and melts

Starting from the concept of a polymer system as a collection of macromolecules forming an effective network, an expression is obtained for the stress tensor of a flowing concentrated polymer solution or melt. It is shown that the variation of the effective viscosity of polymer systems is associated with the orientation of the macromolecules and changes in the equilibrium number of nodes during flow. A system of equations describing the flow of polymer systems characterized by a gradient dependence of the effective viscosity and normal stresses in shear is written in the single relaxation time approximation.Institute of Chemical Physics, Moscow Region, Academy of Sciences of the USSR. Translated from Mekhanika Polimerov, Vol. 4, No. 4, pp. 724–730, July–August, 1968.     

Modelling and Simulation of the Transport of Protein Foams

The behaviour of foams at rest, but particularly during fluid mechanical transport is not sufficiently investigated yet. The present article deals with protein foams as they have a great importance in food production. In the first part, the foaming process of a highly viscous liquid due to gaseous materials dispersed under pressure in the liquid and mass transport of volatile components dissolved in the liquid is considered. The aim is to calculate the foam volume and the concentration of the dissolved, volatile components as a function of the material and process parameters. In the second part, material equations for bubble suspensions with gas volume fractions ϕ ≤ 0.6 and small bubble deformations (i.e. N_Ca ≪ 1) are presented. The basics form two constitutive laws which are used for describing a steady shear flow. If the rates of work of the two models are compared, material equations for the shear viscosity and the normal stress differences can be derived. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Explosive instability in nonlinear waves in media with negative viscosity : PMM vol. 38, n 6, 1974, pp. 991–995

The propagation of a wave of a finite amplitude in a medium with a nonlinearity of the second degree and negative viscosity, is examined. It is shown that in a finite time singularities appear in the solution. The exact solution of the Cauchy problem is given for a specific case. Recently the effects of negative viscosity which cause an increase in the energy of the wave motion have been studied intensively in electrodynamics, plasma physics, the Earth's atmosphere, in the theory of the circulation of the oceans and of flow in open channels [1–4], Wave amplification caused by an energy transfer from turbulent to regular motions, is possible in any medium having space-time fluctuations, provided the correlation time is sufficiently small [5, 6]. As the wave amplitude increases, nonlinear effects become important; they have been taken into account in cases where the interaction of a finite number of harmonics [2, 4] and the structure of steady motions have been examined [3].It is shown in this paper that in a medium with negative viscosity and a second degree dynamic nonlinearity, a solution of the Cauchy problem for an arbitrary “good” form of the initial perturbation, exists over a finite time interval. An example of such a solution is given.     

Normal stresses in non-Newtonian polymer flows

The calculation of the normal stresses from the flow curve is considered on the basis of the method of correlation of the frequency and stationary characteristics of flowing polymer systems. Simple expressions are given for finding the initial normal stress coefficient and the high-elastic modulus from the point corresponding to the beginning of non-Newtonian flow. A necessary condition for the appearance of normal stresses is a viscosity anomaly. It is shown that for a bounded value of the initial normal stress coefficient to exist the derivative of the effective viscosity with respect to shear rate must be zero at the initial point.Topchiev Institute of Petrochemical Synthesis, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 506–514, May–June, 1971.     

Vibrations of a viscoelastic cylinder with an elastic shell

The nonlinear vibrations of a viscoelastic cylinder with an elastic shell subjected to two harmonic forces are investigated using the averaging scheme described in [3, 4]. Nonresonance, resonance, and subharmonic vibrations are examined. It is shown that the presence of viscosity in the system leads to a single stationary equilibrium position for which the stability conditions are given.V. I. Lenin Tashkent State University. Translated from Mekhanika Polimerov, No. 4, pp. 691–697, July–August, 1973.