Rheological Constants Research Articles

Prediction of stationary interfaces in coextrusion flows

AbstractA computation method for the development of the interface in coextrusion flows is proposed. It is based on the transformation of the nonmixing condition at the interface into a transport equation of the rheological constants in the whole domain. The coextrusion flow of a Newtonian fluid and of a Carreau fluid is tested. It is pointed out that the interface location is strongly dependent on the flow rate and on the flow rate ratio.

IMPERFECT SQUEEZING FLOW VISCOSIMETRY WITH A WIDE PLATE AND A SHALLOW CONTAINER 1

ABSTRACT“Imperfect squeezing flow” is defined as the outward and upward flow of a liquid in a shallow container compressed at a constant displacement rate with a wide plate (liquid depth to plate diameter on the order of 1:10–1:20). The viscosity of Newtonian silicon oils could be determined with an accuracy of about 5% using such an array, with a plate and containers having a diameter on the order of 10 and 14 cm, respectively, and liquid depth on the order of 5–6 mm. The same procedure, however, was not very effective for determining the rheological constants of a commercial mustard and especially ketchup. In the latter case this was probably the result of self‐lubrication by a low viscosity liquid film, which distorted the force‐time relationship. The effect was even more prominent when samples of the same ketchups were tested in a coaxial viscosimeter. Because of this problem the procedure as described can only be used as a crude empirical method to distinguish between liquid foods having very different rheological properties.

Mathematical modeling of the human fetal arterial blood circulation

A mathematical model of the human fetal arterial circulation based on mass and momentum conservation for one-dimensional flow is presented. We simplified the fetal arterial vascular system from the heart to the placenta, defined 16 anatomical segments and studied the characteristics of the vascular system in relation to changes in morphology and hemodynamics. The two-step Lax-Wendroff finite difference scheme was used to solve the system of equations, after introducing the rheological constants, the diameter and length of the segments measured by two-dimensional imaging and the mean arterial velocity at the inlet segments obtained by pulsed Doppler. The model was validated by comparing the numerical results to our non-invasive ultrasound direct measurements and to previous published data.

Prediction of Borehole Stability in Tar Sands with the Use of a Rheological Model

Abstract The convergence characteristics of the borehole in tar sand are described by means of a nonlinear equation of state. The geometrical model of a cylindrical cavity was taken as a basis. The viscoelastic behavior of tar sand was investigated with the use of Burger's rheological model. The rheological constants were determined by means of creep tests on original tar sands. The model thus developed was used to investigate the contraction ofwellbore under different bottomhole conditions. The most unfavorable case thereby observed does not pose a serious problem from the point of practical consideration.

Effective rheological parameters of a suspension with polyfractionated filler

We examine a microscopically inhomogeneous medium consisting of a homogeneous nonlinear viscoplastic matrix and a random set of rigid ellipsoidal inclusions of various sizes. A variant of the effective field method is used to calculate the macroscopic rheological constants of the medium.

A model for the penetration of foam into running cotton fabrics

The viscous transport of foam through capillary systems can be described by a so‐called power law. With flow of foam through a stationary substrate a relationship between pressure and foam flow can be found in which a number of geometrical parameters and rheological constants play a part. This model may be extended to the application of foam to moving fabrics in closed systems. As long as the liquor absorption plays a subordinate role during application, the model described explains the behaviour observed, within the limits of experimental error. The model can be considered as a useful basis for further study.

MODELLING THE GELLING BEHAVIOUR OF LINSEED POLYSACCHARIDE

ABSTRACTThe gelling behaviour of linseed polysaccharide was measured in the presence of sucrose as a function of both polysaccharide and sucrose concentrations. Yield stress, consistency index, and flow behaviour index were determined using the Herschel‐Bulkley model. Transition concentrations of 0.7% for the polysaccharide and 55% for sucrose were found. Yield stress and consistency index increased with both polysaccharide and sucrose concentrations while flow behaviour index decreased. A polynomial model of the third degree on centred data after natural log transformation was found to give a satisfactory fit for the variations in rheological constants. The models for both yield stress and consistency index were a complex power law, and for flow behaviour index a complex semi‐log relationship, on sucrose and polysaccharide concentrations.

Rheological behaviour of ‘Cérat Cosmétique, Ph. F.’

Synopsis Rheological analysis during the preparation of dermocosmetic products allows the deduction of properties related to consistency and fluidity, which are very important for cream application. This paper rheologically examines a cold-cream formula, 'Cérat Cosmétique' from the French Pharmacopoeia. 'Cérate', or cold-cream, is one of the most ancient cosmetic preparations. The Rheotest 2 viscometer, which was used for experimental determinations, allowed the rheograms to be plotted and the characteristic rheological constants to be calculated. On the basis of this information, the preparation under study was seen to present plastic behaviour. However, posterior thixotropic studies indicated that 'Cérat Cosmétique, Ph. F.' had no true thixotropic behaviour.

Spreading of non-Newtonian liquids under the gravitational force

A technique is proposed for determining the rheological constants based on the analysis of the spreading of tall cylindrical samples under the gravitational force.

STUDIES ON VISCOSITY EQUATION OF MORTAR AND CONCRETE

It has long been suggested that rationalization of concrete operation can be promoted by utilizing rheological constants obtained by viscosity equation of fresh mortar and concrete. But actually, such studies have been very few.In this paper, the authors pay attention to the fact that mortar and concrete are a type of high concentration suspension, and the suspension medium in the mortar and concrete are considered to be respectively cement paste and mortar, the suspended particles are respectively fine and coarse aggregate.This study aims to establish a direct estimate of the plastic viscosity, using the mortar and concrete's viscosity equation with the factors: material characteristics and mix proportions. The authors also show that the plastic viscosity obtained by using this viscosity equation is very accurate, and so very useful.

Composition and properties of mucilaginous polysaccharide from native and fermented black gram flour

A mucilaginous polysaccharide was isolated from black gram under different processing conditions. The trichloroacetic acid (TCA) extracted and acetone precipitated polysaccharides contained l-rhamnose, l-arabinose, d-xylose and d-galactose along with d-galacturonic acid (12–13%). The polysaccharide preparations showed considerable changes in galactose and rhamnose contents during processing. The α-galactosidase activity as well as the viscosity increased by 25–30% after fermentation. Rheological constants such as yield stress and consistency index showed considerable changes but flow behaviour index did not show much change. The zero shear intrinsic viscosity or consistency index appeared to be related to the galactose content of the polysaccharide.

The heating process in dissolving cellulose xanthate in an apparatus of the screw type

Rheological constants of viscose have been determined which make it possible to describe mathematically the anomalous portion of the flow curves and the temperature dependence of viscose viscosity, and also are necessary for calculating the technological parameters of the process of continuous dissolution of cellulose xanthate and to construct apparatus. The possibility of calculating the heat-up of viscose after treatment in continuous dissolvers and of selecting a continuous solution regime at an assigned temperature for the exiting viscose from calculation relationships has been demonstrated. The advisability of simultaneously carrying out the processes of solution and heating of the viscose in continuous apparatus has been established.

Analytical Study on Deformation of Fresh Concrete

A simulation method of the behavior of fresh concrete is proposed in the present paper. To estimate the flow and deformation of fresh concrete, a method of viscoplastic finite element analysis is applied, in which fresh concrete is treated as a kind of Bingham model. In the analysis, slipping resistance between boundary surface and fresh concrete can be considered, and the dynamic behavior can be analyzed by calculation of the retardation of velocity change. In this paper, some analytical results for the slump test and the flow test are shown and discussed. The relationship between rheological constants and the values measured by the slump test and the flow test are clarified analytically, and the method for estimating rheological constants from the slump value and the flow value is proposed. Then, the adequacy of the analytical method proposed is examined by comparison with experimental results.

Backward facing step flow of viscoelastic fluids.

Two-dimensional flows over a backward facing step of viscoelastic fluids have been solved by the finite difference method. The Maxwell model and Denn model are used as constitutive equations. The result has shown that behavior of a recirculating flow in the rear of the step is dependent of the Reynolds number (R), Weissenberg number (W) and rheological constants (n and s) of viscoelastic fluids. Recovery of velocity profiles in the downstream of the step is slower in viscoelastic fluids than in Newtonian fluids at the same Reynolds number. Using the present numerical method, it is possible to calculate the flow field up to R=100 and W=1.0.

A Method for Prediction of Power Law Rheological Constants Using the Pendulation of a Pseudo Plastic Fluids Column in a Vertical U-Tube

A Method for Prediction of Power Law Rheological Constants Using the Pendulation of a Pseudo Plastic Fluids Column in a Vertical U-Tube

Rheological behaviour of clarified banana juice: Effect of temperature and concentration

The flow behaviour of concentrated (depectinized) banana juice was determined over a wide range of temperatures (30–70°C) and concentrations (20–79·7°Brix), using a coaxial cylinder viscometer. The results indicated that depectinized clarified and filtered banana juice behaves as a Newtonian fluid at all these concentrations. The effect of temperature on the viscosity of the different concentrates followed an Arrhenius-type relationship. The activation energy for viscous flow was in the range 5·99–18·66 kcal g-mol −1, depending on the concentration. The influence of temperature on the viscosity was more pronounced at higher concentration. The effect of concentration on viscosity followed a power-law relationship at the temperatures used. The rheological constants for the Arrhenius and power-law models were determined. The combined effect of temperature and concentration (20–57°Brix only) on the coefficient of dynamic viscosity can be represented by a single equation: n=2·85×10 −11C 2·5exp(3016/T)

Viscosity Pattern of Native and Fermented Black Gram Flour and Starch Dispersions

AbstractThe effects of fermentation and added NaCl on aqueous dispersions of black gram flour were studied. After fermentation the apparent viscosities of cold pastes increased significantly over that of native flour dispersions (NFD). Addition of NaCl caused considerable decrease in apparent viscosities of NFD but only marginal decrease in fermented flour dispersions (FFD). Studies on rheological constants showed that changes brought about in these by fermentation were greater than that exerted by adding NaCl. Brabender viscography indicated that peak viscosity (PV) decreased by both NaCl and fermentation. FFD with salt showed 15% increase in PV over that without salt. FFD with or without NaCl showed greater breakdown (BV) and set back (SV) viscosities, but the values were lower in comparison to NFD.Starch was isolated in 33–35% yield from native and fermented batters. Apparent viscosity in 1M KOH showed increase due to fermentation. Brabender viscography indicated a GT of ∽81°C for both starches. The PV of fermented starch increased by 13%, BV by 15% and SV by 30% over that of native. Intrinsic viscosity of starch increased considerably while solubility and swelling power increased only marginally after fermentation.

Poly(vinyl chloride) blends. III. Rheological properties

AbstractThe rheological properties of unplastified PVC blends with and without addition of clay as filling materials and containing various amounts of chlorinated polyethylene (CPE) have been investigated. The flow curves of the compounds exhibit yield values. The shapes of the curves and the rheological constants are influenced by the blend composition. The dependences of melt viscosity on the shock modifier content exhibit maxima and minima both for the blends with and without filling material, which indicates the heterogeneous structure of these blends. The presence of clay in the samples results in narrowing of the variation range of the conventional viscosity, which facilitates the finding of optimal conditions for the processing of blends with various CPE content.

Anisotropic friction in polymeric models. I. The elastic dumbbell and reptating chain

Expressions for the stress tensor of simple mechanical (bead–spring, bead–rod) models of polymers with anisotropic friction are derived using the phase space kinetic theory of Curtiss, Bird, and Hassager. The correspondence between such expressions and those postulated by Doi and Edwards for concentrated solutions of polymers suggests topological entanglement may be effectively modeled by anisotropic friction. In this first paper we consider the elastic dumbbell with anisotropic friction. A calculation of the zero shear rate rheological material constants η, ψ1,0, and ψ2,0, for a Hookean dumbbell is presented. The second normal stress coefficient ψ2,0 assumes a nonzero value with anisotropic friction. The stress tensor for a chain of such elastic dumbbells is shown to be that postulated by Doi and Edwards for topologically entangled, or reptating, flexible polymers.

フレッシュコンクリートの各種コンシステンシー試験方法に関するレオロジー的考察

In this paper, various consistency tests of fresh concrete or mortar such as slump test, flow test, solid-sphere-lifting viscometer and parallel・plates plastometer are simulated by using the visco-plastic finite element method, which has been proposed by the authors for simulating the deformation of fresh concrete. The relationship between rheological constants and measured values by these tests are clarified theoretically, and then some problems in measuring rheological constants of fresh concrete are discussed. The method for estimating rheological constants from slump value and flow value is proposed, and the adequacy of the analytical method and the estimating method proposed is examined by comparison with experimental results.