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• 1
Electronic Resource
Springer
Rheologica acta 13 (1974), S. 477-489
ISSN: 1435-1528
Source: Springer Online Journal Archives 1860-2000
Topics: Chemistry and Pharmacology , Physics
Description / Table of Contents: Résumé La dynamique des bulles d'air dans deux fluides viscoélastiques (solutions aqueuses :de polyacrylamide et de carboxyméthyle cellulose) et un fluide newtonien (huile de silicone) a été étudiée pour des volumes de bulles variant entre 0,1 et 11 cm3. La vitesse et la forme des bulles ont été déterminées par techniques photographiques avec stroboscope. Le volume des bulles a été mesuré avant chaque injection à l'aide d'une seringue calibrée. Pour les fluides viscoélastiques, trois formes typiques ont été observées: forme goutte d'eau, lentille et calotte sphérique. La vitesse d'ascension et la forme dépendent non seulement du volume mais aussi de la fréquence avec laquelle les bulles sont injectées. Pour la solution de polyacrylamide (0,5% Separan MG-700), l'influence de la fréquence d'injection est très marquée et des plus étonnantes: selon le volume des bulles, la vitesse décroît de façon monotone ou passe par un minimum pour ensuite augmenter avec la période d'injection. Ce comportement ne peut être relié au caractère non newtonien des fluides mais plutôt à l'influence prédominante des propriétés élastiques sur la forme des bulles. Par contre, pour la solution de carboxyméthyle cellulose, l'influence de la fréquence d'injection est très faible. Une analyse dimensionnelle du mouvement de bulles non sphériques dans un fluide décrit par une équation rhéologique non linéaire est présentée. Les données expérimentales sont analysées à l'aide du coefficient de traînée en fonction du nombre deReynolds, Re. Les résultats suggérent qu'à faibles valeurs deRe (〈 0,1), les propriétés élastiques du fluide contribuent principalement au taux de dissipation d'énergie alors qu'à des valeurs plus élevées, l'élasticité affecte également la forme des bulles.
Abstract: Summary The motion of air bubbles in two viscoelastic fluids (aqueous solutions of Polyacrylamide and of Carboxy Methyl Cellulose) and in aNewtonian fluid (Silicone) was studied for volumes ranging from 0.1 to 11 cm3. The velocity and the shape of the bubbles were obtained from photographs with the help of a stroboscope. The volume of the bubbles was measured with a calibrated syringe. Three typical shapes were observed for the viscoelastic fluids: tear-drop, spheroid, spherical cap. The velocity and the shape are not only function of bubble volume, but depend on the injection frequency. For the Polyacrylamide solution (0.5% Separan MG-700), the injection frequency dependence is most striking: depending on the volume, the bubble velocity decreases monotonously, or goes to a minimum and increases with the injection period. This behaviour cannot be attributed to the non-Newtonian character of the fluid, but rather to the influence of the elastic properties on the shape of the bubbles. On the other hand, the injection frequency has little influence on the behaviour in the Carboxy Methyl Cellulose solution. A dimensional analysis for the motion of non spherical bubbles in a fluid described by a nonlinear rheological equation is presented. Correlations of the drag coefficient as a function of theReynolds number are analysed. Experimental results suggest that at smallRe (〈0.1), the fluid elasticity contributes mainly to the energy dissipation, whereas at highRe, the elasticity influences also the shape of the bubbles.
Notes: Nombres adimensionnels Nombre deReynolds Re = D f U ϱ/η0 Nombre deWéber We = D f U 2 ϱ/σ Temps adimensionnels Λ 1 =t 1 U/D f Λ 2 = λU/D f λ/τ
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• 2
Electronic Resource
Springer
Rheologica acta 21 (1982), S. 1-14
ISSN: 1435-1528
Keywords: Generalized hydrodynamics ; entropy principle ; polymeric liquid
Source: Springer Online Journal Archives 1860-2000
Topics: Chemistry and Pharmacology , Physics
Notes: Abstract Three generalizations of classical hydrodynamic theories that are compatible with equilibrium thermodynamics and that are suitable for an appropriate macroscopic dynamical theory of polymeric liquids are considered. The strain tensor, the stress tensor and the chain segment distribution function (introduced in the network theory of polymeric liquids) are accepted as new state variables. We find that the generalized hydrodynamic equations are compatible with equilibrium thermodynamics provided certain conditions restricting the freedom of choice of constitutive relations are satisfied. In some particular cases the conditions are known from other considerations. We say that a dynamical theory is compatible with equilibrium thermodynamics, or equivalently, that it obeys the entropy principle if the properties listed in section 2.1 are satisfied.
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• 3
Electronic Resource
Springer
Rheologica acta 38 (1999), S. 14-25
ISSN: 1435-1528
Keywords: Key words Fumed silica ; Colloidal suspensions ; Non-linear viscoelasticity ; Rheological models
Source: Springer Online Journal Archives 1860-2000
Topics: Chemistry and Pharmacology , Physics
Notes: Abstract Suspensions of fumed silica exhibit a wide range of rheological properties depending on the nature and magnitude of the interparticle forces. In a non-polar fluid, the particles interact through hydrogen bonding and can form a three-dimensional network. The microstructure formation is responsible for the non-linear viscoelastic behavior of fumed silica suspensions, even at very small strain. These non-linear rheological properties have been studied in small amplitude oscillatory experiments as a function of particle size, surface treatment of particles, suspending medium polarity and solids concentration. The non-linear viscoelastic behavior is characterized by a non-sinusoidal waveform of the signal response. For suspensions in a non-polar fluid, both the elastic and the loss moduli are shown to be sensitive to the strain amplitude: the elastic modulus is decreasing with increasing strain whereas the loss moduli is initially increasing with strain. We have chosen to examine the dissipated energy which is clearly related to the breakup of the suspension structure. A comparison of model predictions and the experimental data shows the limitations of these models, recently proposed in the literature to describe the behavior of colloidal suspensions.
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• 4
Electronic Resource
Springer
Rheologica acta 18 (1979), S. 600-608
ISSN: 1435-1528
Source: Springer Online Journal Archives 1860-2000
Topics: Chemistry and Pharmacology , Physics
Description / Table of Contents: Zusammenfassung Es ist beobachtet worden, daß Polymerflüssigkeiten bei schergeschwindigkeitsabhängigem laminarem Fließen häufig ein anormales Wandverhalten aufweisen. In dieser Untersuchung wird eine neue Methode vorgestellt, mittels derer an sechs wäßrigen Polymerlösungen die beim Abfließen an einer geneigten ebenen Fläche beobachteten Anomalien quantitativ erfaßt werden. Die Wandeffekte werden aus den Abweichungen der experimentellen Fließkurven von deren theoretisch vorausgesagten Verläufen bestimmt, wobei für die untersuchten nicht-newtonschen Flüssigkeiten ein Fließgesetz nachEllis vorausgesetzt wird. In allen Fällen übersteigen die gemessenen Fließgeschwindigkeiten die vorausgesagten Werte, und zwar in einigen Fällen bis zu einem Faktor vier. Die Abweichungen werden durch ein Trennphänomen, genauer: durch die Bildung einer Wandschicht mit verminderter Polymerkonzentration, erklärt. Aus der Bestimmung der Viskosität an der Wand wird abgeschätzt, daß die Polymerkonzentration hier zwischen 10 und 56% geringer ist als in der übrigen Flüssigkeit.
Notes: Summary It has been observed that polymeric fluids exhibit frequently anomalous wall effects in rate-dependent laminar flow. In this work, we propose a new technique to obtain quantitative effects of anomalies observed in the gravity flow of six aqueous polymeric solutions on inclined plane surfaces. Wall effects are determined from departures of the experimental flow rates from the theoretical predictions, assuming Ellis behaviour for the non-Newtonian fluids. In all cases, the experimental flow rates exceed the predicted values, by a factor of four in some cases. The deviations are interpreted in the light of the “separation” phenomenon, ascribable to the formation of a layer of dilute polymer solution at the wall. From determination of the viscosity of the wall, it is shown that the polymer concentration is from 10 to 56% less of that of the bulk fluid.
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• 5
Electronic Resource
Springer
Rheologica acta 25 (1986), S. 95-101
ISSN: 1435-1528
Keywords: End effect ; elastic-constant viscosity fluid ; Boger fluid ; primary normalstress difference ; shear-thinning properties
Source: Springer Online Journal Archives 1860-2000
Topics: Chemistry and Pharmacology , Physics
Notes: Abstract In the light of a new interpretation, we have studied the end effects for highly elastic-constant viscosity fluids commonly called Boger fluids. In terms of entrance effect only, the presence of primary normal-stress differences in absence of shear-thinning properties results in a decrease of the entrance correction below the Couette (Newtonian) value, whereas the total end correction can be substantially increased by an amount which is strongly dependent on the Weissenberg number or recoverable shear.
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• 6
Electronic Resource
Springer
Rheologica acta 27 (1988), S. 241-254
ISSN: 1435-1528
Keywords: Rheological equation ; dilute polymersolution ; polyelectrolyte ; shear thickening ; polyacrylamide solution
Source: Springer Online Journal Archives 1860-2000
Topics: Chemistry and Pharmacology , Physics
Notes: Abstract A mathematical model based on the diffusion-convection equations is used to describe the rheological properties of dilute polymer solutions. The model uses a second-order conformation tensor as a measure of the internal strain; this avoids the mathematical complexity resulting from the use of a more detailed description of the macromolecules and also avoids the necessity of introducing additional ad-hoc assumptions (closure approximations) commonly used in other molecular theories. The rheological equation is obtained in terms of the rate-of-deformation tensor $$\dot \gamma$$ and a scalar functionf(σ) relating the extra stress tensorσ to the internal strain tensorc. The functionf(σ) depends on the physical insight introduced in the Helmholtz free energyA(c) of the solvent-polymer system. This approach is illustrated for an intra-molecular potential of a “FENE-charged” type. The concept of an isotropic, but conformation-dependent, friction coefficient, is also introduced to account for the “coil-stretch” transformation of macromolecules in solution. Viscosity and first normal-stress data, of partially hydrolyzed polyacrylamide solutions, (polyelectrolytes) are analyzed and compared to the model predictions in steady shear and elongational flows.
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• 7
Electronic Resource
Springer
Rheologica acta 25 (1986), S. 214-224
ISSN: 1435-1528
Keywords: Constitutive equation ; viscoelastic fluid ; kernel function ; simple shear flow ; uniaxial extension
Source: Springer Online Journal Archives 1860-2000
Topics: Chemistry and Pharmacology , Physics
Notes: Abstract A selection of kernel functions is given to be used in a new integral constitutive equation proposed by Piau whereby the deviatoric stress is calculated from the integral of the history of the past intrinsic rate of rotation and rate of deformation tensors through a representation theorem. Piau has demonstrated the objectivity of a frame moving with a given particle whose axis are directed along the eigenvectors of the rate of deformation tensor. The use of such a framework provides a new approach in the attempt to reduce the computational difficulties associated with conventional constitutive equations written in co-deformational or co-rotational reference frames. The shear and primary normal-stress material functions and the extensional (elongational) stress growth function are defined for the proposed integral constitutive equation. These material functions are used to calculate the kernel functions using steady state, stress relaxation and stress growth data of Attané in simple shear flow for monodisperse polystyrene solutions. The shear and extensional stress growth data of Meissner for a polyethylene melt are also used to show the flexibility of the rheological model. The material functions are first written in terms of five monotonically decreasing functions of the time lag between the past and the present time. Then kernel functions are chosen such that when substituted in the new integral constitutive equation they yield the functions used to describe the data. A further condition imposed on the normalized kernel functions is that they be decreasing functions of time lag.
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• 8
Electronic Resource
Springer
Rheologica acta 36 (1997), S. 416-428
ISSN: 1435-1528
Keywords: Key words Blends ; linear ; viscoelasticity ; emulsion models
Source: Springer Online Journal Archives 1860-2000
Topics: Chemistry and Pharmacology , Physics
Notes: Abstract The linear viscoelastic properties of several molten blends with immiscible components of different viscosity ratio have been investigated. All the blends show a morphology of emulsion type. At low frequencies, the behaviors of these blends are essentially governed by the interface. The Palierne (1990) model is shown to well predict the linear behavior of all the blends. The Lee and Park model (1994), developed to take into account the relationship between the rheological behavior and morphological changes under large strain flows, is also shown to well describe the storage and loss moduli of the blends by adjusting a single fitting parameter. Based on the weighted relaxation spectra, a comparison of both model predictions is made focussing on the time associated to the interface. An approximate method is then proposed to evaluate the interface parameter introduced in the Lee and Park model. At high frequency, discrepancies are observed for the Lee and Park predictions when the viscoelastic properties of both components are considerably different. The description of the bulk properties of the blend, i.e., the mixing rule used by Lee and Park, is modified to obtain a better description of the high frequency data.
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• 9
Electronic Resource
Stamford, Conn. [u.a.] : Wiley-Blackwell
Polymer Engineering and Science 23 (1983), S. 459-464
ISSN: 0032-3888
Keywords: Chemistry ; Chemical Engineering
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
Notes: The rheological properties of three types of fluids that exhibit large normal stresses are examined and compared. These fluids have a constant or nearly constant viscosity and can be used as model viscoelastic fluids, covering a range of viscosity from 0.1 to 124 Pa.s. One lubricant, Emkarox FC 31-45000, is shown to have the characteristics of a second-order fluid. Series difficulties encountered in measuring the rheological properties of the Separan - corn syrup solutions (Boger fluids) are reported. The Emkarox and solutions of polyacrylamide (Pusher 700) in mixtures of glycerine and water are proposed as better model fluids.
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• 10
Electronic Resource
Stamford, Conn. [u.a.] : Wiley-Blackwell
Polymer Engineering and Science 27 (1987), S. 1627-1633
ISSN: 0032-3888
Keywords: Chemistry ; Chemical Engineering
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
Notes: This second paper of a series continues the examination of the tensile properties of two series of linear low density polyethylene/polypropylene, (LLDPE/PP) blends. The blends were prepared using a twin-screw extruder and cover the whole concentration range, An Instron Universal Tensile Tester was used to measure the tensile properties of the blends between 10 and 70°C, and the temperature and composition dependences of the modulus were examined. A comparison is established between the solid state and melt properties to underline the behavior in the PP rich region. Results of dynamic mechanical experiments and differential scanning calorimetry on the same materials are also given, and the mechanical behavior is discussed in terms of the variation of the system's crystallinity.