scholarly journals Theory for the rheology of dense non-Brownian suspensions: divergence of viscosities and– rheology

2019 ◽  
Vol 864 ◽  
pp. 1125-1176 ◽  
Author(s):  
Koshiro Suzuki ◽  
Hisao Hayakawa
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Shear Viscosity ◽  
Stress Ratio ◽  
Volume Fraction ◽  
Microscopic Theory ◽  
Critical Behaviour

A systematic microscopic theory for the rheology of dense non-Brownian suspensions characterized by the volume fraction $\unicode[STIX]{x1D711}$ is developed. The theory successfully derives the critical behaviour in the vicinity of the jamming point (volume fraction $\unicode[STIX]{x1D711}_{J}$), for both the pressure $P$ and the shear stress $\unicode[STIX]{x1D70E}_{xy}$, i.e. $P\sim \unicode[STIX]{x1D70E}_{xy}\sim \dot{\unicode[STIX]{x1D6FE}}\unicode[STIX]{x1D702}_{0}\unicode[STIX]{x1D6FF}\unicode[STIX]{x1D711}^{-2}$, where $\dot{\unicode[STIX]{x1D6FE}}$ is the shear rate, $\unicode[STIX]{x1D702}_{0}$ is the shear viscosity of the solvent and $\unicode[STIX]{x1D6FF}\unicode[STIX]{x1D711}=\unicode[STIX]{x1D711}_{J}-\unicode[STIX]{x1D711}>0$ is the distance from the jamming point. It also successfully describes the behaviour of the stress ratio $\unicode[STIX]{x1D707}=\unicode[STIX]{x1D70E}_{xy}/P$ with respect to the viscous number $J=\dot{\unicode[STIX]{x1D6FE}}\unicode[STIX]{x1D702}_{0}/P$.

scholarly journals Quantification of shear viscosity and wall slip velocity of highly concentrated suspensions with non-Newtonian matrices in pressure driven flows

2021 ◽  
Author(s):  
Patrick Wilms ◽  
Jan Wieringa ◽  
Theo Blijdenstein ◽  
Kees van Malssen ◽  
Reinhard Kohlus
Keyword(s):  
Shear Stress ◽  
Liquid Phase ◽  
Shear Rate ◽  
Shear Viscosity ◽  
Slip Velocity ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Wall Slip ◽  
Flow Index ◽  
Concentrated Suspensions

AbstractThe rheological characterization of concentrated suspensions is complicated by the heterogeneous nature of their flow. In this contribution, the shear viscosity and wall slip velocity are quantified for highly concentrated suspensions (solid volume fractions of 0.55–0.60, D4,3 ~ 5 µm). The shear viscosity was determined using a high-pressure capillary rheometer equipped with a 3D-printed die that has a grooved surface of the internal flow channel. The wall slip velocity was then calculated from the difference between the apparent shear rates through a rough and smooth die, at identical wall shear stress. The influence of liquid phase rheology on the wall slip velocity was investigated by using different thickeners, resulting in different degrees of shear rate dependency, i.e. the flow indices varied between 0.20 and 1.00. The wall slip velocity scaled with the flow index of the liquid phase at a solid volume fraction of 0.60 and showed increasingly large deviations with decreasing solid volume fraction. It is hypothesized that these deviations are related to shear-induced migration of solids and macromolecules due to the large shear stress and shear rate gradients.

scholarly journals PROCESSING ADDITIVES AND RHEOLOGICAL PROPERTIES OF MOLDED PHENOLIC PLASTICS

2019 ◽  
Vol 14 (1) ◽  
pp. 90-96
Author(s):  
P. V. Surikov ◽  
N. L. Shembel ◽  
A. A. Yurkin ◽  
A. V. Petrogradsky ◽  
V. D. Sevruk ◽  
...  
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Phenolic Resin ◽  
Volume Fraction ◽  
Slip Flow ◽  
Capillary Wall ◽  
Flow Curves ◽  
Flow Through ◽  
Capillary Viscosimetry ◽  
Stress Flow

By the method of capillary viscosimetry, the melt flow curves of the molded phenolic resin and its compositions with lubricant, plasticizer and their mixture were obtained. It was shown that the size (diameter) of the capillary channel influences the dependence of the effective shear rate on the shear stress (flow curves) of the studied compositions. Such rheological behavior of the compositions during flow is associated with the effect of sliding along the surface of the capillary wall. According to the Mooney method, the dependences of the effective shear rate at given values of shear stress on the reciprocal of the capillary radius are plotted. The function of the slip velocity on the shear stress on the capillary wall is characterized in terms of the slip coefficient, which relates the shear stress on the capillary wall to the velocity of the composition along it. For the studied compositions, the total flow through the capillary was divided into volume fractions, one of which is associated with a shear flow; the other is determined by the slip effect. It has been shown that the introduction of both a lubricant and a plasticizer into the composition leads to an increase in the fluidity of the compositions. At the same time, adding of lubricant increases the volume fraction of the slip flow. The greatest effect of increasing the fluidity of the composition gives the use of complex modifying additives containing both lubricant and plasticizer.

scholarly journals Aging, Rejuvenation and Thixotropy in Complex Fluids: Time-dependence of the Viscosity at Rest and under Constant Shear Rate or Shear Stress

2008 ◽  
Vol 18 (5) ◽  
pp. 53298-1-53298-13
Author(s):  
Daniel Quemada
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Volume Fraction ◽  
Complex Fluids ◽  
Transient Behaviour ◽  
Volume Fractions ◽  
Constant Shear ◽  
Constant Shear Stress ◽  
Constant Shear Rate ◽  
Viscosity Changes

Abstract Complex fluids exhibit time-dependent changes in viscosity that have been ascribed to both thixotropy and aging. However, there is no consensus for which phenomenon is the origin of which changes. A novel thixotropic model is defined that incorporates aging. Conditions under which viscosity changes are due to thixotropy and aging are unambiguously defined. Viscosity changes in a complex fluid during a period of rest after destructuring exhibit a bifurcation at a critical volume fraction ϕc2. For volume fractions less than ϕc2 the viscosity remains finite in the limit t →∞. For volume fractions above critical the viscosity grows without limit, so aging occurs at rest. At constant shear rate there is no bifurcation, whereas under constant shear stress the model predicts a new bifurcation in the viscosity at a critical stress σB, identical to the yield stress σy observed under steady conditions. The divergence of the viscosity for σ≤σB is best defined as aging. However, for σ > σB, where the viscosity remains finite, it seems preferable to use the concepts of restructuring and destructuring, rather than aging and rejuvenation. Nevertheless, when a stress σA(≤σB) is applied during aging, slower aging is predicted and discussed as true rejuvenation. Plastic behaviour is predicted under steady conditions when σ > σB. The Herschel-Bulkley model fits the flow curve for stresses close to σB, whereas the Bingham model gives a better fit for σ >> σB. Finally, the model’s predictions are shown to be consistent with experimental data from the literature for the transient behaviour of laponite gels.

Rheological Behavior of Highly Filled EPDM Compounds with Calcium Carbonate, Carbon Black, Silica and Zinc Oxide

1996 ◽  
Vol 69 (4) ◽  
pp. 628-636 ◽  
Author(s):  
Li Li Li ◽  
James L. White
Keyword(s):  
Particle Size ◽  
Zinc Oxide ◽  
Calcium Carbonate ◽  
Shear Rate ◽  
Carbon Black ◽  
Shear Viscosity ◽  
Volume Fraction ◽  
Carbonate Carbon ◽  
Yield Value ◽  
Yield Values

Abstract The shear viscosity, creep and constant shear rate transients have been measured for 0.20 volume fraction compounds of an EPDM with calcium carbonate, carbon black, silica and zinc oxide of similar particle size at 100°C. Measurements have been made in a creep sandwich instrument, pressurized rotational rheometer and a capillary rheometer and cover nine decades of shear rate. All of the compounds exhibit enhanced viscosities and yield values; i.e. there are stresses below which there is no flow. The greatest yield values and increased viscosities are with the compounds with calcium carbonate and zinc oxide. More extensive studies were made with the EPDM-calcium carbonate system, where it was shown that, increasing particle size reduces shear viscosity and yield values. Further, surface treating calcium carbonate with stearic acid signifcantly reduces the shear viscosity and yield value of the corresponding EPDM compound.

Rheological Properties and Extrudate Swell of PHBV-Bagasse Composites

2014 ◽  
Vol 931-932 ◽  
pp. 83-89
Author(s):  
Rapeephun Dangtungee ◽  
Suchart Siengchin ◽  
Chayada Puritung
Keyword(s):  
Particle Size ◽  
Shear Stress ◽  
Shear Rate ◽  
Surface Treatment ◽  
Shear Viscosity ◽  
Extrudate Swell ◽  
Melt Mixing ◽  
Capillary Rheometry ◽  
Wide Range ◽  
Twin Screw

Polyhydroxybutylate-co-hydroxyvalerate (PHBV) is biodegradable aliphatic polyester that produced by a wide range of microorganism. In this research aims to study the melt rheological and extrudate swelling behavior of PHBV filled with bagasse. The composites prepared by melt mixing (Two roll mill and Twin screw extruder). The effects of processing techniques for PHBV powder and bagasse loading, aspect ratio (particle size i.e. x<150μm, 150<x<250μm and x>250μm) and, surface treatment of bagasse were investigated by capillary rheometry at 180 °C. The dispersion of the bagasse was inspected by the scanning electron microscopy (SEM). A different compositions based on PHBV/bagasse were investigated according to the following weight ratios, i.e. 100/0, 95/5, 90/10, 80/20 and 70/30 wt% respectively. The results showed that the PHBV/bagasse composites exhibit pseudoplastic behaviour as the shear stress and extrudate swell increased with increasing shear rate while shear viscosity decreased. The apparent shear stress and apparent shear viscosity increased with increasing bagasse loading and, at a given apparent shear rate, the apparent shear stress increased slightly with increasing bagasse particle size. However, detrimental bagasse agglomeration was clearly observed to take place for sample with bagasse loading in excess of 20 wt%. The surface treatment of bagasse was carried out using silane coupling agent and benzoic acid. The results proved the effect of functionalization on the interfacial adhesion between PHBV and bagasse. Also, there was also further confirmed by rheology behaviour and SEM-EDS image.

scholarly journals Analysis and Experimental Study on Rheological Performances of Magnetorheological Fluids

Mechanika ◽  
2020 ◽  
Vol 26 (1) ◽  
pp. 31-34
Author(s):  
Chao LIU ◽  
Jianxin XIE ◽  
Dongling CAI
Keyword(s):  
Magnetic Field ◽  
Experimental Study ◽  
Shear Stress ◽  
Shear Rate ◽  
Volume Fraction ◽  
Magnetorheological Fluids ◽  
Bingham Model ◽  
Shear Thinning Fluids ◽  
Powder Rheometer ◽  
Constant Shear Rate

Silicone-based Magnetorheological Fluids (MRFs) were prepared with 10% volume fraction of carbonyl iron powder. Rheometer Physica MCR 301 was used to test the rheological performances of MRFs.The experimental results show Bingham model and Casson model could well describe rheological behaviors of MRFs. Shear stress of MRFs increases but apparent viscosity is significantly decreased and tends to be stable with the increase of shear rate in the presence of magnetic field. The results also show that MRFs are shear thinning fluids. The dependence of shear stress on magnetic field was tested under the condition of constant shear rate and increasing magnetic field, shear stress of MRFs increases remarkably.

scholarly journals Polymeric suspensions viscosity evolution under a constant electric field

2019 ◽  
Vol 20 (2) ◽  
pp. 272-284
Author(s):  
Ahmed Zelifi ◽  
◽  
Lounis Mourad ◽  
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Electric Field ◽  
Shear Viscosity ◽  
Particle Concentration ◽  
Constant Electric Field ◽  
Foam Layer ◽  
Experimental Apparatus ◽  
White Foam ◽  
Electrochemical Phenomenon

The present paper illustrates the effect of the coupling of an electric field with a shear field on a suspension ER. When the suspensions are simultaneously under flow and under the influence of a low electric field organized into packed lamellar formations, the shear stress increases with the increase of the higher polarisable particle concentration both in the electrostatic and hydrodynamic forces. In the absence of an electric field, the flow, alone, produces no segregation.The curves obtained after analyzes illustrate the changes on the shear viscosity under the simultaneous effect of an electric field and shear rate of the three suspensions study. We also observed the appearance of a white foam layer at the experimental apparatus which results in the electrochemical phenomenon due to some values of electric field. The latter can be exploited for a possible further research.

Melt flow properties of graphite nanoplatelets-filled polypropylene

2016 ◽  
Vol 51 (19) ◽  
pp. 2793-2804 ◽  
Author(s):  
Ayse B Bas ◽  
Oktay Yilmaz ◽  
Anil Ibis ◽  
Mustafa Dogu ◽  
Kadir Kirkkopru ◽  
...  
Keyword(s):  
Shear Rate ◽  
Polymer Matrix ◽  
Shear Viscosity ◽  
Volume Fraction ◽  
Shear Thinning ◽  
Filler Concentration ◽  
Graphite Nanoplatelets ◽  
Rate Region ◽  
Graphite Composites ◽  
Low Shear

Rheological behavior of polypropylene/graphite nanoplatelet composites of varying content, temperature, and filler shape was investigated by capillary and rotational rheometers. Scanning electron microscope images were taken in order to examine the filler shape and interaction between fillers and polymer matrix. Viscosity measurements of polypropylene/graphite composites showed shear thinning behavior like neat polypropylene. Filler inclusion resulted in increase in shear viscosity and shear thinning behavior of composites. The effect of filler concentration on viscosity is more appreciable in the low shear rate region. PP/graphite nanoplatelet composites with larger interface between filler and polymer matrix were of greater shear viscosity values through the entire shear rate range. However, filler morphology did not affect shear viscosity in high shear rate region remarkably. Composite viscosity as a function of volume fraction was modeled by Maron–Pierce equation. As temperature increased, shear viscosities of polypropylene/graphite composites and neat PP melt decreased. Temperature has less effect on composite viscosity than on neat PP viscosity due to the restricting effect of fillers on polymer molecules.

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