Vane Rheometer Research Articles

Dry granular flow in a vane shear cell: flow characteristics and rheological laws

The flow dynamics of dry granular flows is significantly affected by a prominent feature of a granular mass known as dilatancy. Although their rheological behaviour has been characterised via friction and dynamic dilatancy laws, the role of dilatancy in a granular flow has not been much appreciated. In this study, using a vane rheometer, an experimental investigation was conducted on uniform glass beads of (d = 3 mm) at different initial relative densities (15 ≤ Dr ≤ 66%) and shear rates that span over four orders of magnitude. The flow characteristics in terms of effective friction, volume change, and velocity field were obtained and evaluated. The effective friction shows a descending-ascending pattern corresponding to a transitional behaviour from a velocity-weakening solid-like to a velocity-strengthening liquid-like behaviour. The volume-change measurements show that all specimens dilate and reach almost the same density at each shear rate. The velocity field follows a Gaussian pattern characterized by the slipping velocity at the boundary, the interlayer slippage between particles, and the interlayer disorder of the particles. A new non-monotonic friction law and a dynamic dilatancy law are presented as governing rheological laws based on the inertial number and by introducing an effective dilation coefficient. This effective dilation coefficient successfully captures the role of dilation-induced secondary vortex flows in the dry granular flows.

Rheology of eco-friendly mortars - Effect of industrial wastes additions

– Mortar is a mixture of sand, cement, water and eventually additives. With the environmentalissues, mortars are increasingly formulated with mineral additions as a substitute for cement in order toproduce ecological mortars. It is one of the most widely used cementitious materials in the field ofconstruction and civil engineering after concrete. Mortar placement techniques are evolving day by day,such as pumping, spraying and injection. Therefore, knowing the rheological behavior of mortars becomesmore and more crucial to master their implementation techniques. This study presents the development ofa vane rheometer to estimate the plastic viscosity yield stress of mortars. The rheological parameters weredeveloped from measurements using a procedure to convert data from moment torque and rotational speedto shear stresses versus shear rate. The procedure used considered the locally sheared material as a Binghamfluid and calculated the characteristic shear rate from the quilt analogy. The device was tested with threeexperimental programs in which many rheological parameters of the compositions of different mortars werecalculated. The results obtained validated the developed rheometer test procedure and confirmed that thetest results are reproducible and repeatable. Measurements were made on different compositions of mortarof each mineral addition, altering the amount of blast furnace slag (BFS) and fly ash (FA) in order toevaluate the impact of supplemental cementitious materials and industrial wastes on the rheologicalcharacteristics (plastic viscosity and yield stress) of eco-friendly mortar..

The effect of sodium polymethacrylate on the rheology of the positive paste and performance of the lead‐acid battery

AbstractDue to its rheological properties, positive lead‐acid battery paste can be difficult to spread on lead current collectors accurately and efficiently under industry machinery and setting. Sodium polymethacrylate dispersant was studied as an effective positive paste additive that could lower the yield stress of the paste without affecting paste density and battery performance. Under a four‐blade vane rheometer setup, stress growth and oscillatory amplitude strain sweep experiments evaluated the rheological properties of positive paste with the addition of varying amounts of sodium polymethacrylate. Further, the electrochemical effects of sodium polymethacrylate were also evaluated in 2V batteries by testing positive active material utilization and cycle life.

Yield strength determination from slump test

ABSTRACT The routinely determination of the yield strength of muddy beds is particularly important for the assessment of navigation in ports located in estuaries where cohesive sediments are abundant. The use of the nautical bottom concept may allow for a significant increase of the navigation depth. Sediments mixtures rich in clay and silt could behave as either a solid or a fluid depending on the forces acting on them. A concentrated mud sample will retain its shape if subject to shear stresses bellow the yield strength. However, if the same sample is subject to shear stresses above the yield strength, it will flow. One simple way of determining the yield strength is by performing a slump test. In this work, instead of just measuring the deposit final height or radius, as it has been done in the past, we fit an analytical expression to the deposit final geometry to estimate the yield strength. Simultaneous yield strength measurements using a conventional vane rheometer showed to be in very good agreement with the proposed technique independently of the mud sample origin, which is a clear improvement over the existing slump test methods, which just use the final height of the deposit.

Turbulent Flow Promotes Cleavage of VWF (von Willebrand Factor) by ADAMTS13 (A Disintegrin and Metalloproteinase With a Thrombospondin Type-1 Motif, Member 13).

Objective- Acquired von Willebrand syndrome is defined by excessive cleavage of the VWF (von Willebrand Factor) and is associated with impaired primary hemostasis and severe bleeding. It often develops when blood is exposed to nonphysiological flow such as in aortic stenosis or mechanical circulatory support. We evaluated the role of laminar, transitional, and turbulent flow on VWF cleavage and the effects on VWF function. Approach and Results- We used a vane rheometer to generate laminar, transitional, and turbulent flow and evaluate the effect of each on VWF cleavage in the presence of ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type-1 motif, member 13). We performed functional assays to evaluate the effect of these flows on VWF structure and function. Computational fluid dynamics was used to estimate the flow fields and forces within the vane rheometer under each flow condition. Turbulent flow is required for excessive cleavage of VWF in an ADAMTS13-dependent manner. The assay was repeated with whole blood, and the turbulent flow had the same effect. Our computational fluid dynamics results show that under turbulent conditions, the Kolmogorov scale approaches the size of VWF. Finally, cleavage of VWF in this study has functional consequences under flow as the resulting VWF has decreased ability to bind platelets and collagen. Conclusions- Turbulent flow mediates VWF cleavage in the presence of ADAMTS13, decreasing the ability of VWF to sustain platelet adhesion. These findings impact the design of mechanical circulatory support devices and are relevant to pathological environments where turbulence is added to circulation.

The rheology of slurries of athermal cohesive micro-particles immersed in fluid: A computational and experimental comparison

Immersed cohesive particles that aggregate under shear are commonly encountered in chemical engineering contexts. This work concerns the rheology of a particular set of systems, cement pastes, that have been difficult to treat from first-principles. In practice, these pastes exhibit large polydispersity with micron to millimeter sized particles, complicated particle shapes, and non-trivial surface morphology and surface chemistry. Simulations presented here utilize the discrete element model, informed by microscale atomic force microscopy measurements of surface topography, surface energy, and friction, and a simplified version of Stokesian Dynamics. Using these simulations, we study simple shear of two cementitious slurries composed of Portland cement and fly ash particles. These computations are then compared with steady-state vane rheometer experiments. This first-principles approach to comparing simulation and experiment allows us to explore how the microscale and macroscale physics are linked. Both computations and experiments agree qualitatively and are well modeled as Bingham plastics. Computations also show the emergence of percolating clusters, responsible for the rheology. Finally, including the mechanisms that are responsible for frustrated particle motions, such as effects of friction and rough walls at experimental scales, are shown to help give quantitatively better comparisons between simulation and experiment.

Effect of clay fraction and water content on rheological properties of sand–clay mixtures

Debris flow mobility can be expressed through rheological properties including yield stress and viscosity. These rheological properties are major parameters to describe and predict behaviors of debris flow. In the present study, the effect of clay fraction and water content on the rheological properties of sand–clay mixtures with coarse grain particles was investigated using a large vane rheometer. All soil mixtures showed non-Newtonian fluid behavior. When clay content was in the range of 5–30%, yield stress increased with an increase of clay fraction. Yield stress and plastic viscosity exponentially decreased with an increase in water content. Plastic viscosity became more sensitive to the change in clay fraction when water content increased. Empirical equations were proposed to estimate rheological properties of soil. The results indicated that yield stress and plastic viscosity are more sensitive to changes in water content than changes in clay fraction.

Field-oriented tests to evaluate the workability of cob and adobe

Due to its low environmental impact, earth construction has received lot of consideration in recent years. Furthermore, in order to improve the quality of earth construction, there is a need for a better description and control of the earth consistency or rheology. Just as for concrete with the Abrams cone, there is need for a simple and robust test that is able to provide, under field conditions, the consistency of the earth and that has results that can be used to estimate the yield stress of a fine soil used for cob or adobe. Two types of field-oriented tests are optimized for field conditions: the first one is based on the cone penetration test as used for the determination of the Atterberg limits and the second one is the ball dropping test already used onsite to check the adequacy between the earth consistency and the construction process. Finally, an experimental validation carried out on two types of soil shows that the yield stresses computed from the field-oriented tests is in agreement with the yield stresses obtained in a conventional way using a vane rheometer.

A study on the limitations of a vane rheometer for mineral suspensions using image processing

This study presents the results from the rheological measurement of clay suspensions using vane geometry in a wide gap configuration. It focuses on how measurement of viscosity cannot be effective for two reasons: the limits of the vane geometry itself and the limits of the material depending on its content of solid particles. Image analysis of the flow while shearing the material is carried out to relate the flow behavior. Several approaches to compute the shear flow curve from torque-rotational velocity data are used. The results demonstrate that the applied setpoint while applying a logarithmic shear rate ramp can be very different from the calculated shear rate from existing theories. Depending on the solid volume fraction of the particles in the mixture, we relate the macroscopic behavior using image analysis and the shear flow curves to the rheophysical regime of the flow of the suspensions. Therefore, this paper has two simultaneous goals: the first one is to describe the physical phenomena which control macroscopic behavior and the second one is to highlight the limits of the vane geometry for viscosity measurement of mineral suspensions like kaolinite pastes.

Effects of mud slurry on flow resistance of cohesionless coarse particles

Laboratory experiments were performed to investigate the effect of mud slurry on the flow resistance of cohesionless particles in debris flow. For one thing, natural angles of repose were measured for the gravel materials resting in air, in water, and in mud slurry separately. For another, rheological tests were taken using a vane rheometer to measure the torque-time response of sand particles within mud slurries of varying solid concentrations both at low and high rotational speeds. The stable torque obtained at the low rotational rate, which represents flow resistance primarily caused by particle contact friction, was nondimensionalized to compare the internal friction coefficient in each case. Furthermore, flow resistance of sand particles within one of the mud slurries was measured over a wide range of rotational speeds to compare with that in the dry system. It was found that the mud slurry has no significant effects on the frictional coefficient of cohesionless coarse particles. However, the mud slurry tends to decrease flow resistance of the particles, with the effect being more significant at higher rotational speeds or for more concentrated slurries. This derives from excess pore fluid pressure, which is easier to maintain at higher shear rates or within more cohesive slurries.

Design of portable rheometer with new vane geometry to estimate concrete rheological parameters

This paper presents the development of a portable vane rheometer to estimate concrete plastic viscosity and yield stress. The apparatus can be used not only in laboratory but also on construction site. In this study, new blade geometry was proposed to minimize the effect of segregation of concrete during testing, and also to expand the wide range of concrete work­ability with a slump of approximately from 7 cm to fluid concrete, and concrete with high plastic viscosity such as concrete with mineral additions. The used blade (U shaped and reversed) allows reducing the vibration of the apparatus, and ob­taining more stable measurements. The obtained results permit validating the rheometer test procedure and confirmed that the results are reliable, with a low coefficient of variation of 9% for repetitive test and of 5.8% for reproductive tests.

Rheology of powders and nanopowders through the use of a Couette four-bladed vane rheometer: flowability, cohesion energy, agglomerates and dustiness

A new four-bladed vane powder rheometer is proposed to study powder and nanopowder rheology at low and high shear rates. As shear rates increase, the powder flow will evolve from a Newtonian regime (low shear rates) to a Coulombic regime (moderate shear rates) and then to a kinetic regime (high shear rates) at which the powder may become self-fluidized because of intense particles collisions. Viscosity measurements of noncohesive glass beads at low shear rates (Newtonian and Coulombic regimes) do not strongly depend upon the particle size and can reach values much larger than commonly used viscosities in some CFDs models. Since, in the kinetic regime, the shear stress is a strong function of the particle size, agglomerate particle size of cohesive powders can be directly inferred from rheograms. Cohesive carbon black and silica nanopowders have been tested and compared to noncohesive glass beads microparticles, chosen as reference. For noncohesive glass bead micropowders, the “agglomerate” diameter average values found from rheological measurements are of the same order of magnitude as the primary diameters of the powder. This indicates that the kinetic theory of granular flows describes well these high shear rate regimes and that such theory can be used to estimate agglomerate diameters. It is also found that estimated agglomerate sizes of nanometric cohesive materials can reach sizes of hundred micrometers depending upon their cohesion strength. Such agglomerate size measurements have been corroborated with those made by microscopy.

Effect of the hydrodynamic pressure on shaft torque for a 4-blades vane rheometer

Vane type geometries are often used in rheometers to avoid slippage between the sample and the solid boundaries. Thus in commercial firms, universities and research institutes, vane type geometries are often applied to obtain accurate isothermal flow parameters. Recently, a detailed analysis of the complex flow phenomena inside such device was made using the finite element method (Nazari et al., 2013). In particular, the shaft torque was calculated at different angular velocities and compared to experimental data. Here, this work is repeated by using the finite volume method. In addition to this, the effect of hydrodynamic pressure on the shaft torque is analyzed separately and compared to the effect generated by viscous stress. This analysis is done for the two Newtonian fluids reported in Nazari et al. (2013), as well as for two cases of viscoplastic Bingham fluids. Including this, mesh independence is also analyzed. The outcome of the overall analysis is that the effect of hydrodynamic pressure constitutes about 2/3 of the shaft torque, leaving only about 1/3 of the torque to viscous stress.

A Vane Rheometer for Fresh Mortar: Development and Validation

A Vane Rheometer for Fresh Mortar: Development and Validation

A novel rheometer design for yield stress fluids

An inexpensive, rapid method for measuring the rheological properties of yield stress fluids is described and tested. The method uses an auger that does not rotate during measurements, and avoids material and instrument‐related difficulties, for example, wall slip and the presence of large particles, associated with yield stress fluids. The method can be used for many types of yield stress fluids, including concentrated lignocellulosic biomass. Sample preparation prior to measurement is minimal, reducing, or eliminating disruption of the sample. We show that measurements using this technique compare well with measurements obtained with a vane rheometer. A variation of the described method is proposed that would make it easier to measure time‐dependent rheological properties. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1523–1528, 2014

Estimation of cellulose nanofibre aspect ratio from measurements of fibre suspension gel point

Cellulose nanofibre aspect ratio controls the properties of sheets made from nanofibres and processing conditions, but aspect ratio is very difficult to measure. In this paper, aspect ratio was estimated from the gel point of a cellulose nanofibre suspension, the solids concentration at which the transition from a dilute to a semi-dilute suspension occurs. Four batches of cellulose nanofibres were tested. Two were produced from softwood fibres using ball milling. Commercially produced microfibrillated cellulose material was also used, both in as supplied form and after removal of the larger fibres by filtering. The average diameter measured from SEM images of fibres ranged from 33 to 73 nm. One sample was too heavily treated and an average dimension could not be measured. The gel-point was measured both from the height of a layer of cellulose nanofibres sedimented from a dilute suspension or from the lowest solids concentration at which a yield stress could be measured using a vane rheometer. The two methods were closely in agreement for all samples. Aspect ratio was then calculated using either the effective medium (EMT) or crowding number (CN) theories. Aspect ratio calculated with an assumed fibre density of 1,500 kg/m3, using the CN theory ranged from 155 to 60. Use of the EMT theory reduced the calculated aspect ratio by between 11 and 23 %. Reducing the assumed density in suspension from 1,500 to 1,166 kg/m3 reduced the calculated aspect ratio by 12–14 %. The heavily treated sample had by far the lowest aspect ratio.

A three dimensional model of a vane rheometer

Vane type geometries are often used in rheometers to avoid slippage between the sample and the fixtures. While yield stress and other rheological properties can be obtained with this geometry, a complete analysis of this complex flow field is lacking in the literature. In this work, a finite element method is used to calculate the isothermal flow parameters in a vane geometry. The method solves the mass and momentum continuity equations to obtain velocity, pressure and then stress fields. Using the total stress numerical data, we calculated the torque applied on solid surfaces. The validity of the computational model was established by comparing the results to experimental results of shaft torque at different angular velocities. The conditions where inertial terms become important and the linear relationship between torque and stress are quantified with dimensionless groups. The accuracy of a two dimensional analysis is compared to the three dimensional results.

High torque vane rheometer for concrete: principle and validation from rheological measurements

A high torque vane rheometer is used to measure the yield stress of cement-based materials. It is shown that this apparatus is suitable for the evaluation of the yield stress of various concretes and mortars in the fresh state in comparison with slump tests realized with ASTM Abrams cone. Then, the rheological properties (yield stress and shear flow behaviour) of a homogeneous kaolin clay suspension are studied with the apparatus and favourably compared with other rheometers and geometries.

Cement-based mixes: Shearing properties and pore pressure

This study presents original results on the rheological measurement of concrete mixes. It focuses on how to determine their mechanical and physical behavior under shearing stress. More specifically, the influence of aggregate content on shearing properties is studied. A vane rheometer was developed to characterize fresh cement-based materials. In addition to the conventional concrete rheometer, a special hydraulic pressure transducer was fitted to the container to monitor the pore water pressure variation while shearing the material. Experiments on cement paste, mortar, and concrete bring a new approach to help us understand the behavior of fresh-state mixes. The results show 1) a correlation between water pore pressure and torque applied on the vane; 2) a critical sand volume fraction, ϕ c, as a limit between colloidal interaction behavior and frictional behavior in mortars; beyond this critical fraction, a leap in yield stress and a drop in pore pressure due to granular dilatancy are noticed; 3) the granular content clearly influences the increase in yield stress of the cement mixes: above ϕ c, this increase becomes negligible.

Numerical simulation of power law and yield stress fluid flows in double concentric cylinder with slotted rotor and vane geometries

In our previous report, we showed that a rheometer equipped with a double concentric cylinder geometry with slotted rotor could effectively reduce wall slip effects and thus it could be used as an alternative to a rheometer with a vane geometry in yield stress measurements. Here, we use three-dimensional CFD simulation to compare these two geometries for rheological measurements of power law and yield stress fluids. Our results indicate that the double concentric cylinder rheometer with slotted rotor (DCCR/SR) is able to accurately measure rheological properties of a wider spectrum of test fluids than a vane rheometer because of significant reduction of the end and secondary flow effects.