scholarly journals Yield stress of concentrated wheat straw suspensions

2021 ◽  
Author(s):  
Rizwan Bashir
Keyword(s):  
Wheat Straw ◽  
Yield Stress ◽  
Power Law ◽  
Mesh Size ◽  
Pulp Fibers ◽  
Ramp Rate ◽  
Effective Utilization ◽  
Power Law Equation

The yield stress of concentrated wheat straw suspensions was measured by a vane with a Bohlin rheometer. Wheat straw fibers were made by grinding (wet and dry) wheat straw and separated into four sizes by sieving (8, 12, 20, and 40 mesh). The yield stress was found to increase with concentration as well as with the size of the wheat straw fibers. The yield stress data fitted to power law equation proposed by Kerekes et al. (1985) for pulp fibers. It was found that only 40 mesh size wheat straw fibers agreed with the relation. Effect of stress ramp rate was studied on 5% (20 mesh) w/v, wheat straw suspension. It was observed that stress ramp rate had an effect on measured yield stress value. No yield stress was observed in the suspension of 5% (40 mesh) w/v, due to sedimentation of wheat straw fibers. For effective utilization and mixing of enzymes with wheat straw fibers during hydrolysis, knowledge of yield stress of suspension was important.

scholarly journals Yield stress of concentrated wheat straw suspensions

2021 ◽  
Author(s):  
Rizwan Bashir
Keyword(s):  
Wheat Straw ◽  
Yield Stress ◽  
Power Law ◽  
Mesh Size ◽  
Pulp Fibers ◽  
Ramp Rate ◽  
Effective Utilization ◽  
Power Law Equation

The yield stress of concentrated wheat straw suspensions was measured by a vane with a Bohlin rheometer. Wheat straw fibers were made by grinding (wet and dry) wheat straw and separated into four sizes by sieving (8, 12, 20, and 40 mesh). The yield stress was found to increase with concentration as well as with the size of the wheat straw fibers. The yield stress data fitted to power law equation proposed by Kerekes et al. (1985) for pulp fibers. It was found that only 40 mesh size wheat straw fibers agreed with the relation. Effect of stress ramp rate was studied on 5% (20 mesh) w/v, wheat straw suspension. It was observed that stress ramp rate had an effect on measured yield stress value. No yield stress was observed in the suspension of 5% (40 mesh) w/v, due to sedimentation of wheat straw fibers. For effective utilization and mixing of enzymes with wheat straw fibers during hydrolysis, knowledge of yield stress of suspension was important.

Conductivity, Dielectric and Modulus study of NH4PF6 based Zwitterionic polymer electrolyte

2020 ◽  
Vol 13 ◽  
Author(s):  
Manindra Kumar ◽  
Neelabh Srivastava
Keyword(s):  
Polymer Electrolyte ◽  
Power Law ◽  
Loss Tangent ◽  
Electric Modulus ◽  
Relaxation Behavior ◽  
Conductivity Data ◽  
Frequency Range ◽  
Zwitterionic Polymer ◽  
Power Law Equation ◽  
Jonscher’S Power Law

Background and Objective: Zwitterionic polymer electrolyte has been successfully synthesized using NH4PF6 salt. The conductivity of the synthesized polymer membrane is found to be of the order of 10-3Scm-1. Dielectric and Modulus properties of the polymer electrolyte have also been studied which showed well relaxation peaks with both temperature and salt concentrations. Result: This is well depicted with the loss tangent curve. Debye type relaxation behavior has observed from the electric modulus. Conclusion: Frequency dependent conductivity data (fitted with Jonscher's power law equation) confirmed the presence of NCL/SLPL type behavior in the studied frequency range.

Thermorheological Characterization of Elastoviscoplastic Carbopol Ultrez 20 Gel

2015 ◽  
Vol 137 (3) ◽  
Author(s):  
M. A. Hassan ◽  
Manabendra Pathak ◽  
Mohd. Kaleem Khan
Keyword(s):  
Experimental Investigation ◽  
Yield Stress ◽  
Elastic Properties ◽  
Viscous Dissipation ◽  
Power Law ◽  
Effect Of Temperature ◽  
Rheological Parameters ◽  
Frequency Range ◽  
Power Law Index

The temperature and concentration play an important role on rheological parameters of the gel. In this work, an experimental investigation of thermorheological properties of aqueous gel Carbopol Ultrez 20 for various concentrations and temperatures has been presented. Both controlled stress ramps and controlled stress oscillatory sweeps were performed for obtaining the rheological data to find out the effect of temperature and concentration. The hysteresis or thixotropic seemed to have negligible effect. Yield stress, consistency factor, and power law index were found to vary with temperature as well as concentration. With gel concentration, the elastic effect was found to increase whereas viscous dissipation effect was found to decrease. Further, the change in elastic properties was insignificant with temperature in higher frequency range of oscillatory stress sweeps.

scholarly journals Derivation and evaluation of landslide-triggering thresholds by a Monte Carlo approach

2014 ◽  
Vol 18 (12) ◽  
pp. 4913-4931 ◽  
Author(s):  
D. J. Peres ◽  
A. Cancelliere
Keyword(s):  
Monte Carlo ◽  
Slope Stability ◽  
Power Law ◽  
Rainfall Intensity ◽  
Antecedent Rainfall ◽  
Rainfall Events ◽  
Physically Based ◽  
Power Law Equation ◽  
Triggering Rainfall ◽  
Landslide Triggering

Abstract. Assessment of landslide-triggering rainfall thresholds is useful for early warning in prone areas. In this paper, it is shown how stochastic rainfall models and hydrological and slope stability physically based models can be advantageously combined in a Monte Carlo simulation framework to generate virtually unlimited-length synthetic rainfall and related slope stability factor of safety data, exploiting the information contained in observed rainfall records and field-measurements of soil hydraulic and geotechnical parameters. The synthetic data set, dichotomized in triggering and non-triggering rainfall events, is analyzed by receiver operating characteristics (ROC) analysis to derive stochastic-input physically based thresholds that optimize the trade-off between correct and wrong predictions. Moreover, the specific modeling framework implemented in this work, based on hourly analysis, enables one to analyze the uncertainty related to variability of rainfall intensity within events and to past rainfall (antecedent rainfall). A specific focus is dedicated to the widely used power-law rainfall intensity–duration (I–D) thresholds. Results indicate that variability of intensity during rainfall events influences significantly rainfall intensity and duration associated with landslide triggering. Remarkably, when a time-variable rainfall-rate event is considered, the simulated triggering points may be separated with a very good approximation from the non-triggering ones by a I–D power-law equation, while a representation of rainfall as constant–intensity hyetographs globally leads to non-conservative results. This indicates that the I–D power-law equation is adequate to represent the triggering part due to transient infiltration produced by rainfall events of variable intensity and thus gives a physically based justification for this widely used threshold form, which provides results that are valid when landslide occurrence is mostly due to that part. These conditions are more likely to occur in hillslopes of low specific upslope contributing area, relatively high hydraulic conductivity and high critical wetness ratio. Otherwise, rainfall time history occurring before single rainfall events influences landslide triggering, determining whether a threshold based only on rainfall intensity and duration may be sufficient or it needs to be improved by the introduction of antecedent rainfall variables. Further analyses show that predictability of landslides decreases with soil depth, critical wetness ratio and the increase of vertical basal drainage (leakage) that occurs in the presence of a fractured bedrock.

Strength and deformation of frozen saturated sand at −30 °C

1982 ◽  
Vol 19 (1) ◽  
pp. 104-107 ◽  
Author(s):  
V. R. Parameswaran ◽  
M. Roy
Keyword(s):  
Strain Rate ◽  
Power Law ◽  
Quartz Sand ◽  
Peak Strength ◽  
Strain Rates ◽  
Saturated Sand ◽  
Ideal Plastic ◽  
Strength And Deformation ◽  
Power Law Equation

Frozen saturated quartz sand containing 20% moisture by weight, when deformed at −30 °C at various strain rates, showed various modes of behaviour such as visco-plastic, almost ideal plastic, and brittle with little plasticity with increasing order of strain rate. The values of peak strength observed for strain rates between 5 × 10−7 and 6 × 10−3 s−1 were in the range 15–42 MPa, stress being related to strain rate by a power-law equation.

scholarly journals Rheological behavior of cereal straw suspensions

2021 ◽  
Author(s):  
Sandra Ukaigwe
Keyword(s):  
Rheological Properties ◽  
Yield Stress ◽  
Rheological Behavior ◽  
Xanthan Gum ◽  
Mesh Size ◽  
General Purpose ◽  
Measuring Instrument ◽  
Fiber Concentration ◽  
Cereal Straw ◽  
Malt Barley

The rheological properties (yield stress and viscosity) of cereal straw suspensions are especially important in bioethanol production as they determine the mixing behaviour of the suspension during enzymatic hydrolysis. Yield stress measurements are generally difficult to perform in straw suspensions due to sedimentation, which commonly occur in the suspensions because of the difficulty encountered in loading the suspension into the measuring equipment. The process of placing the suspension in the measuring instrument causes a disturbance likely to induce the yielding of the suspension before the actual measurements are taken. Moreover cereal suspensions at high straw concentration (10-40 wt%) are soft solids and pourability is particularly difficult with solids. Rheological behavior of staw suspensions made from wheat, Oats and malt barley of fiber sizes 0.15 mm-4.20 mm (mesh sizes 20 to 100) and concentrations 5.0-15.0 wt% were studied. The suspensions were initially prepared by dispersing milled and sieved straws in distilled water at room temperature, followed by vortexing to aid the dispersion process; this was later modified to include a 30-minute de-aeration of the suspensions using vacuum and 2-minute mixing using a general purpose mixer at about 162 rpm. However, none these procedures produced a homogenous suspension. The viscosity of the dispersion medium was modified by the addition of Xanthan gum. This produced homogenous suspensions which remained suspended for about 20 minutes. The rheological properties of these suspensions were measured on a Bohlin rheometer in the controlled stress mode using a vane and cup measuring instrument, and the suspension yield stress determined by extrapolation and by regression of Herschel-Bulkley, Casson and Bingham models. Yield stress obtained from extrapolation ranged from 2-19 Pa, while model results ranged from 0.96- 8.15 Pa, for 5.0 wt% Oats straw suspensions with Xanthan gum strengths of 0.1-0.5 wt%. Extrapolation results for 7.5 wt% Oats staw suspensions with Xanthan gum strengths of 0.1-0.5 wt% ranged from 20-36 Pa while model results were in the range of 4.38-18.76 Pa. Wheat and malt barely straw suspensions evaluated using Herschel-Bulkley model at similiar Oats straw suspension conditions of 5.0 wt% fiber concentration with 0.3 wt% Xanthan gum strength produced statistically equivalent yields stress to Oats straw suspensions in the range of 2.31-4.04 Pa for fibers of mesh size 40-100. Cereal straw suspenions are non-Newtonian fluids with yield stresses that are highly straw concentration dependent.

scholarly journals Staggered Semi-Implicit Hybrid Finite Volume/Finite Element Schemes for Turbulent and Non-Newtonian Flows

Mathematics ◽  
2021 ◽  
Vol 9 (22) ◽  
pp. 2972
Author(s):  
Saray Busto ◽  
Michael Dumbser ◽  
Laura Río-Martín
Keyword(s):  
Finite Element ◽  
Finite Elements ◽  
Yield Stress ◽  
Finite Volume ◽  
Power Law ◽  
Source Terms ◽  
Cartesian Grids ◽  
Rans Equations ◽  
Edge Based ◽  
Finite Element Schemes

This paper presents a new family of semi-implicit hybrid finite volume/finite element schemes on edge-based staggered meshes for the numerical solution of the incompressible Reynolds-Averaged Navier–Stokes (RANS) equations in combination with the k−ε turbulence model. The rheology for calculating the laminar viscosity coefficient under consideration in this work is the one of a non-Newtonian Herschel–Bulkley (power-law) fluid with yield stress, which includes the Bingham fluid and classical Newtonian fluids as special cases. For the spatial discretization, we use edge-based staggered unstructured simplex meshes, as well as staggered non-uniform Cartesian grids. In order to get a simple and computationally efficient algorithm, we apply an operator splitting technique, where the hyperbolic convective terms of the RANS equations are discretized explicitly at the aid of a Godunov-type finite volume scheme, while the viscous parabolic terms, the elliptic pressure terms and the stiff algebraic source terms of the k−ε model are discretized implicitly. For the discretization of the elliptic pressure Poisson equation, we use classical conforming P1 and Q1 finite elements on triangles and rectangles, respectively. The implicit discretization of the viscous terms is mandatory for non-Newtonian fluids, since the apparent viscosity can tend to infinity for fluids with yield stress and certain power-law fluids. It is carried out with P1 finite elements on triangular simplex meshes and with finite volumes on rectangles. For Cartesian grids and more general orthogonal unstructured meshes, we can prove that our new scheme can preserve the positivity of k and ε. This is achieved via a special implicit discretization of the stiff algebraic relaxation source terms, using a suitable combination of the discrete evolution equations for the logarithms of k and ε. The method is applied to some classical academic benchmark problems for non-Newtonian and turbulent flows in two space dimensions, comparing the obtained numerical results with available exact or numerical reference solutions. In all cases, an excellent agreement is observed.

Measuring the onset of mine tailings erosion

2007 ◽  
Vol 44 (4) ◽  
pp. 473-489 ◽  
Author(s):  
M Haneef-Mian ◽  
Ernest K Yanful ◽  
Robert Martinuzzi
Keyword(s):  
Shear Stress ◽  
Power Law ◽  
Mine Tailings ◽  
Laser Doppler Anemometry ◽  
Critical Shear Stress ◽  
Laser Doppler ◽  
Shear Stresses ◽  
Cohesive Sediments ◽  
Fine Grained ◽  
Power Law Equation

The present study gives details of a methodology for estimating the critical shear stress for erosion of mine tailings and other naturally occurring cohesive sediments. Erosion of a cohesive sediments bed occurs when the critical shear stress is exceeded to break the interparticle bond. Experiments were conducted in a 30 cm diameter laboratory column and calibrated using laser Doppler anemometry. The results showed that the erosion pattern of mine tailings particles was similar to those of fine-grained cohesive sediments. A power-law relation of the form E = α[(τ – τcr)/τcr]n is suggested for mine tailings, where E is the erosion rate, α is a coefficient, τ is the shear stress, τcr is the critical shear stress, and n is an exponent. The computed values of α, n, and τcr in the power-law equation were found to be comparable to values derived from experiments in a rotating circular flume. The derived expression for rate of erosion may be incorporated in resuspension and transport models for fine mine tailings of a similar nature.Key words: mine tailings, laser Doppler velocimetry, wall shear stresses, critical shear stress for erosion, erosion – shear stress relationship.

Determination of an effect of 3-chlorophenol on hydroxyl radical generation during ozonation through kinetic study in the power law type

2004 ◽  
Vol 4 (5-6) ◽  
pp. 305-311
Author(s):  
Y.-H. Han ◽  
I. Koshiishi ◽  
H. Utsumi
Keyword(s):  
Power Law ◽  
Ozone Decomposition ◽  
Oh Radical ◽  
Catalytic Intermediates ◽  
Stable Adduct ◽  
Solution Proceeds ◽  
Radical Generation ◽  
Power Law Equation ◽  
The Relationship

Ozone decomposition in aqueous solution proceeds through a radical type chain mechanism. These reactions involve the very reactive and catalytic intermediates hydroxyl (OH) radical, O2− radical, HO2 radical, OH−, H2O2, etc. OH radical is proposed as an important factor in the ozonation of water. In the previous study, generation of OH radical in the ozonation of water containing 3-chlorophenol was mathematically evaluated. In this study, we estimated the kinetic equation for the effect of 3-chlorophenol on OH radical generation during ozonation using the power law equation, in order to analyze it more correctly. The OH radical was trapped with a 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a stable adduct, DMPO-OH. The relationship between the ozone concentration, 3-chlorophenol content, and the initial velocity (ν0) of DMPO-OH generation was analyzed mathematically, and the following equation was obtained: ν0 (10−6 M/s)=(1.58×10−5)×[3-chlorophenol (10−6 M)]×[ozone (10−6 M)]2.40+(3.09×10−5)×[ozone (10−6 M)]1.72. The equation fitted very well with the experimental results, and square of the correlation coefficient was larger than 0.9.

Influence of epoxidation conditions on the rheological properties of gel-like dispersions of epoxidized kraft lignin in castor oil

Holzforschung ◽  
2017 ◽  
Vol 71 (10) ◽  
pp. 777-784 ◽  
Author(s):  
Esperanza Cortés-Triviño ◽  
Concepción Valencia ◽  
José M. Franco
Keyword(s):  
Power Law ◽  
Castor Oil ◽  
Complex Modulus ◽  
Softening Temperature ◽  
Gel Strength ◽  
Rheological Characterization ◽  
Scanning Calorimetry ◽  
Small Amplitude Oscillatory Shear ◽  
Power Law Equation ◽  
Power Law Parameters

Abstract The modification of castor oil (CO) with lignin was the focus of this research to create a lubricating medium with improved gel-like properties. Namely, an alkali lignin (L) was epoxidized with epichlorohydrin (EP) and the resulting LEPs were dispersed in CO. The parameters of LEP synthesis were varied and the epoxidation index (EPI) of the LEPs was determined. The LEPs were also submitted to thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. Rheological responses of the LEP/CO dispersions were investigated through small-amplitude oscillatory shear (SAOS) tests. Linear viscoelasticity functions are quantitatively affected by the epoxidation parameters, such as temperature, reaction time and L/EP and L/NaOH ratios. In general, lignins with higher EPI show higher values of the SAOS functions, which are indicative of better gel-strength due to a higher cross-linking density between the LEPs and CO. A power-law equation describes well the evolution of the complex modulus, G*, with frequency of gel-like dispersions, where the power-law parameters were found to increase almost linearly with the EPI. The thermo-rheological characterization provides a softening temperature beyond 50°C.

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