Rheology Casson

Casson, N., 1959. In Mill. C.C. (ed.), Rheology of Disperse Systems, Pergamon Press, London. 

The square root of viscosity is plotted against the reciprocal of the square root of shear rate (Fig. 3). The square of the slope is Tq, the yield stress the square of the intercept is, the viscosity at infinite shear rate. No material actually experiences an infinite shear rate, but is a good representation of the condition where all rheological stmcture has been broken down. The Casson yield stress Tq is somewhat different from the yield stress discussed earlier in that there may or may not be an intercept on the shear stress—shear rate curve for the material. If there is an intercept, then the Casson yield stress is quite close to that value. If there is no intercept, but the material is shear thinning, a Casson plot gives a value for Tq that is indicative of the degree of shear thinning. 

Casson, N., MUl, C. (1959) Rheology of disperse systems. Pergamon Press, New York... 

Corn stover, a well-known example of lignocellulosic biomass, is a potential renewable feed for bioethanol production. Dilute sulfuric acid pretreatment removes hemicellulose and makes the cellulose more susceptible to bacterial digestion. The rheologic properties of corn stover pretreated in such a manner were studied. The Power Law parameters were sensitive to corn stover suspension concentration becoming more non-Newtonian with slope n, ranging from 0.92 to 0.05 between 5 and 30% solids. The Casson and the Power Law models described the experimental data with correlation coefficients ranging from 0.90 to 0.99 and 0.85 to 0.99, respectively. The yield stress predicted by direct data extrapolation and by the Herschel-Bulkley model was similar for each concentration of corn stover tested. 

Three empirical models were utilized to fit the rheologic characteristics of the wet grain slurries power law, Herschel-Bulkley, and Casson. The power law and Casson models are two-parameter models and are ideal for... 

Experimental rheologic data were fit to the power law, Herschel-Bulkley, and Casson models. The power law model does not predict yield stress. Yield stress for 21% grain slurries predicted by the Herschel-Bulkley model was a negative value, as shown in Table 6. Yield stress values predicted by the Herschel Bulkley model for 23 and 25% solids were 8.31 and 56.3 dyn/cm2, respectively. Predicted yield stress values from the Casson model were 9.47 dyn/cm2 for 21% solids, 28.5 dyn/cm2 for 23% solids, and 44.0 dyn/cm2 for 25% solids. 

There are numerous other GNF models, such as the Casson model (used in food rheology), the Ellis, the Powell-Eyring model, and the Reiner-Pillippoff model. These are reviewed in the literature. In Appendix A we list the parameters of the Power Law, the Carreau, and the Cross constitutive equations for common polymers evaluated using oscillatory and capillary flow viscometry. 

Tg and . This is shown in Fig. 7 both for the extrapolated (Bingham) and Casson s yield value. In both cases the linear relationship is maintained indicating that such crude models may be applied to the rheology of the complex system of bentonite clay plus pesticide suspension. It should be mentioned, however, that the elastic floe model is a more realistic description of the system, since the assumption of a maximum of doublets in the floe rupture model is not justified with a concentrated suspension with many body interactions. 

Casson, N., "Rheology of Disperse Systems" (C.C. Mill Ed.) Pergamon Press London (1959). van Olphen, H. "An Introduction to Clay Colloid Chemistry", Interscience, London, 1977. 

It is clear from the above discussion that the rheological properties of FCOJ will depend on the °Brix, pulp content, size and shape of the pulp particles, and pectin content of FCOJ sample, and the temperature at which the data were obtained. Carter and Buslig (1977) studied particle size distribution in commercial frozen FCOJ samples. Mizrahi and coworkers conducted systematic studies on FCOJ that they described as a physicochemical approach (Mizrahi and Berk, 1970 Mizrahi and Firstenberg, 1975 Mizrahi, 1979). They used a modified Casson equation to describe the flow behavior of FCOJ. 

While application of structure-based models to rheological data, such as the Casson model, provides useful information, structure-based analysis can provide valuable insight in to the role of the structure of a dispersed system. Bodenstab et al. (2003)... 

Chevalley, J. 1991. An adaptation of the Casson equation for the rheology of chocolate.. 7 Texture Stud. 22 219-229. 

Casson, N. "Rheology of Disperse Systems" Mill, C. C., Ed. Pergamon Press New York, 1959 Chapter 5. 

Figure 10 compares the pressure dependence of the rheological parameters of the Casson model (high shear viscosity k 2), the Bingham... 

Figure 10. Pressure dependence of parameters from various models of the rheology of invert emulsion oil-based drilling fluids at various temperatures. Casson high shear viscosity Bingham plastic viscosity consistency, power law exponent, and yield stress from Herschel-Bulkley model. (Reproduced with permission from reference 69. Copyright 1986 Society of Petroleum Engineers.)...

Casson models were used to compare their yield stress results to those calculated with the direct methods, the stress growth and impeller methods. Table 2 shows the parameters obtained when the experimental shear stress-shear rate data for the fermentation suspensions were fitted with all models at initial process. The correlation coefficients (/P) between the shear rate and shear stress are from 0.994 to 0.995 for the Herschel-Bulkley model, 0.988 to 0.994 for the Bingham, 0.982 to 0.990 for the Casson model, and 0.948 to 0.972 for the power law model for enzymatic hydrolysis at 10% solids concentration (Table 1). The rheological parameters for Solka Floe suspensions were employed to determine if there was any relationship between the shear rate constant, k, and the power law index flow, n. The relationship between the shear rate constant and the index flow for fermentation broth at concentrations ranging from 10 to 20% is shown on Table 2. The yield stress obtained by the FL 100/6W impeller technique decreased significantly as the fimetion of time and concentration during enzyme reaction and fermentation. 

The Casson equation (equation 5.1) is often used to describe the rheology of liquid chocolates and couvertures. The relation between the shear stress (a) and the shear rate (y) depends on two parameters the yield stress, Oy, i.e. the shear stress required to initiate flow, and the plastic viscosity, i.e. the viscosity after yield. 

Rheology experiments also give information in the determination of wax appearance temperatures of crude oils. In this research, WATs of crude oils were determined by viscometry from the point where the experimental curve deviates from the extrapolated Arrhenius curve (Figure 4). It was observed that all crude oils, except highly asphaltenic samples, are Newtonian fluids above their wax appearance temperatures. The flow behaviour of crude oils is considerably modified by the crystallization of paraffins corresponding to the variation of the apparent viscosity with temperature. Below the WAT, flow becomes non-Newtonian and approaches that of the Bingham and Casson plastic model [17,18]. 

The heuristic extension of the rheological state equation from Bingham to Casson materials is straightforward. It can be derived directly from Eqn. (7) by introducing a strain rate dependant viscosity 77(72) instead of Tjg... 

The following rheological data for milk chocolate at 313 K are available. Determine the Bingham plastic (equation 1.16) and Casson model (equation 1.18) parameters for this material. What are the mean and maximum deviations for both these models ... 

The rheology of a polymer solution can be approximated reasonably well by either a power-law or a Casson model over the shear rate range of 20-100 s . If the power law consistency coefficient, m, is lOPa s" and the flow behaviour index, n, is 0.2, what will be the approximate values of the yield stress and the plastic viscosity in the Casson model ... 

Casson, M., in Rheology of Dispersive Systems, C. C. Mills, ed Pergamon Press, Oxford, 1959. 

Casson equation n. Rheology expression used to relate share rate, viscosity, and at infinite shear rate for dispesrsions (pigment coatings, etc.). Patton TC (1979) Paint flow and pigment dispersion a... 

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