Casson fluid

Case materials, in electronic materials packaging, 77 837-840 Case nitrided steels, properties of, 76 207 Case polymers, uses for, 25 481 82 Cash flows, 9 540-542 CASLINK software, 73 250 Caspian Sea, 5 784 CAS Registry, 73 242, 246 Cassegrain condenser, reflective, 74 233 Cassia, 23 165-166 Cassie-Baxter equation, 22 112, 113 Cassiterite, 24 783, 791 Casson-Asbeck plots, 27 709 Casson fluid flow model, 27 705 CASS test, 9 790... 

A Casson fluid is Theologically identified by two parameters yield value and plastic viscosity. The plastic viscosity relates to the asymmetry of the flow particles and the yield value is connected with the forces of attraction between particles. The... 

Power law with sdeld value Casson fluid... 

The Casson fluid is essentially the same as its Bingham cousin, but with all the components raised to the half power, so... 

Casson fluids. These fluids exhibit a fluidifying plastic behavior. They are described by the Casson equation ... 

Bingham plastics are fluids which remain rigid under the application of shear stresses less than a yield stress, Ty, but flow like a. simple Newtonian fluid once the applied shear exceeds this value. Different constitutive models representing this type of fluids were developed by Herschel and Bulkley (1926), Oldroyd (1947) and Casson (1959). 

Plastic fluids are Newtonian or pseudoplastic liquids that exhibit a yield value (Fig. 3a and b, curves C). At rest they behave like a solid due to their interparticle association. The external force has to overcome these attractive forces between the particles and disrupt the structure. Beyond this point, the material changes its behavior from that of a solid to that of a liquid. The viscosity can then either be a constant (ideal Bingham liquid) or a function of the shear rate. In the latter case, the viscosity can initially decrease and then become a constant (real Bingham liquid) or continuously decrease, as in the case of a pseudoplastic liquid (Casson liquid). Plastic flow is often observed in flocculated suspensions. 

In the case of fluids with yield stress, viscoplastic fluids differ from elastoplastic fluids. With the application of a shear stress o above the yield strength o0. Bingham fluids show a linear dependence of shear stress on shear rate, whereas Casson and Herschel-Bulkley fluids show a nonlinear dependence on these parameters. 

Note that the Casson model (the third model in Table 6.3) fairly well describes various varnishes, paints, blood, food compositions like cocoa mass, and some other fluid disperse systems [443]. 

In Equation (2), n is the flow behavior index (-),K is the consistency index (Pa secn), and the other terms have been defined before. For shear-thinning fluids, the magnitude of nshear-thickening fluids n>l, and for Newtonian fluids n=l. For PFDs that exhibit yield stresses, models that contain either (Jo or a term related to it have been defined. These models include, the Bingham Plastic model (Equation 3), the Herschel-Bulkley model (Equation 4), the Casson model (Equation 5), and the Mizrahi-Berk model (Equation 6). 

COJ of 65 °Brix is a mildly shear-thinning fluid 160) with magnitudes of flow behavior index of the power law model (n) (Equation 2) of about 0.75 that is mildly temperature dependent. In contrast, the consistency index (K) is very sensitive to temperature for example, Vital and Rao (hi) found for a COJ sample magnitudes of 1.51 Pa sec11 at 20 °C and 27.63 Pa secn at -19 °C. Mizrahi and Firstenberg (hi) found that the modified Casson model (Equation 5) described the shear rate-shear stress data better than the Herschel-Bulkley model (Equation 4). 

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.)...

Figure 16. Variation of Casson high shear viscosity (kf) and yield stress (k02) on polymer concentration for simple bentonite-polymer (CMC) drilling fluids. Bentonite content fixed at 20.6 g/L. (Reproduced with permission from reference 32. Copyright 1993 Society of Petroleum Engineers.)...

Casson high shear rate viscosity (Pa s) consistency of power law fluid (Pa - sn) constant (Pa - sn) length (m) constant... 

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]. 

An additional well-known mathematical expression for viscoplastic fluids is the Casson model ... 

For the above pseudo-plastic flow, one may apply a power law fluid model, a Bingham model [9] or a Casson model [10]. These models are represented by the following equations respectively. 

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