Pseudo-plastic fluid

Bhi KNER. J. L. and Smith, J. M- Trans. Inst. Chem. Eng. 44 (1966) T224. Anchor-agitated systems Power input with Newtonian and pseudo-plastic fluids. 

Grenville, R. K., Blending of viscous and pseudo-plastic fluids , Ph.D. Thesis, Cranfield Institute of Technology, Cranfield (UK) (1992). 

Emulsion viscosities have been measured as a function of water content (10, 20 and 40S), temperature and shear rate in a thermostatted rotating viscometer. The shear rates were varied between 0.277 and 27.7 s"1 with measurements taken at temperatures between 5 and 20° C. Above 20°C, separation of water from the emulsion occurred, rendering viscosity measurements unreliable. The apparent viscosity of the emulsion below 20° C increases drastically with the watercut in the emulsion and decreases with Increasing shear rate (Fig. 5). Emulsions containing more than 20X water were found to behave as pseudo-plastic fluids. 

For a power law fluid valid for dilatant and pseudo-plastic fluids, the following relationship holds ... 

For the Reiner—Philippoff model [2] for pseudo-plastic fluids. 

Boger, D.V. Demonstration of upper and lower Newtonian fluid behaviour in a pseudo-plastic fluid. Nature 1977,265, 126-128. 

Fig. 2.7. Pseudo-plastic fluid with yield stress.

Fig. 7.4 Illustration of several conventional Non-Newtonian fluids deviating from the Newtonian fluids. N represents Newtonian fluids, d represents dilatant fluids, p represents pseudo-plastic fluids, and B represents Bingham fluids...

If the shear rates are constants, the non-Newtonian fluids can also be classified according to their viscosity dependence on time. This classification has been widely applied to describe the rheological characteristics of coatings. For the development of deformation, the time evolution corresponds to the effect of the increase of shear rate. Three typical cases occur with the time evolution the thixotropic fluids exhibit the decrease of viscosity, corresponding to pseudo-plastic fluids the rheopectic fluids exhibit the increase of viscosity, corresponding to dilatant fluids while the viscoelastic fluids exhibit partial recovery of the deformation of pseudo-plastic fluids after the removal of the stress. Since polymers can perform a large scale of elastic deformation, this character appears extremely significant. 

Flow properties See melt-flow index, viscosity, pseudo-plastic fluid, and rheology. 

Flow curves of a dilatant fluid, a Newtonian fluid, and a pseudo-plastic fluid... 

In the previous section, it was discussed that polymer melts are pseudo-plastic fluids. The fact that the polymer melt viscosity reduces with shear rate is of great importance in the extrusion process. It is, therefore, important to know the extent of... 

For a Newtonian fluid (n = 1), the familiar linear output-pressure relationship is found. However, when the power law index is less than unity, substantial deviations from Newtonian characteristics occur. The deviations increase as the material becomes more pseudo-plastic (more strongly non-Newtonian). The result is that for a pseudo-plastic fluid, the pressure generating capability is drastically reduced compared to a Newtonian fluid. Or, at the same pressure gradient, the output is drastically reduced. For a fluid with a power law index less than 0.8, the use of the equations for Newtonian fluids will result in large errors ... 

It should be noted that fundamentally it is not entirely correct to take an expression derived for a Newtonian fluid and insert a power law viscosity form into it. However, if this simplification is not made, the analysis becomes much more complex and analytical solutions much more difficult to obtain, if not impossible. Results of the analytical solutions have been compared to results of numerical computations for a two-dimensional flow of a power law fluid. In most cases, the results are within 10 to 20% [2]. It should be noted that the results are exact when the power law index is unity, i. e., for Newtonian fluids. However, if the optimum depth and helix angle for a pseudo-plastic fluid are calculated using expressions valid for Newtonian fluids only, very large errors can result, particularly when the power law index is about one-half or less. It is therefore very important to take the pseudo-plastic behavior into account, because the large majority of polymers are strongly non-Newtonian. 

Solomon, J., A. W. Nienow, and G. W. Pace (1981). Flow patterns in agitated plastic and pseudo-plastic fluids, in Fluid Mixing, Inst. Chem. Eng. Symp. Ser., 64, A1-A13. 

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