Flow curves, nonnewtonian fluids

Power consumption for impellers in pseudoplastic, Bingham plastic, and dilatant nonnewtonian fluids may be c culated by using the correlating lines of Fig. 18-17 if viscosity is obtained from viscosity-shear rate curves as described here. For a pseudoplastic fluid, viscosity decreases as shear rate increases. A Bingham plastic is similar to a pseudoplastic fluid but requires that a minimum shear stress be exceeded for any flow to occur. For a dilatant fluid, viscosity increases as shear rate increases. 

FIGURE 10.1 Flow curves for newtonian fluid and shear-thinning and shear-thickening nonnewtonian fluids [4]. 

Much of the past and present research in nonnewtonian fluids has consisted of measuring their stress-rate-of-strain curves (such as Fig. 1.5) and trying to find mathematical descriptions of these curves. The study of the flow behavior of materials is called rheology (from Greek words meaning the study of flow ), and diagrams like Fig. 1.5 are often called rheograms. 

For nonnewtonian fluids we can experimentally determine a plot like Fig. 1,5 of the shear stress as a function of dVIdy (which [equals dV/dr for circular pipe flow). From this plot we can find the equivalent of Poiseuille s equation by two graphical integrations.. This is tedious and has prompted much of the work of trying to find equations that will represent the data in curves such as Fig. 1.5. If the data can be fit by the power law (Eq. 15.2), then the two... 

Friction factor plot for power-law nonnewtonian fluids. The line at the left is the laminar-flow curve, which is the same for newtonian and nonnewtonian fluids. The upper solid curve at the right is the turbulent, smooth-tubes line for newtonian fluids from Fig. 6.10. The other solid curves at the right are based on turbulent-flow data of Dodge and Metzner for nonnewtonian fluids which do not suppress turbulence. The dotted curves at the right are based on the data of Shaver and Merrill [7] for nonnewtonian fluids which do suppress turbulence. ]... 

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