Velocity yield-stress slurries

The slurry behaves as a non-Newtonian fluid, which can be described as a Bingham plastic with a yield stress of 40 dyn/cm2 and a limiting viscosity of 100 cP. Calculate the pressure gradient (in psi/ft) for this slurry flowing at a velocity of 8 ft/s in a 10 in. ID pipe. 

Figure 4.5 Velocity profile for slurries with a yield stress...

As with slurries following a power-law flow model, it is necessary to reliably predict the pressure drop in a horizontal pipe of diameter D under laminar, fully developed flow conditions. A fundamental analysis of the Bingham plastic model yields the following expression for the mean velocity in terms of the yield stress Ty and the wall shear stress tq. 

A mud slurry is draining from the bottom of a large tank through aim long vertical pipe with a 1 cm inside diameter. The open end of the pipe is 4 m below the level in the tank. The mud behaves as a Bingham plastic with a yield stress of 10 N/m, an apparent viscosity of 0.04kg/m/s, and a density of 1500 kg/m. At what velocity will the mud slurry drain from the hose ... 

Terminal velocity of falling particles Transition velocity from laminar to turbulent flows Ratio of sUp velocity to slurry speed Ratio of the yield stress to the wall shear stress... 

Tests conducted with the iron ore concentrate in the 0.105 m pipe showed that at concentrations above 35% by volume, the deposition velocity began to increase. This was probably associated with the approach of laminar flow since a 40% slurry had a significant yield stress. Deposition for slurries in laminar flow will be discussed later. 

It is known, however, that settling is enhanced or initiated when the slurry is subjected to an externally imposed strain rate. Early experiments were performed by Highgate and Warlow [3] using spheres in a pseudoplastic fluid that was sheared in the space between coaxial cylinders. As the fluid had no yield stress, the particles settled slowly in the quiescent case. When shear was applied by rotating the outer cylinder, the settling velocity increased reaching five times the initial value at high strain rates. 

Due to the yield stress a core part of the slurry is moving as plug with uniform velocity Up. In the gap between the plug and the pipe wall rp< r < R) the velocity distribution is given as... 

The magnitude of the effect.s that can be observed with non-Newtonian slurries is illustrated in Fig. 4-14, where the critical velocity for the onset of turbulence is shown to be a strong function of the slurry yield stress and almost independent of coefficient of rigidity and pipe diameter [59]. The usefulness of laminar-flow measurements in characterizing different su.spcnsions, a.s well as the application of these constants to a variety of correlations, will be given in the following sections. 

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