Linear liquid velocity

Empirical equations are available [Durand and Condolios (1955)], which predict values for the minimum and standard velocities for various slurries. Spells analysed the experimental data of a number of investigators for aqueous slurries of sands, boiler ash and lime flowing in horizontal pipes. He obtained the following empirical equations which give the mean minimum liquid velocity U and the mean standard linear liquid velocity u2 respectively for slurries in horizontal pipes ... 

The Taylor vortices described above are an example of stable secondary flows. At high shear rates the secondary flows become chaotic and turbulent flow occurs. This happens when the inertial forces exceed the viscous forces in the liquid. The Reynolds number gives the value of this ratio and in general is written in terms of the linear liquid velocity, u, the dimension of the shear gradient direction (the gap in a Couette or the radius of a pipe), the liquid density and the viscosity. For a Couette we have ... 

Empirically, the plate height h has been found to depend on the linear liquid velocity u through the column in the manner described by Eq. (8.81), as found by van Deemter (1961). 

Head of liquid equivalent to the frictional flow resistance in the downcomer and in the passage of the fluid from the downcomer onto the plate. This head is usually relatively small, but it can be estimated as three, kinetic heads for the liquid, based on the linear liquid velocity at the minimum cross-sectional area for downooming liquid flow, or... 

Figure 5 Natural pulse frequency as a function of the difference in linear liquid velocity. (---------------- correlation of Rao, Eq 4)...

The superficial liquid velocity cannot be directly measured and is usually determined from the knowledge of the linear liquid velocity (Vl) and gas holdup. In airlift reactors, and Vl have both riser and downcomer components, yet the riser superficial liquid velocity (I/lj) is the parameter of greatest interest and the one commonly reported in the literatnre. 

As already discussed in context with the single-phase simulations, boundary conditions at the impeller are predicted from measured data of the averaged velocities. The gassed linear liquid velocities differ from the ungassed velocities because impeller power consumption and pumping capacity of the impeller decrease due to gassing. 

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