Distribution of solids upon suspension

If the stirrer speed is varied much more strongly (n = 459-1377 min ). Fig. 5.3 shows its greater effect upon the distribution of solids in the tank. These experi- 

The solids distribution with height can be described by a statistical average value. In Fig. 5.3 and 5.4 the variance from the experimental data, which were obtained at N = 13 measuring points distributed over the liquid height, is also cited. The variance is defined by the following relationship  

Measurements at = 0.25 and 0.95 have additionally shown that the stirrer speed required to realize this distribution quality initially increases with p but remains constant from = 0.15-0.20. This also demonstrates the relevance of the sinking velocity iVss in the swarm, which decreases with increasing 

The circumstance that the stirrer speed no.g needed for h = 0.9 is related to the sinking behavior of the particle, is clearly evident from Fig. 5.5, which represents the stirrer speed for h = 0.9 = a = 0.5 as a function of particle diameter dp. For small dp, n oc dp applies, for large dp on the other hand n oc dp is found. This is consistent with the particle sinking behavior. According to Stokes s law, iVjs oc dp applies to very small particles (laminar flow round particles), Wss oc d° for large particles (turbulent flow round particles). The exponents in the two dependences differ by a factor of 4. The transition range lies approximately between Rep = 10 and 100. 

A phase Doppler velocimeter was used to measure the axial, radial and tangeni-tial mean velocities u and the mean velocity fluctuations v of the continuous (water) and dispersed phase (glass beads, dp = 250 pm, = 0.5%) in dependence upon 

---