Two techniques for on-line particle size measurement areWe compare this with a scanning back scatter instrument which evaluated on the reproducibility of their volume distribution is directly inserted in highly concentrated slurries. We present determinations. A forward scattering laser light devise is inter-the methods used to improve the robustness of the conversion faced with a dilutor to examine the potential of this technique of the output of the back scatter instrument to volume distribufor high concentration streams. The forward scattering in-tions. The output of the back scatter instrument is inherently struments are capable of outputting extremely reproducible less stable but with the proper methods one can obtain reprodistributions and here we show that when the dilutor is well ducibilities of the order of 2 to 6 percent. designed, the on-line instrument can have similar performance.

The rheological behaviour of a fluidised bed of alumina powder was determined using a specially designed form of rotating viscometer. Several different geometries of the inner and outer cylinder were tested. In the machine the two cylinders can be rotated independently, in either direction, which enables both their relative velocity and absolute velocity to be varied. Thus, the torque on the inner cylinder, strain-rate and the absolute velocity have been chosen as the consistency variables. Some examples of the derived consistency surface are given. The characteristics of these surfaces could be explained by assuming different states of structure, to which a certain mobility can be ascribed. It is proposed that any state of structure which can exist in the bed is an intermediate of two extremes the first being the immobile state which is elastic and has a yield value and the second being the dynamic state which behaves like a Newtonian fluid.