ON MEASURING AND MODELING LOCAL AVERAGE PARTICLE VELOCITIES FOR PARTICLE ENSEMBLES IN CLASSIFYING SYSTEMS

In most multi-phase flow problems, the particulate phase is exposed to an external field which causes dispersion. Therefore, local velocity measurements of the disperse phase are no longer equivalent with respe ct to averaging in time and averaging in volume. While the local time- averaged velocity still characterizes the transport of the ensemble in the Eulerian sense, one has to be be careful in modeling this velocit y average by considering the ensemble's composition. It is shown for d ifferent particle ensembles that the conventional particle velocity av erage M(1,0) calculated with respect to the dispersion relationship an d a particle size number density distribution is far below the measure d ensemble average; the deviation depends on the width of the particle size distribution. It is deduced that Eulerian particle velocity valu es referring to a certain time interval can be modeled by a ratio of v elocity moments M(2,0)/M(1,0) calculated with particle size number dis tributions referring to a certain probe volume. This relationship was confirmed by measurements.