(215e) Energy Dissipation Trends in Tumbling Beds of Geldart  Α/C and Α/B Powder Revealed By Speckle Visibility Spectrometry

The behaviour of powder in rotating drums is proving to be a useful tool for characterizing powder systems and providing insights to fundamental behaviour as well as having direct practical relevance to the process industries. In this investigation we have tracked the movement of avalanches using a drum fitted with a load cell sensor, while simultaneously measuring granular temperature in the powder bed using speckle visibility spectrometry, a laser technique that can measure time-resolved collisional motion of grains in dense systems with fine spatio-temporal resolution. We have taken measurements on two different model lactose powders, one close to the Geldart A/C boundary and the other lying close to the A/B boundary. Our results show high correlation between slumping and intermittent collisional dynamics in the bulk of the bed, particularly for the cohesive particles Geldart A/C particles; this correlation is weaker the A/B powder, apparently a result of fluidization in the bulk of the bed. The use of the SVS technique in combination with synchronous tracking of avalanche movement indicates avalanche magnitude and collisional dissipation as distinct energy dissipation mechanisms in the drum, with collisional dissipation dominant for the cohesive Geldart A/C powder and avalanche dissipation dominant for the Geldart A/B powder.