Transitions in beds of aerated powders

Conference Dates

May 22-27, 2016


The apparent changes that take place a static bed powder subjected to an incrementally increasing upward gas flow are widely documented and underpin our perception and understanding of fluidized systems. However, there continues to be debate on approaches to the precise identification of the onset of bubbling. This paper examines data obtained from a suite of 12 powders, eight nominally from Geldart Group A and four from Group B; Sauter mean diameters ranged from 36 to 222 microns and particle density, 1540 – 3000 kg m-3. Onset of bubbling when fluidized by air, identified by inspection, is broadly consistent with values obtained from analysis of pressure fluctuation data, using two classical statistical reductions, standard deviation and the (reciprocal of) von Neumann index. Evidence is presented that the (reciprocal of) the von Neumann index, obtained from pressure fluctuation data, also has utility in identifying the establishment of a uniformly bubbling bed –a bed where bubbling activity takes place over the whole bed cross-section; this is supported by bed height measurements. Inevitably, there can be some subjectivity when visual phenomena are logged, and one of the drivers for this work was the removal of operator bias from estimates of bubbling velocity transitions.

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