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Experimental determination of the dispersivity of (unrealizable) perfectly random packings of identical spheres.

By: Ulrich Scheven
From: Univ. Nova Lisboa
At: Complexo Interdisciplinar, Anfiteatro
[2009-12-09]

There is no such thing as a perfectly random pack of mono-disperse spheres, in any laboratory. Consequently tracer dispersion experiments in random packs of mono-disperse solid spheres exhibit quite considerable scat­ter in reported results, which is due to the inevitable presence of order-inducing boundaries, differing packing protocols, or non-uniform flow injection. By contrast, the conceptual random packs of theory and simulations with periodic boundary conditions are unaffected by these hard experimental realities, and quantitative compa­rison of theory, simulation, and experiment has therefore been elusive for decades. PFG-NMR experiments and a novel data analysis (Scheven et al., Phys. Rev. Lett., 99, 054502, (2007)) established the missing link between theory and experiment. The experiments and results will be reviewed. Then I will present a related re-analysis of published elution data obtained with traditional step-function tracer experiments by (Han, Bakhta and Carbonell, AIChE J. 31, 277 (1985)) and compare with the ideal random pack. The re-analyzed elution results are consistent with NMR, theory, and simulation (AIChE Journal, DOI: 10.1002/aic.11993).