In this work the effect of air humidity on powder flow properties was studied by means of a ring shear tester. Powder sample moisture content was conditioned by humid air in a fluidization column. In spite of the very low moisture contents in the powder (<0.2%) obtained by this technique, a significant change in the powder cohesion was observed. The Kelvin equation was used to infer on the pressure increase inside the capillary bridge and the resulting typical interparticle force. This result was used to derive the powder tensile strength following the Rumpf approach and compare it with values derived from shear experiments. A single fitted value of the unknown capillary bridge gap is able to provide quantitative agreement for experiments with highly humid air. Model estimation indicates that water mainly condenses on rough surfaces of the particles and only a small portion of this condensed humidity contributes to change the powder flow properties in interparticle capillary bridges.

Flow properties of powders conditioned by humid air

LANDI, GIOVANNA;BARLETTA, Diego;DONSI', Giorgio;FERRARI, Giovanna;POLETTO, Massimo
2008-01-01

Abstract

In this work the effect of air humidity on powder flow properties was studied by means of a ring shear tester. Powder sample moisture content was conditioned by humid air in a fluidization column. In spite of the very low moisture contents in the powder (<0.2%) obtained by this technique, a significant change in the powder cohesion was observed. The Kelvin equation was used to infer on the pressure increase inside the capillary bridge and the resulting typical interparticle force. This result was used to derive the powder tensile strength following the Rumpf approach and compare it with values derived from shear experiments. A single fitted value of the unknown capillary bridge gap is able to provide quantitative agreement for experiments with highly humid air. Model estimation indicates that water mainly condenses on rough surfaces of the particles and only a small portion of this condensed humidity contributes to change the powder flow properties in interparticle capillary bridges.
2008
888819813X
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11386/1868112
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