Experimental investigation of particle resuspension from a powder layer induced by an ascending flat object

To obtain basic information about the prevention of dust generation in powder handling operations and to evaluate the dustiness of particles, particle resuspension from a powder layer induced by an ascending flat circular plate was investigated experimentally. The ascent of a flat plate from a powder layer is a simple model of a powder handing operation causing a negative pressure, such as the opening of a container, bottle or reactor vessel. In the experiments, spherical silica particles of five sizes from nano to micron order were used as test particles. It was found that the ascending flat plate induces resuspension of particles, adhesion of particles to the plate and uplift of the powder layer. Experiments using the adhesive plate and a thin powder layer confirmed that the adhesion of particles and uplift of the powder layer have no effect on the amount of resuspended particles. This implies that the amount of particles resuspended is dominated by the airflow induced by the ascending plate. It was also found that the effect of plate diameter and ascending velocity on the resuspended mass from a unit area of the plate can be evaluated from the excluded volumetric flow rate, defined as the product of crosssectional area of the plate and the ascent velocity. With increase of the excluded flow rate, the resuspended mass increased and reached a maximum value. Except for the largest silica particles used in this study, the maximum resuspended masses of all particles were almost equal. Observation of the resuspended particles revealed that they are agglomerates of similar size, regardless of the primary particle size. This implies that the resuspended mass depends on the size of the agglomerates in the powder layer rather than the primary particle size.