Particle Reentrainment from a Fine Powder Layer in a Turbulent Air Flow

Abstract

ABSTRACT. Particle reentrainment from a fine powder layer was investigated both in a steady-state flow and in an unsteady-state (accelerated) flow. Experiments were conducted in a rectangular channel, where a powder layer of fly ash was placed. The average air velocity was increased at a constant rate in the range of 0.01-0.6 m / s 2 up to a certain velocity and, thereafter, it was maintained at the velocity. The reentrainment flux was measured automatically by an electrostatic method. Microscopic observation showed that small aggregates were reentrained randomly from the surface of the powder layer, and then the reentrainment gradually progressed through the depth of the powder layer. Through these processes, surface renewal of the powder occurred. The experimental results also showed that the distribution of adhesive strength (wall shear stress) was approximated by a log-normal distribution. Further, the time-delay of the reentrainment was found to be represented by two simple exponential functions with different time constant. A new reentrainment model is presented to explain the time-dependence of the reentrainment flux, which is based on the adhesive strength distribution, surface renewal of the powder layer, and the time-delay of the reentrainment. The reentrainment flux increases with time elapsed in an accelerated flow, while it decreases in a steady state flow. Air acceleration has a significant effect on the reentrainment flux not only in the accelerated flow but also in the steady-state flow. Furthermore, the critical (incipient) reentrainment velocity decreases with increasing air acceleration. The experimental results agreed well with the results calculated based on the new model.

Monolayer and Multilayer Particle Deposits on Hard Surfaces: Literature Review and Implications for Particle Resuspension in the Indoor Environment

“…Only a few experimental wind tunnel studies have explored resuspension from multilayer deposits, including those by Fromentin (1989), Matsusaka and Masuda (1996), Loosmore and Hunt (2000), Adhiwidjaja et al (2000), Chiou and Tsai (2001), Huang et al (2005), Gomes et al (2007), and Nitschke and Schmidt (2010). As shown in Table 1, only a few of these studies evaluated the impact of dust loading on resuspension, and none have systematically studied resuspension from both monolayer and multilayer deposits on indoor surfaces.…”

“…Matsusaka and Masuda (1996) studied the resuspension of particle aggregates from multilayer deposits. They deposited a multilayer of 3 μm fly ash particles and found resuspension to typically occur in small aggregates, with diameters ranging from 10 to 30 μm.…”

“…As we transition from a sparse monolayer to a complex multilayer deposit, additional parameters begin to influence resuspension, most notably particle-to-particle adhesion (Lazaridis and Drossinos 1998); layer location (Lazaridis and Drossinos 1998;Friess and Yadigaroglu 2001); aggregate formation and deaggregation (Matsusaka and Masuda 1996;Kurkela et al 2006;Gac et al 2008;Gotoh et al 2011); possible saltation effects (Bagnold 1941;Shao et al 1993;Kok et al 2012); dust loading (Fromentin 1989;Nitschke and Schmidt 2010); and the deposit's structure and porosity (Friess and Yadigaroglu 2002).…”

Morphological Change of Hardened Oil Particles Induced by Impaction against a Solid Surface

“…ence of particle adhesive force and aerodynamic removal force (Matsusaka and Masuda, 1996). Most of the relatively large particles rebound or are reentrained into the air flow after impaction.…”

Control of Particle Re-Entrainment by Wetting the Exposed Surface of Dust Samples

“…When the wind velocity increased, the resuspension rate also increased. Matsusaka and Masuda 12 found that the re-entrainment flux increased with time elapsed in an accelerated flow, while it decreased in a steady-state flow.…”