The modelling of particle resuspension in turbulent flow

The dynamics of particle rebound and resuspension were examined by using uranine particles, polymer microspheres, spores, and pollen in wind tunnel experiments. Particle diameters were 5-42 pm. Results show that both the fraction of rebound and the resuspension rate are strongly dependent on the free stream velocity, particle size, and relative humidity. The effects of relative humidity are more significant at lower windspeeds; a greater relative humidity appears to change the shape of the distribution of adhesion force, mainly affecting the lower range but not greatly affecting the upper end of the distribution. Resuspension rates decrease with time, essentially defining two regimes. The first regime lasts for < 1 min; after this time, the most easily resuspended particles have been removed, Leaving only particles with much smaller resuspension rates for the second regime. At a windspeed of 6 m/s, the upper 20% of the distribution of turbulent fluctuations is responsible for -65% of the particle resuspension.Once resuspended, the particles have trajectories which depend on characteristics of the turbulent airflow and not on the initial velocity of release from the surface. Overall, the data show that resuspension is more sensitive to the type of particle than to the type of surface; particle shape and composition may he more important than particle size,

Section: Comparison Of Adhesion Force and Dragsupporting

confidence: 70%

Controlled Wind Tunnel Experiments for Particle Bounceoff and Resuspension

Davidson

Russell

1992

“…For small values of δ/y VSL , minimal resuspension was found to occur. When the particle deposit is completely immersed in the viscous sublayer (y VSL >> δ), as is the case for monolayer deposits at low velocities, particles will not experience the enhanced removal associated with frequent collisions with turbulent eddies, and resuspension only occurs due to the periodic penetration of turbulent bursts from the fully turbulent sublayer (Cleaver and Yates 1973;Braaten et al 1990;Jurcik and Wang 1991). As δ begins to approach y VSL , a sharp increase in is observed.…”

Section: Impact Of Particle Deposit Height and Viscous Sublayer Thickmentioning

confidence: 98%

Wind Tunnel Study on Aerodynamic Particle Resuspension from Monolayer and Multilayer Deposits on Linoleum Flooring and Galvanized Sheet Metal

Boor

Siegel

Novoselac

2013

Resuspension is an important source of indoor particles and the amount of dust loading is an important factor in resuspension emission rates. Field studies have shown that light to heavy dust loads can be found in the indoor environment, on both the surfaces of flooring and ventilation ducts. These diverse particle deposits can be broadly classified as either a monolayer, in which particles are sparsely deposited on a surface, or a multilayer, in which particles are deposited on top of one another and there is particle-to-particle adhesion and interaction. This experimental wind tunnel study explores the role of the type of particle deposit on aerodynamic resuspension from linoleum flooring and galvanized sheet metal. Resuspension fractions are reported for both monolayer and multilayer deposits exposed to a wide range of air velocities. The type of particle deposit is found to strongly influence resuspension. In general, the results show that resuspension from multilayer deposits can occur at significantly lower velocities compared with monolayer deposits. For example, resuspension fractions at an air velocity of 5 m/s for the canopy layer of multilayer deposits were similar to those found for monolayer deposits at 50 m/s. Additionally, for multilayer deposits, resuspension fractions for the canopy layer increased with increasing dust load and negligible resuspension occurred along the surface layer. It was found that the relationship between the particle deposit height and the viscous sublayer thickness of the airflow can help explain the differences in resuspension that were observed between the two types of deposits. The impact of the type of particle deposit on

“…Here, it is interesting to compare the present model with other published models (Reeks et al 1988;Wen and Kasper 1989a;Jurcik and Wang 1991), where the timedelay of the reentrainment is given by a function of adhesive and/or separation strength. And these models showed shortdelay reentrainment and long-delay reentrainment.…”

Section: Time Dependence Of Reentrainmentmentioning

confidence: 99%

“…In addition, the time-dependence of the reentrainment can-not be explained solely with a balance of the steady-state forces. Although a number of reentrainment models have been put forward (Cleaver and Yates 1973;Reeks et al 1988;Wen and Kasper 1989a;Braaten et al 1990;Jurcik and Wang 1991), they deal with only the reentrainment of primary particles from a wall surface in a steady-state flow. On the other hand, the authors have been studying the reentrainment of aggregates to clarify the actual phenomena in industrial aerosol and powder processes (Masuda et al 1985(Masuda et al , 1990Ikumi et al 1986).…”

Section: Introductionmentioning

confidence: 99%

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

Matsusaka

Masuda

1996

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.