Reentrainment of deposited particles by drag and aerosol collision

The reentrainment of deposited particles in turbulent aerosol flow has been studied theoretically and experimentally. The moments of forces, i.e., particle adhesion, gravity, aerodynamic drag, and aerosol collision, acting on a small aggregate adhering to a wall are calculated as a function of particle diameter. The analytical solutions indicate that the collision of an aerosol particle larger than several micrometers plays an important role in the reentrainment, whereas, the effect of the aerodynamic drag dominates for sub-micron particles. Furthermore, the critical velocity of aerosol flow for the reentrainment is calculated on the basis of a moment balance. The critical velocity decreases with increasing particle diameter. Experiments were conducted using alumina particles of size 3.3–10.3 μm in mass median diameter. The particles were fully dispersed into airflow and fed into a glass tube. The variation in the state of the particle deposition layer was observed through a digital video camera, and the critical velocities for no particle layer formation were obtained under various conditions. Although the experimental data on the critical velocities deviate somewhat from the theoretical values, the trends are in reasonable agreement. In particular, it was found that the inertial collision by aerosol particles is efficient for the removal of the particle deposition layer.