Dynamics of the Aerosol Movement

Study of the dynamics of fluid flow is concerned with the forces acting on the bodies in the fluid. In the earher chapters on soUd dispersions, emulsions, and foams, fluid dynamics was largely ignored in favor of the true colloidal interactions. In aerosols, the nature of the continuous medium makes the subject of fluid dynamics much more important to the understanding of the system, so that the following discussion will introduce a few basic relationships that can be important in the study of aerosols. 

When Re 1 the system is said to be in laminar flow (Fig. 13.1 ) and the Stokes equation [Eq. (10.20)] is found to apply. When Re 10, the system is in fully turbulent flow (Fig. 13.1h) and flow resistance is controlled by drag forces due to the medium given by 

In the region 1 Re 10, a transition occurs from laminar (Fa v) to turbulent flow (Fa and the relationship between fa and v becomes more complex. Also, since drag forces actually apply only to the relative velocity 

FIGURE 13.1. In the movement of aerosol particles, the type of flow in the gas phase will significantly affect the fate of the particles. For Reynolds number, Re, 1, laminar flow will prevail (a). However, since gases are usually of very low viscosity compared to liquids, it is more common to encounter the situation where Re 1000. In that case, turbulent flow is common and particle dynamics is much more difficult to model. 

Even under ideal conditions, the dynamic flow behavior of aerosols in contrast to other colloids can be markedly different. In stUl air, the average distance a particle will travel before colliding with another particle, the mean 

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