Aerosol Transport – Inertia

:: Section 10

Summary

Now that you have reviewed this module, take a moment to reflect what you have learned about the transport of aerosols.

First, we defined the Reynolds number to determine whether the flow around a given particle is laminar, turbulent or transitional. By knowing the value of Re_p, we can decide whether Newton's Law or Stokes's Law should be applied to the calculation of drag force.

We then derived expressions for settling velocity when gravitational and drag forces are balanced. We also defined mechanical mobility, relaxation time and stopping distance to help us get a sense how easy/fast it is for a particle of a given size to respond to an external force. Slip correction factor was then developed to account for the effect of slip of gas molecules on particle surface.

We then learn how to describe the movement of an aerosol particle in a straight-line or in a curvilinear fashion. Finally we discussed inertial impaction, the collection efficiency of which is a function of the Stokes number (Stk). We also learned how to determine the cutoff size of a given nozzle.

Think about how the aforementioned physical phenomena and properties depend on particle size. (e.g. how do mechanical mobility, relaxation time and stopping distance change if particle size increases.) You may also want to refresh your memory how environmental parameters affect the movement of a given particle (e.g. the effect of velocity or viscosity on impaction).

For aerosol instrument based on inertial transport, you may want to visit the Aerosol Instrumentation - Inertial module. If you are interested in other aerosol topics, click here to visit other modules.