:: Section 9
II. Impaction Efficiency
Impaction, as can be seen, is the mechanism for the collection in the system, and it is more effective for larger particles. Stokes number (Stk) can be used to classify the potential whether the particle will be collected. It contains both flow velocity and particle diameter. In addition, we use "nozzle diameter" to represent the obstacle. Stk therefore can be expressed as:
where ρp is particle density, dp is particle diameter, U is flow velocity, η is air viscosity, Dj is nozzle diameter.
The impaction efficiency (EI) is a function of the Stokes number, and it increases as Stk increases.