Theory 29/Stokes Number/Air filtration
Filtration Peaks at a Stokes
The claim
Particle capture in a fibrous filter is set by the Stokes number of the particle, so filters have a minimum efficiency at an intermediate particle size.
01Mechanism
Very small particles diffuse to fibres while large ones impact; between the two, neither mechanism is efficient.
02Prediction
Efficiency should show a minimum at an intermediate size.
03Refutation
Efficiency increasing monotonically with size would remove diffusion.