:: Section 6
Slip Correction Factor
III. Corrected Drag Force and Settling Velocity
Because the effect of 'slip', the drag force decreases and the settling velocity increases. Therefore, we have to modify our formula for them.
For the drag force,
For the settling velocity,
where Cc is the slip correction factor, and
where λ is the mean free path of the gas and dp is diameter of the particle. For air, λ is 0.066 μm at standard temperature and pressure. The above equations are applicable to Rep < 1.0. The slip correction factor for a 1.0 μm particle at standard condition is 1.15, i.e., the settling velocity is 15% higher than without the slip.
Now try different particle sizes (e.g. 10 μm, 1 μm, 0.1 μm and 0.01 μm) and see how much slip correction is needed: