Aerosol Transport – Inertia

:: 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 C_c is the slip correction factor, and

where λ is the mean free path of the gas and d_p is diameter of the particle. For air, λ is 0.066 μm at standard temperature and pressure. The above equations are applicable to Re_p < 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: