Aerosol Transport – Inertia

:: Section 3

Newton's Resistance Law and Stokes's Law

I. Newton's Law

If you drop a ball, it falls due to the gravitational force. Meanwhile, the resistance of gas molecules (drag) tend to slow down the movement.

To describe the drag force resulting from gas resistance, F_D, the following equation can be used:

where C_D is the drag coefficient. This is the general form of Newton's resistance equation.

This Newton's resistance equation is valid in the turbulent flow regime (i.e. Re_p > 1000), where inertial forces are much larger than viscous forces. The drag coefficient C_D has a nearly constant value of 0.44.

Which of the following condition(s) can the Newton's Law be applied? (a) A particle with a diameter of 10 μm having a velocity of 1 m/s. (b) A particle with a diameter of 100 μm having a velocity of 10 m/s. (c) A particle with a diameter of 1 mm (1000 μm) having a velocity of 20 m/s.

To calculate the Re_p values, you can use the web-calculator below: