What is the Knudsen number?... | Filo

The Knudsen number plays an important role in low-density flow problems. It is defined as Kn=(λ)/(L) where λis the mean free path and L a characteristic length. Flow for which Kn ≥1 is called free molecular flow because very few collisions take place over the distance L. Consider a 30-cm sphere traveling through the atmosphere and take the diameter as the characteristic length. Find the altitude above which free molecular flow prevails. Assume a collision diameter of 3.7 Åand a temperature of 28