Definition
The Knudsen number is a dimensionless number defined as:
where
- = mean free path
- = representative physical length scale .
For an ideal gas, the mean free path may be readily calculated so that:
where
- is the Boltzmann constant (1.3806504(24) × 10−23 J/K in SI units),
- is the thermodynamic temperature,
- is the particle hard shell diameter,
- is the total pressure, .
For particle dynamics in the atmosphere, and assuming standard temperature and pressure, i.e. 25 °C and 1 atm, we have ≈ 8 × 10−8 m.
Read more about this topic: Knudsen Number
Famous quotes containing the word definition:
“... if, as women, we accept a philosophy of history that asserts that women are by definition assimilated into the male universal, that we can understand our past through a male lens—if we are unaware that women even have a history—we live our lives similarly unanchored, drifting in response to a veering wind of myth and bias.”
—Adrienne Rich (b. 1929)
“One definition of man is “an intelligence served by organs.””
—Ralph Waldo Emerson (1803–1882)
“The man who knows governments most completely is he who troubles himself least about a definition which shall give their essence. Enjoying an intimate acquaintance with all their particularities in turn, he would naturally regard an abstract conception in which these were unified as a thing more misleading than enlightening.”
—William James (1842–1910)