Issue Section:
Boiling and Condensation
Keywords:
kinetic theory, interface phenomena, slip flow, momentum, mass transfer, Boiling, Evaporation, Heat Transfer, Non-Equilibrium, Vaporization
Topics:
Equilibrium (Physics), Evaporation, Heat transfer, Kinetic theory, Mass transfer, Momentum, Temperature, Condensation, Stress, Phase interfaces, Slip flow

Contributed by the Heat Transfer Division for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received by the Heat Transfer Division May 23, 2000; revision received November 13, 2000. Associate Editor: D. Poulikakos.

The Knudsen number (Kn) is defined as the ratio of the mean free path of a gas, λ, to a dimension of an object which interacts with the gas, x,
(1)
According to Rohsenow and Choi 1, when fluid velocities are small relative to the speed of sound, the dynamics of a gas can be loosely classified into four regimes, the boundaries of which are determined by characteristic Knudsen numbers.

When Kn<0.01, the mean free path of a gas is small compared with the dimensions of the system, and the gas may be approximated as a continuous medium. This is known as the Continuum regime. At...

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