Knudsen Number

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Knudsen Number

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A number used to describe the flow of a low density gas, equal to the ratio λ/l where λ is the mean free path of the gas molecule and l is a characteristic length, such as boundary layer thickness, or apparatus dimension. </dd>
The Knudsen number is used most commonly to define the extend to which the gas behaves like a collection of independent particles (free-molecule regime, Knudsen number much larger than unity), or like a viscous fluid (continuous regime, Knudsen number much smaller than unity). Intermediate regimes are termed transition region, and slip flow region. See rarefied gas dynamics, note. [[/a>|/a> ]]

References

This article is based on NASA's Dictionary of Technical Terms for Aerospace Use