# Knudsen number

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+ | [[Category: Dimensionless parameters]] | ||

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The Knudsen number is defined as | The Knudsen number is defined as | ||

:<math> Kn\equiv \frac{\lambda}{L} </math> | :<math> Kn\equiv \frac{\lambda}{L} </math> | ||

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*<math> L </math> is the characteristic dimension | *<math> L </math> is the characteristic dimension | ||

- | Knudsen number is a measure of the rarefaction of the flow.The various [[Flow regimes ]] can be classifed based on Knudsen number. | + | Knudsen number is a measure of the rarefaction of the flow. The various [[Flow regimes ]] can be classifed based on Knudsen number. |

+ | |||

+ | The Knudsen number is related to the [[Mach number]] and the [[Reynolds number]] by the following relation: | ||

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+ | :<math> | ||

+ | Kn = \frac{Ma}{Re} \; \sqrt{ \frac{\pi \gamma}{2}} | ||

+ | </math> | ||

+ | |||

+ | where <math>\gamma</math> is the [[ratio of specific heats]]. |

## Latest revision as of 20:23, 22 September 2005

The Knudsen number is defined as

where

- is the mean free path of the molecules
- is the characteristic dimension

Knudsen number is a measure of the rarefaction of the flow. The various Flow regimes can be classifed based on Knudsen number.

The Knudsen number is related to the Mach number and the Reynolds number by the following relation:

where is the ratio of specific heats.