Knudsen layer
Encyclopedia
The Knudsen layer, also known as evaporation
layer, is the thin layer between liquid and vapour. It is named after Danish
physicist Martin Knudsen
(1871–1949).
can be hard to define. From kinetic theory
, it can be derived that if liquid is in contact with vapour, there is a small layer where the phase is between liquid and vapour. This region, several mean free path
lengths thick, is called the Knudsen layer.
, given by
,
where
is Boltzmann's constant, 
is the temperature, 
is the molecular diameter and 
is the pressure.
Evaporation
Evaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....
layer, is the thin layer between liquid and vapour. It is named after Danish
Denmark
Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...
physicist Martin Knudsen
Martin Knudsen
This article is about the Danish physicist Martin Knudsen. For the Norwegian footballer, see Martin Knudsen .Martin Hans Christian Knudsen was a Danish physicist who taught and conducted research at the Technical University of DenmarkHe is primarily known for his study of molecular gas flow and the...
(1871–1949).
Definition
On molecular level, the state of matterState of matter
States of matter are the distinct forms that different phases of matter take on. Solid, liquid and gas are the most common states of matter on Earth. However, much of the baryonic matter of the universe is in the form of hot plasma, both as rarefied interstellar medium and as dense...
can be hard to define. From kinetic theory
Kinetic theory
The kinetic theory of gases describes a gas as a large number of small particles , all of which are in constant, random motion. The rapidly moving particles constantly collide with each other and with the walls of the container...
, it can be derived that if liquid is in contact with vapour, there is a small layer where the phase is between liquid and vapour. This region, several mean free path
Mean free path
In physics, the mean free path is the average distance covered by a moving particle between successive impacts which modify its direction or energy or other particle properties.-Derivation:...
lengths thick, is called the Knudsen layer.
Knudsen layer thickness
The knudsen layer thickness can be approximated by, given by,where
is Boltzmann's constant, is the temperature, is the molecular diameter and is the pressure.