Thermal diffusion may refer to:
* A thermal force on a gas due to a
temperature gradient
A temperature gradient is a physical quantity that describes in which direction and at what rate the temperature changes the most rapidly around a particular location. The temperature gradient is a dimensional quantity expressed in units of degree ...
, also called ''thermal diffusion'' or
Thermal transpiration
Thermal transpiration (or thermal diffusion) refers to the thermal force on a gas due to a temperature difference. Thermal transpiration causes a flow of gas in the absence of any other pressure difference, and is able to maintain a certain pressu ...
.
** It is used to drive a gas pump with no moving parts called a
Knudsen pump The Knudsen pump also referred to as "thermal transpiration pump" or "Knudsen compressor" is a gas pump that utilizes no moving parts. Instead it uses thermal transpiration, the phenomenon that gas molecules drift from the hot end to the cold end o ...
.
** It is the currently accepted theory for the rotation of the
Crookes radiometer.
* Diffusion in a temperature gradient, also called ''thermodiffusion'' or
thermophoresis.
** It can be used as an obsolete method of making
enriched uranium (see
enriched uranium ยง thermal diffusion).
** Thermal diffusion can be used to measure fluid flow, including perfusion and
rCBF
Cerebral circulation is the movement of blood through a network of cerebral arteries and veins supplying the brain. The rate of cerebral blood flow in an adult human is typically 750 milliliters per minute, or about 15% of cardiac output. Arterie ...
at one location over time.
*
Brownian motion (at a constant ''non-zero
absolute temperature'').
See also:
*
Molecular diffusion
*
Heat conduction
Conduction is the process by which heat is transferred from the hotter end to the colder end of an object. The ability of the object to conduct heat is known as its ''thermal conductivity'', and is denoted .
Heat spontaneously flows along a te ...
(i.e., diffusion of heat)
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