Diffusivity is a rate of
diffusion
Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...
, a measure of the rate at which particles or heat or fluids can spread.
It is measured differently for different mediums.
Diffusivity may refer to:
*
Thermal diffusivity
In thermodynamics, thermal diffusivity is the thermal conductivity divided by density and specific heat capacity at constant pressure. It is a measure of the rate of heat transfer inside a material and has SI, SI units of m2/s. It is an intensive ...
, diffusivity of heat
*Diffusivity of mass:
**
Mass diffusivity
Diffusivity, mass diffusivity or diffusion coefficient is usually written as the proportionality constant between the molar flux due to molecular diffusion and the negative value of the gradient in the concentration of the species. More accurate ...
, molecular diffusivity (often called "diffusion coefficient")
**
Eddy diffusion, eddy diffusivity
*
Kinematic viscosity
Viscosity is a measure of a fluid's rate-dependent drag (physics), resistance to a change in shape or to movement of its neighboring portions relative to one another. For liquids, it corresponds to the informal concept of ''thickness''; for e ...
, characterising momentum diffusivity
*
Magnetic diffusivity
Dimensions and units
Diffusivity has dimensions of length
2 / time, or m
2/s in
SI units
The International System of Units, internationally known by the abbreviation SI (from French ), is the modern form of the metric system and the world's most widely used system of measurement. It is the only system of measurement with official st ...
and cm
2/s in
CGS units.
See also
*
Diffusibility
References
Former disambiguation pages converted to set index articles
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