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 heat transfer analysis, thermal diffusivity is the thermal conductivity divided by density and specific heat capacity at constant pressure. It measures the rate of transfer of heat of a material from the hot end to the cold end. It has the SI ...
, diffusivity of heat
*Diffusivity of mass:
**
Mass diffusivity
Diffusivity, mass diffusivity or diffusion coefficient is a proportionality constant between the molar flux due to molecular diffusion and the gradient in the concentration of the species (or the driving force for diffusion). Diffusivity is enco ...
, molecular diffusivity (often called "diffusion coefficient")
**
Eddy diffusion
Eddy diffusion, eddy dispersion, or turbulent diffusion is a process by which substances are mixed in the atmosphere, the ocean or in any fluid system due to eddy motion. In other words, it is mixing that is caused by eddies that can vary in size f ...
, eddy diffusivity
*
Kinematic viscosity, characterising momentum diffusivity
*
Magnetic diffusivity
The magnetic diffusivity is a parameter in plasma physics which appears in the magnetic Reynolds number. It has SI units of m²/s and is defined as:W. Baumjohann and R. A. Treumann, ''Basic Space Plasma Physics'', Imperial College Press, 1997.
:\e ...
Dimensions and Units
Diffusivity has dimensions of length
2 / time, or m
2/s in
SI units
The International System of Units, known by the international abbreviation SI in all languages and sometimes Pleonasm#Acronyms and initialisms, pleonastically as the SI system, is the modern form of the metric system and the world's most wid ...
and cm
2/s in
CGS units.
References
Former disambiguation pages converted to set index articles
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