Thermal_diffusivity

In heat transfer analysis, thermal diffusivity (symbol: $\backslash kappa\backslash ,$, but note that the symbols $\backslash alpha$, $D$, and $k$ are all commonly used) is the ratio of thermal conductivity to volumetric heat capacity.

$\backslash kappa\; =\; \{k\; \backslash over\; \{\backslash rho\; c\_p\}\}$

where: $k\backslash ,$ is thermal conductivity (SI units: watts per metre-kelvin, W∙m^-1∙K^-1) $\backslash rho\; c\_p\backslash ,$ is the volumetric heat capacity (density kg∙m^-3 times specific heat capacity J∙kg^-1K^-1; SI units: joules per cubic metre-kelvin, J∙m^-3∙K^-1)

The SI units for thermal diffusivity are square metres per second or m²∙s^-1.

Substances with high thermal diffusivity rapidly adjust their temperature to that of their surroundings, because they conduct heat quickly in comparison to their thermal \'bulk\'.

For common rock material, $\backslash kappa\backslash ,$ ~ 10^-6 m²∙s^-1.

Thermal diffusivity of air at 300 K is 0.000024 m²/s.

For a plot of thermal diffusivity of air as a function of absolute temperature see James Ierardi\'s Fire Protection Engineering Site

See also

• Thermodiffusion
• Heat capacity
• Specific heat capacity
• Heat equation
• Thermal conductivity
• Thermal effusivity
• Thermal time constant

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